Point Protection with Transfluthrin against Musca domestica L. in a Semi-Field Enclosure

House flies are notoriously difficult to control, owing to their tendency to live in close relationships with humans and their livestock, and their rapid development of resistance to chemical controls. With this in mind, we explored an alternative chemical control, a spatial repellent to deter Musca domestica L. from points we wanted to protect (i.e., a baited trap). Our results demonstrated that the synthetic spatial repellent, transfluthrin, is effective in preventing M. domestica adults from entering protected traps for both a susceptible strain (CAR21) and a field-acquired permethrin-resistant strain (WHF; 24 h LD50 resistance ratio of 150), comprising 22% and 28% of the total number of flies collected, respectively. These results are promising and demonstrate that transfluthrin can be an effective spatial repellent to protect points of interest where needed.

Effects of larval diets on some biological parameters and morphometric and biochemical analysis of ovaries of Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae)

The effects of three larval diets (beef meat, chicken meat, and beef liver) on development of Lucilia cuprina (Wiedemann) were evaluated. Egg hatching rates were higher on chicken meat and beef meat (99.5%) than on beef liver (96.5%). Pupation success was higher on chicken meat (99.0%) and beef meat (98.0%) than on beef liver (87.1%). Adult emergence rates were higher in flies reared on chicken meat (99.0%) and beef meat (98.5%) than on beef liver (93.5%). Proportions of female flies were somewhat higher in flies reared on chicken meat or beef meat (54-56% female) than on beef liver (52.5%). Flies that were reared on chicken meat and beef meat had shorter egg-adult development times (16.3 days) than flies reared on beef liver (18.5 days), and the generation time of flies reared on chicken meat or beef meat (51-52 days) was several days shorter than flies reared on beef liver (54 days). Flies reared on chicken meat had larger ovaries and more ovarioles per ovary when larvae were reared on chicken than flies reared on beef meat or beef liver. The ovaries of flies reared on chicken meat had significantly higher amounts of protein (21 mg/g body weight) than flies reared on beef liver (12 mg). Analysis of the larval diets showed that beef liver had the lowest amounts of protein and carbohydrate of the three tested diets, whereas the amounts of lipids did not differ among the diets.

Susceptibility of the adult house fly (Diptera: Muscidae) and 3 of its principal parasitoids (Hymenoptera: Pteromalidae) to the GHA strain of Beauveria bassiana and 4 isolates from field-collected muscid flies

House fly (Musca domestica L.) (Diptera: Muscidae) populations can negatively impact poultry layer facilities, posing a risk to human and animal health and egg food safety. House flies quickly develop resistance to traditional chemical control methods; therefore, improved biological control may provide opportunities for improved integrated pest management (IPM) programs. Biological control methods currently used include augmentative releases of pteromalid pupal parasitoids and application of the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin. This study used bioassays to compare the impact of different B. bassiana strains on survival of house flies and of 3 species of filth fly parasitoids. The B. bassiana that were compared were 3 new field-collected isolates, an older field-collected isolate (L90), and a common commercially available strain (GHA). Flies and parasitoids were exposed to filter paper treated with 1.5 × 109 spores of each strain and a control. All field-isolated strains induced lower mean survival times in house flies than GHA did. The results for all species of parasitoids demonstrated less difference among the treatment groups and the control than in-house flies. Although there was some effect of B. bassiana exposure on parasitoid mortality, the expected spatial separation of parasitoids from areas of application may offer some protection. Using the most effective tested strains of B. bassiana and filth fly parasitoids jointly could be a biological component of an IPM plan for fly control in poultry facilities.

Rescuing the Inhibitory Effect of the Salivary Gland Hypertrophy Virus of Musca domestica on Mating Behavior

Infection with salivary gland hypertrophy virus (MdSGHV) of Musca domestica prevents female flies from accepting copulation attempts by healthy or virus-infected males. This study focused on supplemental hormonal rescue therapy for mating behavior in virus-infected female house flies. The inhibitory effect of the virus on mating behavior in females injected with MdSGHV was reversed by hormonal therapy in the form of octopamine injections, topical application of methoprene, or both therapies combined along with 20-hydroxyecdysone. Infected females whose mating responsiveness had been restored continued to have other viral pathologies associated with infection such as hypertrophy of the salivary glands and a lack of ovarian development.

New insights into the genome and transmission of the microsporidian pathogen Nosema muscidifuracis

Introduction

Nosema is a diverse genus of unicellular microsporidian parasites of insects and other arthropods. Nosema muscidifuracis infects parasitoid wasp species of Muscidifurax zaraptor and M. raptor (Hymenoptera: Pteromalidae), causing ~50% reduction in longevity and ~90% reduction in fecundity.

Methods and Results

Here, we report the first assembly of the N. muscidifuracis genome (14,397,169 bp in 28 contigs) of high continuity (contig N50 544.3 Kb) and completeness (BUSCO score 97.0%). A total of 2,782 protein-coding genes were annotated, with 66.2% of the genes having two copies and 24.0% of genes having three copies. These duplicated genes are highly similar, with a sequence identity of 99.3%. The complex pattern suggests extensive gene duplications and rearrangements across the genome. We annotated 57 rDNA loci, which are highly GC-rich (37%) in a GC-poor genome (25% genome average). Nosema-specific qPCR primer sets were designed based on 18S rDNA annotation as a diagnostic tool to determine its titer in host samples. We discovered high Nosema titers in Nosema-cured M. raptor and M. zaraptor using heat treatment in 2017 and 2019, suggesting that the remedy did not completely eliminate the Nosema infection. Cytogenetic analyses revealed heavy infections of N. muscidifuracis within the ovaries of M. raptor and M. zaraptor, consistent with the titer determined by qPCR and suggesting a heritable component of infection and per ovum vertical transmission.

Discussion

The parasitoids-Nosema system is laboratory tractable and, therefore, can serve as a model to inform future genome manipulations of Nosema-host system for investigations of Nosemosis.

Filth Fly Parasitoid (Hymenoptera: Pteromalidae) Monitoring Techniques and Species Composition in Poultry Layer Facilities

Muscid flies, especially house flies (Musca domestica L.) (Diptera: Muscidae), are a major pest of poultry layer facilities. Augmentative biological control of muscid flies with pteromalid wasps has gained increased attention in recent years. Knowing which pteromalid species are present in a specific area could produce more effective filth fly control. The purpose of this project was to survey parasitoid populations in poultry layer facilities in central and southeastern Pennsylvania from June through September. Two genera of parasitoids, Spalangia and Trichomalopsis, were collected over the course of the survey. Overall, out of 3,724 parasitized pupae the species collected in order of most to least common were Spalangia cameroni Perkins, Spalangia nigroaenea Curtis, Trichomalopsis spp., and Spalangia endius Walker. House fly parasitism overall and by each parasitoid species varied by location and over the four study months. A second objective was to evaluate a new parasitoid trap for surveying parasitoid wasp populations. This device uses a combination of house fly third instars and development media. This was compared to a more traditional method, the sentinel bag, which uses only fly pupae. A higher proportion of Spalangia spp. emerged from the new trap design and more Trichomalopsis spp. emerged from the sentinel bag. This suggests that using this new device alongside the traditional collection method may result in more accurate sampling of pteromalid populations.

Laboratory Evaluation of Pupal Parasitoids for Control of the Cornsilk Fly Species, Chaetopsis massyla and Euxesta eluta

Cornsilk flies are serious pests of sweet corn through damage to cobs and secondary fungal establishment. As pupae are generally outside the infested cob on the ground, there can be potential for use of pupal parasitoids for control. Two species of gregarious parasitoids, Muscidifurax raptorellus and Nasonia vitripennis, and three species of solitary parasitoids, Spalangia endius, Spalangia cameroni and Muscidifurax raptor, were evaluated against pupae of the two cornsilk fly species, Euxesta eluta and Chaetopsis massyla. House fly pupae, the most common host for most of the parasitoids, were included for comparison. All of the parasitoids killed and successfully parasitized pupae of the two cornsilk fly species at rates that were similar to house fly pupae. Adult parasitoids that emerged from cornsilk fly hosts were somewhat smaller than parasitoids reared from house flies and had proportionally fewer females. These parasitoids, which are widely and commercially available for filth fly control, warrant further consideration for their potential against cornsilk flies in the field.

Comparative Virulence of Metarhizium anisopliae and Four Strains of Beauveria bassiana Against House Fly (Diptera: Muscidae) Adults With Attempted Selection for Faster Mortality

Entomopathogenic fungi such as Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae/brunneum (Metchnikoff)/Petch have shown promising results for managing the house fly, Musca domestica L. A primary challenge of using these biological control agents (BCAs) in field situations is the time required to induce high adult house fly mortality, typically 6-7 d post-exposure. In this study, virulence of M. anisopliae (strain F52) and four B. bassiana strains were compared. The B. bassiana strains GHA and HF23 are used in commercial products and those were compared with two strains that were isolated from house flies on dairy farms (NFH10 and L90). Assays were conducted by exposing adult house flies to fungal-treated filter paper disks for 2 h. The lethal time to 50% mortality (LT50) at the high concentration of 1 × 109 conidia ranged from 3.8 to 5.2 d for all five strains. GHA, NFH10, and L90 killed flies faster than M. anisopliae strain F52; HF23 did not differ from either the M. anisopliae or the other B. bassiana strains. Attempts with the NFH10 strain to induce faster fly mortality through selection across 10 fungal to fly passages did not result in shorter time to fly death of the selected strain compared with the unselected strain.

Insecticide Resistance Development in the Filth Fly Pupal Parasitoid, Spalangia cameroni (Hymenoptera: Pteromalidae), Using Laboratory Selections

Filth flies remain one of the most prevalent pest groups affecting the animal production industry. Spalangia spp. and Muscidifurax spp. are beneficial parasitic wasps that often are utilized to manage filth fly populations such as house flies, Musca domestica L. (Diptera: Muscidae), and stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae). These wasps search for filth fly pupae as hosts in areas potentially treated with insecticides, which may result in nontarget insecticide selection effects. However, research regarding resistance development in parasitic wasps such as S. cameroni Perkins (Hymenoptera: Pteromalidae) is limited. Therefore, a study was conducted to determine the potential of S. cameroni to develop resistance to the commonly used insecticide permethrin, as well as compare permethrin susceptibility among several S. cameroni strains. After 10 selected generations, susceptibility was significantly lower for the selected strain when compared with that of its unselected parent strain. A comparison of several parasitoid strains collected from different U.S. states indicated that permethrin susceptibility was not significantly different between a baseline strain and more recently established field strains. The potential implications of this previously unrecognized nontarget insecticide exposure effect on filth fly parasitoids are discussed.

Exposure Timing and Method Affect Beauveria bassiana (Hypocreales: Cordycipitaceae) Efficacy Against House Fly (Diptera: Muscidae) Larvae

House flies, Musca domestica L., are widely recognized for their ability to develop resistance to chemical insecticides so alternative control strategies are desired. The use of entomopathogenic fungi such as Beauveria bassiana (Balsamo) Vuillemin to manage house fly populations has shown promising results; however, the success of using this fungus against larval house flies varies widely. The overall objective of this study was to examine factors that may influence efficacy of B. bassiana treatments against larvae. When a high concentration (4 × 1011 conidia/ml) was applied to first- and second-instar larvae in rearing medium, there was a significant reduction in pupation and adult emergence rates. Treating third-instar larvae at the same concentration did not result in a significant reduction of pupation or adult emergence. Temperature (22 versus 32°C) and media composition (diets with- and without propionic acid) did not affect the B. bassiana treatment efficacy against house fly larvae. The narrow time window of vulnerability of larvae and the high doses required to infect them indicate that B. bassiana has little potential as an operational biocontrol agent for house fly larvae.

Beauveria bassiana Culturing and Harvesting for Bioassays With House Flies

The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae) has been widely studied against a wide range of arthropod pests, including many of medical and veterinary importance. New investigators must sort through a wide array of published methods for the production, harvest, storage, and bioassay methods for this pathogen. Simplified methods for production of conidia using Sabouraud dextrose agar with yeast (SDYA) plates and two conidial harvesting methods are described. Dry harvesting yields conidia that are ready to incorporate into dusts and food baits, but the fungal product includes mycelial debris that can hamper quantification and introduces variable amounts of unwanted bulk. Wet harvesting with filtration produces a cleaner product that is immediately ready for testing in liquid formulations. Examples of bioassays with house flies are presented that include conidia applied topically to the dorsal thorax for dose-mortality assays and conidial suspensions applied to filter paper disks for concentration mortality assays.

Oral and Topical Insecticide Response Bioassays and Associated Statistical Analyses Used Commonly in Veterinary and Medical Entomology

Veterinary and medical entomologists who are involved in research on pest control often need to perform dose-response bioassays and analyze the results. This article is meant as a beginner's guide for doing this and includes instructions for using the free program R for the analyses. The bioassays and analyses are described using previously unpublished data from bioassays on house flies, Musca domestica Linnaeus (Diptera: Muscidae), but can be used on a wide range of pest species. Flies were exposed topically to beta-cyfluthrin, a pyrethroid, or exposed to spinosad or spinetoram in sugar to encourage consumption. LD50 values for beta-cyfluthrin in a susceptible strain were similar regardless of whether mortality was assessed at 24 or 48 h, consistent with it being a relatively quick-acting insecticide. Based on LC50 values, spinetoram was about twice as toxic as spinosad in a susceptible strain, suggesting a benefit to formulating spinetoram for house fly control, although spinetoram was no more toxic than spinosad for a pyrethroid-resistant strain. Results were consistent with previous reports of spinosad exhibiting little cross-resistance. For both spinosad and spinetoram, LC50 values were not greatly different between the pyrethroid-resistant strain and the susceptible strain.

Improved Sentinel Method for Surveillance and Collection of Filth Fly Parasitoids

Parasitoids are important natural enemies of house flies and other muscoid flies. The two most commonly used methods for collecting fly parasitoids from the field have distinct advantages and disadvantages. Collections of wild puparia depend on the ability to find puparia in sufficient numbers and are prone to localized distortions in relative species abundance because of the overrepresentation of samples from hot spots of fly larval activity. Placement and retrieval of sentinel puparia is convenient and allows consistent sampling over time but is strongly biased in favor of Muscidifurax spp. over Spalangia spp. An improved sentinel method is described that combines some of the advantages of these two methods. Fly medium containing larvae is placed in containers, topped with a screen mesh bag of puparia, and placed in vertebrate-proof wire cages. Cages are placed at sites of actual or potential fly breeding and retrieved 3-7 d later. The modified method collected species profiles that more closely resembled those of collections of wild puparia than those from sentinel pupal bags. A method is also described for isolating puparia individually in 96-well tissue culture plates for parasitoid emergence. Use of the plate method provided a substantial saving of time and labor over the use of individual gelatin capsules for pupal isolation. Puparia from the collections that were housed individually in the wells of tissue culture plates had a higher proportion of emerged Spalangia species than puparia that were held in groups.

Heat Adaptation of the House Fly (Diptera: Muscidae) and Its Associated Parasitoids in Israel

Insects are ectothermic organisms; hence, all aspects of their biology are strongly influenced by ambient temperatures. Different insect species respond differently with phenotypic plasticity and/or genetic adaptation to changing temperatures. Here, we tested the thermal adaptation of the house fly and three of its parasitoids species by comparing life-history parameters in populations from a hot climate region (Jordan Valley) and from a moderate-climate region (Galilee). No significant differences were found between the two house fly populations, both under hot and moderate experimental conditions. Life-history parameters of the parasitoids (Muscidifurax raptor Girault & Sanders, Spalangia endius Walker, and Spalangia cameroni Perkins [Hymenoptera: Pteromalidae]) varied markedly between origins, species, sexes, and experimental conditions. Of the three species tested, only M. raptor collected in the Jordan Valley proved better adapted to experimental heat conditions, compared to its counterpart population that was collected in the Galilee. Additionally, we tested the effect of elevating temperatures on a house fly lab population for 17 consecutive generations and found no evidence for heat adaptation. We discuss our results in the context of house fly control and global warming.

Efficacy and repellency of some essential oils and their blends against larval and adult house flies, Musca domestica L. (Diptera: Muscidae)

House flies are global pests and notoriously difficult to control. Essential oils of vetiver, cinnamon, and lavender and their blends were tested for toxic and repellent effects against larval and adult flies. All of the oils had moderate toxicity for eggs. Mortality of 2^nd instar larvae was 57-78% in dipping assays, 38-100% in contact assays, and 94-100% in treated media. Lavender was less effective (38% mortality) than the others (91-100%) in contact bioassays. Oil blends were not more effective against larvae than individual oils. Vetiver and cinnamon oils were strongly repellent (84 and 78%, respectively) for larvae in treated media. None of the oils were repellent for adult house flies in olfactometer assays, but testing of additional products demonstrated significant repellency for neem oil, p-menthane-3,8-diol (PMD), and vanillin. Contact/fumigant toxicity of vetiver, cinnamon, and lavender oils was 100%, significantly higher than mortality from sunflower oil (67%). Blends of oils were not more effective against adults than the individual oils, but blends diluted with sunflower oil were as effective as the individual oils. Essentials oils of vetiver and cinnamon may have potential for fly management in situations where conventional insecticides cannot be used.

Effect of Fluctuating High Temperatures on House Flies (Diptera: Muscidae) and Their Principal Parasitoids (Muscidifurax spp. and Spalangia spp. [Hymenoptera: Pteromalidae]) From the United States

Colonies of house flies (Musca domestica L. [Diptera: Muscidae]) and four species of parasitoids (Muscidifurax raptor Girault and Sanders, Muscidifurax zaraptor Kogan and Legner, Spalangia cameroni Perkins and Spalangia endius Walker) were established by making collections from dairy farms near Bell, FL, Beatrice, NE, Minneapolis, MN, and San Jacinto, CA. Colonies were assessed for heat tolerance by comparing life history parameters at 25-27°C and fluctuating hot (26.7-41.7°C) temperatures. Muscidifurax raptor, S. cameroni, and S. endius produced 24-28% as many progeny under hot conditions as at 25°C. Colonies of M. zaraptor were more heat-tolerant and produced an average 46.9% as many progeny under the hot regime compared with moderate conditions. There was little evidence for higher heat tolerance in parasitoid populations from historically hot locations (CA desert and FL). Colonies of M. raptor and S. endius that had been in culture for 24 yr were the least heat-tolerant with regard to progeny production. House flies collected from the same locations varied little in longevity, fecundity, or egg-to-adult survival under either hot or moderate regimes. Flies reared under hot conditions laid about half as many eggs (89/female) and had about half the egg-adult survival rate (47.3%) under hot compared with moderate conditions, indicating that heat stress had less effect on flies than on all of the parasitoids except M. zaraptor. An attempt to select for heat tolerance in flies by subjecting them to incremental increases in rearing temperatures for 20 generations resulted in little change in tolerance among the selected flies.

Larvicidal potential of the polyol sweeteners erythritol and xylitol in two filth fly species

The house fly, Musca domestica (L.) (Diptera: Muscidae), and the stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), are two filth flies responsible for significant economic losses in animal production. Although some chemical control products target adults of both species, differences in mouthpart morphology and behavior necessitates distinct modalities for each. For these reasons, larvicides are an attractive means of chemical control. We assessed the potential of the polyol sweeteners erythritol and xylitol as larvicides to the house fly and stable fly. LC₅₀ values of erythritol against 2^nd instar larvae were 34.94 mg/g media (house fly) and 22.10 mg/g media (stable fly). For xylitol, LC₅₀ values were 74.91 mg/g media (house fly) and 41.58 mg/g media (stable fly). When given a choice, neither species showed a preference for ovipositing in media treated with either sweetener at various concentrations or in media without sweetener. Significantly lower development from egg to adult was observed when the 2^nd instar LC₅₀ equivalent of each sweetener was present in the media compared to controls. Erythritol and xylitol both have larvicidal qualities, however their effective concentrations would necessitate creative product formulation and deployment methods to control all stages of developing flies.

Mortality Effects of Three Bacterial Pathogens and Beauveria bassiana When Topically Applied or Injected Into House Flies (Diptera: Muscidae)

The house fly, Musca domestica L., is a global pest of public health and agricultural importance. The efficacy of conventional management has been waning due to increasing insecticide resistance. A potential management tool is the entomopathogenic fungus, Beauveria bassiana Vuillemin (Hypocreales: Cordycipitaceae) (strain L90), although time-to-death is slower than desired by potential users. This research investigated the effectiveness of three gram-negative bacteria (Pseudomonas protegens Ramette (Psuedomonadales: Pseudomonadaceae) pf-5, Photorhabdus temperata Fischer-Le Saux (Enterobacteriales: Enterobacteriaceae) NC19, and Serratia marcescens Bizio (Enterobacteriales: Enterobacteriaceae) DB11) on house fly mortality when topically applied, compared to B. bassiana. Each pathogen's virulence was measured by injection into adult female house flies or by topical applications to their thorax. All bacterial strains were highly virulent after injection with 1 × 104 colony forming units (cfu), causing fly mortality within 24 h. Beauveria bassiana resulted in high mortality, 3 d postinjection at the high dose of 1 × 104 conidia/µl. Mortality due to topical treatments of P. temperata and S. marcescens was low even at the highest dose of 1 × 106 cfu/µl. Mortality after topical treatments with P. protegens was evident 4 d after application of 1 × 106 cfu/µl. Mortality from B. bassiana was low at 4 d but increased at 5 d. These results imply that P. protegens holds great potential as a biological control agent for incorporation into an integrated pest management program against adult house flies.

Potential of essential oils to prevent fly strike and their effects on the longevity of adult Lucilia sericata

Lucilia sericata is a facultative ectoparasite causing fly strike or myiasis in warm-blooded vertebrates. It is controlled by traps or insecticides, but both have drawbacks and alternative ways of control are urgently needed. Essential oils (EOs) of vetiver (Chrysopogon zizanioides), cinnamon (Cinnamomum zeylanicum), and lavender (Lavandula angustifolia) and their blends (OBs); OB1 (2 ml of each EO plus 4 ml of sunflower oil as a carrier) and OB2 (2 ml of each EO) were tested. Oils were tested at 5% for deterrence assays, and a dose response assay 0.01-0.6%, was conducted to determine forced-contact toxicity. We evaluated the efficacy of oils as oviposition deterrents, repellents/attractants, and their effects on mortality and longevity of adult L. sericata. Our data indicated that 0.2% EOs killed all flies by 5 min post-treatment and that vetiver oil greatly deterred flies from the oviposition medium and reduced adult longevity. Sunflower oil repelled all flies from ovipositing and greatly reduced the lifespan of treated adults. The blend of the four oils (OB1) had the greatest repellent effect on the flies. EOs have insecticidal, repellent, and oviposition-deterrent activities against L. sericata that could be used for suppression of blow fly populations.

Reproducible dsRNA Microinjection and Oviposition Bioassay in Mosquitoes and House Flies

Synthetic dsRNAs, used to induce RNA interference, may have dose dependent phenotypic effects. These effects are difficult to define if the dsRNAs are delivered using a non-quantitative method. Accurate delivery of known quantities of nucleic acids or other chemicals is critical to measure the efficacy of the compound being tested and to allow reliable comparison between compounds. Here we provide a reproducible, quantitative microinjection protocol that ensures accurate delivery of specific doses of dsRNA, reducing the mortality typically induced by injection injury. These modifications include the addition of Rhodamine B, a graduated injection needle, and an improved recovery method borrowed from Isoe and Collins. This method allows calculation of dose responses and facilitates comparisons between compounds. Versions of this method have been successfully used on three genera of mosquitoes as well as house flies to assess the reduction in fecundity resulting from gene silencing of ribosomal RNA transcripts. This protocol provides strategies to reduce several challenges of small insect microinjection. Together, mechanical delivery of dsRNAs accompanied by visual verification, identification of effective locations for delivery, and inclusion of a post-injection recovery period ensure accurate dosing and low injury mortality. This protocol also describes an oviposition bioassay for uniform determination of effects on fecundity.

Mortality of the House Fly (Diptera: Muscidae) After Exposure to Combinations of Beauveria bassiana (Hypocreales: Clavicipitaceae) With the Polyol Sweeteners Erythritol and Xylitol

Documented resistance to traditional insecticides in the house fly, Musca domestica L. (Diptera: Muscidae), has expedited a need for alternative forms of control. One such method is the use of biological control organisms, such as the entomopathogenic fungus, Beauveria bassiana (Balsamo - Crivelli) Vuillemin (Hypocreales: Clavicipitaceae). Administering B. bassiana with a calorically rich phagostimulant such as sucrose may have the unintended effect of increasing fly vitality and thus reproduction before mortality sets in. Therefore, finding a phagostimulant with lower caloric value that can replace sucrose is valuable. Here B. bassiana was combined with the sweeteners erythritol and xylitol as potential low-calorie substitutes for sucrose. Female flies consumed as much xylitol alone as they did sucrose alone, but less erythritol than both. After 24 h of exposure, B. bassiana administered at 1 mg in erythritol and in sucrose were equally effective at reducing survival and better than xylitol. B. bassiana administered at 10 mg worked equally well at reducing survival in all three sweeteners. When exposed to 10 mg of B. bassiana in sweetener for 1 h, sucrose reduced survival more than in erythritol or xylitol, but mortality was still in excess of 97% after 8 d in all three sweeteners. Each sweetener mixed with B. bassiana worked as well in an environment with additional food sources and stimuli as they did in an environment lacking these additions. Erythritol and xylitol appear to be strong candidates to replace sucrose in baits formulated around B. bassiana.

Effects of pyriproxyfen on wild populations of the housefly, Musca domestica, and compatibility with its principal parasitoids

BACKGROUND

The housefly, Musca domestica L., is an important pest of animal agriculture. Effective fly management requires integration of manure management, mass trapping, biological control, and selective insecticide use. Insecticidal control of houseflies is difficult due to the rapidity of resistance development, yet the insect growth regulator pyriproxyfen (PPF) is one of few insecticides that may still be effective. Here, we tested the susceptibility of wild housefly populations in the USA and in Israel to PPF, as well as the effect of PPF on housefly parasitoids of the genera Muscidifurax and Spalangia.

RESULTS

Most housefly populations from both countries were completely eliminated at PPF concentrations of 100 mg kg^-1 (USA) and 600 mg kg^-1 (Israel). One population from each country exhibited initial levels of PPF tolerance. PPF efficacy significantly decreased in cow manure. Emergence rates of parasitoids developing in PPF-treated hosts at concentrations of ≥600 mg kg^-1 were significantly affected, whereas other fitness parameters were moderately to non-affected.

CONCLUSIONS

PPF is still an effective tool for housefly control, but resistance management practices should be employed to avoid resistance. PPF is compatible with principal housefly parasitoids at concentrations <600 mg kg^-1 , and is suitable for use in integrated pest management. © 2017 Society of Chemical Industry.

Effects of four commercial fungal formulations on mortality and sporulation in house flies (Musca domestica) and stable flies (Stomoxys calcitrans)

The house fly Musca domestica L. (Diptera: Muscidae) and stable fly Stomoxys calcitrans (L.) (Diptera: Muscidae) are major pests of livestock. Biological control is an important tool in an integrated control framework. Increased mortality in filth flies has been documented with entomopathogenic fungi, several strains of which are commercially available. Three strains of Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) and one strain of Metarhizium brunneum (Petch) (Hypocreales: Clavicipitaceae) were tested in commercial formulations for pathogenicity against house flies and stable flies. There was a significant increase in mortality of house flies with three of the formulations, BotaniGard^® ES, Mycotrol^® O, and Met52^® EC, during days 4-9 in comparison with balEnce™ and the control. In stable flies, mortality rates were highest with Met52^® EC, followed by Mycotrol^® O, BotaniGard^® ES and, finally, balEnce™. There was a significant fungal effect on sporulation in both house flies and stable flies. Product formulation, species differences and fungal strains may be responsible for some of the differences observed. Future testing in field situations is necessary. These commercial biopesticides may represent important tools in integrated fly management programmes.

Discovery, Development, and Evaluation of a Horn Fly-Isolated (Diptera: Muscidae) Beauveria bassiana (Hypocreales: Cordyciptaceae) Strain From Florida, USA

The horn fly, Haematobia irritans (L.) is an important cattle pest and traditionally has been managed using insecticides; however, many horn fly populations are insecticide-resistant in United States. Use of alternative control techniques has been limited because of the challenges of managing a fly pest on pastured cattle. After the discovery of a wild horn fly infected with Beauveria bassiana in Florida, the fungus was cultured and evaluated for efficacy against laboratory-reared horn flies. This fungal strain was selected for increased virulence by passage through laboratory-reared horn fly hosts to shorten interval from infection to fly death and subsequent conidia formation, properties important to future use of the fungus as a biological control agent against horn flies. After seven passages through horn fly hosts, fly mortality was not significantly accelerated as evaluated through LT50 values, but conidia were readily produced from these killed flies. Although further development is needed to improve fungal efficacy, this fungal strain holds promise as a biological control agent for inclusion in horn fly integrated pest management programs.

Manure Preferences and Postemergence Learning of Two Filth Fly Parasitoids, Spalangia cameroni and Muscidifurax raptor (Hymenoptera: Pteromalidae)

The efficiency of host-seeking behavior is crucial to the reproductive performance of female parasitoids. Initially, parasitoids may use chemical information garnered from the microhabitat in which they emerge to locate hosts. Spalangia cameroni and Muscidifurax raptor are commercially available parasitoids of filth flies. Postemergence exposure to a specific manure may provide a way to increase parasitism in specific microhabitats found at livestock facilities upon release. In this study, female parasitoids of both species were exposed to equine manure, bovine manure, or clean pupae. Females from each emergence exposure were tested in a two-choice arena (house fly hosts in bovine manure versus clean pupae, equine manure versus clean pupae, and equine manure versus bovine manure) for progeny production. There was a detectable but small effect of postemergence exposure on S. cameroni, but it was not sufficient to reverse innate preferences. Females consistently produced more progeny in hosts found in any manure over clean pupae, and in equine manure over bovine manure. The effect of postemergence exposure on M. raptor was also detectable but small. Females produced equal numbers of progeny in bovine manure versus clean pupae, as opposed to preferring to oviposit in clean pupae as with all other treatments. Preferences by M. raptor were overall less marked than for S. cameroni; indeed most of the variability observed for this species did not result from the treatment design. Residual host mortality was also detectably altered by exposure in both species, but the effect was small. Thus, postemergence exposure did not consistently and effectively manipulate these parasitoids to producing progeny in different exposure manures, suggesting that microhabitat preferences are largely determined by other factors.

Oviposition Deterrence and Immature Survival of Filth Flies (Diptera: Muscidae) When Exposed to Commercial Fungal Products

Filth flies are pests of livestock, and can transmit pathogens that cause disease to animals and their caretakers. Studies have shown successful infection of adult filth flies following exposure to different strains and formulations of entomopathogenic fungi. This study aimed to examine the effects of commercial formulations of Beauveria bassiana (Balsamo) (Moniliales: Moniliaceae) (i.e., BotaniGard ES, Mycotrol O, balEnce), and Metarhizium brunneum (Metsch.) (Ascomycota: Hypocreales) (i.e., Met52 EC), on filth fly oviposition and immature fly survival after exposure. House flies, Musca domestica L., laid significantly fewer eggs on Met52 EC-treated surfaces than on surfaces treated with all other products and the control. Similar numbers of eggs were laid on surfaces treated with all B. bassiana products, but egg production was half of the control. Stable flies, Stomoxys calcitrans (L.), laid the fewest eggs on Met52 EC- and Mycotrol O-treated surfaces. This species did not distinguish between the remaining products and the control. In a second experiment, house fly eggs were placed on treated cloths so that hatched larvae contacted the treatment prior to development. Met52 EC had the greatest effect on immature survival with a significant reduction in recovered pupae at the medium and high doses of fungi. Overall, Met52 EC, containing M. brunneum, had the greatest effect on house fly and stable fly oviposition deterrence and immature development of house flies. Management implications are discussed.

Comparison of the Olfactory Preferences of Four of Filth Fly Pupal Parasitoid Species (Hymenoptera: Pteromalidae) for Hosts in Equine and Bovine Manure

House flies (Musca domestica L.) and stable flies (Stomoxys calcitrans (L.)) (Diptera: Muscidae) are common pests in equine and cattle facilities. Pupal parasitoids, primarily in the genera Spalangia and Muscidifurax (Hymenoptera: Pteromalidae), can be purchased for biological control of these flies. However, little is known about the host-habitat preferences associated with host-seeking by these parasitoids. The preferences of two Spalangia and two Muscidifurax species to odors associated with house fly hosts in equine and bovine manure were investigated in the laboratory using a Y-tube olfactometer. Odor stimuli from manure without developing flies, third-instar house flies in manure, and fly host puparia in manure were evaluated. In choice tests, S. cameroni and S. endius were strongly attracted to odor associated with equine manure against clean air. Although S. cameroni was attracted to all bovine manure-containing treatments against clean air, S. endius was only attracted to the bovine manure with third-instar flies. There were no significant differences between the Spalangia species in odor responses. Neither Muscidifurax species were attracted to equine manure treatments and were only attracted to the bovine manure with puparia over clean air. In manure comparison studies, bovine treatments with developing flies were more attractive than the equivalent equine treatments to both Muscidifurax species The data suggest that coexistence between the competing pteromalid parasitoids might be promoted by different host-seeking behaviors. Additionally, manure preferences may indicate parasitoid suitability for releases on different livestock and equine facilities.

Comparison of Host-Seeking Behavior of the Filth Fly Pupal Parasitoids, Spalangia cameroni and Muscidifurax raptor (Hymenoptera: Pteromalidae)

The pupal parasitoids, Spalangia cameroni Perkins and Muscidifurax raptor Girault and Sanders, can be purchased for biological control of house flies Musca domestica L. and stable flies Stomoxys calcitrans (L.) (Diptera: Muscidae). Little is known about the odors involved in host-seeking behavior of these two species, so odors associated with house flies were investigated in the laboratory using a Y-tube olfactometer. Odor stimuli from house fly host puparia, larvae, pine-shavings bedding with horse manure, and developing flies in the pine-shavings-manure substrate were evaluated in bioassays using the two pteromalid species. In choice tests, naïve female S. cameroni were strongly attracted to odor from the substrate containing house fly larvae and secondarily from the uninfested substrate and substrate with puparia versus humidified and purified air. This species also selected the substrate with larvae versus the substrate with the house fly puparia or uninfested substrate. Muscidifurax raptor was attracted to odor from the substrate containing puparia, washed puparia, and substrate with puparia removed. The data suggest that coexistence between the two pteromalid parasitoids, S. cameroni and M. raptor, might be promoted by different host-seeking behavior.

Competition between the filth fly parasitoids Muscidifurax raptor and M. raptorellus (Hymenoptera: Pteromalidae)

Competition bioassays were conducted with the filth fly pupal parasitoids Muscidurax raptor (Girault & Sanders) and M. raptorellus (Kogan & Legner) (Hymenoptera: Pteromalidae) using house fly Musca domestica L. (Diptera: Muscidae) hosts at different host densities. Muscidifurax raptor had a significant impact on M. raptorellus when hosts were limiting in sequential parasitism tests. Fewer than six M. raptorellus adult progeny emerged from groups of 50 fly pupae that were parasitized by M. raptor at the same time or when M. raptor parasitism preceded M. raptorellus by 48 h, respectively, compared with 42-55 M. raptorellus progeny produced when this species was tested alone. Production of M. raptor was significantly lower when parasitism by this species was preceded by M. raptorellus (25) than when M. raptor was tested alone (43). When the two species parasitized hosts at the same time in different proportions at low host:parasitoid densities (5:1), M. raptorellus produced 13 progeny per parent female when it was the sole species present and fewer than two when M. raptor was present. No negative impact of M. raptorellus on M. raptor was observed. Neither species had a substantial effect on the success of the other at higher host:parasitoid densities.

Development and Oviposition Preference of House Flies and Stable Flies (Diptera: Muscidae) in Six Substrates From Florida Equine Facilities

House flies, Musca domestica L., and stable flies, Stomoxys calcitrans (L.), (Diptera: Muscidae), common pests on equine facilities, were studied in the laboratory to determine the success and duration of larval development and oviposition preferences on six substrates commonly found on equine facilities. Substrates tested were hay soiled with urine and manure, fresh horse manure, pine shaving bedding soiled with urine and manure (<12 h old), pine shaving bedding soiled with urine and manure (aged >72 h in a manure pile), builders sand bedding soiled with urine and manure aged 3 d, and soil from an overgrazed pasture mixed with urine and manure of variable age. House fly larvae failed to develop into adults in hay, soil, and sand substrates. Stable flies preferred to oviposit on substrates with plant material and not on fresh manure. However, when eggs were added to the substrates, pupariation was maximal in fresh manure and the fresh pine shaving substrate. Stable flies developed in all six equine substrates, but development was less successful on the substrates with soil. In choice tests, fresh manure and the fresh pine shaving substrates were the most attractive for house fly oviposition. These substrates also yielded the greatest number of house fly puparia from artificially added eggs. An understanding of oviposition preferences and differential larval development of house flies and stable flies on these substrates may help develop options for reducing pest populations by effectively managing equine waste and selecting appropriate bedding materials.

A Mathematic Model That Describes Modes of MdSGHV Transmission within House Fly Populations

In this paper it is proposed that one potential component by which the Musca domestica salivary gland hypertrophy virus (MdSGHV) infects individual flies is through cuticular damage. Breaks in the cuticle allow entry of the virus into the hemocoel causing the infection. Male flies typically have a higher rate of infection and a higher rate of cuticular damage than females. A model for the transmission of MdSGHV was formulated assuming several potential and recognized means of transmission. The model yields results that are in agreement with field data that measured the infection rate in house flies on dairy farms in Florida. The results from this model indicate that MdSGHV will be maintained at a stable rate within house fly populations and support the future use of MdSGHV as a birth control agent in house fly management.

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.

High-throughput mosquito and fly bioassay system for natural and artificial substrates treated with residual insecticides

A high-throughput bioassay system to evaluate the efficacy of residual pesticides against mosquitoes and muscid flies with minimal insect handling was developed. The system consisted of 4 components made of readily available materials: 1) a CO2 anaesthetizing chamber, 2) a specialized aspirator, 3) a cylindrical flat-bottomed glass bioassay chamber assembly, and 4) a customized rack.

Muscavirus (MdSGHV) disease dynamics in house fly populations--how is this virus transmitted and has it potential as a biological control agent?

The newly classified family Hytrosaviridae comprises several double-stranded DNA viruses that have been isolated from various dipteran species. These viruses cause characteristic salivary gland hypertrophy and suppress gonad development in their hosts. One member, Muscavirus or MdSGHV, exclusively infects adult house flies (Musca domestica) and, owing to its massive reproduction in and release from the salivary glands, is believed to be transmitted orally among feeding flies. However, results from recent experiments suggest that additional transmission routes likely are involved in the maintenance of MdSGHV in field populations of its host. Firstly, several hours before newly emerged feral flies begin feeding activities, the fully formed peritrophic matrix (PM) constitutes an effective barrier against oral infection. Secondly, flies are highly susceptible to topical virus treatments and intrahemocoelic injections. Thirdly, disease transmission is higher when flies are maintained in groups with infected conspecifics than when flies have access to virus-contaminated food. We hypothesize that interactions between flies may lead to cuticular damage, thereby providing an avenue to viral particles for direct access to the hemocoel. Based on our current knowledge, two options seem plausible for developing Muscavirus as a sterilizing agent to control house fly populations: The virus may either be formulated with PM-disrupting materials to facilitate oral infection from a feeding bait system, or amended with abrasive materials to enhance infection through a damaged cuticle after topical aerosol applications.

Pyriproxyfen and house flies (Diptera: Muscidae): effects of direct exposure and autodissemination to larval habitats

Pyriproxyfen is an insect growth regulator with juvenile hormone-like activity that has potential uses for dipterans that are difficult to manage with conventional insecticides, such as house flies (Musca domestica L.). The objectives of this study were to determine the efficacy of this insect growth regulator against house flies using variety of delivery systems and target life stages, including an evaluation of the potential for autodissemination by female flies to larval development sites. Adult female house flies exposed to filter paper (3.75% active ingredient) or sugar treated with pyriproxyfen (0.01-0.1%) produced significantly fewer F1 pupae than untreated flies. Adult emergence from pupae was unaffected. In contrast, treatment of larval rearing medium with 0.35 ml/cm2 of a 12 mg pyriproxyfen/liter preparation had no effect on the number of pupae developing from eggs but markedly inhibited adult emergence from those pupae. There was little difference in susceptibility between an insecticide-susceptible and a wild strain of house fly. The LC50 for inhibiting fly emergence of dust formulations in diatomaceous earth incorporating commercial pyriproxyfen products ranged from 8 to 26 mg/liter, with little difference among products. Compared with untreated flies, significantly fewer pupae were produced at concentrations > 0.5% and no adults were produced at concentrations > 0.05% pyriproxyfen. When gravid females were exposed for 1 h to treated fabric (6 mg pyriproxyfen/cm2) and allowed to oviposit in rearing media containing eggs, sufficient pyriproxyfen was autodisseminated to reduce adult emergence from those eggs by > 99%. Intermittent contact with treated fabric over 2 d reduced adult emergence by 63-76%.

Disease dynamics and persistence of Musca domestica salivary gland hypertrophy virus infections in laboratory house fly (Musca domestica) populations

Past surveys of feral house fly populations have shown that Musca domestica salivary gland hypertrophy virus (MdSGHV) has a worldwide distribution, with an average prevalence varying between 0.5% and 10%. How this adult-specific virus persists in nature is unknown. In the present study, experiments were conducted to examine short-term transmission efficiency and long-term persistence of symptomatic MdSGHV infections in confined house fly populations. Average rates of disease transmission from virus-infected to healthy flies in small populations of 50 or 100 flies ranged from 3% to 24% and did not vary between three tested geographical strains that originated from different continents. Introduction of an initial proportion of 40% infected flies into fly populations did not result in epizootics. Instead, long-term observations demonstrated that MdSGHV infection levels declined over time, resulting in a 10% infection rate after passing through 10 filial generations. In all experiments, induced disease rates were significantly higher in male flies than in female flies and might be explained by male-specific behaviors that increased contact with viremic flies and/or virus-contaminated surfaces.

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

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%. None of the stable flies (Stomoxys calcitrans), rat-tail maggot flies (Eristalis tenax) or yellow dung flies (Scathophaga stercoraria) collected from MdSGHV-positive farms displayed characteristic salivary gland hypertrophy (SGH). In laboratory transmission tests, SGH symptoms were not 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 among the five species tested. Virulence of Danish and Florida isolates of MdSGHV was similar with three virus delivery protocols, as a liquid food bait (in sucrose, milk, or blood), sprayed onto the flies in a Potter spray tower, or by immersiion in a crude homogenate of infected house flies. The most effective delivery system was immersion in a homogenate of ten 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.

Seasonal abundance of stable flies and filth fly pupal parasitoids (Hymenoptera: Pteromalidae) at Florida equine facilities

Beginning in November 2007 and continuing until December 2009, weekly stable fly, Stomoxys calcitrans (L.), surveillance was conducted at four equine facilities near Ocala, FL, by using alsynite sticky traps for adults and by searching immature developmental sites for pupae. Adult stable fly trap captures were highly variable throughout the year, ranging from 0 to 1,400 flies per trap per farm. The greatest adult stable fly activity was observed during the spring months of March and April, with weekly three-trap means of 121 and 136 flies per farm, respectively. The importance of cultural control measures was most apparent on the only farm with no reported insecticide use and the lowest stable fly trap captures, where an intense daily sanitation and composting program was conducted. A survey of on-site filth fly pupae revealed that 99.9% of all parasitoids recovered were Spalangia spp., consisting of Spalangia cameroni Perkins (56.5%), Spalangia nigroaenea Curtis (34.0%), Spalangia endius Walker (5.8%), and Spalangia nigra Latreille (3.7%). The implications of these findings are discussed.

The ability of selected pupal parasitoids (Hymenoptera: Pteromalidae) to locate stable fly hosts in a soiled equine bedding substrate

The ability of Spalangia cameroni Perkins, Spalangia endius Walker, and Muscidifurax raptorellus Kogan and Legner to locate and attack stable fly hosts was evaluated under laboratory conditions. Postfeeding third-instar stable fly larvae were released and allowed to pupate in two arena types: large 4.8 liter chambers containing a field-collected, soiled equine bedding substrate; or 120-ml plastic cups containing wood chips. At the time of fly pupariation, parasitoids were released and permitted 72 h to locate and attack hosts. On average, parasitism rates of freely accessible stable fly pupae in cups were not significantly different between parasitoid species. However, parasitism rates in chambers containing either Spalangia spp. were ≈50-fold more than M. raptorellus. Additional intraspecies analysis revealed that parasitism rates both by S. cameroni and S. endius were not significantly different when pupae were freely accessible or within bedding, whereas M. raptorellus attacked significantly more pupae in cups than in the larger chambers where hosts were distributed within bedding. These results suggest that Spalangia spp. are more suited to successfully locate and attack hosts in habitats created by equine husbandry in Florida. Therefore, commercially available parasitoid mixtures containing Muscidifurax spp. may be ineffective if used as a control measure at Florida equine facilities.

Salivary gland hypertrophy viruses: a novel group of insect pathogenic viruses

Salivary gland hypertrophy viruses (SGHVs) are a unique, unclassified group of entomopathogenic, double-stranded DNA viruses that have been reported from three genera of Diptera. These viruses replicate in nuclei of salivary gland cells in adult flies, inducing gland enlargement with little obvious external disease symptoms. Viral infection inhibits reproduction by suppressing vitellogenesis, causing testicular aberrations, and/or disrupting mating behavior. Historical and present research findings support a recent proposal of a new virus family, the Hytrosaviridae. This review describes the discovery and prevalence of different SGHVs, summarizes their biochemical characterization and taxonomy, compares morphological and histopathological properties, and details transmission routes and the influence of infection on host biology and reproduction. In addition, the potential use of SGHVs as sterilizing agents for house fly control and the deleterious impact of SGHVs on colonized tsetse flies reared for sterile insect technique are discussed.

Potential for stable flies and house flies (Diptera: Muscidae) to transmit Rift Valley fever virus

Rift Valley fever (RVF), a disease of ruminants and humans, has been responsible for large outbreaks in Africa that have resulted in hundreds of thousands of human infections and major economic disruption due to loss of livestock and to trade restrictions. As indicated by the rapid spread of West Nile viral activity across North America since its discovery in 1999 and the rapid and widespread movement of chikungunya virus from Africa throughout the Indian Ocean Islands to Asia and Europe, an introduced exotic arbovirus can be rapidly and widely established across wide geographical regions. Although RVF virus (RVFV) is normally transmitted by mosquitoes, we wanted to determine the potential for this virus to replicate in 2 of the most globally distributed and common higher flies: house flies, Musca domestica, and stable flies, Stomoxys calcitrans. Neither species supported the replication of RVFV, even after intrathoracic inoculation. However, S. calcitrans was able to mechanically transmit RVFV to susceptible hamsters (Mesocricetus auratus) after probing on infected hamsters with high viral titers. Therefore, S. calcitrans, because of its close association with domestic animals that serve as amplifying hosts of RVFV, should be considered a possible mechanical vector of RVFV, and it may contribute to the rapid spread of a RVF outbreak. Other Stomoxys species present in Africa and elsewhere may also play similar roles.

Selection for resistance to imidacloprid in the house fly (Diptera: Muscidae)

The house fly, Musca domestica L. (Diptera: Muscidae), continues to be a primary pest of livestock facilities worldwide. This pest also has shown a propensity for pesticide resistance development when under high selection pressures. In this study the house fly strain FDm was created by a 20% contribution from each of five colonies collected from dairies in Florida with known imidacloprid resistance. The FDm strain was used to evaluate the level ofimidacloprid resistance after five selections near the LC70 value of each selected generation. Overall, the mean selection mortality was 72.7, with males being considerably more susceptible than females. The unselected (F0) FDm strain showed considerable susceptibility to imidacloprid after its creation, compared with the five parental strains. Between 9500 and 14,000 virgin house flies were used in each selection. After the fifth and final selection, a 331-fold increase in imidacloprid resistance at the LC70 was observed over the parental FDm strain. In parallel studies, the FDm strain showed increasing tolerance of the commercial imidacloprid product QuickBayt. These results suggest that livestock producers should use caution when choosing pesticides and consider rotating fly baits, as is encouraged with other pesticide treatment regimes on farms.

Nicotinoid and pyrethroid insecticide resistance in houseflies (Diptera: Muscidae) collected from Florida dairies

BACKGROUND

The housefly, Musca domestica L., continues to be a major pest of confined livestock operations. Houseflies have developed resistance to most chemical classes, and new chemistries for use in animal agriculture are increasingly slow to emerge. Five adult housefly strains from four Florida dairy farms were evaluated for resistance to four insecticides (beta-cyfluthrin, permethrin, imidacloprid and nithiazine).

RESULTS

Significant levels of tolerance were found in most field strains to all insecticides, and in some cases substantial resistance was apparent (as deduced from comparison with prior published results). At the LC(90) level, greater than 20-fold resistance was found in two of the fly strains for permethrin and one fly strain for imidacloprid. Beta-cyfluthrin LC(90) resistance ratios exceeded tenfold resistance in three fly strains. The relatively underutilized insecticide nithiazine had the lowest resistance ratios; however, fourfold LC(90) resistance was observed in one southern Florida fly strain. Farm insecticide use and its impact on resistance selection in Florida housefly populations are discussed.

CONCLUSION

Housefly resistance to pyrethroids is widespread in Florida. Imidacloprid resistance is emerging, and tolerance was observed to both imidacloprid and nithiazine. If these insecticides are to retain efficacy, producer use must be restrained.

Host ranges of gregarious muscoid fly parasitoids: Muscidifurax raptorellus (Hymenoptera: Pteromalidae), Tachinaephagus zealandicus (Hymenoptera: Encyrtidae), and Trichopria nigra (Hymenoptera: Diapriidae)

Attack rates, progeny production, sex ratios, and host utilization efficiency of Muscidifurax raptorellus (Kogan and Legner) (Hymenoptera: Pteromalidae), Tachinaephagus zealandicus Ashmead (Hymenoptera: Encyrtidae), and Trichopria nigra (Nees) (Hymenoptera: Diapriidae) were evaluated in laboratory bioassays with five dipteran hosts: house fly (Musca domestica L.), stable fly (Stomoxys calcitrans L.), horn fly (Hematobia irritans L.), black dump fly [Hydrotaea aenescens (Weidemann)] (Diptera: Muscidae), and a flesh fly (Sarcophaga bullata Parker) (Diptera: Sarcophagidae). M. raptorellus killed and successfully parasitized all five host species and produced an average 2.6 parasitoid progeny from each host. Host attack rates were highest on stable fly and lowest on horn fly; there were no differences among hosts in the total number of progeny produced. T. zealandicus killed larvae of all fly host species in similar numbers, but parasitism was most successful on H. aenescens and S. bullata and least successful on horn fly and house fly hosts. Significantly more parasitoid progeny emerged from S. bullata (10.2 parasitoids per host) than the other hosts; only 2.5 progeny were produced from parasitized horn fly hosts. Most of the killed puparia that produced neither adult flies nor parasitoids ("duds") contained dead parasitoids; in house fly, stable fly, and horn fly hosts, >30% of these dudded pupae contained adult wasps that failed to eclose. T. nigra successfully parasitized pupae of all host species except house fly and was most successful on stable fly. Significantly more parasitoid progeny emerged from S. bullata (30.6 parasitoids per host) than the other hosts; only 5.7 progeny were produced from horn fly hosts.

Evaluation of commercial and field-expedient baited traps for house flies, Musca domestica L. (Diptera: Muscidae)

A comparison of nine commercial baited fly traps on Florida dairy farms demonstrated that Terminator traps collected significantly more (13,323/trap) house flies (Musca domestica L.) than the others tested. Final Flight, Fly Magnet, and FliesBeGone traps collected intermediate numbers of flies (834-2,166), and relatively few were caught with ISCA, Advantage, Fermone Big Boy, Squeeze & Snap, or OakStump traps (<300). Terminator traps collected about twice as many flies (799.8/trap) as FliesBeGone traps (343.8) when each trap was baited with its respective attractant, but when the attractants were switched between the two trap types, collections were significantly lower (77-108) than was observed with traps baited with their respective attractant. Solutions of molasses were significantly more attractive to house flies than honey, maple syrup, or jaggery (date palm sugar). Field-expedient traps constructed from discarded PET water bottles were much less effective than commercial traps, but painting the tops of such traps with black spray paint resulted in a six-fold increase in trap capture.

Transmission of MdSGHV among adult house flies, Musca domestica (Diptera: Muscidae), occurs via oral secretions and excreta

The MdSGHV is a double-stranded DNA virus that replicates in the salivary glands of infected adult house flies. Transmission of this non-occluded, enveloped virus is believed to be mediated orally via deposition and consumption of oral secretions composed of salivary gland secretions and crop contents. In this study, transmission electron micrographs of crops from infected flies showed numerous enveloped virions in the crop lumen adjacent to the cuticular intima, as well as on the hemocoel side in close vicinity to muscle cells. Oral treatments of newly emerged flies with viremic salivary gland homogenates, crop homogenates, or gradient-purified virus resulted in an average 44% infection. Virus released via oral secretion was infectious when ingested by newly emerged adult flies, resulting in an average 66% infection. Using quantitative real-time PCR, MdSGHV DNA was quantified in oral secretions and excreta obtained from viremic flies. Between 2 and 4 days post-infection (dpi), viral copy numbers in oral secretions increased exponentially and from 5 to 21 dpi each infected fly released an average 10(6) MdSGHV copies per feeding event. Excreta samples collected overnight from individual infected flies at 5 dpi contained an average 6.5 x 10(5) viral copies. Low but detectable infection rates were produced when newly emerged flies were challenged with excreta samples. In summary, evaluation of the quantity and infectivity of MdSGHV released by individual infected house flies clearly showed that deposition of oral secretions and excreta onto a shared food substrate is the main route of natural MdSGHV transmission among adult house flies.

Seasonal prevalence and transmission of salivary gland hypertrophy virus of house flies (Diptera: Muscidae)

A survey (2005-2006) of house fly, Musca dormestica L. (Diptera: Muscidae) populations on four Florida dairy farms demonstrated the presence of flies with acute symptoms of infection with salivary gland hypertrophy (SGH) virus on all farms. Disease incidence varied among farms (farm averages, 0.5-10.1%) throughout the year, and it showed a strong positive correlation with fly density. Infections were most common among flies that were collected in a feed barn on one of the farms, especially among flies feeding on wet brewers grains (maximum 34% SGH). No infections were observed among adult flies reared from larvae collected on the farms, nor among adults reared from larvae that had fed on macerated salivary glands from infected flies. Infected female flies produced either no or small numbers of progeny, none of which displayed SGH when they emerged as adults. Healthy flies became infected after they fed on solid food (a mixture of powdered milk, egg, and sugar) that had been contaminated by infected flies (42%) or after they were held in cages that had previously housed infected flies (38.6%). Healthy flies also became infected after they fed on samples of brewers grains (6.8%) or calf feed (2%) that were collected from areas of high fly visitation on the farms. Infection rates of field-collected flies increased from 6 to 40% when they fed exclusively on air-dried cloth strips soaked in a suspension of powdered egg and whole milk. Rates of virus deposition by infected flies on food were estimated by quantitative polymerase chain reaction at approximately 100 million virus copies per fly per hour. Electron microscopy revealed the presence on enveloped virus particles in the lumen of salivary glands and on the external mouthparts of infected flies.