Colour pattern polymorphism and chemical defence in Harmonia axyridis

Abstract: Chemical defence has long been considered to play some sort of role in relation tocolour pattern polymorphism in ladybirds. A recent idea is that intraspecific variation in colour orpattern is an indicator of the strength (i.e. concentration) of defensive chemicals in the individual.This has received support from a recent study showing that in non-melanic Harmonia axyridis theproportion of the elytra that is orange is positively correlated with the concentration of thealkaloid harmonine. In this paper I discuss palatability experiments with H. axyridis designed totest whether the finding can be extended across colour pattern morphs, specifically whethermelanic H. axyridis are less well defended than non-melanics. Feeding experiments using spiders(Araneus diadematus) and earwigs (Forficula auricularia) gave no indication that melanics wereless well defended than non-melanics. However, the spiders exhibited a generally high level ofacceptance of ladybird prey, making the detection of intraspecific differences in prey palatabilityunlikely, while data from earwigs is currently of too small a scale to be unequivocal. Furtherpalatability tests are required as well as additional analytical work covering the full range of H.axyridis morphs and defensive chemicals.