Interspecific differences of ladybirds (Coleoptera: Coccinellidae) in their repellency to ants

Alkaloids and methoxypyrazines play a crucial role in the defence strategies of ladybirds against both arthropod and vertebrate predators. We investigated the response of the black garden ant (Lasius niger) to extracts from various ladybird species mixed with honey solution at decreasing concentrations. The tested ladybird species included Adalia bipunctata, Hippodamia undecimnotata, Coccinella septempunctata, Harmonia axyridis, Halyzia sedecimguttata, and Tytthaspis sedecimpunctata, with the lesser mealworm (Alphitobius diaperinus) serving as a control. The acceptance rate of the mixtures by ants decreased almost linearly with increasing concentrations of ladybird extract, while the acceptance of the control mealworm extract remained constant. Furthermore, no correlation was observed between the degree of deterrence and the body size, conspicuousness of aposematic coloration, or feeding specialization of the tested ladybirds. The degree of deterrence exhibited significant statistical differences among the ladybird species, with the concentration required to deter 50% of ants ranging from 3 to 7% of crude extract in a 4% honey solution. However, these differences were small and variable, suggesting limited biological significance. The degree of deterrence of individual species of ladybirds to ants that we found should be compared with their deterrence to other predators.