Feeding and Nutrition of Insects Associated with Soybeans. 2. Soybean Resistance and Host Preferences of the Mexican Bean Beetle, Epilachna varivestis1

Abstract

Dual choice tests were used to analyze food preferences by the Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera: Coccinellidae). Seven series of tests including 26 comparisons of Clark normal, Harosoy normal, and Bragg soybeans with 6 Clark and Harosoy isolines, 9 resistant selections, and 5 other species of legumes were performed. It is suggested that there is no evidence for an influence of leaf pubescence on the acceptance of Clark and Harosoy soybeans. All Clark isolines were preferred to Harosoy normal, regardless of leaf pubescence. The selections Pi's 227,687 and 171,451 were low in the food preference scale indicating a strong nonpreference type of resistance. Pi's 229,358, 243,519, and 81,777 were partially rejected by adult beetles. F1 cross of Bragg × PI 229,358 showed a preference index intermediate between that of the parent lines suggesting a semidominance type of inheritance of the resistance trait. Soybean-associated Mexican bean beetles do not seem to have drastically shifted their food preferences, as they prefer snap and lima beans even under action of possible induction effect of a continuous soybean diet. The paired comparison test seems to be a useful subsidiary bioassay in a breeding program for soybean insect resistance.