Mortality of native and invasive ladybirds co-infected by ectoparasitic and entomopathogenic fungi

Harmonia axyridisis an invasive alien ladybird in North America and Europe. Studies show that multiple natural enemies are usingHa. axyridisas a new host. However, thus far, no research has been undertaken to study the effects of simultaneous infections of multiple natural enemies onHa. axyridis. We hypothesized that high thallus densities of the ectoparasitic fungusHesperomyces virescenson a ladybird weaken the host’s defenses, thereby making it more susceptible to infection by other natural enemies. We examined mortality of the North American-nativeOlla v-nigrumandHa. axyridisco-infected withHe. virescensand an entomopathogenic fungus—eitherBeauveria bassianaorMetarhizium anisopliae. Laboratory assays revealed thatHe. virescens-infectedO. v-nigrumindividuals are more susceptible to entomopathogenic fungi, butHa. axyridisdoes not suffer the same effects. This is in line with the enemy release hypothesis, which predicts that invasive alien species in new geographic areas experience reduced regulatory effects from natural enemies compared to native species. Considering our results, we can ask howHe. virescensaffects survival when confronted by other pathogens that previously had little impact onHa. axyridis.