Environmental Determinants of Seasonal Body Size Variation in the Milkweed Leaf Beetle, Labidomera clivicollis (Kirby) (Coleoptera: Chrysomelidae)

Abstract

Milkweed leaf beetles, Labidomera clivicollis (Kirby), eclosing later in the fall in central Texas have smaller adult sizes. Laboratory studies show that this seasonal decline is more probably due to deteriorating larval food supplies than to decreasing temperature, decreasing photoperiod, or maternal effects on egg weight. Adult size can vary greatly, because larvae in the last stadium become competent to metamorphose at weights much lower than those normally attained under favorable nutritional conditions. Because Labidomera can diapause only in the adult stage, the ability to complete development at low larval weights should be adaptive when the environment becomes increasingly foodand time-limited.