Oviposition preference, population growth and digestive enzymatic function of Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) on six legume grains

The cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is one of the most pernicious pests of stored legume grains in tropical and subtropical areas. Population performance and digestive enzymatic function of C. maculatus can be affected by nutritional quality and antinutritional compounds of legume grains on which it was fed. We reared C. maculatus on six legume grains (cowpea, chickpea, mung bean, soybean, faba bean, and peanut) to investigate the effects of the insect feeding on free-choice oviposition preference, population growth and digestive enzyme activity. The laboratory experiments were conducted at 28 ± 1 °C, relative humidity of 65 ± 5% and 24 h darkness. In a free-choice situation with other legume grains present, females laid the highest number of eggs on cowpea, and avoided laying eggs on peanut. Pre-adult survival of the weevil was the lowest on peanut and highest on mung bean. The developmental period on soybean and faba bean was longer than on mung bean and cowpea. Fecundity (number of eggs laid per female) of C. maculatus on cowpea grains was about 3.7-fold more than on peanut. The intrinsic rate of increase (r) and finite rate of increase (λ) on cowpea, mung bean and chickpea were higher than on soybean, faba bean and peanut. Amylolytic activity of fourth instar larvae fed with peanut, soybean and cowpea was higher than faba bean. Total proteolytic activity of these larvae fed with cowpea was higher than chickpea and mung bean. Our results indicate that cowpea, mung bean and chickpea are the most vulnerable hosts to C. maculatus infestation. The grain coat thickness and phenolic content of tested legumes play an important role in the development and population growth of C. maculatus, and these features could be used to develop effective management of this pest by the production of genetically engineered cultivars.