Divergent life-history traits of Callosobruchus Chinensis (L.) (Coleoptera: Bruchidae) infesting stored pulses

Abstract

This study examined divergent life-history traits of the bean weevil, Callosobruchus chinensis (L.) fed on large-seeded gardenpea (Pisum sativum Linn., cv Pusa-257; 48.3±0.4 mm2/seed and 250.5±0.2 mg dry/seed) and small-seeded lentil (Lens esculanta Moench, cv B-256; 16.7±0.2 mm2/seed and 26.2±0.1 mg dry/seed) cotyledons. All experiments were conducted in the laboratory maintaining 27±2.5°C temperature, 70±10% relative humidity and 12±1.8L natural photoperiod at Burdwan (23°16' N and 87°54' E) over March 1997 – February 1998. Head-capsule widths, length and biomass of the four larval stages differed significantly (P<0.05), and the beetle fed these cotyledons showed four distinct larval instars. The hatching rates and biomass of larvae fed on gardenpea were higher than those fed on lentil, but the egg incubation, larval periods, and mortality of larvae fed on gardenpea showed inverse relationships. The length and biomass of the pupae raised on gardenpea were higher than those raised on lentil, while the pupal period and mortality of the pupae raised on gardenpea showed inverse relationships. Freshly emerged females were slightly longer (1.01:1) and heavier (1.01:1) than males fed on both host plants. Females outlived males by 49.9 to 52.2 h, and showed 10.3 – 6.2% higher survival rates. The male: female ratios of the newly emerged beetles did not deviate much from the expected 1:1, and the heterogeneity chi-square showed that results were consistent between host beans and sexes. The reproductive potential (rm) of females fed on gardenpea was slightly higher (10.02) than those fed on lentil. The rm was maximum (0.24 and 0.20) during July–August 1997 generations, and minimum (0.06 and 0.04) during December 1997 – February 1998 generations. The fecundity was highest (168.8±2.6 and 86.2±2.3 eggs/female fed on gardenpea and lentil, respectively) and lowest (4.8±0.3 and 2.5±0.15 eggs/female fed on gardenpea and lentil, respectively) during July–August 1997, and December 1997 – February 1998 generations. Beetles reared on gardenpea and lentil cotyledons had four distinct life-history stages of various durations and measurements, and took 43–53 and 44–66 days, respectively, to complete their life cycle.