Geographical variation and sexual dimorphism of phenoloxidase levels in Japanese beetles (Popillia japonica).

Phenoloxidase (PO) production can be used as an indicator of pathogen defence in insects. The geographical mosaic of coevolution implies that traits associated with pathogen defence will vary across a geographical range. Bateman's principle implies that the benefit of increased defence levels is greater for females than males. To test both of these hypotheses, we sampled four populations of Japanese beetles, Popillia japonica, across Vermont: two were from locations using biological pest control, and two locations did not use biocontrol. We quantified defence levels (PO) and parasite resistance in males and females from each population. Populations from areas with biocontrol exhibited greater PO production, females produced more PO, populations with higher levels of PO suffered less mortality from pathogen exposure, and PO levels positively correlate with increased mortality in the absence of parasitism. Results support the geographical mosaic of coevolution and the implications of Bateman's principle.