Contact Info:
Illinois Natural
History Survey
607 E. Peabody Dr.
Champaign, Illinois 61820
Phone: 217-244-5047
Fax: 217-333-4949
Email:
l-solter@uiuc.edu
Contact Info:
Illinois Natural
History Survey
607 E. Peabody Dr.
Champaign, Illinois 61820
Phone: 217-244-5047
Fax: 217-333-4949
Email:
l-solter@uiuc.edu
Leellen Solter
Assistant Professional Scientist, Illinois Natural History Survey
Ph.D., University of Illinois
Safe introduction of exotic organisms to control agricultural, horticultural or forest insect pests is a serious undertaking that requires complex information about the natural enemies. We must be able to positively identify a biological control agent, both in the areas in which it originates and where it is introduced. Its taxonomic relationships should also be known. In addition, it is important to understand the life cycle and other biological and ecological characteristics, including interactions with the natural host and with other species. At the Illinois Natural History Insect Pathology Laboratory, we have teamed up with scientists at the USDA Forest Service and several overseas laboratories to study microsporidia, protozoan-like pathogens recently aligned genetically with the Fungi. These pathogens are being considered as control agents for U.S. populations of the gypsy moth, a forest tree pest. We are determining their taxonomic relationships and placement, effects on the gypsy moth host, and potential effects on native moth species.
Gypsy moth populations in Western and Central Europe naturally harbor several microsporidian species that have been placed in what are now considered to be three genera, Nosema, Vairimorpha, and Endoreticulatus. Parasitoids, viruses and a fungal disease were either introduced to North America when the gypsy moth was introduced 130 years ago or were later introduced purposely or accidentally. Microsporidia, however, never have been found in North American gypsy moth populations. Although microsporidia are typically chronic pathogens and won't be used as microbial pesticides, at least in this system, their role in suppressing gypsy moth populations in Europe suggests that they might be added to the natural enemy complex to reduce gypsy moth outbreaks in the U.S.
Field explorations in Europe have yielded approximately 25 isolates of microsporidia from different host populations that are held in the INHS liquid nitrogen collection of viable microsporidia. We are continuing to recover new isolates and are revising the taxonomy of this pathogen complex based on new electron microscopy and genetic information. We are also studying genetic variability between isolates from different host populations. We have named one new species and are currently revising the description of a second isolate.
In addition to taxonomic research, we are studying the biology of various isolates, including early developmental stages of the pathogens, host tissues targeted by different species, and transmission mechanisms. We are also investigating various physiological effects of disease on the gypsy moth; for example, we correlated the strongest effects on food utilization and protease production to an early stage of pathogen development when the microsporidium first begins to proliferate and mature in the target tissues. The growth and development of infected gypsy moth larvae were subsequently reduced compared to uninfected larvae.
We noted during the course of field collections and from historical data sets that it is rare to find more than one microsporidian species in an isolated gypsy moth host population and we therefore studied the interactions of three species of microsporidia when each possible combination of two species infected the same host larva. It appears that one species moderates the effects of the other two as it develops within the same host. Competition between species could theoretically cause extinction of one or both pathogens after introduction.
One of the most important issues in classical biological control, where a natural enemy is expected to cycle and maintain itself in the host population, is whether the introduced agent will have detrimental effects on native species that are not pests. We have performed a series of laboratory and field tests to determine whether these pathogens are a threat to native species of moths should they be introduced. Data collected in laboratory studies suggested that some species can infect multiple hosts, but few of the 'nontarget' infections were transmissible to individuals of the same species. Field studies in Bulgaria corroborated our predictions that gypsy moth microsporidia are quite host specific- no nontarget species were infected with any of the three enzootic gypsy moth microsporidian species. We are beginning final field studies in Slovakia to determine if spraying the food source (oak trees) with the microsporidia will kill or infect nontarget species.
Transmission of microsporidian infections to nontarget hosts could potentially be mediated by wasps that lay their eggs in insect hosts. Some wasps inject a symbiotic virus that suppresses the host immune system to protect their eggs. In addition to the above mentioned host specificity research, we are studying the potential of the virus to make a nontarget host more susceptible to a microsporidium.
Team of Collaborators: