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The overall goal of this proposal is to develop a biologically based pest management tool for populations of the house fly, Musca domestica L. (Diptera: Muscidae), an important insect pest in livestock and poultry production areas. This research involves the manipulation of a novel, endemic viral pathogen to control insect populations through a reduction in reproductive fitness. The MdSGHV is orally transmitted by adult feeding and induces the viremic state within days after exposure. Infection by MdSGHV acts as a natural sterilant, rapidly and completely inhibiting egg production in viremic females. Importantly, the biology of the house fly has been detailed, providing a framework to delineate the effects of viral infection on the performance of this host insect. Preliminary studies have provided the technology required to produce and isolate MdSGHV. Virus-specific PCR primers have been developed that are capable of detecting and quantifying virus in the insect and in environmental samples. In addition, several methods have been tested to incorporate this virus into adult fly food, to conduct mating experiments, and to measure house fly reproductive fitness parameters. Lastly, several adult house fly attractants and bait materials are commercially available to deliver this virus to local fly populations. This proposal will address two fundamental hypotheses concerning population regulation with agents that suppress the intrinsic rate of increase of insect pests. First, we hypothesize that a virus that inhibits reproduction can be used to manipulate local pest population levels. Our second hypothesis is that an attract-and-infect approach will amplify the contact frequency between pathogen and target pest providing a mechanism for the pathogen to operate in a density-independent manner. <P>The specific objectives of the project include the following: <ol> <LI>Examine virus acquisition and the impact of viral replication on the reproductive fitness of female house flies. <LI> Investigate viral transmission in house fly populations. <LI> Evaluate MdSGHV as a biological control for house fly populations under laboratory and controlled field conditions and optimize delivery systems within confined house fly populations.
NON-TECHNICAL SUMMARY: Musca domestica is an economically important insect pest of livestock and poultry. Throughout the United States, this insect is also considered a nuisance pest at the rural/urban interface and is a recognized vector of various food-borne and vertebrate diseases. Due to the high costs associated with insecticide use and application, the increasing resistance of filth fly pests to insecticides, and the increasing environmental concern of both producers and consumers, there has been growing interest in cultural and biological control methods as alternative management strategies. This project is designed to provide insight as to how the endemic MdSGHV influences the mating behavior and reproductive fitness of adult female house flies and how it affects the intrinsic rate of increase of the host The development of a novel microbial control agent as an environmentally sound management strategy will help to achieve decreased inputs for livestock and poultry protection.<P>APPROACH: A. Define virus acquisition and the impact of viral replication on the reproductive fitness of female house flies. Experiments will examine the effects of dosage, carrier substrate, and exposure time on virus acquisition by female house flies. Demographic growth parameters will be estimated from fecundity experiments using control and infected females of different age groups and healthy 4-day-old males. In order to determine the approximate physiological age of infected and uninfected flies field collected flies will be examined for ovarian stage and prior oviposition history by inspecting the lateral oviducts for the presence of follicular relics. B. Characterize the levels of viral transmission in house fly populations. We hypothesize that the virions are released into salivary secretions and contaminate the food substrate during the feeding event. These infectious virions are picked up by healthy conspecifics, resulting in horizontal disease transmission. Molecular methods will be used both to quantify the virus released in the salivary secretions during feeding by infected flies and to determine the infectivity of released virus to healthy conspecifics. To address these issues, groups of adult flies will be infected per os. At intervals, flies will be dissected and the degree of hypertrophy recorded and the relative number of infectious particles will be calculated. These assays are designed to determine the kinetics of SGHV production. C. Determine the potential of MdSGHV as a biological control for housefly populations under laboratory and controlled field conditions and optimize delivery systems within confined house fly populations. Initially, the virus will be incorporated into and tested using three bait systems: 1) dry bait composed of sucrose and the sex attractant (Z)-9-tricosene 2) dry bait composed of corn grits, confectioners sugar, and a commercial fly feeding attractant; and 3) liquid bait composed of diluted farm-grade blackstrap molasses, a known feeding attractant. Baits of each type without virus will be used as controls. Initial tests will be conducted using both a low and high viral dosage. Bait tests will be conducted on three separate occasions using different cohorts of flies and batches of virus, with three cages per treatment plus controls for each replication. We hypothesize that the spread of virus is favored by high-density fly populations. This will be tested initially in the laboratory by introducing infected flies into cages containing uninfected flies at varying densities. The most promising baits from the preceding trials will be tested in outdoor cages fitted with dataloggers to monitor abiotic factors. Flies will be released in cages from which 8000 flies are expected to emerge. A sample of 100 flies from each cage will be selected and scored for infection status and ovarian development on day 7. In addition, F1 progeny will be produced in these cages and reared and held for emergence to provide an estimate of progeny production by flies in virus-treated versus control cages under semi-field conditions.