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Title: Salivary gland hypertrophy virus of house flies in Denmark: Prevalence, host range, and comparison with a Florida isolate.

item Geden, Christopher - Chris
item STEENBERG, T. - Aarhus University
item LIETZE, V.-U. - University Of Florida
item BOUCIAS, D. - University Of Florida

Submitted to: Journal of Vector Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2010
Publication Date: 12/1/2011
Citation: Geden, C.J., Steenberg, T., Lietze, V., Boucias, D.G. 2011. Salivary gland hypertrophy virus of house flies in Denmark: prevalence, host range, and comparison with a Florida isolate. Journal of Vector Ecology. 36(2):231-238.

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 USDA-ARS’s Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL), Aarhus University (Denmark), and the University of Florida (Gainesville) provide new information on the distribution and host range of the virus and report on the effectiveness of different application methods. Over half of the fly collections made from Danish farms included SGHV-infected flies. None of other species of filth flies collected from these farms showed SGHV symptoms. However, when flies were infected in the laboratory, two species (stable fly and black dump fly) became infected and experienced ovarian shutdown similar to what is observed in house flies. When house flies were treated with virus using a variety of methods, the most effective method was direct application of a crude homogenate of infected whole flies blended with water. The results suggest that natural rates of SGHV infection in the field could be greatly increased using such homogenates applied with conventional spray equipment.

Technical Abstract: House flies (Musca domestica) infected with Musca domestica salivary gland hypertrophy virus (MdSGHV) were found in fly populations collected from 12 out of 18 Danish livestock farms that were surveyed in 2007 and 2008. Infection rates ranged from 0.5% to 5% and averaged 1.2% overall. None of the stable flies (Stomoxys calcitrans), rat-tail maggot flies (Eristalis tenax) or yellow dung flies (Scathophaga stercoraria) that were collected from MdSGHV-positive farms displayed characteristic salivary gland hypertrophy (SGH). In laboratory transmission tests, no SGH symptoms were observed in stable flies, flesh flies (Sarcophaga bullata), black dump flies (Hydrotaea aenescens), or face flies (Musca autumnalis) that were injected with MdSGHV from Danish house flies. However, in two species (stable fly and black dump fly), virus injection resulted in suppression of ovarian development similar to that observed in infected house flies, and injection of house flies with homogenates prepared from the salivary glands or ovaries of these species resulted in MdSGHV infection of the challenged house flies. Mortality of virus-injected stable flies was the highest of the five species tested. A comparison of the virulence of Danish and Florida isolates of MdSGHV indicated that there was no difference between the strains regardless of whether the virus was delivered as a liquid food bait (in sucrose, milk or blood), sprayed onto the flies in a Potter spray tower, or by immersing flies in a crude homogenate of infected house flies. The most effective delivery system was a brief immersion in a homogenate of 10 infected flies/ml of water, resulting in 56.2% and 49.6% infection of the house flies challenged with the Danish and Florida strains, respectively.