Avoidance of intraspecific competition via host modification in a grazing, fruit-eating insect

Insects feeding on plants may induce chemical and physical changes in the host plants. Here, we present evidence of host plant modification following an insect attack that may be associated with a reduction in intraspecific competition for food. We demonstrate that feeding by larvae of the cranberry fruitworm, Acrobasis vaccinii, induces a change in fruit colour (from green to red) of cranberry fruits, Vaccinium oxycoccos, that is associated with a significant increase in the concentration of anthocyanin. Host fruit colour affected larval foraging behaviour and food acceptance: significantly more cranberry fruitworm larvae were attracted to, and accepted, green rather than red fruits. Our experiments suggest that fruit reddening also prevents exploitation by conspecific larvae of other green fruits adjacent to the attacked fruit.