The effects of attacks by the mutualistic ant, Lasius japonicus Santschi (Hymenoptera: Formicidae) on the foraging behavior of the two aphidophagous ladybirds, Coccinella septempunctata brucki Mulsant (Coleoptera: Coccinellidae) and Propylea japonica (Thunberg) (Coleoptera: Coccinellidae)

Abstract

As difference in food requirements of aphidophagous ladybirds might have an influence on the strength of interactions between the ladybirds and mutualistic ants, the effects of ant attacks on the foraging behavior of the two ladybird species, Coccinella septempunctata brucki and Propylea japonica, were investigated in relation to their developmental stages (adults and larvae). Large-sized C. septempunctata adults preyed on more aphids and were more frequently attacked by the ants than another species and developmental stage. Escape rates of the ladybirds after attacking tended to be higher in adults than in larvae. The percentage of C. septempunctata adults remaining on the plant in the ant-present treatments was significantly lower than in ant-excluded treatments, while there was no significant difference in the proportion of P. japonica adults between the two treatments. The proportion of larvae of both species was high even in ant-present treatments. This study revealed that the effects of ant attacks on the ladybirds differed between the two species in relation to their developmental stages, suggesting that food requirement of ladybirds would be one of important factors to understand the relationship between aphidophagous ladybirds and mutualistic ants.