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Browsing by Author "Roberts, James E. Sr."

Now showing 1 - 4 of 4
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    Determination of the possible role of arthropods as vectors for "Potomac Horse Fever" in equines
    Fletcher, Michael Gordon (Virginia Polytechnic Institute and State University, 1987)
    Potomac Horse Fever (PHF) is a disease of great concern to many horse owners in the Potomac River area of Maryland and Virginia. It is caused by a rickettsia, Ehrlichia risticii. The involvement of an arthropod vector has been suspected because of the seasonal epidemiology of the disease. This research was an attempt to identify and evaluate potential arthropod vectors. A seasonal activity study of biting arthropods attacking horses in endemic areas of Maryland and Virginia identified five potential vectors: (1) Simulium jenningsi (Diptera: Simuliidae), (2) Stomoxys calcitrans (Diptera: Muscidae), (3) Culicoides obsoletus (Diptera: Ceratopogonidae), (4) C. variipennis, and (5) Dermacentor variabilis (Acari: Ixodidae). These five arthropod species were given status as potential vectors because they were collected feeding on horses just prior to and throughout the PHF season. Simulium jenningsi and D. variabilis have the closest seasonal association with the occurrence of PHF as presented in this study. D. variabilis was determined to have the greatest potential due to its reported association with other rickettsial diseases. A series of laboratory and field studies were designed to examine the potential role of D. variabilis in the transmission of E. risticii. We first attempted to transmit E. risticii by feeding adult D. variabilis collected from an endemic farm on susceptible horses. Other laboratory studies included mouse to horse and mouse to mouse transmission attempts using ticks fed on mice inoculated with E. risticii. A serological survey of 105 trapped field rodents (host of immature D. variabilis) on endemic farms in Maryland showed all specimens collected to be negative for PHF antibodies. These studies and others gave no indication of D. variabilis's involvement in the transmission of the disease in nature. The other species mentioned above were not examined.
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    Developmental and reproductive ecology of Melanoplus femurrubrum (De Geer) and some other melanopline grasshoppers (Orthoptera, Acrididae)
    Bellinger, Robert Glenn (Virginia Polytechnic Institute and State University, 1985)
    The red-legged grasshopper, Melanoplus femurrubrum femurrubrum (De Geer), was found to be developmentally polymorphic. Local field populations in Virginia had five, six, seven, and eight instars, determined by antennal segment counts. Adults with five instars were uncommon, and six and seven-instar adults were the most abundant morphs. Laboratory studies showed that decreasing temperature decreased both the number of instars, and developmental rate. Grasshoppers with fewer instars had the differential number of instars deleted from between the third and penultimate instars, thus, temperature must affect instar number early in the life cycle, i.e., before the third instar. The laboratory study produced no five-instar grasshoppers. Most individuals had six or· seven instars, depending on temperatures. Few eight-instar individuals were produced in the laboratory. Grasshoppers with more instars had longer developmental times and larger body sizes. Females were larger than males and tended to go through more instars, however, males and females which developed with the same number of instars did not differ in developmental time. In field populations, instar number was positively correlated with accumulated heat units the month of hatch, but body size was negatively correlated. Mean population in Melanoplus spp. grasshoppers is positively correlated with mean species body size. In the laboratory, ovariole number in M. femurrubrum was related to the size of the egg from which the female hatched, and in field populations mean population ovariole number in was determined by mean length of the growing season, and rainfall in the maternal generation. In field populations number of pods laid was less than two, and was related to rainfall in September, while pod size was related to body size and rainfall in October. Numbers of pods laid and total eggs were negatively correlated with the tegmen/femur ratio.
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    Pest management guide for soybeans
    McPherson, Robert M.; Smith, John C.; Roberts, James E. Sr.; Phipps, Patrick M.; Rud, O. E.; Wilson, H. P.; Foy, Chester L. (Virginia Cooperative Extension Service, 1981-01)
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    The synthetic pyrethroid Ectiban permethrin as a treatment in the pest management of flies in caged-layer poultry houses
    Townsend, Lee Hill (Virginia Tech, 1977)
    The objective of my research was to evaluate the synthetic pyrethroid permethrin (Ectibantm permethrin, ICI, Americas, Inc.) (Fig. 1) as a potential treatment in the integrated control of synanthropic flies in poultry houses. I used a variety of application techniques including feed additive, direct topical application to manure for larval control, and residual sprays for adult control. In addition to investigating the effects of the pyrethroid on the house fly, I determined its effect on selected nontarget parasites and predators which may occur in chicken houses. The goal of the research is potent insecticide compatible with an integrated control approach for synanthropic flies.