Seasonal decline of body mass in adults of the wood-dwelling caddisfly Lype phaeopa (Psychomyiidae)

Abstract

Larvae of the psychomyiid caddisfly Lype phaeopa (Stephens 1836) were reared under close to outdoor temperature conditions to investigate the seasonal fluc- tuations in body masses of emergent adults. The adult emergence period lasted from late February until late September, with two emergence peaks of males (March and August) and one for females (September). Females were always larger than males, illustrating a strong sexual size dimorphism. Decreasing body mass of emergent adults coincided with increasing temperature during the seasons until the end of the emer- gence period. Both sexes showed a significant relationship between body mass and wing length, which allowed me to estimate the loss of female body mass due to oviposition (55.7% ± 4.9). Egg size remained constant throughout the study (ovoid shape, mean length 216 µm, width 186 µm) but number of eggs decreased. The results imply that increasing temperature could be responsible for the decline in size and body mass of emergent adults (both sexes). A reason for this size reduction could be a constant growth rate (biomass increment) but an accelerated developmental rate induced by increasing tem- perature.