Impact of house fly salivary gland hypertrophy virus (MdSGHV) on a heterologous host, Stomoxys calcitrans

Authors: Geden, Christopher - Chris; GARCIA-MARUNIAK, A. - University Of Florida; LIETZE, V.-U. - University Of Florida; MARUNIAK, J. - University Of Florida; BOUCIAS, D. - University Of Florida

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2011
Publication Date: 11/1/2011
Citation: Geden, C.J., Garcia-Maruniak, A., Lietze, V., Maruniak, J., Boucias, D.G. 2011. Impact of house fly salivary gland hypertrophy virus (MdSGHV) on a heterologous host, Stomoxys calcitrans. Journal of Medical Entomology. 48(6):1128-1135.

Interpretive Summary: House flies are important pests associated with animals and humans and transmit a wide array of disease organisms. Efforts to manage flies have traditionally relied on chemical insecticides, but flies have become resistant to most insecticides and there is increasing public demand to reduce pesticide use around animals that are used in the production of meat, milk and eggs. Most biological control research on flies has concentrated on targeting fly pupae with parasitic wasps. In recent years a promising new biological control agent for adult flies has been discovered, salivary gland hypertrophy virus (SGHV). Female flies infected with the virus do not produce any eggs, and infected males do not compete well with healthy males. In this paper, scientists at USDA-ARS’s Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL) and the University of Florida (Gainesville) provide information on the effect of the virus on stable flies, which have not been found to be infected in nature. Stable flies that were injected with virus did not produce eggs and had much shorter lifespans than healthy flies. Infected flies also produced 50-75% less feces, suggesting decreased feeding as well. Using microscopy and PCR methods, the authors demonstrated that the virus replicated in stable flies and that same tissue types were infected as in the virus’s natural host (house flies). If a suitable method could be developed for exposing stable flies in the field to the virus, SGHV could have a significant impact on fly abundance and biting pressure on animals and humans.

Technical Abstract: The effect of Musca domestica salivary gland hypertrophy virus (MdSGHV) on selected fitness parameters of stable flies (Stomoxys calcitrans [L.]) was examined in the laboratory. Virus-injected stable flies of both genders suffered substantially higher mortality than control flies. By day 9, female mortality was 59.3 ± 10.1% in the virus group compared with 23.7 ± 3.7% in the controls; mortality in virus-injected males was 78.1 ± 3.1% compared with 33.3 ± 9.3% for controls. Fecundity of control flies on days 6-9 was 49-54 eggs deposited per live female per day (total, 8,996 eggs deposited), whereas virus-injected flies produced 4-5 eggs per female on days 6-7 and <1 egg per female per day thereafter (total, 251 eggs). Fecal spot deposition by virus-injected flies was comparable to controls initially but decreased to about 50% of control levels by day 4 after injection; infected flies produced only 26% as many fecal spots as healthy flies on days 6 and 7. None of the virus-injected stable flies developed symptoms of salivary gland hypertrophy. Quantitative real-time PCR demonstrated virus replication in injected stable flies, with increasing titers of virus genome copies from one to four days after injection. MdSGHV in stable flies displayed tissue tropism similar to that observed in house fly hosts, with higher viral copy numbers in fat body and salivary glands compared to ovaries. Virus titers were about two orders of magnitude higher in house fly than in stable fly hosts, and this difference was probably due to the absence of salivary gland hypertrophy in the latter species.