Predators and microsporidia transmission in forest insects

Transmission of the pathogen from infected to susceptible individuals is a key aspect of interactions between insect hosts and their pathogens. The intimate relationships of hosts and pathogens can be influenced by abiotic and biotic factors; the latter include other pathogens, parasitoids or predators. Only little knowledge exists about predator-prey-pathogen interactions in forest Lepidoptera. The behavior of predators may be an important factor in transmission success of the pathogen, either by removing the host from the population or by dispersing viable pathogenic stages. We propose to use the following model system to investigate how the transmission of a pathogen in forest insect populations is influenced by the action of predators. The gypsy moth, Lymantria dispar will serve as host for two different microsporidia, Vairimorpha disparis and Nosema lymantriae, as well as prey for two different predators, the generalist ant Formica fusca and the specialist beetle Calosoma sycophanta. Previous and ongoing research has provided important information about the transmission pathways of both microsporidian species that utilize different host tissues. But it also showed gaps in our knowledge, including the role of predators in pathogen dispersal. The proposed study will produce experimental data on the effects of infected prey on the predators. We will also determine whether the predators discriminate between infectious and uninfected prey and which is preferred. In a next experimental step we will quantify the amount of disseminated spores and test their infectivity to susceptible host larvae. Experiments under semi-field conditions will determine the ability of the predators to disseminate spores in the environment and thereby enhance pathogen transmission to susceptible hosts. The study will allow us to evaluate and compare the ability of predators to enhance or diminish the transmission of microsporidia in their lepidopteran host and whether these predators might influence the success of microsporidia when the latter are inoculatively released as biological control agents. We will also determine whether the predators are susceptible to the pathogens of the host.