Mortality and repellent effects of microbial pathogens on Coptotermes formosanus (Isoptera: Rhinotermitidae)

BACKGROUND: Two entomopathogenic fungi, Isaria fumosorosea and Metarhizium anisopliae, and one bacterium, Bacillus thuringiensis, were tested for their ability to cause mortality of Formosan subterranean termites (FST), Coptotermes formosanus (Shiraki), after liquid exposure, and for their lack of propensity to repel FST. RESULTS: The fungus Isaria fumosorosea at 10(8) spores/ml caused 72.5% mortality on day 7, significantly higher than the control and 10(6) spores/ml treatment. On day 14, the 10(6) and 10(8) concentrations caused 38.8% and 92.5% mortality, respectively, significantly higher than the control. On day 21, 82.5% and 100% of the termites were killed by the 10(6) and 10(8) treatments, respectively. I. fumosorosea did not repel termites at 10(6) nor 10(8) spores/g in sand, soil or sawdust. The fungus Metarhizium anisopliae at 10(8) spores/ml caused 57.5% mortality on day 7, 77.5% mortality on day 14 and 100% mortality on day 21. CONCLUSIONS: On all three days the rate of mortality was significantly higher than that of the control and 10(6) spores/ml treatment with I. fumosorosea. Neither I. fumosorosea nor M. anisopliae caused repellency of FST in sand, soil or sawdust. The bacterium Bacillus thuringiensis did not cause significant mortality on days 7, 14 or 21. When termites were exposed to cells of B. thuringiensis in sawdust and when termites were exposed to a mixture of spores and cells in sand, a significantly higher number remained in the control tubes. Repellency was not seen with B. thuringiensis spores alone, nor with the above treatments in the other substrates.