A phenotypic and genetic comparison of egg to adult life-history traits between and within two strains of the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Abstract

Using a transplantation technique, a phenotypic comparison of egg to adult life-history traits between Costa Rican and Togo strains of the Larger Grain Borer, Prostephanus truncatus, revealed differences in egg weight, development period and body weight at emergence with the heavier Costa Rican strain ovipositing heavier eggs. A genetic comparison revealed differences in body weight at emergence, confirming that the strains are genetically distinct. For both strains assayed at low density (1 egg/maize kernel) females were heavier than males but development periods were the same, sex ratio was unity and egg hatchability and egg to adult survivorship were high. Adult life-history traits were measured on the Costa Rican strain. Productivity was found to increase initially but then to decrease steadily with age. Longevity was prolonged (> 100 d). For both strains offspring-parent regression analyses revealed significant ‘narrow-sense’ heritabilities for body weight at emergence but not for development period. For the Costa Rican strain full sib/half sib analyses showed significant additive genetic variation for body weight at emergence but not for development period, no genetic but a strong negative environmental correlation. There was no indication that an increase in development rate was genetically associated with a decrease in body weight as predicted by the ‘trade-off’ theory.