CROWDING, MATERNAL AGE, AGE AT PUPATION, AND LIFE-HISTORY OF ZOPHOBAS-ATRATUS (COLEOPTERA, TENEBRIONIDAE)

In Zophobas atratus (F.), crowding of larvae inhibits pupation, wherea s isolation of crowded larvae triggers pupation, allowing duration of the larval stage to be manipulated experimentally. Effects of larval a nd adult crowding, birth order (maternal age), and duration of larval stage (Iarval age at pupation) on larval growth, adult reproduction, a nd adult longevity were determined in a factorial experiment spanning 2 1/2 generations. Larval growth decreased with density and increased with birth order. As larvae grew, they became repelled by other larvae and dispersed for pupation: the proportion pupating successfully firs t rose with age, then fell as death at metamorphosis became more frequ ent. Experimental isolation of larvae produced cohorts of adults that had spent 4, 7, and 10 mo as larvae. Body weight of these adults incre ased with larval age, decreased with larval density, and was higher fo r males. These F1 adults were allowed to breed at high and low density until they died. Lifetime egg and larval production generally decreas ed with birth order and larval age and increased with adult density. M ale (but not female) longevity was strongly reduced by adult crowding. Both male and female longevity declined with birth order and larval a ge. The experimental factors acted on lifetime reproduction largely th rough their effects on longevity, but there remained a direct negative effect of birth order and larval age. Body weight and reproduction we re uncorrelated because females of early birth order and early pupatio n were lowest in body weight but had the highest reproductive output. Females produced their highest-quality offspring early in life, but th e effect was delayed until their offspring reproduced. These effects a re discussed in light of their possible importance in this beetle's li fe history and population dynamics.