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 10⁶ MdSGHV copies per feeding event. Excreta samples collected overnight from individual infected flies at 5 dpi contained an average 6.5 × 10⁵ 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.     

Does behaviour play a role in house fly resistance to imidacloprid‐containing baits?

The objective of this research was to examine the role and type of behavioural mechanisms that function in house fly, Musca domestica L. (Diptera: Muscidae), resistance to an imidacloprid‐containing commercial fly bait, QuickBayt^®, using an insecticide‐susceptible and an imidacloprid‐resistant strain. Mortality and feeding behaviour were observed through choice bioassays of three post‐imidacloprid selected house fly generations to determine whether flies would consume the bait in the presence of an alternative food source. Mortality rates in choice containers progressively decreased in post‐selection flies as QuickBayt^® no‐choice selections proceeded. There were no differences between the proportions of flies observed contacting QuickBayt^® and sugar, respectively, a finding that eliminates repellency as a mechanism of stimulus‐dependent behavioural resistance. However, differences in QuickBayt^® consumption and subsequent mortality between choice and no‐choice containers provided strong support for the evolution of consumption irritancy‐ or taste aversion‐related behavioural resistance. The results of this study support the responsible rotation of insecticide bait formulations for house fly control.     

Orcadian Rhythm of Trehalose in the Face Fly Musca Autumnalis De Geer

Trehalose levels were determined over two 24 hr spans in groups of face fly adults 3-4 days after emergence from the puparium. Face fly pupae were placed in rearing chambers at 27° C in a staggered light-dark regimen, LD 16:8, so that at a given clock hour, samples could be obtained at several different hours after lights on (HALO). Trehalose was determined in hemolymph collected from a puncture in the intersegmental membrane of the abdomen. Treated hemolymph samples were passed through a Bio-Rad Amino S-S disaccharide column and a Waters 410 refractive index detector was used to differentiate among sugars. The circadian acrophase derived by cosinor analysis in hemolymph trehalose (when the values were 25.49 and 26.86μg/μ¹ on the first and second days respectively) occurred at -226° (ca 15 HALO) and the bathyphase at 24 HALO. The mesor = 11.82μg/μ¹ trehalose, the amplitude = 8.57/μg/μ¹ trehalose and the P-value for presence of a rhythm was 0.003. Based on these data, differences between control and test flies in a bioassay of hypertrehalosemic activity would be most easily observed at 0-8 HALO, while exogenous hypotrehalosemic activity would be best assayed at 12-20 HALO.     

Stable fly, Stomoxys calcitrans, mouthpart removal influences stress and anticipatory responses in mice

Abstract Biting fly attack induces a variety of stress and anxiety related changes in the physiology and behaviour of the target animals. Significant reductions in pain, or more appropriately, nociceptive sensitivity (latency of a foot-lifting response to an aversive thermal stimulus), are evident in laboratory mice after a 1 h exposure to stable flies, Stomoxys calcitrans. The role of the various components of biting fly attack in the development of this stress-induced reduction in pain sensitivity (analgesia) is, however, unclear. This study demonstrates that fly-naive mice do not exhibit a stress-induced analgesia when exposed to stable flies whose biting mouthparts have been removed. In contrast, mice that have been previously exposed to intact stable flies exhibit significant analgesia when exposed to flies that are incapable of biting. However, the level of analgesia induced is lower than that elicited by exposure to intact stable flies. Exposure to non-biting house flies, Musca domestica , has no effect on nociceptive sensitivity. It appears that the actual bite of the stable fly is necessary for the induction of analgesia and probably other stress and anxiety associated responses in fly naive mice. However, mice rapidly learn to recognize biting flies and exhibit significant, possibly anticipatory analgesic responses to the mere presence of biting flies.     

Parasitism of house fly (Musca domestica) pupae by four species of Pteromalidae (Hymenoptera): effects of host–parasitoid densities and host distribution

Parasitoid-induced mortality of house fly, Musca domestica L., pupae and parasitoid progeny emergence by four species of pteromalid parasitoids, Muscidifurax raptor Girault & Sanders, M.zaraptor Kogan & Legner, Spalangia cameroni Perkins and S.endius Walker, were determined for a 24 h exposure period using parasitoid: host ratios ranging from 1:2 to 1:50. When the number of parasitoids was held constant (n = 5) and the numbers of hosts varied, and when the number of hosts was held constant (n = 100) and the number of parasitoids varied, both the number of pupae killed per parasitoid and the number of parasitoid progeny per parasitoid increased with increasing parasitoid:host ratios to reach an upper limit asymptotically. Maximum values were, respectively: M.raptor (14.7, 11.1), M.zaraptor (12.3, 9.3), S.cameroni (16.9, 5.5), S.endius (14.8, 9.7) with no consistent effects attributed to parasitoid interference. For M.raptor and S.cameroni at parasitoid:host ratios of 1:10, the pupal mortality and progeny emergence were determined for a 24 h exposure period when hosts were distributed in poultry manure at four levels of aggregation ranging from clumped to uniform. Pupal mortality was least in clumped distributions, while parasitoid progeny emergence was not significantly different.     

Temperature-dependent development and parasitism rates of four species of Pteromalidae (Hymenoptera) parasitoids of house fly (Musca domestica) pupae

Parasitoid development, parasitoid-induced host mortality and parasitoid progeny emergence were determined at five constant temperatures for Muscidifurax raptor Girault and Sanders, Muscidifurax zaraptor Kogan and Legner, Spalangia cameroni Perkins and Spalangia endius Walker using pupae of the house fly, Musca domestica L., as hosts. At temperatures of 20, 25, 30 and 35 degrees C the median development times (days from oviposition to adult emergence), respectively, were M. raptor (28.4, 20.7, 14.3, 14.5), M. zaraptor (30.6, 22.8, 14.1, 14.2), S. cameroni (55.6, 35.2, 21.8, 25.0) and S. endius (52.4, 31.5, 16.3, 14.6). All species failed to emerge at 15 degrees C. Using densities of five parasitoids and 100 hosts and a 24 h exposure period, Muscidifurax species oviposited at a greater rate over a wider range of temperatures than Spalangia species. At 15, 20, 25, 30 and 35 degrees C the mean number of pupae killed per parasitoid were, respectively, M. raptor (1.4, 7.4, 10.5, 13.7, 14.1), M. zaraptor (0.0, 3.3, 8.9, 14.4, 15.0), S.cameroni (0.0, 7.8, 11.0, 11.9, 7.4), S.endius (0.6, 4.0, 7.5, 12.0, 11.7), and means of the number of parasitoid progeny per parasitoid were, respectively, M.raptor (0.2, 5.2, 7.9, 11.8, 11.6), M.zaraptor (1.3, 4.4, 8.2, 13.0, 13.7), S.cameroni (0.0, 2.4, 4.7, 5.1, 1.0), S.endius (0.0, 0.9, 3.4, 7.5, 4.9). Development and ovipositional activity in S.cameroni was strongly inhibited at 35 degrees C. The model by Sharpe & DeMichele (1977) was used to describe temperature-dependent development and the number of parasitoid progeny produced per parasitoid at temperatures of 15-30 degrees C in all species.     

In vivo and in vitro effects of 20-hydroxyecdysone and methoprene on diapause maintenance and reproductive development in Musca autumnalis

Abstract. Face flies overwinter as adults in reproductive diapause. Administration of 20-hyroxyecdysone and/or methoprene induced reproductive development in diapausing flies which were maintained in a diapause-inducing environment. Hormone effects were additive and female flies were more sensitive than males. Release of vitellogenin from cultured fat body was stimulated by 20-hydroxyecdysone or methoprene. Transfer of flies from diapause to diapause-breaking environments induced some to break diapause, but this decreased with the time flies had been in a diapause-inducing environment. In contrast, topical application of methoprene to diapausing flies induced reproductive development irrespective of their ages even when they were kept in the diapause-inducing environment for 80 day degrees above a 12°C base temperature (14.5 days). Therefore diapause induction must depend on hormone levels less than some threshold level. The putative threshold varied according to diapause propensities of different genetic lines. Lines showing high frequencies of diapause required greater amounts of methoprene for reproductive development in diapause conditions than did lines showing low frequencies of diapause.