Submitted to: Journal of Applied Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/24/2005
Publication Date: 7/1/2005
Citation: Meikle, W.G., Mercadier, G., Rosengaus, R.B., Kirk, A., Derouané, F., Quimby, P.C. 2005. Evaluation of an entomopathogenic fungus, paecilomyces fumosoroseus (wize) brown and smith (deuteromycota: hyphomycetes) obtained from formosan subterranean termites (isoptera: rhinotermitidae). Journal of Applied Entomology. Interpretive Summary: 1. Problem. Termite control is usually conducted using strong pesticides. Some form of biological control of termites may help reduce the need for pesticide use. It may be possible to find one or more strains of fungal disease which, when released in a termite colony, can cause heavy losses.Although termites are susceptible to many fungal diseases, they also clean themselves and their nestmates very carefully. The first step is to find one or more fungal strains, and then to conduct laboratory tests to see if the fungal disease can kill termites that are kept alone. Once a disease is identified that can kill solitary termites, it needs to be tested with termites kept in groups. If a disease agent can kill termites in groups, it may be able to avoid detection and might be useful in a termite management program. 2. Approach. This study had three main parts. The first part was foreign exploration to find a fungal disease strain from termites themselves, since that strain would have a good chance of being able to evade termite detection and resistance. The second part was the treatment of termites with different spore concentrations in a spray tower (a experimental device used to apply precise spray doses) and measure the actual spore concentration on the surface of the termite. The third part was the treatment of termites with two different kinds of disease-causing fungi: one kind was found during the foreign exploration, and the other kind is a commercial strain available in the US. Once the termites were sprayed, they were either kept alone or kept in groups of 10, in order to see how well the diseases worked in each situation. The termites were kept under observation until almost all of them had died, and then the data were statistically analyzed. 3. Results. After visiting Africa, Asia, Australia and Europe, we found 99 isolates of disease-causing fungi on termites. We chose one of these samples, a yellow muscardine fungus, to test against a commercial fungus strain, a green muscardine fungus. Using the spray towers, we found we could apply a relatively consistent and low dose of spores to each termite. Termites kept as groups lived much longer, even when all the termites were treated with fungus, and termites sprayed with the commercial disease strain died fastest of all. However, among termites that were kept in groups after treatment, termites sprayed with the new isolate that was found in China died significantly faster than the commercial strain. These studies indicate that pathogens may interact in complex ways with termites, and that there may be pathogen strains that are better suited to attacking social insects such as termites.
Technical Abstract: As part of a USDA-ARS project on the control of Formosan subterranean termites, Coptotermes formosanus, termite natural enemies were collected in several countries by the European Biological Control Laboratory. A total of 99 fungal isolates was obtained, including one isolate of Paecilomyces fumosoroseus collected from C. formosanus collected in Hong Kong that was selected for further virulence tests. Shipments of C. formosanus were obtained from China and were used in the following experiments. Termites were treated with aqueous suspensions of P. fumosoroseus conidia with the use of a spray tower and the cuticular dose per termite was estimated. Termites treated at 5 x 106 conidia/ml had an overall average (± s.e.) of 94.0 ± 7.6 conidia per termite, while termites treated at 5 x 107 conidia/ ml had on average 519.4 ± 48.8 conidia per termite. Survivorship of termites treated with the P. fumosoroseus isolate in a spray tower was compared to those treated with a commercial strain of Metarhizium anisopliae in experiments involving termites either kept alone or in groups of 10 after treatment. Survivorship of termites treated with a suspension of 5 x 105 M. anisopliae conidia/ml and kept alone declined more rapidly than for those treated at the same concentration of P. fumosoroseus conidia. At a 5 x 106 conidia/ml concentration, no significant differences in terms of termite survivorship were observed between the two fungal species. However, among termites kept in groups, those sprayed with P. fumosoroseus conidia at either 5 x 105 and 5 x 106 conidia/ml had significantly lower survivorship than those sprayed with M. anisopliae conidia.