Effects of a larval antipredator response and larval diet on adult phenotype in an aposematic ladybird beetle

Abstract

Many ladybird beetles respond to a potential predation event by `reflex bleeding' or secreting a noxious defensive chemical that is similar to hemolymph. Both adults and larvae show this response. Reflex bleeding is known to reduce predator attack rates and increase prey survival after an attack, especially when reflex bleeding is employed in combination with other cues such as odor and warning coloration. In this experiment, we examined how variability in the number of reflex bleeding events and food quality in the larval stage of the aposematic ladybird beetle Harmonia axyridis affected elytral color, development time, and terminal size in adults. Effects of reflex bleeding were subtle and may have been influenced by diet treatments. Adult color did not differ between bleed treatment groups but beetles that reflex bled tended to take longer to develop and grow to smaller sizes than control group beetles. There were clear and strong effects of larval diet on adult phenotype: an ad libitum pollen diet resulted in paler adult coloration, shorter development time, and larger adult size relative to a limited-availability aphid diet. Our results suggest that the best environment for producing bright-red coloration may not be the best environment for favorable expression of life history characters, especially under stressful conditions. Interactions between different life history stages of H. axyridis are also discussed.