Resistance to the Bean Weevil and the Mexican Bean Weevil (Coleoptera: Bruchidae) in Noncultivated Common Bean Accessions

Abstract

Low levels of resistance were found in cultivated genotypes of the common bean, Phaseolus vulgaris L., to the bean weevil, Acanthoscelides obtectus (Say), and to the Mexican bean weevil, Zabrotes subfasiatus (Boheman). However, high levels of resistance to each weevil were found in noncultivated wild forms of beans; some wild accessions were resistant to both insects. Resistance was expressed as reduced oviposition, a prolonged larval developmental period, and reduced progeny weight. Although weevil resistance was related to small seed size, other factors were probably more important. Resistance levels were maintained when the insects were reared for three generations on the same accession; on two accessions, A. obtectus colonies died. Bruchid reproduction on a susceptible variety was reduced when adults that had emerged from a resistant variety were used. Adults of both species preferred seeds of susceptible lines for oviposition or larval penetration. Resistance was expressed not only in the seed but also in the podwalls. Fewer pods were perforated by adults and larvae of A. obtectus , and fewer eggs were laid by both species in pods of resistant accessions under both free-choice and no-choice conditions.