Secondary (i.e. facultative) endosymbionts (SS) have recently been found to influence the resistance of their host, Acyrthosiphon pisum Harris (Hemipter: Aphidae), to parasitoids and fungal pathogens. If the presence of maternally-transmitted secondary endosymbionts influences host survival or reproduction, then disparate selection pressures among populations should influence infection frequencies on a geographic level. Only some individuals of an invasive psyllid (Glycaspis brimblecombei) that colonizes eucalyptus in California possess one particular type of facultative SS. The frequency of SS-infection varies dramatically among G. brimblecombei populations, and is positively related to parasitism pressure by a wasp natural enemy. This project will investigate whether parasitism is a key mechanism that maintains SS-infection frequencies among populations. The diversity, occurrence, and effects of endosymbionts harbored in insects are largely unknown. This project will address the relationship between the frequency of infection by secondary endosymbionts and parasitism. A primary goal is to determine if there is a fitness advantage or cost for a host insect to possess secondary endosymbionts when parasitism by its natural enemy (P. bliteus) is present or absent. Broader impacts of the project include student training and potential application to management of agricultural insect pests and invasive species.
