Resistance of important bean genotypes to the Mexican bean beetle [Zabrotes subfasciatus (Bohemann)] during storage and its control with chemical synthetic and botanical insecticides

Abstract

During storage, beans can be infested with many insect-pests including Zabrotes subfasciatus, a key pest of these crops. This study aimed to identify bean genotypes demonstrating antixenosis and/or antibiosis to Z. subfasciatus and to test their integration with chemical control. The ultimate goal of assessment was to distinguish whether genotypic and insecticidal factors can provide effective beetle control. The tested genotypes were (a) Phaseolus vulgaris group: CCB, BSCB, BCB and PCB; (b) Vicia faba group: YBB, WBB and SBB; and (c) Vigna unguiculata group: C and GC. Initial assays were run to select genotypes (without insecticide treatment) that would be further tested with insecticides. Final assays included genotypes with varying degree of antibiosis and antixenosis treated with a neem formulation (Natuneem) and distilled water (control) plus deltamethrin (Decis) which latter was used only in the final antibiosis assay. The insecticides were used at the rates of 3 and 0.1 mL of Natuneem and Decis, respectively, per 30 mL of distilled water. There were no differences in preference of Z. subfasciatus adults among non-treated genotypes (initial assays), although neem-treated genotypes altered the preference and reduced infestation from 40.54-100% (final assays). In antibiosis tests, oviposition and density of emerged adults were reduced among C and SBB, and SBB also reduced the weight of emerged adults. Insecticides reduced oviposition in 53-100% and yielded half to five-fold fewer emerging insects weighting 35%-40% less in antibiotic genotypes. SBB was the most antibiotic genotype and this and other genotypes possessing antibiosis had a synergistic effect with neem or deltamethrin.