Alec C. Gerry

Biting Rates of Culicoides Midges (Diptera: Ceratopogonidae) on Sheep in Northeastern Spain in Relation to Midge Capture Using UV Light and Carbon Dioxide-Baited Traps

ABSTRACT Biting midges in the genus Culicoides (Diptera: Ceratopogonidae) were collected near sunset by direct aspiration from sheep in northeastern Spain to determine species-specific biting rates and crepuscular activity. Midges were also collected by UV-baited light traps and CO2-baited traps over the same period to compare species diversity and abundance using these common surveillance methods to actual sheep attack rates. Culicoides aspirated from sheep included C. obsoletus, C. parroti, C. scoticus, C. punctatus, and C. imicola. Peak host-seeking activity during the time period examined for the two most commonly collected species (C. obsoletus and C. parroti) occurred just before sunset and activity ceased within 1 h after sunset. Host attack rates near sunset averaged 0.9 midges/min for both species with maximum attack rates of 3/min for C. obsoletus and 4/min for C. parroti. For both species, ≈35% of midges collected from the sheep were engorged, giving a maximum biting rate of 1.1/min for C. obsoletus and 1.5/min for C. parroti. Traps baited with CO2 collected fewer midges of each species relative to other collection methods. Traps baited with UV light provided a good indication of species richness but significantly underestimated the host attack rate of C. obsoletus and C. parroti while overestimating the host attack rate of C. imicola. Animal-baited collecting is critical to interpret the epidemiological significance of light trap collections used for surveillance of the midge vectors of bluetongue virus and African horse sickness virus.

Seasonal Transmission of Bluetongue Virus by Culicoides sonorensis (Diptera: Ceratopogonidae) at a Southern California Dairy and Evaluation of Vectorial Capacity as a Predictor of Bluetongue Virus Transmission

Abstract Vectorial capacity of Culicoides sonorensis Wirth & Jones for the transmission of bluetongue (BLU) virus was examined at a southern California dairy from January 1995 to December 1997. Insects were collected one to two times per week in five CDC-type suction traps (without light) baited with CO2 at a constant release rate of 1,000 ml/min. BLU virus was detected in midges collected from May through December with an estimated overall infection rate of 0.08%. The BLU virus infection rate of field-captured midges was not correlated with sentinel calf seroconversions to BLU virus. Sentinel calf seroconversions were highly seasonal, occurring from August through November with most calves seroconverting during September and October. Vector competence of field-collected nulliparous flies fed a locally acquired serotype of BLU virus in the laboratory was stable among years (17–23%). Vectorial capacity was strongly correlated with BLU virus transmission (measured by sentinel calf seroconversions) during 1995 and 1996, but not during 1997. Host biting rate estimated for traps nearest to the sentinel calves was the index best correlated with BLU virus transmission for all study years and was most highly correlated with sentinel seroconversions 4 wk later. The utility of vectorial capacity and its component variables is discussed for this system.

Seasonal Abundance and Survivorship of Culicoides sonorensis (Diptera: Ceratopogonidae) at a Southern California Dairy, with Reference to Potential Bluetongue Virus Transmission and Persistence

Abstract Seasonal abundance and survivorship of Culicoides sonorensis Wirth & Jones were examined at a dairy in southern California from January 1995 to December 1997. Insects were collected one to two times per week using five CDC-type suction traps (without light) baited with CO2 at a constant release rate of 1,000 ml/min. Female and male abundance was greatest during late summer and early fall and was directly correlated with mean monthly air temperature. Parity of females was lowest during late summer and early fall. The gonotrophic cycle was estimated to require 3–4 d during hot summer months and up to 14 d during cool winter months. Estimated extrinsic incubation of bluetongue virus (BLU) was 9–10 d during August and September. The estimated daily survival ranged from <60% in the summer to >95% in the winter, resulting in an expectation of life of only 2–3 d in summer and >10 d in winter. The probability of females surviving the extrinsic incubation period for BLU virus, and the expectation of infective life were both lowest during late summer and early fall. During 1997, midge abundance during late summer was not high enough to overcome very low survivorship, and the absolute number of females expected to survive the extrinsic incubation period was relatively low. However, in 1995 and 1996, very high midge abundance compensated for low survivorship during summer and the number of females expected to survive the extrinsic incubation period was relatively high. Although abundance was generally very low during the cool winter and spring, host-seeking females were captured throughout the year, and their winter survival was high. Overwintering of BLU virus by continued transmission of the virus by active midges appears possible.

House Fly (Diptera: Muscidae) Activity near Baits Containing (Z)-9-tricosene and Efficacy of Commercial Toxic Fly Baits on a Southern California Dairy

Abstract Sticky card captures of house flies, Musca domestica L. (Diptera: Muscidae), were used to compare efficacy of screen-covered baits containing sugar, sugar and 0.1% (Z)-9-tricosene, sugar and 1.0% (Z)-9-tricosene, Golden Malrin [1.1% methomyl and 0.049% (Z)-9-tricosene], and QuickBayt [0.5% imidacloprid and 0.1% (Z)-9-tricosene]. The QuickBayt treatment caught more flies per hour (mean = 116.5) than sugar alone (mean = 81.0), but the addition of (Z)-9-tricosene to sugar did not increase fly capture compared with sugar alone. More males (65% of total) than females were collected on the sticky cards for all treatments. Fly kill by plain sugar (control) and the commercial baits Golden Malrin, QuikStrike Fly Abatement strips (1.0% nithiazine), and QuickBayt was tested over a 90-min period. An average of 1.4, 5.6, 363.0, and 1,266.0 flies were killed using sugar, Golden Malrin, QuikStrike, and QuickBayt, respectively. The similarity between Golden Malrin and plain sugar reflects severe resistance to this once effective methomyl bait. A no-choice feeding assay using lab-reared methomyl-susceptible and methomyl-resistant house flies was conducted with and without (Z)-9-tricosene. Adult mortality was significantly higher in the methomyl-susceptible strain exposed to treatments containing methomyl. Lower consumption of the methomyl treatments by resistant flies suggested resistance was behavioral and mortality was not influenced by (Z)-9-tricosene for either fly strain.

Insecticide resistance in house flies from the United States: Resistance levels and frequency of pyrethroid resistance alleles

Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein, we report the first widespread survey of insecticide resistance in the USA ever undertaken for the house fly, Musca domestica, a major pest in animal production facilities. The levels of resistance to six different insecticides were determined (using discriminating concentration bioassays) in 10 collections of house flies from dairies in nine different states. In addition, the frequencies of Vssc and CYP6D1 alleles that confer resistance to pyrethroid insecticides were determined for each fly population. Levels of resistance to the six insecticides varied among states and insecticides. Resistance to permethrin was highest overall and most consistent across the states. Resistance to methomyl was relatively consistent, with 65-91% survival in nine of the ten collections. In contrast, resistance to cyfluthrin and pyrethrins + piperonyl butoxide varied considerably (2.9-76% survival). Resistance to imidacloprid was overall modest and showed no signs of increasing relative to collections made in 2004, despite increasing use of this insecticide. The frequency of Vssc alleles that confer pyrethroid resistance was variable between locations. The highest frequencies of kdr, kdr-his and super-kdr were found in Minnesota, North Carolina and Kansas, respectively. In contrast, the New Mexico population had the highest frequency (0.67) of the susceptible allele. The implications of these results to resistance management and to the understanding of the evolution of insecticide resistance are discussed.

Arthropod Surveillance Programs: Basic Components, Strategies and Analysis

ABSTRACT Effective entomological surveillance planning stresses a careful consideration of methodology, trapping technologies, and analysis techniques. Herein, the basic principles and technological components of arthropod surveillance plans are described, as promoted in the symposium “Advancements in arthropod monitoring technology, techniques, and analysis” presented at the 58th annual meeting of the Entomological Society of America in San Diego, CA. Interdisciplinary examples of arthropod monitoring for urban, medical, and veterinary applications are reviewed. Arthropod surveillance consists of the three components: 1) sampling method, 2) trap technology, and 3) analysis technique. A sampling method consists of selecting the best device or collection technique for a specific location and sampling at the proper spatial distribution, optimal duration, and frequency to achieve the surveillance objective. Optimized sampling methods are discussed for several mosquito species (Diptera: Culicidae) and ticks (Acari: Ixodidae). The advantages and limitations of novel terrestrial and aerial insect traps, artificial pheromones and kairomones are presented for the capture of red flour beetle (Coleoptera: Tenebrionidae), small hive beetle (Coleoptera: Nitidulidae), bed bugs (Hemiptera: Cimicidae), and Culicoides (Diptera: Ceratopogonidae) respectively. After sampling, extrapolating real world population numbers from trap capture data are possible with the appropriate analysis techniques. Examples of this extrapolation and action thresholds are given for termites (Isoptera: Rhinotermitidae) and red flour beetles.

Failure of a Permethrin Treatment Regime to Protect Cattle Against Bluetongue Virus

Abstract Holstein heifers in a confined feedlot setting on a southern California dairy were either sprayed individually along the ventral midline using 0.2% permethrin (250 ml/animal) (two pens) or were not treated (two pens). Treatments (n = 6 dates) were applied every 2 wk during the peak fall bluetongue virus transmission season (22 August–29 October). Animals seronegative for bluetongue virus antibodies at the initial bleeding on 15–18 September (n = 106 in the treatment pens and n = 117 in the control pens) were bled again for testing 2 mo later (12–13 November). Seroconversion rates were not significantly different: 56% for the treated animals and 48% for the controls (P > 0.2). The area has many essentially contiguous, confinement dairies with wastewater ponds that produce large numbers of Culicoides sonorensis Wirth & Jones, the primary bluetongue virus vector. Further, these dairies presumably provided a large reservoir of virus-infected cattle to infect vectors in the immediate area. Under these severe virus challenge conditions, permethrin applied at 2-wk intervals failed to reduce exposure to bluetongue virus.

Feeding and survival of Culicoides sonorensis on cattle treated with permethrin or pirimiphos-methyl.

The persistence of permethrin (5% a.i.) and pirimiphos‐methyl (27% a.i.), applied to the dorsum of calves in the field against Culicoides sonorensis Wirth and Jones (Diptera: Ceratopogonidae), was estimated using a hair‐blood‐feeding bioassay in the laboratory. Hair clippings were taken before treatment and 3, 7, 14, 21, 28, 42 and 56 days after treatment from the dorsum, side and belly of treated and control calves. Laboratory‐reared insects were allowed to feed through thin hair layers and a parafilm membrane on sheep blood warmed using a water‐jacketed feeder. Some intoxication after exposure to hair was noted up to 28 days after treatment with permethrin and up to 14 days after treatment with pirimiphos‐methyl. Hair from the dorsum caused more intoxication for a longer period than hair from other body regions. Permethrin and pirimiphos‐methyl applied to the back did not significantly reduce overall engorgement (body regions pooled) after treatment. Permethrin residues on hair remained far higher on the back than other body regions and were related to insect intoxication and reduction in engorgement in the laboratory. Residues on belly hair never exceeded 12 p.p.m. and did not result in significantly reduced feeding at any time. Engorged insects that exhibited sublethal intoxication from feeding through permethrin‐treated hair did recover and matured numbers of eggs comparable to controls. Field trials using treated and control calves and enclosure nets showed that dorsal applications of 5% permethrin were not effective in reducing engorgement, despite some intoxication. Vacuum samples from a calf showed that C. sonorensis fed primarily on the belly. A 0.2% permethrin application on the belly (250 ml) did result in > 80% reduction of C. sonorensis in the enclosure nets at 3 and 7 days after treatment, but activity had subsided by 10 days after treatment. The utility of insecticidal treatments for suppression of this vector is discussed.

Field Studies on Culicoides (Diptera: Ceratopogonidae) Activity and Response to Deltamethrin Applications to Sheep in Northeastern Spain

ABSTRACT An enclosure trapping experiment compared numbers and engorgement of Culicoides spp. taken from treated sheep (7.5% deltamethrin) to Culicoides from untreated sheep. Attack rates were low (0.2/ min), but 58% of Culicoides obsoletus s.l. and 67% of Culicoides parroti Kieffer engorged on untreated sheep, and no engorgement occurred on treated sheep on 0 and 4 d posttreatment. A UV light trap in a livestock barn collected eight Culicoides spp. (510 individuals), dominated by C. obsoletus (Meigen) (68%), Culicoides imicola Kieffer (19%), Culicoides circumscriptus Kieffer (8%), and Culicoides alazanicus Dzhafarov (4%). A more powerful but nonattractive fan trap collected five species (121 individuals) dominated by C. obsoletus (48%), C. imicola (36%), C. alazanicus (8%), and C. circumscriptus (7%). Parity of C. obsoletus and C. imicola did not vary between the light and fan traps. Engorged Culicoides in the barn (33 C. obsoletus and three C. imicola) had fed on sheep or goats (precipitin test).

The combination of abundance and infection rates of Culicoides sonorensis estimates risk of subsequent bluetongue virus infection of sentinel cattle on California dairy farms

Bluetongue (BT) is an important viral disease of ruminants that is transmitted by hematophagous Culicoides midges. We examined the seasonal patterns of abundance and infection of Culicoides sonorensis at four dairy farms in the northern Central Valley of California to develop estimates of risk for bluetongue virus (BTV) transmission to cattle at each farm. These four farms were selected because of their similar meteorological conditions but varying levels of vector abundance and BTV infection of cattle. C. sonorensis midges were collected weekly at each farm during the seasonal transmission period, using three different trapping methods: traps baited with either carbon dioxide (CO(2)) alone or traps with CO(2) and UV light, and by direct aspiration of midges from sentinel cattle. Analysis of BTV-infected midges using group and serotype-specific quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) assays confirmed that BTV serotypes 10, 11, 13 and 17 are all present in the region, but that midge infection rates and the number of BTV serotypes circulating differed markedly among the individual farms. Furthermore, more serotypes of BTV were present in midges than in sentinel cattle at individual farms where BTV circulated, and the virus was detected at each farm in midges prior to detection in cattle. BTV infection rates were remarkably lower among female C. sonorensis midges collected by CO(2) traps with UV light than among midges collected by either animal-baited aspirations or in CO(2) traps without light. A subsample of female midges examined from each collection method showed no overall differences in the proportion of female midges that had previously fed on a host. Findings from this study confirm the importance of using sensitive surveillance methods for both midge collection and virus detection in epidemiological studies of BTV infection, which is especially critical if the data are to be used for development of mathematical models to predict the occurrence of BTV infection of livestock.