Threshold weight for starvation-triggered metamorphosis in the yellow-spotted longicorn beetle, Psacothea hilaris (Coleoptera: Cerambycidae)

Abstract The development of 4th stadium Psacothea hilaris larvae under various feeding and starving regimens was investigated to determine whether there is a threshold weight for metamorphosis. In larvae fed ad libitum, 56% of individuals spent a mean of 13 d in the 4th stadium and 18 d in the 5th stadium before pupation, whereas the rest remained in the 4th stadium for 24 d and pupated. When starved upon ecdysis to the 4th stadium, no larvae molted to the 5th stadium and most eventually died without pupation. In contrast, when larvae were fed for 1 d and then starved. 47% prematurely metamorphosed into small pupae after a mean of 18 d in the 4th stadium. Pupation success from the 4th stadium increased as the feeding period was extended. reaching 97% in the larvae that had fed for four days. All these pupae gave rise to small but morphologically normal adults. The relationships between the weight changes of experimental larvae during starvation and their pupation success suggested the threshold weight for metamorphosis to be 180 mg. The adaptive significance of premature pupation in starved P. hilaris is discussed as a life history strategy under unpredictable food conditions for larval growth.