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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.

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.

Many insect species harbor facultative microbial symbionts that affect their biology in diverse ways. Here, we studied the effects, interactions, and localization of two bacterial symbionts—Wolbachia and Rickettsia—in the parasitoid Spalangia endius. We crossed between four S. endius colonies—Wolbachia only (W), Rickettsia only (R), both (WR), and none (aposymbiotic, APS) (16 possible crosses) and found that Wolbachia induces incomplete cytoplasmic incompatibility (CI), both when the males are W or WR. Rickettsia did not cause reproductive manipulations and did not rescue the Wolbachia-induced CI. However, when R females were crossed with W or WR males, significantly less offspring were produced compared with that of control crosses. In non-CI crosses, the presence of Wolbachia in males caused a significant reduction in offspring numbers. Females’ developmental time was significantly prolonged in the R colony, with adults starting to emerge one day later than the other colonies. Other fitness parameters did not differ significantly between the colonies. Using fluorescence in situ hybridization microscopy in females, we found that Wolbachia is localized alongside Rickettsia inside oocytes, follicle cells, and nurse cells in the ovaries. However, Rickettsia is distributed also in muscle cells all over the body, in ganglia, and even in the brain.

Spalangia endius Walker, a pupal parasitoid of the alien invasive pest Zeugodacus cucurbitae (Coquillett), causes 33% host mortality. This study assessed whether combining S. endius with insecticides (abamectin, thiamethoxam, nitenpyram, emamectin benzoate, or beta-cypermethrin)—all effective against Z. cucurbitae—could enhance control efficacy. Among these, abamectin was the least toxic to adult S. endius. Surface contact treatments with 12 and 15 mg a.i./kg of abamectin did not significantly increase S. endius mortality. However, mixing 12 mg a.i./kg of abamectin into a honey solution to encourage ingestion decreased the survival, parasitism, and fecundity of S. endius. In olfactometer assays, S. endius adults avoided abamectin-treated host pupae, though prior exposure to abamectin mitigated this avoidance. The timing of abamectin soil application relative to host pupation and S. endius release affects host mortality. The most effective timing is spraying abamectin before host pupation (to expose Z. cucurbitae larvae) and then releasing S. endius. Field trials confirmed that combining abamectin (12 mg a.i./kg) with S. endius increased host mortality more than either treatment alone. In conclusion, abamectin (12 mg a.i./kg) is a suitable insecticide for combination with S. endius to control Z. cucurbitae. The application sequence should be spraying abamectin before hosts pupate and, only after that, releasing the parasitoid.

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.

In nature, competing species often achieve coexistence through niche differentiation. We examined this phenomenon for Pachycrepoideus vindemmiae and Spalangia endius (Hymenoptera: Pteromalidae), two species of pupal parasitoids that are considered biological control agents of house fly, Musca domestica (Diptera: Muscidae). We examined the ability of each species, alone and in combination, to locate host pupae buried at different depths (0, 1, 2, 4, and 6 cm) in three types of substrate (sand, dry wheat bran, and spent fly diet). We then evaluated the competitiveness of each species by allowing first one species, then the other species, to parasitise host individuals within time periods ranging from less than 2 hours to 96 hours of each other. Spalangia endius exhibited greater ability than did P. vindemmiae to locate host pupae buried at depths below one centimetre. Conversely, P. vindemmiae exhibited a greater competitive ability, being more likely to emerge from pupae co-parasitised by S. endius, regardless of oviposition interval or sequence. Our findings suggest that these two parasitoid species coexist through niche differentiation. Our findings also indicate that to increase the effectiveness of biological control, the environmental conditions and risk of interspecific competition should be considered when selecting parasitoid species for release.

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.

Filth flies, including house flies, Musca domestica L., develop in animal manure. Adult house flies often are controlled with pesticides such as imidacloprid. How imidacloprid disseminates and persists after it contaminates manure was measured at a dairy farm. A week after application of imidacloprid via fly bait to cattle manure, a mean of approximately 4 ppm of imidacloprid, and as high as 15 ppm, was quantifiable up to 12 cm from the application site, but not farther. Laboratory experiments addressed the impact of 15 ppm of imidacloprid in manure on egg-to-adult development of house flies and on the biological control ability of a house fly pupal parasitoid, Spalangia endius Walker. In uncontaminated manure, 93% of eggs developed to adults, versus 7% in contaminated manure. In the parasitoid experiment, fly pupae were placed in contaminated or uncontaminated manure with or without S. endius. In the absence of S. endius, nearly 100% of flies emerged, with or without imidacloprid. In the presence of S. endius, only 11% of flies emerged from uncontaminated manure, versus 36% from contaminated manure; and parasitoids emerged from 82% of hosts in uncontaminated manure versus 53% in contaminated manure. These results suggest that realistic concentrations of imidacloprid in filth fly breeding habitat may interfere with house flies developing to the pupal stage, but also with parasitoids locating and utilizing house flies. However, after 1 wk, the effects on parasitoids will be low 12 cm beyond where bait was applied.

We studied the parasitism capacity of Spalangia endius as a pupal parasite of Bactocera dorsalis after switching hosts. We used pupae of B. dorsalis and M. domestica as the hosts and studied parasitism by S. endius in the laboratory. The parasitism capacities were compared at different host densities and different parasitoid ages. The two functional responses of S. endius fitted a Holling Type II equation. More M. domestica were parasitized than B. dorsalis at all the densities. The ability of S. endius to control M. domestica was α/Th (parasitism capacity) = 32.1950, which was much stronger than that of control B. dorsalis, which was α/Th = 4.7380. The parasitism rate of wasps that had parasitized B. dorsalis had decreased by the emergence time of parasitoids. These results suggest that the parasitoid-pest ratio should be 1:25 to maintain a relatively stable parasitism rate for control of B. dorsalis. The S. endius colony reared on M. domestica successfully controlled a low-density population of B. dorsalis in the lab. We provide evidence suggesting that the parasitism capacity of S. endius needs to be improved.

Both the parasitoid wasp Spalangia endius Walker and the insecticide imidacloprid are used to control house flies. A recent study found that negative sublethal effects of imidacloprid on killing flies and on offspring production by this parasitoid wasp are eliminated when females have the opportunity to crawl through decaying matter. An enzyme-linked immunosorbent assay showed that the presence of decaying matter reduces the amount of pesticide on their bodies. This study examined whether this was also true for sublethal effects on mating. S. endius were exposed to a realistic concentration of imidacloprid that induces very low mortality. Then, individual parasitoids were allowed to burrow through decaying organic matter or not, followed by mating tests in the absence of decaying matter. Even after 24 h with the decaying matter, copulation for both males and females that had previously been exposed to imidacloprid was delayed compared with no-pesticide controls. Furthermore, for pesticide-exposed males, subsequently burrowing through media made copulation even more delayed than if they were not exposed to media. For pesticide-exposed females, subsequently burrowing through media neither increased or decreased the negative effect of the pesticide exposure. Together with other studies, these results reinforce that use of S. endius and use of imidacloprid are incompatible, even at much lower than recommended concentration, unless application is sufficiently separated in place and time.