Management of North American Culicoides Biting Midges: Current Knowledge and Research Needs

Abstract

Culicoides biting midges (Diptera: Ceratopogonidae) are biological vectors of two important viruses impacting North American ruminants—bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV). These viruses have been identified for over 60 years in North America, but we still lack an adequate understanding of the basic biology and ecology of the confirmed vector, Culicoides sonorensis, and know even less about other putative Culicoides vector species. The major gaps in our knowledge of the biology of Culicoides midges are broad and include an understanding of the ecology of juveniles, the identity of potential alternate vector species, interactions of midges with both pathogens and vertebrates, and the effectiveness of potential control measures. Due to these broad and numerous fundamental knowledge gaps, vector biologists and livestock producers are left with few options to respond to or understand outbreaks of EHD or BT in North America, or respond to emerging or exotic Culicoides-transmitted pathogens. Here we outline current knowledge of vector ecology and control tactics for North American Culicoides species, and delineate research recommendations aimed to fill knowledge gaps.

Introduction

C ulicoides midges transmit numerous arboviruses that cause significant morbidity, mortality, and economic losses to livestock and wildlife around the world (Mellor et al. 2000, Borkent 2005). Two of these viruses are particularly important in affecting ruminants and are endemic in the United States—bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV). Both BTV and EHDV (genus Orbivirus, family Reoviridae) are maintained in nature in a Culicoides vector–ruminant host cycle (Du Toit 1944, Price and Hardy 1954, Jones et al. 1977, Foster et al. 1977). While we have much to learn regarding exactly which Culicoides species are important vectors of EHDV and BTV throughout much of the world, the Culicoides genus exhibits some general ecological and biological characteristics (Borkent 2005). Adult females blood feed and some, but not all, require a blood meal for maturing eggs. Because only females feed on animals, they are responsible for pathogen transmission. Both adult sexes will feed on sugars, but little is known about the frequency of feeding, sugar sources utilized, or importance of this behavior in the field. The semiaquatic larvae go through four instars, and developmental sites have been generally outlined for many species (e.g., shoreline mud, animal waste, tree cavity materials); however, little detail exists for most North American species about site selection, variation in habitat quality, and feeding ecology (Mullen and Hribar 1988).

Recent outbreaks of BT in Europe (Mellor et al. 2008) and EHD in the Middle East and United States (Savini et al. 2011, Stallknecht et al. 2015) highlight the near-global impact of these diseases. The BT outbreaks in northern Europe demonstrate just how rapidly a new vector–virus association can appear, as C. obsoletus and C. pulicaris group midges began multiyear transmission of BTV-8 in areas previously free of infection (Carpenter et al. 2009, Wilson and Mellor 2009). In contrast, the North American situation surrounding orbiviruses is quite different from that in Europe, because BTV and EHDV have been enzootic in parts of the United States for decades. However, there is still reason for concern in North America, as multiple exotic BTV and EHDV serotypes have been confirmed in the United States since 1999. Furthermore, parts of the northeastern United States and Canada are considered free of BTV and ruminants there would be immunologically naïve for all BTV serotypes (Gibbs et al. 2008). Additionally, C. sonorensis is common in some of the southern portions of Canada's western provinces (Lysyk 2006), and outbreaks could occur within its range despite historically rare incursions of EHDV and BTV (Pare et al. 2012, Pybus et al. 2014). The potential impact of climate change on Culicoides spp. populations and virus transmission in Canada and the northeastern United States are not known, but these regions should be considered at risk given the northward expansion of orbiviral hemorrhagic disease in wild ruminants in these areas (Stallknecht et al. 2015). Despite these recent outbreaks and the dynamic nature of the disease systems, it is remarkable that there are no proven vector control options (Carpenter et al. 2008) and limited vaccines are available to protect animals (McVey and MacLachlan, in press).

As with all vector-borne diseases, mitigation strategies can be targeted at the host or the vector. In Europe, the development and deployment of effective inactivated vaccines for BTV-8 helped to control a BTV-8 epizootic; however, effective vaccines are not available for most North American BTV and EHDV serotypes (McVey and MacLachlan, in press). Thus, strategies to control the vector or block virus transmission often are the primary control options for livestock producers. Furthermore, due to the length of time associated with vaccine development, approval, and production, vector control strategies are likely the most readily and rapidly deployed, especially in the event of an emerging or exotic Culicoides-vectored pathogen in North America.

Much of our discussion on vector control in North America centers on C. sonorensis Wirth and Jones, a confirmed BTV and EHD vector in the United States (Tabachnick 1996, Holbrook et al. 2000), but we will also address the potential for additional vector species. Likewise, the intent is to focus on information and technology that may be relevant to vectors of BTV and EHDV in North America. In addition to the traditional target ruminants, such as cattle, sheep, and horses, the captive white-tailed deer industry is growing in the United States (Anderson et al. 2007). Mitigation strategies to lessen the impact of EHD and BT are needed, but currently none exist. In some ways, captive white-tailed deer can be reared and handled similar to livestock, which potentially enables the use of mitigation strategies not possible with free-ranging cervids. Although wild deer also are greatly impacted during EHD outbreaks, little can be done in a preventive or protective sense due to the unpredictable host and vector distribution. However, understanding the epizootiology of BT and EHD in this system is important because virus transmission and maintenance cycles are likely to involve a variety of susceptible ruminant hosts, both free-ranging and domestic (Ruder et al., in press).

Insect pest and vector control tactics generally fall into four categories—chemical, biological, cultural, and molecular. Integrated control approaches often combine these methods in an effort to reduce pathogen transmission. (1) Chemical control involves implementing treatments such as insecticide applications, which are applied directly to hosts and/or their environments. An example would include spraying ruminants with insecticides or repellents to prevent adult female Culicoides from blood feeding or to reduce survival following feeding. (2) Biological control involves using natural enemies (e.g., predators, parasites, pathogens, or competitors) to impact pest populations negatively. An example would be introducing mermithid nematodes into C. sonorensis habitats where they do not already occur. Novel methods of biological control employ other organisms, such as bacterial symbionts, that impact vector competence rather than decrease vector populations. (3) Cultural control involves altering the environment or modifying farming methods to hinder the pest in some way. For example, altering the slopes of water source edges (e.g., making them steeper) or nutrient input (e.g., decreasing waste loading) may make breeding environments less favorable for C. sonorensis. (4) “Molecular” control involves potential alterations of the insect genetic makeup, thereby decreasing vectorial capacity (reproductive success, vector competence, population biology). For example, genes associated with refractoriness or survival can be manipulated and then driven into wild vector populations. Biological and molecular control options are currently unavailable for Culicoides control but are starting to be explored in the search for long-term solutions. Chemical and cultural controls are the most likely to have an immediate impact should effective techniques be discovered.

Vector control techniques and virus transmission–blocking strategies should be distinguished conceptually. For example, strategic use of repellents or barriers may not impact or reduce vector populations, yet they decrease virus transmission by reducing vector–host contact. Similarly, reducing the vector population using control techniques (e.g., insecticides) may have no significant impact on the number of infected or diseased hosts in the field. Vector control should not be the standalone goal when mitigating vector-borne diseases. Our ultimate goal is to reduce or eliminate virus transmission, which may be more difficult to achieve. In this review, we discuss the current knowledge of Culicoides vectors of BTV and EHDV in North America, highlight recent work that relates to control of Culicoides vectors both worldwide and in North America, and identify key gaps in our knowledge that must be overcome to reduce EHD and BT disease incidence.

Current Status of Culicoides Species in North America

Carpenter et al. (2008) lamented “the most striking aspect of the current review is its revelation of how little we know of even the most basic aspects of the biology of the C. obsoletus and C. pulicaris groups,” both of concern for transmission of BTV in Europe. They commented that gaps in knowledge of documented and putative Culicoides vectors of BTV hinder the development of control tactics. The situation in North America is similar to that lamented for Europe. We have major gaps in our knowledge of the identity, ecology, and behavior of Culicoides vectors of orbiviruses, and the design and implementation of control strategies is impossible without closing some of those gaps.

Confirmed and potential Orbivirus vectors in North America

In the United States, outbreak investigations, serosurveys, and sentinel animal studies indicate that BTV and EHDV infections are common in livestock and wildlife in western, midwestern, and southeastern states (Odiawa et al. 1985, Shapiro et al. 1991, Nettles and Stallknecht 1992, Pearson et al. 1992, Ostlund et al. 2004, Aradaib et al. 2005, Boyer et al. 2008, Rodman and Johnson 2012). Although the known distributions of BTV and EHDV in North America are similar, they are not identical and we should therefore consider that regional vector species may be different (Ruder et al., in press).

The distribution of C. sonorensis in the United States correlates approximately with the geographic distribution of BTV (Tabachnick 1996). Prior to 2000, C. sonorensis was known as C. variipennis sonorensis in the literature but was elevated to species status by Holbrook et al. (2000). This midge was incriminated as a vector of BTV over 50 years ago (Foster et al. 1963), and subsequent field and laboratory studies have confirmed and fortified that foundation. C. sonorensis is one of the very few species in the genus that has been colonized in the laboratory (Jones 1960, Hunt et al. 1999); thus, laboratory research has focused on this species. For instance, many Orbivirus infection and vector competence trials have been performed with C. sonorensis, both in the United States as well as other parts of the world where C. sonorensis does not occur. This species is considered the primary vector of BTV throughout much of North America (Price and Hardy 1954, Foster et al. 1963), especially in domestic ruminant production settings in the western United States and occasionally Canada (Gibbs and Greiner 1994, Tabachnick 1996, Mellor et al. 2000). However, additional competent Culicoides spp. are likely to exist, especially in the eastern United States where C. sonorensis appears to be rare, even during disease outbreaks (Smith and Stallknecht 1996, Smith et al. 1996). A second species, C. insignis, is a confirmed vector of BTV in the extreme southeastern United States (Tanya et al. 1992), and several additional species are suspected vectors in this region, such as C. stellifer, C. debilipalpis, C. paraensis, C. spinosus, C. obsoletus, C. biguttatus, among others (Mullen et al. 1985, Gibbs and Greiner 1989, Smith and Stallknecht 1996, Smith et al. 1996, Ruder et al., in press). Species that are known vectors of BTV in Europe such as C. chiopterus and C. obsoletus, also occur in the northern United States and Canada, but their role in virus transmission is unknown.

The transmission of EHDV in North America is more ambiguous because the distribution of this virus does not correlate as convincingly with the distribution of C. sonorensis, especially in parts of the central and eastern United States (Ruder et al., this issue). In fact, light trap and deer-baited Culicoides surveys in the southeastern United States identified numerous suspect vector species, but C. sonorensis was rare or absent in the collections (Mullen et al. 1985, Smith and Stallknecht 1996, Smith et al. 1996, Becker et al. 2010). Several potential vectors of BTV and EHDV have been identified during these studies by virtue of their feeding on white-tailed deer (e.g., C. debilipalpis [lahillei], C. stellifer, and others), but their competence as vectors has yet to be confirmed. Becker et al. (2010) detected BTV (via PCR) in trap catches from Louisiana of Culicoides species other than C. sonorensis. Schmidtmann et al. (1980) identified several Culicoides spp. feeding on cattle and ponies in New York, including C. bigutattus, C. obsoletus, and C. stellifer. Collections from livestock in Virginia were dominated by C. bigutattus, C. stellifer, and C. variipennis (Zimmerman and Turner 1983). No similar efforts have been made in the Great Plains or the Midwest, regions where EHD is epizootic and significantly affects both cattle and white-tailed deer (Stallknecht et al. 2015, Ruder et al., in press). Species of Culicoides other than C. sonorensis may be involved in EHDV–ruminant cycles in these regions. To mitigate disease incidence in livestock or captive cervids, the vector species responsible for virus transmission during epizootics must first be identified.

Developmental habitats for North American Culicoides spp.

Developmental habitats are key targets in the management of vectors, primarily for mosquitoes (Small 2005), but habitat manipulation also has potential for controlling Culicoides (Carpenter et al. 2008, Gonzalez et al. 2013, Zimmer et al. 2014). Whereas some Culicoides species develop in a wide array of habitats, others may develop in habitats with more restricted characteristics (Mullen and Hribar 1988, Borkent 2005). However, little information is available about the specific biotic and abiotic characteristics that define the habitats of most Culicoides spp. in North America. Thus, if the goal is to modify or treat habitats to reduce Culicoides populations and pathogen transmission, understanding developmental site preferences is both critical and paramount. Obtaining this knowledge for the Culicoides vectors of BTV and EHDV in North America will contribute to targeted control options.

Developmental habitats have been best described for the C. variipennis group, including C. sonorensis, and often include waste-enhanced mud (Jones 1959, Schmidtmann et al. 1980, Mullens and Rodriguez 1988, Mullens 1989, Gerry et al. 2001). Presence of the species in the C. variipennis group correlated with soil and salinity profiles (Schmidtmann et al. 2000, 2006, 2011). Unfortunately, these correlations lacked data on temporal variability of substrate characteristics (e.g., pH, salinity). Also, sites without midges in the C. variipennis group were not reported, and variation in C. sonorensis abundance was not included in analyses. It is not known why populations vary significantly among apparently similar sites; most likely there are determinants of breeding site quality that have not yet been revealed.

C. sonorensis larvae are regarded as inhabitants of manure-polluted, open, silty mud at the margins of habitats such as dairy wastewater ponds (Mullens and Rodriguez 1988, Tabachnick 1996). However, larvae of this species also are found in nonenriched habitats, such as the shallow, quiet, silty edges of desert mountain streams in southern California (Mullens, personal observation). Additionally, not all manure-polluted habitats within this species' range become colonized (Mayo et al 2012, Pfannenstiel, personal observation), and abundance can vary significantly among study sites (Jones 1959, O'Rourke et al. 1983, Schmidtmann et al. 1983, Mullens 1989, Lysyk 2006). Nonetheless, the success of this species in some polluted waters is remarkable; the most productive wastewater ponds can contain densities in the range of 10,000 larvae per 30 mL of shoreline mud (Mullens and Rodriguez 1988).

Unfortunately, we have little data on C. sonorensis ecology and population dynamics in locations other than California dairies, and their true relationship with epizootics is unknown. Interestingly, the actions of people, or aggregations of domestic or sometimes wild ruminants, typically are integral in creating the conditions favoring large populations of C. sonorensis, and human/animal activity may also influence many other members of the genus. Knowledge of other Culicoides developmental sites in the United States is restricted to primarily descriptive studies (e.g., Jones 1961, Battle and Turner 1972). Larval habitats of other potential vectors of BTV and EHDV in the United States include mud in various settings (e.g., C. biguttatus, C. stellifer), animal waste (e.g., C. chiopterus, C. obsoletus), and substrate within tree cavities (e.g., C. debilipalpis). However, other than the general use of these substrates for development, few details are available on the ecology of these Culicoides in and around these habitats.

Long-term studies on Culicoides spp. use of different habitat types with varying biotic and abiotic conditions will help us obtain an accurate quantification of resource use. Studies of Culicoides spp. population dynamics are necessary to identify specific habitat characteristics that support or inhibit development and survival of juvenile stages. Careful characterization of abiotic variables (e.g., soil and water chemistry), biotic variables (e.g., substrate faunal characteristics, including bacteria and other prey organisms), flora characteristics (e.g., plant communities in the littoral zone or tree type for tree cavity breeders), or the presence of important natural enemies (e.g., mermithid nematodes; Mullens et al. 2008) is needed. Multiyear studies of Culicoides diversity and abundance are needed to appreciate the potential importance of species originating from different habitats under variable environmental conditions. For example, cyclical variation in drought or high temperatures has been linked over time to epizootics of EHD (Sleeman et al. 2009, Boyer et al. 2010, Stallknecht et al. 2015), BT (Purse and Rogers 2009), and the Culicoides-transmitted Orbivirus causing African horse sickness (Baylis et al. 1999), but there are no data explaining specifically how these grossly descriptive variables might alter habitats, influence Culicoides populations, or otherwise lead to epizootics. Drought causes numerous changes in potential developmental sites, such as changes in water chemistry, access to different substrate profiles, as well as changing the foraging behavior and local density of animal hosts. The congregation of hosts around diminishing water sources may be a key aspect of epizootics through bringing both vectors and hosts in close proximity. More work including correlating weather patterns (particularly rainfall) with specific developmental site characteristics and vector populations may elucidate risk factors for epizootics and reveal ways to mitigate their impact on livestock (e.g., manipulation of critical Culicoides developmental sites, application of insecticides at times of peak vector activity).

Review of Culicoides Control Literature 2008 to Present (Excluding North America)

Studies on tactics to control Culicoides species in Europe were initially reviewed by Carpenter et al. (2008). Much of the work on Culicoides control in Europe before the 2006 BTV outbreak was directed at nuisance species, such as C. nubeculosus, rather than known vectors of animal pathogens. For nuisance species, a simple reduction in biting rates can be considered a success, whereas disease reduction through vector control is more complicated and difficult. Carpenter et al. (2008) identified options for vector control, but no tactics were deemed effective at the time of the review. They listed treatment of animals and animal housing with pyrethroids, stabling of high-value animals, and the promotion of tactics to eliminate local breeding sites as potential control methods worthy of future research.

Publication trends can illuminate gaps in current knowledge and can be used as a measure of research needs. Since Carpenter et al. (2008), we have tracked Culicoides publications in eight journals—Journal of Medical Entomology, Medical and Veterinary Entomology, Parasites and Vectors, PLoS One, Journal of Vector Ecology, Veterinary Parasitology, Journal of the American Mosquito Control Association, and Vector-Borne and Zoonotic Diseases. From 2008 to January, 2015, these journals included 131 publications on Culicoides, comprising topics such as species composition/seasonal dynamics (22.1%), surveillance technology (14.9%), evaluation of control techniques (14.9%), identification technology (11.9%), identification of animal hosts (9.0%), studies of vector competence (7.5%), and attempts to identify larval habitats (8.2%). Most studies occurred in Europe and were related to BTV. The basic nature of these papers provides evidence of the global lack of knowledge regarding most aspects of the ecology and behavior of Culicoides, a critical deficiency that must be alleviated to develop sustainable control practices. In most areas, we still lack a clear understanding of Culicoides feeding/host selection, competence for orbiviruses, larval habitats, and population drivers. Since 2008, relatively few evaluations of control tactics for Culicoides spp. have been performed, but have most frequently evaluated treatment of animals with insecticides to prevent or reduce biting by Culicoides.

Recent studies on insecticides for prevention of feeding by Culicoides

Insecticide applications to animals through pour-on or direct spray applications have been the primary tactic tested for the reduction of Culicoides biting rates in the last 7 years. Alphacypermethrin (12.5–15%) pour-on treatments to cattle and sheep reduced feeding by C. nubeculosus (Papadopoulous et al. 2009), and high mortality was achieved for 21 days before declining rapidly. Hair clippings from horses to which cypermethrin (5%) had been applied with a sponge also killed C. nubeculosus; however, mortality never exceeded 80% for clippings from the belly or legs (Papadopoulos et al. 2010), suggesting that blood feeding would have continued. Treatment caused mortality to midges for 35 days or more, but mortality never reached 100%. Venail et al. (2011) showed that Culicoides spp. were quite susceptible to deltamethrin in the lab. Applications to sheep in the field with a 7.5% deltamethrin pour-on resulted in limited midge mortality and only lasted for about 4 days. When an entire animal was treated with a gloved hand, the same treatment of 7.5% deltamethrin prevented field engorgement of female Culicoides for at least 4 days (Mullens et al. 2010). The use of a 3.6% permethrin treatment similarly reduced blood feeding by females, and trap catch near treated sheep, yet significant numbers of Culicoides spp. still fed on treated animals (Griffioen et al. 2011).

Many of the studies summarized above concluded that dorsal applications of insecticides could not prevent midges from biting livestock along the underside and legs. Because the belly/legs are the preferred feeding area for some midges, full body treatment would likely be necessary for reducing virus transmission. Most of the treatments caused significant mortality (e.g., when evaluating hair clippings under laboratory conditions) and resulted in lower biting rates. However, whether reductions in blood feeding result in significant reduction in virus transmission rates and subsequently disease remains to be determined. Furthermore, many other factors need to be evaluated to understand the impact of specific insecticide applications on varying combinations of host species and Culicoides species, because each may potentially have unique ecological and behavioral characteristics.

Treated barriers (insecticide-impregnated nets/fences) were also evaluated for their effects on Culicoides. Cypermethrin-treated canvas barriers (0.5 gram/L) significantly reduced the capture of C. imicola in livestock pens versus those with untreated netting (Calvete et al. 2010). Unfortunately, because midge-biting rates on livestock remain unclear, the real impact of these barriers on feeding is unknown. Cypermethrin-treated screens (1% cypermethrin solution) were tested by Del Río et al. (2014), but they found no treatment impact, concluding midges must have traversed the screen (2-mm gap width) without meaningful pesticide contact. In circumstances where animals are typically penned (e.g., feedlots, dairies), the use of insecticide-treated barriers might reduce populations of host-seeking Culicoides. As with all potential treatment options, details of the target Culicoides ecology and behavior (or in this case of netting Culicoides size) will be critical.

Recent studies on cultural controls for Culicoides

Keeping ruminant hosts separated from Culicoides vectors is a type of cultural control approach to reducing virus transmission. Baylis et al. (2010) considered whether stabling cattle reduced exposure to Culicoides spp., particularly those of the obsoletus group. Trap catch was lower in stables than outside, suggesting that inside midge biting rates and BTV exposure would be reduced, although this was not determined. Culicoides spp. vary in their proclivity to enter stables, Viennet et al. (2012) discovered that C. brunnicans was strictly exophagous (would not enter stables), whereas the vector species C. obsoletus was found inside mostly closed stables (3% of the wall area open to outside), although in smaller numbers than outside. Entry into the stables could possibly negate the purported benefits of stabling. Additional studies with C. imicola discovered that trap catch within stables was much higher than outside of stables (Calvete et al. 2009), suggesting that in the presence of this species stabling might expose animals to increased biting rates. As with pesticide studies, details on the level of reduction in biting rates that translate to meaningful reductions in virus transmission and subsequent disease incidence are unknown. As a result, we unfortunately cannot adequately assess the impact of incremental biting rate reductions or provide target levels of control.

Another cultural control approach, habitat modification, has been discussed for Culicoides control but has yet to be carefully evaluated. Harrup et al. (2014) attempted to reduce populations of Culicoides vectors of BTV (C. obsoletus group and others) in England by covering muck heaps that certain Culicoides spp. apparently used for breeding. Unfortunately, the study did not assess midge immigration from neighboring farms. More critically, Culicoides presence in or emergence from the muck heaps was not evaluated, and therefore the researchers could not discern more directly whether covering the muck heaps had any effect on reproductive success. Nonetheless, this control method was not successful at controlling midges locally, because light trap catches showed no evidence of population reductions.

Recent studies on biological and molecular control of Culicoides

Only a single study assessed putative biological control agents in the last 7 years. Ansari et al. (2011) examined the susceptibility of C. nubeculosus adults to several entomopathogenic fungi. In both laboratory and greenhouse bioassays, these fungi significantly reduced the survival of adults during the 6-day exposure period. These fungal isolates have yet to be assayed in the field, and their incorporation into a control program is difficult to envision. No studies have been conducted to date on molecular control of Culicoides spp.

Current status of techniques for control of C. sonorensis in North America

Insecticides are used in combination with other management strategies for controlling Culicoides populations (Borkent 2005). However, as discussed previously, insecticide evaluations against Culicoides spp. have yielded mixed results and much more information is needed. In spite of the concern for virus transmission in North America, relatively few studies have evaluated insecticides for C. sonorensis control, and none have targeted other potential Culicoides spp. vectors of orbiviruses in North America. Treating larval habitats is a potential control option, but is problematic due to the difficulty in accessing larvae in highly organic substrates and environmental toxicity concerns (Holbrook and Agun 1984). Targeting adults with insecticide-treated ear tags on cattle caused significant mortality to laboratory-reared C. sonorensis for up to 70 days (Holbrook 1986), but rainfall caused large short-term reductions in efficacy. Additionally, the effect of ear tags on decreasing midge-biting rates was not assessed. Permethrin and pirimiphos-methyl applied to the belly of dairy heifers resulted in reduced C. sonorensis feeding or survival (Mullens et al. 2000). However, in a hyperendemic disease region, applying permethrin to cattle at 2-week intervals did not prevent BTV infection, even when the insecticide was carefully applied to the belly, which is the preferred feeding site for C. sonorensis (Mullens et al. 2001). Reeves et al. (2010) demonstrated that several pesticides repelled colony-reared C. sonorensis from feeding on sheep for 3–5 weeks, depending on the formulation; however, these treatments did not completely prevent feeding. Ivermectin fed to females through their bloodmeals did not yield promising results for C. sonorensis control; the conclusion was that animals could not be fed enough ivermectin to bring blood titers high enough to have an effect (Holbrook and Mullens 1994).

Mayo et al. (2014) tested the impact of habitat modification on C. sonorensis reduction in the United States. A dairy wastewater pond complex known to support a large population of C. sonorensis was completely removed, and midge population abundance was compared before and after to another nearby dairy with unmodified ponds. Surprisingly, they found no significant reduction of adult C. sonorensis populations despite the destruction of what was thought to be the primary reproduction site on the treated farm. Both studies results highlight our limited understanding of the developmental habitats of Culicoides spp. and the distances midges might disperse from these sites. Effective mitigation strategies involving habitat management should consider species-specific dispersal distances and rates and incorporate an area large enough to prevent immigration from other developmental habitats. Little is known about the dispersal and migration of Culicoides species apart from a handful of studies. Lillie et al. (1981) observed that C. sonorensis could disperse at least 2.8 km in a single night and as much as 4 km in two nights. They suggested that controlling adults might require insecticide application to a daunting 3.57 km² around an individual developmental site. Kirkeby et al. (2013) demonstrated that the C. pulicaris group could disperse, even upwind, between farms that were 1750 meters apart within 24 hr. Much work will be required to employ habitat manipulation as a control strategy, and implementation will require that these efforts not be cost prohibitive to producers or face regulatory issues (e.g., destruction of wetlands in the United States and the European Union) that limit their practical use.

Mermithid nematodes have been observed parasitizing many species of Culicoides worldwide, and infestation rates can sometimes exceed 50% (Mullens et al. 2008). Preliminary field trials with laboratory-reared Heleidomermis magnapapula demonstrated significant impacts on C. sonorensis emergence. Given the difficulties with insecticidal control of Culicoides, greater efforts should be undertaken to evaluate the potential of these nematodes in both laboratory and field settings.

Culicoides Ecology and Vector Control: Research Gaps and Recommendations

Here we suggest general actions aimed at addressing key deficiencies in our vector control knowledge base. Gaps are listed from more proximal to more ultimate, recognizing that among control techniques, there are some that can be attempted in the short-term whereas others will depend on significant investments in time and might not be available for many years. Both types of contributions are critical to long-term reductions in pathogen transmission. These recommendations reflect the publications reviewed here as well as those reviewed by Carpenter et al. (2008) and should be prioritized in research efforts.

Culicoides ecology

(1) Gap: Information on which species are feeding on large ruminants in North America is lacking. As a result, the complete list of Culicoides species vectoring North American orbiviruses is unknown. This is especially evident in some wildlife habitats and in the eastern United States where C. sonorensis populations appear scattered, small, or nonexistent.

Recommendation: A combination of studies using sentinel animals and blood meal identification of field-collected midges will help determine the diversity of hosts being attacked and which Culicoides species are biting ruminants. The simultaneous use of traps and observations of Culicoides feeding on animals will specifically establish a relationship between easier-to-use monitoring tools (traps) and animal biting rates. This will improve both our predictive models and estimates of the level of control needed to reduce virus transmission. Targeted surveys should be encouraged in regions of expanding Orbivirus ranges (e.g., upper Midwest and northeast for EHDV) and areas where C. sonorensis likely is not the sole or predominant vector (e.g., eastern United States).

(2) Gap: Our knowledge of immature Culicoides habitats is extremely poor for most species and is lacking even for the well-studied species outside of very specific habitats (e.g., C. sonorensis outside of California dairy environments). The abundance, nature, and productivity of immature habitats are likely to be the most critical determinants of vector distributions and densities. Even if integrated management strategies are developed, they cannot be used without knowing where the biting midges are coming from or what constitutes a productive larval habitat.

Recommendation: Conduct field surveys to determine the developmental sites of key vector species and how environmental variation affects their utilization and quality. Describe and characterize the biological attributes of those habitats, with attention to biotic components (e.g., coexisting macro- and microorganisms) and abiotic features (e.g., moisture level, pH, or chemical description) and how Culicoides populations and these features correlate over time. For example, although EHD outbreaks appear to be associated with droughts (Stallknecht et al. 2015), we lack information on the variability in Culicoides population dynamics and reproductive success associated with rainfall patterns and drought that potentially contribute to epizootics.

(3) Gap: We know very little about the behavior and ecology of adult Culicoides. Critical aspects of adult vector ecology that could directly inform control strategies remain unknown or understudied. Notable knowledge gaps include: (1) adult resting site selection (i.e., where adult midges spend almost all their time when not searching for blood or oviposition sites), (2) the role of sugar feeding on vector fitness, (3) mate and mating site location, (4) the location and selection of oviposition sites, and (5) virtually all aspects of dispersal.

Recommendation: Because so little is known with respect to all of these topics, obtaining information on any of them for suspect and potential vector species would be useful. Field surveys to determine adult resting sites around livestock facilities and the use and location of natural sugar sources may be very helpful when designing insecticide applications. Constituent sugars from insect honeydews can differentially affect C. sonorensis survival (Reeves and Jones 2010), but we do not know where and how frequently adults feed in the field. Toxic sugar bait studies in the lab have demonstrated chemical formulations using synthetic pyrethroids are highly effective at killing colonized C. sonorensis (Cohnstaedt, unpublished data). However, because the broadcast use of these synthetic pyrethroids is an off-label use, the use of toxic sugar bait stations represents one of the only safe and legal means to apply this insecticide. The cues for oviposition site selection and its relationship to larval populations (e.g., location, structure) in nature need to be determined. Of particular importance is information on the distance and rate at which adults disperse (e.g., dispersal from breeding sites to locate bloodmeals) that will help in determining the distribution and movement of Culicoides vectors in the environment. The development of inexpensive insect marking techniques (Hagler and Jackson 2001, Jones et al. 2006, Sanders et al. 2014) offers the potential to address dispersal of these small insects. Understanding these principal components of midge distributation in the landscape is critical for evaluating the threat of virus transmission and will help in designing and evaluating the effectiveness of local control efforts.

Culicoides control strategies

(1) Gap: There is a need for more information on the efficacy of insecticides/repellents applied to ruminants for protection from Culicoides, especially their value in preventing pathogen transmission. Most insecticide trials on animals have measured the mortality of midges exposed to animal hair from different regions of the body, the effect on midge biting rates, or effect on trap catch after insecticides were applied to structures. Only one study evaluated the effect of insecticide application in preventing pathogen transmission and found no significant effect of biweekly permethrin applications on BTV seroconversion rates (Mullens et al. 2001). Additional tests are needed to determine if insecticide applications reduce virus transmission. The efficacy of individual materials as well as application techniques should be evaluated more thoroughly as a means to ultimately develop a cost-effective control tactic for livestock producers

Recommendation: Experimental on-animal field testing, particularly in areas of active Orbivirus transmission, will help in determining the effectiveness of various materials and application technologies on midge landing, feeding, and virus transmission. Studies should be structured not only to evaluate the effects of treatments on midge feeding and mortality, but also to correlate those variables to virus transmission to sentinel herds.

(2) Gap: We lack information on how, when, and in what combinations animal-applied control materials should be used against particular target vectors. This includes vector host preference and the time of day and the location on the animal host body pesticides or repellents should be applied. In a larger sense, improved understanding of the seasonal phenology of vectors would also allow livestock producers to target control tactics more effectively, both for applications of pesticides to control adult Culicoides and for any potential strategies to reduce availability and productivity of breeding sites. There also have been only a few studies evaluating either multiple products against a single species, or evaluating multiple products against a suite of species; both would be helpful in building a database of the effects of insecticides on Culicoides.

Recommendation: Field and laboratory studies should be designed to characterize host attack behavior and identify better materials (including toxicants, repellents, kairomones, etc.) that reduce midge biting rates. Behavioral studies documenting the interactions between female midges and animal hosts or insecticidal materials would lead to improved control methods and better evaluation of putative materials. These materials ultimately need to be field tested for effectiveness and applicability. The seasonal phenology of vector species should be more adequately described across a range of environments.

(3) Gap: Many control methods have never been tested outside of the initial study settings (e.g., defined environments like dairy wastewater ponds), or for their ultimate effects on adult Culicoides populations. As a result, the currently recommended control methods are speculative or are based on very specific applications. Evidence supporting any assertions of effectiveness or the ability to apply protocols across different types of locations is absent.

Recommendation: Carefully controlled field studies across a variety of settings are necessary to determine if manipulations such as water source elimination or modification, biological control methods, and pesticide applications indeed cause reductions of vector populations and whether there is an impact of population control on preventing virus transmission. Improved collaborations between laboratories will be critical to reduce redundancies among research programs and develop frameworks for building upon current Culicoides control efforts.

(4) Gap: There is an absence of field data quantifying the reduction of vector populations that would be necessary to successfully reduce virus transmission. These targeted numbers are needed to guide any of our control efforts. The impact that vector abundance has on Culicoides biting rates and the dissemination of virus between individuals or groups of animals needs to be described. Because changes in BTV and EHDV distribution in both North America and Europe have occurred recently, the role of environmental variability and climate change in driving vector populations and disease incidence also should be quantified and used to delineate disease risk.

Recommendation: To relate vector activity, abundance, and virus infection level to transmission, sentinel hosts and vector population monitoring (e.g., trapping) should be used in long-term field trials in both enzootic and epizootic areas for orbiviruses. Initially these studies would be correlational (time series), but subsequent field studies that incorporate testing of vector control tactics should follow. In the eastern United States, comparisons of Culicoides diversity and abundance and the infection of sentinel herds in years with and without epizootics would be particularly informative.

Control of disease through manipulations of vector competence

(1) Gap: The interactions between orbiviruses and midge vectors have been understudied. We need a greater understanding of the molecular and biological components underlying vector competence, including the role vector genetics, mechanisms of refractoriness and permissiveness, and overall vector physiology. There also is a paucity of information on the microbial ecology of biting midges, including both adults and larvae, which is an area that is expanding rapidly in other vector-pathogen systems (Volf et al. 2002, Azambuja et al. 2005, Cirimotich et al. 2011, Boissière et al. 2012). There is ample evidence from the mosquito literature that genetic techniques have great potential for the control of disease vectors (Alphey 2014); however, our knowledge of Culicoides microbial ecology, functional genomics, and genetic manipulation capabilities is in its infancy.

Recommendation: Knowledge of the processes underlying midge vector competence provides an opportunity to identify targets for novel transmission-blocking strategies. Experimental investigation of the genetic influence on vector competence both within and across Culicoides spp. can serve as a platform for applied studies designed to manipulate those genes. More detailed physiological studies should be aimed at determining the midgut (primary) and systemic (secondary) barriers to arbovirus infection in biting midges and the role of midge defenses and gut microbiota in fortifying those barriers. Efforts toward laboratory colonization of alternate Culicoides vector species should be intensified, as vector competence studies have largely focused on colonized C. sonorensis both in the United States and the United Kingdom. Although the utilization of molecular methods for the study of Culicoides vector biology has expanded very recently (Nayduch et al. 2014a), these tools have not yet been brought to bear on control tactics. However, the recent release of the C. sonorensis reference transcriptome (Nayduch et al. 2014b) as well as a demonstration of RNA interference (RNAi) in vivo (Mills et al. 2015) present new tools in the molecular biological toolbox to use in vector competence studies. These advancements will allow scientists to identify physiological and genetic mechanisms related to pathogen defense (Nayduch et al. 2014c) and use reverse genetics approaches to elucidate their role in vector competence.

Conclusions

To date, strategies for controlling Culicoides spp., including C. sonorensis, have focused on the use of pesticides or habitat modification. Much of the early research on insecticide management of Culicoides targeted nuisance species rather than vectors. Unfortunately, we do not know whether reductions in biting rates, for example, by using repellents, would result in reduced virus transmission, nor do we know the magnitude by which populations of Culicoides must be reduced for control efforts to be truly effective. Habitat modifications, for all of their presumed potential, have proven more complex to implement than expected. Significant efforts to understand basic aspects of vector–host–virus cycles, vector ecology and behavior, and vector–pathogen interactions are necessary before we develop effective strategies to manage Culicoides spp. vectors in the variety of ruminant systems where they pose a threat.

Footnotes

Acknowledgments

We would like to thank the organizing committee and the USDA Agricultural Research Service (ARS), National Program for Animal Health for sponsoring and conducting a gap analysis workshop for BTV and EHDV during May, 2013, in Manhattan, Kansas, at the Center for Grain and Animal Health Research (CGAHR, USDA-ARS). Additional thanks are extended to Justin Talley (Oklahoma State University) and Dustin Swanson (Thomas Moore College), as well as two anonymous reviewers for their comments and improvement of this manuscript.

Author Disclosure Statement

No competing financial interests exist.

References

Alphey

. Genetic control of mosquitoes. Ann Rev Entomol, 2014; 59:205–224.

Anderson

, Frosch

, Outlaw

. Economic impact of the United States cervid farming industry. Agricultural & Food Policy Center, The Texas A&M University System, APFC Research Report 07-4, August 2007 [20 pp.]. Available at https://www.afpc.tamu.edu/pubs/2/480/rr-2007-04.pdf

Ansari

, Pope

, Carpenter

, Scholte

E-J

, et al. Entomopathogenic fungus as a biological control for an important vector of livestock disease: The Culicoides biting midge. PLoS One, 2011; 6:e16108.

Aradaib

, Mederos

, Osburn

. Evaluation of epizootic haemorrhagic disease virus infection in sentinel calves from the San Joaquin Valley of California. Vet Res Commun, 2005; 9:447–451.

Azambuja

, Garcia

, Ratcliffe

. Gut microbiota and parasite transmission by insect vectors. Trends Parasit, 2005; 21:568–572.

Battle

, Turner

Jr.

EC. Some nutritional and chemical properties of the larval habitats of certain species of Culicoides (Diptera: Ceratopogonidae). J Med Entomol, 1972; 9: 32–35.

Baylis

, Mellor

, Meiswinkle

. Horse sickness and ENSO in South Africa. Nature, 1999; 397:574.

Baylis

, Parkin

, Kreppel

, Carpenter

, et al. Evaluation of housing as a means to prectect cattle from Culicoides biting midges, the vectors of bluetongue virus. Med Vet Entomol, 2010; 24:38–45.

Becker

, Reeves

, DeJean

, Emery

, et al. Detection of bluetongue virus RNA in field-collected Culicoides spp. (Diptera: Ceratopogonidae) following the discovery of bluetongue virus serotype 1 in white-tailed deer and cattle in Louisiana. J Med Entomol, 2010; 47:269–273.

10.

Boissière

, Tchioffo

, Bachar

, Abate

, et al. Midgut microbiota of the malaria mosquito vector Anopheles gambiae and interactions with Plasmodium falciparum infection. PLoS Pathog, 2012; 8:e1002742.

11.

Borkent

. The Biting Midges, the Ceratopogonidae (Diptera). In: Marquardt

, ed. Biology of Disease Vectors, 2nd ed. Burlington, MA: Elsevier Academic Press, 2005:113–126.

12.

Boyer

, Ward

, Wallace

, Zhou

, et al. Exploratory spatial data analysis of regional seroprevalence of antibodies against epizootic hemorrhagic disease virus in cattle from Illinois and Indiana. Am J Vet Res, 2008; 69:1286–1293.

13.

Boyer

, Ward

, Wallace

, Singer

. Climate, landscape, and the risk of orbivirus exposure in cattle in Illinois and western Indiana. Am J Trop Med Hyg, 2010; 83:789–794.

14.

Calvete

, Estrada

, Miranda

, Del Rio

, et al. Entry of bluetongue vector Culicoides imicola into livestock premises in Spain. Med Vet Entomol, 2009; 23:202–208.

15.

Calvete

, Estrada

, Miranda

, Del Rio

, et al. Protection of livestock against bluetongue virus vector Culicoides imicola using insecticide treated netting in open areas. Med Vet Entomol, 2010; 24:169–175.

16.

Carpenter

, Mellor

, Torr

. Control techniques for Culicoides biting midges and their application in the U.K. and northwestern Palaearctic. Med Vet Entomol, 2008; 22:175–187.

17.

Carpenter

, Wilson

, Mellor

. Culicoides and the emergence of bluetongue virus in northern Europe. Trends in Micro, 2009; 17:172–178.

18.

Cirimotich

, Ramirez

, Dimopoulos

. Native microbiota shape insect vector competence for human pathogens. Cell Host Microbe, 2011; 10:307–310.

19.

Del Rio

, Barceló

, Lucientes

, Miranda

. Detrimental effect of cypermethrin treated nets on Culicoides populations (Diptera: Ceratopogonidae) and non-targeted fauna on livestock farms. Vet Parasitol, 2014; 199:230–234.

20.

Du Toit

. The transmission of bluetongue and horse-sickness by Culicoides . Onderstepoort J Vet Sci Anim Indust, 1944; 19:7–16.

21.

Foster

, Jones

, McCrory

. Preliminary investigations on insect transmission of bluetongue virus in sheep. Am J Vet Res, 1963; 24:1195.

22.

Foster

, Breckon

, Luedke

, Jones

. Transmission of two strains of epizootic hemorrhagic disease virus in deer by Culicoides variipennis . J Wildl Dis, 1977; 13:9–16.

23.

Gerry

, Mullens

, Maclachlan

, Mecham

. Seasonal transmission of bluetongue virus by Culicoides sonorensis (Diptera: Ceratopogonidae) at a Southern California dairy and evaluation of vectorial capacity as a predictor of bluetongue virus transmission. J Med Entomol, 2001; 38:197–209.

24.

Gibbs

EPJ

, Greiner

. Bluetongue and epizootic hemorrhagic disease. In: Monath

, ed. Arboviruses: Epidemiology and Ecology, vol. 2. Boca Raton, FL: CRC Press Inc., 1989:39–70.

25.

Gibbs

EPJ

, Greiner

. The epidemiology of bluetongue. Comp Immunol Microbiol Infect Dis, 1994; 17:207–220.

26.

Gibbs

EPJ

, Tabachnick

, Holt

, Stallknecht

. US concerns over bluetongue. Science, 2008; 320:872–872.

27.

Gonzalez

, Lopez

, Mullens

, Baldet

, et al. A survey of Culicoides developmental sites on a farm in northern Spain, with a brief review of immature habitats of European species. Vet Parasitol, 2013; 191:81–93.

28.

Griffioen

, van Gemst

DBJ

, Pieterse

, Jacobs

, et al. Culicoides species associated with sheep in The Netherlands and the effect of a permethrin insecticide. Vet J, 2011; 190:230–235.

29.

Hagler

, Jackson

. Methods for marking insects: current techniques and future prospects. Ann Rev Entomol, 2001; 46:511–543.

30.

Harrup

, Gubbins

, Barber

, Denison

, et al. Does covering of farm-associated Culicoides larval habitat reduce adult populations in the United Kingdom. Vet Parasitol, 2014; 201:137–145.

31.

Holbrook

. Exposure of Culicoides variipennis (Diptera: Ceratopogonidae) to hair clippings to evaluate insectide-treated ear tags in cattle. J Econ Entomol, 1986; 79:1127–1129.

32.

Holbrook

, Agun

. Field trials of pesticides to control larval Culicoides variipennis (Ceratopogonidae). Mosq News, 1984; 44:233–235.

33.

Holbrook

, Mullens

. Effects of ivermectin on survival, fecundity, and egg fertility in Culicoides variipennis (Diptera: Ceratopogonidae). J Amer Mosq Cont Assoc, 1994; 10:70–73.

34.

Holbrook

, Tabachnick

, Schmidtmann

, McKinnon

, et al. Sympatry in the Culicoides variipennis complex (Diptera: Ceratopogonidae): A taxonomic reassessment. J Med Entomol, 2000; 37:65–76.

35.

Hunt

, Mullens

, Tabachnick

. Colonization and maintenance of species of Culicoides . In: Maramarosch

and Mahmood

, eds. Maintenance of Human, Animal and Plant Pathogen Vectors. Boca Raton, FL: Science Publishers Inc., 1999:35–55.

36.

Jones

. Culicoides breeding in human sewage sites of dwellings in Texas. Mosq News, 1959; 19:164–167.

37.

Jones

. Mass-production methods for the colonization of Culicoides variipennis sonorensis . J Econ Entomol, 1960; 53:731–735.

38.

Jones

. Observations on the larval habitats of some North American species of Culicoides (Diptera: Ceratapogonidae). Ann Entomol Soc Am, 1961; 51:702–710.

39.

Jones

, Roughton

, Foster

, Bando

. Culicoides, the vector of epizootic hemorrhagic disease in white-tailed deer in Kentucky in 1971. J Wildl Dis, 1977; 13:2–8.

40.

Jones

, Hagler

, Brunner

, Baker

, Wilburn

. An inexpensive immunomarking technique for studying movement patterns of naturally occurring insect populations. Env Entomol, 2006; 35:827–836.

41.

Kirkeby

, Bødker

, Stockmarr

, Lind

, et al. Quantifying dispersal of European Culicoides (Diptera: Ceratopogonidae) vectors between farms using a novel mark-release-recapture technique. PLoS One, 2013; 8:e61269.

42.

Lillie

, Marquardt

, Jones

. The flight range of Culicoides variipennis (Diptera: Ceratopogonidae). Can Entomol, 1981; 113:419–426.

43.

Lysyk

. Abundance and species composition of Culicoides (Diptera: Ceratopogonidae) at cattle facilities in southern Alberta, Canada. J Med Entomol, 2006; 43:840–849.

44.

Mayo

, Gardner

, Mullens

, Barker

, et al. Anthropogenic and meteorological factors influence vector abundance and prevalence of bluetongue virus infection of dairy cattle in California. Vet Microbiol, 2012; 155:158–164.

45.

Mayo

, Osborne

, Mullens

, Gerry

, et al. Seasonal variation and impact of waste-water lagoons as larval habitat on the population dynamics of Culicoides sonorensis (Diptera: Ceratpogonidae) at two dairy farms in northern California. PLoS Onw, 2014; 9:e89633.

46.

McVey

, MacLachlan

. Vaccines for prevention of bluetongue and epizootic hemorrhagic disease in livestock—a North American perspective. Vector Borne Zoonotic Dis, 15:385–396.

47.

Mellor

, Boorman

, Baylis

. Culicoides biting midges: Their role as arbovirus vectors. Ann Rev Ent, 2000; 45:307–340.

48.

Mellor

, Carpenter

, Harrup

, Baylis

, et al. Bluetongue in Europe and the Mediterranean Basin: History of occurrence prior to 2006. Prevent Vet Med, 2008; 87:4–20.

49.

Mills

, Nayduch

, Michel

. Inducing RNA interference in the arbovirus vector, Culicoides sonorensis . Insect Mol Biol, 2015; 24:105–114.

50.

Mullen

, Haves

, Nusbaum

. Potential vectors of bluetongue and epizootic hemorrhagic viruses of cattle and white-tailed deer in Alabama. Prog Clin Biol Res, 1985; 178:201–206.

51.

Mullen

, Hribar

. Biology and feeding behaviour of ceratopogonid larvae (Diptera: Ceratopogonidae) in North America. Bull Soc Vect Ecol, 1988; 13:60–81.

52.

Mullens

. A quantitative survey of Culicoides variipennis (Diptera: Ceratopogonidae) in dairy waste water ponds in southern California. J Med Entomol, 1989; 26:559–565.

53.

Mullens

, Rodriguez

. Colonization and response of Culicoides variipennis (Diptera: Ceratopogonidae) to pollution levels in experimental dairy wastewater ponds. J Med Entomol, 1988; 25:441–451.

54.

Mullens

, Velten

, Gerry

, Braverman

et al. Feeding and survival of C. sonorensis on cattle treated with permethrin or pirimiphos-methyl. Med Vet Entomol, 2000; 14:313–320.

55.

Mullens

, Gerry

, Velten

. Failure of a permethrin treatment regime to protect cattle against bluetongue virus. J Med Entomol, 2001; 38:760–762.

56.

Mullens

, Sarto I Monteys

, Przhiboro

. Mermithid parasitism in Ceratopogonidae: A literature review and critical assessment of host impact and potential for biological control of Culicoides . Russian Entomol J, 2008; 17:87–113.

57.

Mullens

, Gerry

, Sarto I Monteys

, et al. Field studies on Culicoides (Diptera: Ceratopogonidae) activity and response to deltamethrin applications to sheep in Northeastern Spain. J Med Entomol, 2010; 47:106–110.

58.

Nayduch

, Cohnstaedt

, Saski

, Lawson

, et al. Studying Culicoides vectors of BTV in the post-genomic era: Resources, bottlenecks to progress and future directions. Vir Res, 2014a; 182:43–49.

59.

Nayduch

, Lee

, Saski

. The reference transcriptome of the adult female biting midge (Culicoides sonorensis) and differential gene expression profiling during teneral, blood, and sucrose feeding conditions. PLoS One, 2014b; 9:e98123.

60.

Nayduch

, Lee

, Saski

. Gene discovery and differential expression analysis of humoral immune response elements in female Culicoides sonorensis (Diptera: Ceratopogonidae). Parasit Vectors, 2014c; 7:388.

61.

Nettles

, Stallknecht

. History and progress in the study of hemorrhagic disease of deer. In: McCabe

, ed. Transactions of the 57th North American Wildlife & Natural Resources Conference. Washington, DC: Wildlife Management Institute, 1992:499–516.

62.

Odiawa

, Blue

, Tyler

, Shotts

. Bluetongue and epizootic hemorrhagic disease in ruminants in Georgia: Survey by serotest and virologic isolation. Am J Vet Res, 1985; 46:2193.

63.

O'Rourke

, Loomis

, Smith

. Observations on some Culicoides variipennis (Diptera: Ceratopogonidae) larval habitats in California. Mosq News, 1983; 43:147–152.

64.

Ostlund

, Moser

, Johnson

, Pearson

. Distribution of bluetongue in the United States of America, 1991–2002. Vet Ital, 2004; 40:83–88.

65.

Pare

, Geale

, Koller-Jones

, Hooper-McGrevy

, et al. Serological status of Canadian cattle for brucellosis, anaplasmosis, and bluetongue in 2007–2008. Can Vet J, 2012; 53:949–956.

66.

Papadopoulos

, Bartram

, Carpenter

, Mellor

, et al. Efficacy of alpha cypermethrin applied to cattle and sheep against the biting midge Culicoides nubeculosus . Vet Parasitol, 2009; 163:110–114.

67.

Papadopoulos

, Rowlinson

, Bartram

, Carpenter

, et al. Treatment of horses with cypermethrin against the biting flies Culicoides nubeculosus, Aedes aegypti and Culex quinquefasciatus . Vet Parasitol, 2010; 169:165–171.

68.

Pearson

, Gustafson

, Shafer

, Alstad

, et al. Distribution of bluetongue in the United States. In: Walton

, Osburn

, eds. Bluetongue, African Horse Sickness, and Related Orbiviruses: Proceedings of the Second International Symposium. Boca Raton, FL: CRC Press Inc., 1992; 128–139.

69.

Price

, Hardy

. Isolation of the bluetongue virus from Texas sheep-Culicoides shown to be a vector. J Am Vet Med Assoc, 1954; 124:255–258.

70.

Purse

, Rogers

. Bluetongue virus and climate change. In: Mellor

, Baylis

, Mertens

, eds. Biology of Animal Infections: Bluetongue. Boston, MA: Academic Press, 2009:343–364.

71.

Pybus

, Ravi

, Pollock

. Epizootic hemorrhagic disease in Alberta, Canada. J Wildl Dis, 2014; 50:720–722.

72.

Reeves

, Jones

. Effects of melezitose and stachyose on adult longevity and virus persistence in Culicoides sonorensis (Diptera: Ceratopogonidae). West N Amer Nat, 2010; 70:114—116.

73.

Reeves

, Lloyd

, Stobart

, Stith

, et al. Control of Culicoides sonorensis (Diptera: Ceratopogonidae) blood feeding on sheep with long-lasting repellent pesticides. J Am Mosq Cont Assoc, 2010; 26:302–305.

74.

Rodman

, Johnson

. Report of the Committee on Bluetongue and Related Orbiviruses, In: United States Animal Health Association Annual Meeting, October 18–24, 2012, Greensboro, NC, 2012.

75.

Ruder

, Lysyk

, Stallknecht

, Foil

, et al. Transmission and epidemiology of bluetongue and epizootic hemorrhagic disease in North America: Current perspectives, research gaps and future directions. Vector Borne Zoonotic Dis, 15:348–363.

76.

Sanders

, Carpenter

. Assessment of an immunomarking technique for study of dispersal of Culicoides biting midges. Infec Genet Evol, 2014; 28:583–587.

77.

Savini

, Afonso

, Mellor

, Aradaib

, et al. Epizootic haemorrhagic disease. Res Vet Sci, 2011; 91:1–17.

78.

Schmidtmann

, Jones

, Gollands

. Comparative host-seeking activity of Culicoides (Diptera: Ceratapogonidae) attracted to pastured livestock in central New York State, USA. J Med Entomol, 1980; 17:221–231.

79.

Schmidtmann

, Mullens

, Schwager

, Spear

. Distribution, abundance and a probability model for larval Culicoides variipennis (Diptera: Ceratopogonidae) on dairy farms in New York State. Environ Entomol, 1983; 12:768–773.

80.

Schmidtmann

, Bobian

, Belden

. Soil chemistries define aquatic habitats with immature populations of the Culicoides variipennis Complex (Diptera: Ceratopogonidae). J Med Entomol, 2000; 37:58–64.

81.

Schmidtmann

. Testing the relationship between dissolved salts in aquatic habitats and immature populations of the Culicoides variipennis complex (Diptera: Ceratopogonidae). J Med Entomol, 2006; 35:1154–1160.

82.

Schmidtmann

, Herrero

, Green

, Dargatz

, et al. Distribution of Culicoides sonorensis (Diptera: Ceratopogonidae) in Nebraska, South Dakota, and North Dakota: Clarifying the epidemiology of bluetongue disease in the Northern Great Plains region of the United States. J Med Entomol, 2011; 48:634–643.

83.

Shapiro

, Wiegers

, Dulac

, Bouffard

, et al. A survey of cattle for antibodies against bluetongue and epizootic hemorrhagic disease of deer viruses in British Columbia and southwestern Alberta in 1987. Can J Vet Res, 1991; 55:203–204.

84.

Sleeman

, Howell

, Knox

, Stenger

. Incidence of hemorrhagic disease in white-tailed deer is associated with winter and summer climatic conditions. EcoHealth, 2009; 6:11–15.

85.

Small

. Environmental management for vector control. In: Marquardt

, ed. Biology of Disease Vectors, 2nd ed. Burlington, MA: Elsevier Academic Press, 2005:639–647.

86.

Smith

, Stallknecht

. Culicoides (Diptera: Ceratopogonidae) collected during epizootics of hemorrhagic disease among captive white-tailed deer. J Med Entomol, 1996; 33:507–510.

87.

Smith

, Stallknecht

, Sewell

, Rollor

, et al. Monitoring of Culicoides spp. at a site enzootic for hemorrhagic disease in white-tailed deer in Georgia, USA. J Wildl Dis, 1996; 32:627–642.

88.

Stallknecht

, Allison

, Park

, Phillips

, et al. Apparent increase in reported hemorrhagic disease in the Midwest and northeast United States. J Wildl Dis, 2015; 51: doi: 10.7589/2013-12-330.

89.

Tabachnik

. Culicoides variipennis and bluetongue-virus epidemiology in the United States. Annu Rev Entomol, 1996; 41:23–43.

90.

Tanya

, Greiner

, Gibbs

. Evaluation of Culicoides insignis (Diptera: Ceratopogonidae) as a vector of bluetongue virus. Vet Microbiol, 1992; 32:1–14.

91.

Venail

, Mathieu

, Setier-Rio

M-L

, Borba

, et al. Laboratory and field-based tests of deltamethrin insecticides against adult Culicoides biting midges. J Med Entomol, 2011; 48:351–357.

92.

Viennet

, Garros

, Rakotoarivony

, Allène

, et al. Host-seeking activity of bluetongue virus vectors: Endo/exophagy and circadian rhythm of culicoides in western Europe. PLoS ONE, 2012; 7:e48120.

93.

Volf

, Kiewegová

, Nemec

. Bacterial colonisation in the gut of Phlebotomus duboscqi (Diptera: Psychodidae): Transtadial passage and the role of female diet. Folia Parasit, 2002; 49:73–77.

94.

Wilson

, Mellor

. Bluetongue in Europe: past, present and future. Phil Trans Royal Soc B Biol Sci, 2009; 364:2669–2681.

95.

Zimmer

, Brostaux

, Haubruge

, Francis

. Larval development sites of the main Culicoides species (Diptera: Ceratopogonidae) in northern Europe and distribution of the coprophilic spceis larvae in Belgian pastures. Vet Parasitol, 2014; 205:676–686.

96.

Zimmerman

, Turner

Jr. . Seasonal abundance and parity of common Culicoides collected in blacklight traps in Virginia pastures. Mosq News, 1983; 43:63–69.