Diet and chemical defence in ladybird beetles (Coleoptera: Coccinellidae)

In this paper, I review the effects of the diet of ladybirds on chemical defence in this group of beetles. The tendency to reflex bleed and the diversity of autogenously produced alkaloids in different taxa may be evolutionarily related to diet and the likelihood of food limitation. Within predatory species, both prey quantity and quality have been shown to affect autogenous alkaloid production. A few ladybird predators have been suggested to adaptively sequester toxins from their prey for their own defence. However, in most cases the evidence for this is limited, with questions remaining about the costs of accumulated toxins and their defensive value, especially over and above pre-existing autogenous defence. Only a single case (Hyperaspis trifurcata and carminic acid) is well supported. In the case of ladybird predators acquiring pyrrolizidine alkaloids from the ragwort aphid Aphis jacobaeae, I show that toxin accumulation is not very costly and the aphid is even an essential prey for some ladybirds. However, the defensive value of pyrrolizidine alkaloids to ladybirds is still not investigated. Intraspecific diversity in autogenous chemical defence could be reinforced further if chemical protection is conferred via sequestered chemicals. However, to understand better how ladybird diet and chemical defence interact, we need a clearer grasp of how the defensive chemicals of food are resisted or tolerated by ladybirds.