SOURCES OF RESISTANCE IN WILD MATERIALS OF BEANS TO THE ATTACK OF THE COMMON BEAN SPEAT, Acanthoscelides obtectus (SAY)

Abstract

Since no acceptable levels of resis­tance to Acanthoscelides obtectus (Coleoptera: Bruchidae) were found in cultivated bean lines, over 200 Mexican wild accessions were tested. Eighty-five percent of them were classified as intermediate or resistant to the insect attack. The rearing of A. obtectus for 3 generations in re­sistant lines reduced the reproductive capacity of the insect by up to 100%. In free-choice and no-choice test adult oviposition preference and larvae, seed­penetration preference was tested. A mean of 49.8 eggs per pod in resistant varieties versus 136,4 eggs per pod in susceptible varieties were found. When an age-specific life table was developed, the net reproductive rate (Ro) calculated was lower in the resistant variety than in the susceptible check. Pods and seed-coat were studied as factors negatively influencing the capacity of the insect to successfully colonize the wild accessions. The seed coat affected insect development slightly but the greatest effect was found when the insect fed on the cotyledons.