Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2006
Publication Date: 11/28/2006
Citation: Riddick, E. W. 2006. Influence of host gender on infection rate, density and distribution of the parasitic fungus, Hesperomyces virescens on the multicolored Asian lady beetle Harmonia axyridis. J. Insect Sci. 6:42,1-15; available online: insectscience.org/6.42.
Interpretive Summary: The multicolored Asian lady beetle has received considerable attention in recent years for its usefulness as a natural enemy of soft-bodied insects (such as aphids) in various crops during the spring and summer. Unfortunately, it is also known for its annoying behavior of invading houses during the fall and winter seasons. A parasitic fungus was found infecting this lady beetle and we found that the infection spread during contact between infected and uninfected lady beetles. The presence of the fungal parasite may affect commercial shipment and storage of this lady beetle for the biological control of pests.
Technical Abstract: Infection rate, density and distribution of a parasitic fungus, Hesperomyces virescens Thaxter (Laboulbeniales: Laboulbeniaceae), on the multicolored Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) were determined in this study. Adult H. axyridis were sampled from pecan, Carya illinoinensis (Wangenh.) K. Koch, trees at an urban site in northern Mississippi, USA, during summer and early fall 2003 – 2004. When averaged over the entire season, the percentage of H. axyridis infected with H. virescens was not influenced by host gender. In 2003, a seasonal average of 54 and 39% of males and females, respectively, were infected; whereas in 2004, 36 and 41% of male and female beetles, respectively, were infected. The percentage of males infected with H. virescens was correlated with the number of males captured at the site in 2003; infection rate decreased as male abundance increased. Infection rate did not correlate with female abundance in 2003 or male or female abundance in 2004. Hesperomyces virescens mature thalli were denser on male rather than female beetles. Also, thallus density was often greatest on the elytra, meso- and metathorax, and abdomen of males and elytra of females, than on other body parts, in 2003. In 2003 and 2004, approximately 59 and 97% and 67 and 96% of males and females, respectively, had mature thalli distributed on the elytra. Prevalence of H. virescens thalli on the dorsum of H. axyridis females suggests that mating behavior is important in fungal transmission. However, prevalence of thalli on the dorsum of H. axyridis males suggests that behaviors other than mating contribute to the transmission of H. virescens onto male beetles.