Interspecific Variation in Aggressive Fighting Behavior of Shelter-Building Caterpillars

Abstract

Herbivorous insects rarely directly compete over food resources, except in the case of concealed feeders when the food source also serves as shelter and territory. The objective of this study was to characterize the competitive behaviors of four common, co-occurring caterpillar species that tie together overlapping leaves on white oak – Psilocorsis quercicella (Oecophoridae), P. cryptolechiella, P. reflexella, and Pseudotelphusa quercinigracella (Gelechiidae). Artificial leaf ties were created by clipping a piece of transparency paper to a white oak leaf. An ‘occupant’ caterpillar was allowed to build a shelter between the transparency paper and leaf, after which an ‘intruder’ caterpillar was introduced into the leaf tie. Caterpillars were observed pushing and hitting one another to gain or maintain access to the shelter. The occupant caterpillar maintained possession of the shelter in 52 % of the interactions, the intruder usurped the shelter from the occupant in 24 % of the interactions, and the caterpillars shared the shelter in 24 % of the interactions. The four species examined differed significantly in their behavior toward other caterpillars, and ordered most to least aggressive are P. reflexella, P. cryptolechiella, P. quercicella, and Pse. quercinigracella. There were also behavioral differences within and between species when acting as an occupant or an intruder. Psilocorsis cryptolechiella was more aggressive and Pse. quercinigracella was less aggressive when defending a shelter than when attempting to usurp a shelter. It was also found that the four focal caterpillar species, when collected from naturally colonized leaf ties, co-occur significantly less often than expected when compared to a null model. It appears that direct competition for shelters that serve as a territory as well as a food source is frequent and influences the composition of the leaf-tying caterpillar community.