Measurement of the Tolerance in Improved Bean Lines Bred for Resistance to the Bean Leafhopper Empoasca Kraemeri Ross & Moore (Homoptera: Cicadellidae)

In order to measure the efficiency of improved bean lines bred for tolerance to the bean leafhopper Empoasca kraemeri Ross & Moore, the tolerant bean lines EMP 414 and EMP 419 were compared with a susceptible check, BAT 41. These materials were subjected to varying levels of chemical protection. Regressions of nymphal populations on yield and number of insecticide applications on yield were used to calculate yield functions, and yield losses at different population levels. Economic analysis of the data was also performed. Consistently, the susceptible check BAT 41 showed high levels of susceptibility compared with tolerant lines bred for resistance, resulting in high losses at all levels of insect population pressure. The only way in which BAT 41 can compete with the tolerant lines is by means of total chemical protection. The economic analysis showed that the susceptible variety BAT 41 competes in economic terms with lines tolerant to the insect when it receives five applications of insecticide (the treatment called 'farmer'); and in a low but still acceptable level, when it receives three applications (at level 2 nymphs/leaf). The material achieves its greatest yield potential when free from insect damage. The advantage of the tolerant lines becomes evident when controlled at a level of 4 nymphs/leaf (two applications), and reaches its maximum expression when no chemical control is used. The benefit/cost ratios (B/C) for the breeding lines EMP 419 and EMP 414 were 1.4 and 2.5 times higher than that of BAT 41, respectively.