ABSTRACT
Laboratory and screenhouse experiments were conducted to identify antibiosis and tolerance in four wild accessions of cowpea, Vigna unguiculata subsp. dekindtiana, to Clavigralla tomentosicollis Stål, the most damaging pod-sucking bug on cultivated Vigna genotypes in West Africa. The wild accession TVnu 151 showed antibiosis resistance, causing >50% mortality of the nymphs within 3 d of placing them on pods. Nymphs died more quickly on TVnu 151 than on TVnu 72, the wild and resistant control of the V. vexillata species which affected the weights of surviving insects to a much greater degree than TVnu 151. The three other accessions of the subspecies dekindtiana (TVnu 369, TVnu 517, and TVnu 707) did not cause significant mortality to the bugs, but rather extended their developmental time, with surviving adults showing lower weights and slower oviposition rates than those on the susceptible control IT84S-2246. Wild accessions affected male and female bugs differently, resulting in differential survival. This was reflected by the sex ratio which was male biased on the wild accessions (1:0.3-1:0.9), and female biased on IT84S-2246 (1:1.5). No evidence of tolerance was found in the four accessions of V. unguiculata subsp. dekindtiana. Overall, seed traits seemed to be the major resistance component in these wild accessions.
Subject(s)
Fabaceae , Hemiptera/growth & development , Animals , Seeds , Species SpecificityABSTRACT
Laboratory and screenhouse studies were carried out to assess the relationship between pod age and pod position of cowpea and damage by different pod bug species. The coreids Clavigralla tomentosicollis Stäl and Riptortus dentipes Fabricius caused significant damage to young pods of cultivated genotypes, in contrast to the coreid Anoplocnemis curvipes Fabricius and the pentatomid Aspavia armigera Fabricius which exhibited minor feeding activity. Percent seed damage declined with pod age, the critical stage for pod bug infestation being when pods were about eight days old. Clavigralla tomentosicollis and R. dentipes caused significantly higher damage to pods located within the leaf canopy, thus behaving differently from Anoplocnemis curvipes which showed a distinct preference for pods growing above the leaf canopy. The feeding activity of Aspavia armigera was not affected by the position of pods on the plant. Overall, the study suggests that cowpea genotypes with a short flowering period and pods held above the leaf canopy offer the most promise in the management of pod-sucking pests.
