SYMBIOCONTROL · The role of the bacterial symbiont Cardinum in shaping the ecology and evolution of an insect parasitoid wasp: fundamental studies and implications for biological control of plant pests

Arthropods can be infected by facultative symbionts with diverse effects on host reproduction and fitness. Cytoplasmic reproductive incompatibility (CI) appears to be the most prevalent effect, and is caused by two unrelated bacteria: Wolbachia and the recently discovered Cardinium. Bacteria-induced CI is of special interest as it may play a role in reproductive isolation and speciation of insect hosts. Reproductive barriers can arise also by incompatibility due to hybridization (HI). Cardinium-induced CI occurs in the parasitoid wasp Encarsia pergandiella, a natural enemy of agricultural pests, and may have important implications for its use in biological control. Indeed, CI may lead to a suppression of population growth when populations with a different infection status interact. Nevertheless, understanding the role of heritable bacterial symbionts in the biology of natural enemies has not yet been widely recognized as a key research objective of biocontrol programmes.The project aims to: 1) evaluate the role of CI-inducing bacteria and genetic isolation mechanisms in reproductive isolation and competitive interactions of parasitoid populations; 2) evaluate how the introduction of a new biocontrol agent that is partially reproductively isolated (via CI or HI) from an established parasitoid population affects the biological control of a key agricultural pest. The project will use fundamental studies of CI and HI to develop quantitative models of population interactions, and then test model predictions in population cage and greenhouse studies. The data collected will be used to develop a conceptual model for biocontrol agents with different geographical ranges and reproductive incompatibilities in order to understand the consequences for biological control.