Assessing temporal dynamics of predation and effectiveness of caterpillar visual defense using sawfly larval color and resting posture as a model.

Abstract

Caterpillars (Lepidoptera and Symphyta larvae) employ diverse visual defensive tactics, and effectiveness of such tactics may be highly dynamic across time due to seasonal changes in the predator assemblages and their preferences. However, this has rarely been studied especially in tropical regions. Here we assessed temporal changes in the defensive value of caterpillar color and shape, using six types of plasticine dummy caterpillars: three colors (green, black, and white) × two shapes (curled and straight). These dummy caterpillars were deployed five times over different seasons in tropical forests of Xishuangbanna (China) and, as a comparison, twice in a temperate forest of Hirosaki (Japan). The colors and shapes of dummy caterpillars simulate visual traits of black sawfly larvae which take the curled resting posture in tropical rainforests of Xishuangbanna, apparently masquerading excrements commonly found on plants, while in Hirosaki there is no black-curled sawfly larvae and few excrements on plants. We found no significant effects of caterpillar colors or shapes on predation in Hirosaki. In contrast, black and curled caterpillars received significantly lower predation by birds in Xishuangbanna constantly across time. However, we were unable to provide evidence that the black-curled sawfly larvae are masquerading as excrements. Shapes of the dummy caterpillars also affected the predation by ants and parasitoid wasps at certain times. This is the first report on ecological function of the curled posture of sawfly larvae, and we demonstrated the importance to assess the temporal dynamics of predation and effectiveness of defensive tactics in tropical forests.