TIME AND ENERGY COSTS OF COPULATION FOR THE SPHINX MOTH, MANDUCA-SEXTA

In some insects copulation may represent a significant fraction of rep roductive effort, yet its energetics are unexamined. The hawkmoth Mand uca sexts, recognized for its endothermy and high metabolic scope (> 1 00), was largely quiescent during copulation, which averaged about 3 h (n = 31). However, we occasionally observed long bouts of abdominal p umping by both sexes, suggesting elevated respiratory rates. The CO2 p roduction of 1-d-old copulating pairs was recorded in an open-flow res pirometry system and averaged 0.508 cc g(-1) h(-1) (n = 6). Comparison of these rates with the resting metabolic rates of the same males and females on the days before (0.545 cc g(-1) h(-1)) and after (0.435 cc g(-1) h(-1)) copulation shows that metabolic rates during copulation are not different from resting rates. Thoracic temperatures of mating moths averaged 0.31 degrees C above ambient temperatures (n = 11), als o indicating resting metabolism. Body mass measurements before and aft er copulation suggest that males transfer a maximum of about 0.16 g, o r 7% of body mass. We conclude that copulation in Manduca, while repre senting a substantial time investment, is metabolically inexpensive.