Development rates of Callosobruchus maculatus (Coleoptera: Chrysomelidae) in landrace cowpea varieties occurring in southwestern Amazonia

Abstract

Cowpea, Vigna unguiculata (L.), constitutes an important source of protein in various parts of the world, and landrace varieties are widespread in the southwestern Amazon. The population growth of insects is related to survival strategies in response to the feeding substrate. Thus, the development of Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae) in four landrace varieties of cowpea (VBRL 02, VSNA 02 VRDR 02 and VRBC 02) was determined through daily and accumulated emergence rates. These varieties were selected for this study because they are well distributed throughout the Amazonian communities. Cowpea samples (150 g) of each variety were infested with 50 unsexed adults, and the insects were removed 13 days after beginning the bioassays. To determine the daily emergence rates in the varieties, the adult progeny obtained from the feeding substrate was counted and removed on alternate days after the first emergence, until the end of the emergence period (45 days after the beginning of bioassays). The sum of the daily emergence was accumulated since the initial emergence and resulted in the sum of accumulated emergence (SEa, % day), calculated by SEa = ∑ SEd. We found variations in daily and accumulated emergence rates between the four varieties, and the lowest rates of daily emergence of C. maculatus occurred in the varieties VBRL 02 and VSNA 02. The accumulated emergence was delayed in the variety VBRL 02. These results indicate that landrace varieties of cowpea occurring in the southwestern Amazon are a source of features of resistance to bruchids.