Female beetles facilitate leaf feeding for males on toxic plants

Milkweed plants produce latex, which works as a defence against some herbivorous insects. The cerambycid beetles Tetraopes femoratus ( LeConte ) puncture the leaf midrib vein to extravasate the latex, and thus render the leaf edible. Nonetheless, it has not yet been investigated whether there is any further implication beyond food acquisition regarding this behaviour. The present study examined the hypothesis that leaf latex drainage is done mainly by females of T. femoratus , and that the males opportunistically prefer to feed on those ‘disarmed’ leaves. The experiments revealed that puncturing the leaf midrib vein to extravasate latex is done mainly by females of T. femoratus and not only serves their purpose of food acquisition, but also mediates an opportunistic feeding behaviour among males. Males of T. femoratus preferred to feed on milkweed leaves that had previously been fed upon by females. In addition, field observations showed that mating occurred more frequently on recently ‘disarmed’ leaves, suggesting increased copulation opportunities for females during leaf feeding. In sum, the results reveal that the feeding defence strategy of T. femoratus females to toxic milkweed foliage has created an opportunity for males to feed on milkweed leaves with a reduced risk of latex exposure and entanglement. Thus, this research provides empirical evidence of plant–insect interactions contributing to the appearance of an opportunistic adaptive feeding behaviour, which has broader implications for eco‐evolutionary systems.