Mitsuru Hattori

To feed on prey efficiently, predators must overcome the prey's defensive traits. However, there are fewer reports on the antagonistic traits of predators than there are on the defensive traits of prey. Here, we focus on prey–predator interactions between social aphids and aphidophagous lepidopteran larvae. Larvae of Taraka hamada (Lepidoptera: Lycaenidae) are specialist predators of the social aphid Ceratovacuna japonica (Homoptera: Aphididae), and later instar larvae have long lateral body setae. Because this aphid produces defensive individuals (soldiers), we hypothesised that T. hamada larvae have an antagonistic trait that prevents attacks by soldiers and tested whether that trait might be their lateral body setae. To test whether a larva's lateral body setae constitute an antagonistic trait against the soldier's physical defence, we compared the rate of aphid consumption per unit time and the vulnerability to attack by soldiers between larvae with short lateral body setae and larvae with long lateral body setae in the presence of soldiers. Our results showed that the aphid consumption rate of larvae with long lateral body setae was significantly higher than that of larvae with short lateral body setae. Furthermore, the larvae with short lateral body setae were more vulnerable to soldier attacks than the larvae with long lateral body setae. These results imply that the length of the lateral body setae of T. hamada larvae affects their vulnerability to soldier attacks and that the lateral body setae are an antagonistic trait against the soldiers of this social aphid.