Egg Development, Growth, and Metabolism of Sigara Alternata (Say) (Hemiptera: Corixidae) in Fluctuating Thermal Environments

Abstract

Egg development and growth of Sigara alternata in southeastern Pennsylvania, USA were evaluated in six fluctuating temperature regimes with daily maxima ranging from 12.0° to 21. 5°C. Developmental rate was positively correlated with increased magnitude of the diel temperature pulse. Developmental acceleration was most apparent for environments pulsing beyond 15.0°C for both stages. Oviposition rates were studied at natural temperatures during the initial days of reproduction. Egg deposition was sporadic but highly correlated with maximum diel temperatures. A critical temperature region of 11.0—12.5°C was observed for initiation and maintenance of egg laying. Metabolic rates were measured using a different respirometer. The thermal response of metabolism varied with animal soze and the range of test temperatures. The energy demand per uniy weight of tissue was inversely related to body size at all temperatures. Adult population metabolism decreased exponentially during the peak reproductive period due to high mortality. Energy budgets were determined for nymphal development in all thermal regimes. Net growth efficiencies and production/respiration ratios for Sigara alternata ranged from 49.7—73.4% and 0.9—2.7 respectively. Assimilation rates increased with rinsing temperatures and varied between 1.05 and 3.52 J.mg—1.day—1 [=0.25 —0.84 cal.mg—1.day—1]. Net growth efficiencies tended to decrease with increased temperatures due to higher maintenance costs. The significance of fluctuating temperatures to the bioenergetics, developmental dynamics, and ecology are discussed .