Factors determining larval cannibalistic behavior in invasive and native populations of the multicolored Asian ladybird, Harmonia axyridis

The frequency of interlarval cannibalism between individuals from native (Siberian) and invasive (Caucasian) populations of the multicolored Asian ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) was investigated under laboratory conditions by placing two individuals without any food in a Petri dish for 24 h. Combinations of all larval instars were used and each larva was weighed before the test. Interlarval cannibalism frequency significantly increased with the size (weight) of the potential predator and decreased with the size of the potential prey. The threshold of this dependence (50% frequency of cannibalism) was observed when the large larva was about three times heavier than the small one. Ladybird larvae that fed on the green peach aphid Myzus persicae (Sulz.) (Hemiptera: Aphididae) before the test began showed higher propensity for cannibalism than those fed on frozen eggs of the grain moth Sitotroga cerealella Oliv. (Lepidoptera: Gelechiidae). The diameter of the Petri dish (from 4 to 9 cm) had no effect on cannibalism. Previous experience of cannibalism did not increase further cannibalism frequency. With all other conditions being the same, individuals from the invasive population showed significantly higher propensity for interlarval cannibalism than individuals from the native population. The vulnerability to cannibalism, however, did not differ between the two populations. The results of the study can be used for the analysis of biological invasions, for the modeling of population dynamics, and for the development of the methods of mass rearing of H. axyridis and other predatory ladybirds.