A Comparative Examination of Life-Span and Fecundity in Parasitoid Hymenoptera

Abstract

(1) Body size and ecological differences are often assumed to be related to measures of life-span and fecundity in insects. These relationships have never been demonstrated across species while controlling for the effects of taxonomic relatedness. (2) Here I present the first tests of the hypotheses that life-span and fecundity are correlated with adult size and ecological differences across species within an insect taxon, using 474 species of parasitoid Hymenoptera. (3) No evidence is found for relationships between adult length and either adult lifespan or fecundity. Body length correlates less well with life-history variation in parasitoids than it does in vertebrate taxa. Adult length is found to correlate with other components of life-span, although the proportion of variance it explains is low. (4) None of the components of life-span are found to correlate with any of the ecological variables with which relationships are predicted. Fecundity only correlates significantly with parasite window (the period for which an individual host is vulnerable to attack by a given parasitoid species), but this relationship is not in the predicted direction. (5) Several ecological differences are correlated with components of preadult life-span when the effects of body size are controlled for: parasitoids of poorly concealed hosts have shorter incubation periods, koinobionts (species in which the host is not killed until the immature parasitoid has almost completed development) have longer pupal periods and preadult life-spans than idiobionts (species in which the host is permanently paralysed or killed by the adult parasitoid before oviposition), temperate species have longer developmental periods than tropical species, and the developmental periods of egg parasitoids are longer than those of pupal parasitoids. Parasitoids with more vulnerable juvenile stages spend less time in these stages. (6) The results are interpreted as reflecting different degrees of variation in the environments of adult and immature parasitoids: immatures may face less variable, more precisely defined environments, as the result of their close associations with their hosts. As a consequence, life-history variation can be more precisely related to environmental differences for immature parasitoids than it can for adults.