Stage Sensitivity to Food Limitation for a Generalist Arthropod Predator, Pterostichus cupreus (Coleoptera: Carabidae)

Abstract

Adults and larvae of the ground beetle Pterostichus cupreus L. were reared at 3 feeding regimes in the laboratory to assess how food availability affects fitness correlates in different developmental stages. Adults were collected from 3 localities in early spring at emergence from overwintering. Origin of adults was recorded to investigate differences in response to food level among localities. The importance of food availability for adult mortality, fecundity, wing muscle development, egg size, larval growth rate and mortality, and pupal weight was assessed. Overwintering mortality at 2 food levels was estimated in 2 experiments, in 1994–1995 on young adults and in 1995–1996 on 1-yr-old adults. Fecundity of adults and body mass increased markedly with feeding rate. Feeding by adults provides most resources for reproduction in P. cupreus . The relationship between food supply and fecundity in the laboratory was affected by the origin of the beetles, suggesting that poor teneral conditions in the field are not compensated by better conditions later in development. Pupal weight, which is a function of larval growth, decreased with decreasing food availability. Mortality of adults and larvae was not affected by food availability, and prewinter food levels did not affect overwintering mortality. Egg size was unaffected by food availability and wing musculature did not increase with decreasing food availability, giving no indication of a trade-off between fecundity and migratory capacity. A nondestructive measure of adult feeding rate was developed by relating body mass and size to observed energy reserves (measured as fat bodies) in dissected beetles.