Evidence for activation of endogenous opioid systems in mice following short exposure to stable flies

Biting flies influence both physiology and behaviour of domestic and wild animals. This study demonstrates that brief (30 min) exposure of male and female mice to stable flies leads to significant increases in nociceptive responses, indicative of the induction of analgesia. The biting fly-induced analgesia was mediated by endogenous opioid systems as it was blocked by the prototypic opiate antagonist naloxone. Exposure for 30 min to the bedding of biting fly-exposed mice also induced significant opioid mediated analgesic responses in mice. Exposure to either house flies or the bedding of house fly-exposed mice had no significant effects on nociception. These results indicate that brief exposure to either stable flies, or to olfactory cues associated with mice exposed to stable flies, activates endogenous opioid systems leading to the induction of analgesia and likely other opioid mediated behavioural and physiological stress responses. These results suggest the involvement of endogenous opioid systems in the mediation of the behavioural and physiological consequences of biting fly exposure in domestic and wild animals.     

Epidemiology of bluetongue in Central America and the Caribbean: initial entomological findings

Abstract. Forty-four species of Culicoides (Diptera: Ceratopogonidae) were caught in insect light traps during the first 2 years of studies on the epidemiology of bluetongue virus in the Caribbean and Central America. Traps were operated near sentinel ruminants which were bled monthly for serologic evaluation and then virus isolation. More than 570,000 individuals were identified. Culicoides insignis Lutz accounted for 90% of the catch, C.filarifer Hoffman/C.ocumarensis Ortiz 5%, C.furens Poey 3% and C.pusillus Lutz 2%. Other species accounted for less than 1% of the total catch. Sentinel ruminants became seropositive when C.insignis populations were high at many study sites. At a few sites C.pusillus and C.filarifer I C.ocumarensis were predominant or were present in large numbers during seroconversions of sentinels. Virus isolations were obtained from sentinel ruminants during times when these same species were present in large populations.     

Isolation of haemolytic bacilli from field‐collected Culicoides oxystoma and Culicoides peregrinus: potential vectors of bluetongue virus in West Bengal,India

Two haemolytic bacterial strains of Bacillus pumilus (CU1A, CU1B) and one blood‐utilizing strain of Bacillus licheniformis (CU2B) were isolated from relatively low numbers of field‐collected females of Culicoides oxystoma and Culicoides peregrinus (Diptera: Ceratopogonidae). A total of 36 females, including 18 of each of C. oxystoma and C. peregrinus (consisting of one and a pool of eight blood‐engorged specimens, and one and a pool of eight non‐engorged specimens for each species), were tested. In C. oxystoma, all three strains of bacteria were isolated from the one non‐engorged, the pool of non‐engorged and the pool of blood‐engorged females tested, but CU1A and CU2B were not found in the one blood‐engorged female tested. In C. peregrinus, all three strains were present in the pool of blood‐engorged females. However, the strain CU2B was not found in the pool of non‐engorged females. In the one blood‐engorged and one non‐engorged female tested, CU1A and CU2B were detected. The bacterial strains were identified based on Gram staining, enzyme activity (amylase and protease) and alignment of the 16S rRNA partial gene sequence to that available in the National Center for Biotechnology Information (NCBI) database GenBank. The functional role and significance of these haemolytic and blood‐digesting bacteria within the genus Culicoides remain to be determined.     

Seasonal variation in abundance and diversity of eavesdropping frog‐biting midges (Diptera,Corethrellidae) in a neotropical rainforest

1. In the tropics, precipitation patterns result in seasonal fluctuations in the abundance and distribution of plant and animal species. Tropical predators and parasites are therefore faced with seasonal changes in prey and host availability. 2. This study investigates the seasonal interaction among a specialised ectoparasite, eavesdropping frog‐biting midges (Corethrella spp.), and their anuran hosts, examining how the abundance and diversity of the frog‐biting midge community fluctuate between the rainy (host abundant) and dry (host sparse) seasons. 3. Midges were captured in both the rainy and dry seasons using acoustic playbacks of calls from a common frog species that breeds during the rainy season, the túngara frog (Engystomops, Physalaemus, pustulosus). During the dry season túngara frog choruses are absent. To explore seasonal shifts in host preference or changes in the midge community due to host specificity, midges were also captured using playbacks of calls from a frog that breeds during the dry season, the pug‐nosed tree frog (Smilisca sila). 4. While the overall abundance of midges decreased in the dry season, only slight differences in the relative abundance between midge species were found. These results suggest that midge populations can shift between hosts as they become available across seasons, allowing adult populations of frog‐biting midges to persist year‐round. To overcome the challenge of detecting and localising different host species, it is proposed that frog‐biting midges have evolved a generalised acoustic template, allowing them to respond to a broad range of available hosts, regardless of seasonal host composition.     

Bacillus thuringiensis serovar. israelensis (ABG-6108) against chironomids and some nontarget aquatic invertebrates

A wettable powder formulation (ABG-6108) of Bacillus thuringiensis serovar. israelensis was tested against chironomid larvae in experimental ponds at 1, 2, 3, 4 and 10 kg/ha (0.25–2.5 ppm), and in a golf pond at 3 kg/ha (0.5 ppm). Significant reductions (18–88%) in populations of Chrinomini and Tanytarsini experimental ponds, and 27–65% reduction of midges in the golf pond occurred during the 4-week evaluation period. The highest dose in experimental ponds had no adverse effects on rotifers, Cyclops spp., Daphnia sp., ostracods, Baetis sp., corixids and notonectids, and Coleoptera. The nontarget invertebrates in the golf pond also remained unaffected.     

Light and suction trap catches of Culicoides midges in southern England

1. The seasonal flight periods are given for eleven species or species groups of Culicoides midges at Pirbright, Surrey, U.K., from 1979 to 1981 and in 1983. 2. Most species were relatively uniformly distributed both within the study site and between years; only C.clintoni Boorman was limited in its spatial distribution and only C.segnis Campbell and Pelham-Clinton varied greatly in numbers between years. 3. Species fall into one of three patterns of seasonal abundance: spring emergers, summer emergers, or spring to autumn emergers. 4. Only the C.obsoletus group showed a pattern of emergence that could correspond to distinct generations, of one or more species in the group. Three distinct emergences were observed, and possible explanations for these discussed. 5. For all species except C.impunctatus Goetghebuer the catches from suction/light and suction only traps are poorly correlated whereas for C.impunctatus they are highly correlated. This may suggest that this species is not greatly attracted to light.     

Modified veranda‐trap hut for improved evaluation of vector control interventions

Experimental huts with veranda traps have been used in Tanzania since 1963 for the study of residual insecticides for use with insecticide‐treated nets and indoor residual spraying. Mosquitoes are allowed unrestricted entry through the eaves to facilitate the collection of an estimable proportion of mosquitoes that attempt to exit through the eave gaps, which are left open on two sides of the hut. This study was designed to validate the use of eave baffles to funnel entry and to prevent mosquito escape, and to determine biting times of Anopheles arabiensis (Patton) (Diptera: Culicidae). Anopheles arabiensis and Culex quinquefasciatus (Say) (Diptera: Culicidae) were released into the room at 20.30 hours and collected the following morning from veranda traps, window traps and the room. Centers for Disease Control light traps hung overnight next to volunteers were emptied every 2 h to determine peak biting times. A total of 55% of An. arabiensis were trapped before 22.30 hours and the highest peak in ‘biting’ was recorded during 18.30–20.30 hours. Of the released An. arabiensis that exited into veranda traps, 7% were captured in veranda traps entered through baffles and 93% were captured in traps entered through unmodified eaves. When veranda screens were left open to allow for escape outdoors, recapture rates were 68% for huts with eave baffles and 39% for huts with unmodified eaves. The comparison of open eaves with baffled eaves validated the assumption that in huts of the traditional non‐baffled design, 50% of mosquitoes escape through open eaves. Eave baffles succeeded in reducing the potential for mosquito exit and produced more precise estimates of effect.     

Biting and resting behaviour of anophelines in western Venezuela and implications for control of malaria transmission

A study was conducted in three villages in western Venezuela between February 1988 and October 1989 to determine the biting and resting activity of anophelines in relation to human habits, rainfall and fenitrothion spraying of houses. Mosquitoes were collected landing on humans inside and outside experimental huts throughout the night. Only three mosquitoes were found resting in the huts in the morning, but 2470 were collected resting on vegetation in the early morning. The collections yielded eleven species of anopheline, the most abundant being Anopheles nuneztovari, comprising over 75% of the total anophelines collected, followed by An.triannulatus, An.albitarsis s.l. and An.oswaldoi. The four most abundant species showed different diel patterns of biting. For An.nuneztovari the peak of activity was close to midnight indoors and outdoors, for An.triannulatus between 19.00 and 20.00 hours outdoors, for An.albitarsis mainly before midnight indoors and outdoors and for An.oswaldoi outdoors at 19.00 hours, with an additional smaller peak indoors at midnight. Most of the human population use bednets, go to bed before 22.00 hours and are therefore most exposed to mosquitoes that bite outdoors early in the night. Fenitrothion house-spraying failed to prevent large mosquito populations developing in the wet season, presumably because of their exophilic resting habits. The possible advantages of impregnation of existing bednets with pyrethroids, and provision of nets for people who do not have them, are discussed.