Bodily stimulus gradients and precopulatory orientation in the midge, Culicoides melleus

ABSTRACT. The male Culicoides melleus (Coquillett) (Diptera: Ceratopogonidae) is able to orientate extremely rapidly to the copulatory position on a C. melleus female and, remarkably, assumes an equivalent position on a mosquito female (Aedes taeniorhynchus). To test for possible similarity between the midge and mosquito females, the ability of their different bodily parts to stimulate sexual response from C. melleus males was assayed. Males were known to respond sexually to a contact pheromone. Males showed increasing response posteriorly on both female C. melleus and A. taeniorhynchus , and greater response to ventral positions than dorsal. Experiments involving transpositions of bodily parts of C. melleus females prove that orientation, at least in the later stages of precopulatory behaviour, is to cues on the female abdomen. It is suggested that the orientation behaviour of the C. melleus male is achieved in response to contact pheromone gradients on the female body.     

Do tsetse flies ‘see’ zebras? A field study of the visual response of tsetse to striped targets

Abstract A field study in Zimbabwe of Glossina pallidipes Austen and G. morsitans morsitans Westwood supported Waage's (1981) hypothesis that the striped pattern of zebras may protect them from being bitten by blood-sucking flies. In addition, the results suggest that the orientation of the stripes may be crucially important for the unattractiveness of zebras. The relative attractiveness of five different stationary targets (black, white, grey, vertically-striped and horizontally-striped; stripe width = 5 cm) were each tested on their own and in pairs of all combinations, with artificial host odour (CO₂ plus acetone) always present. Electric nets were used to catch flies as they attempted to land on or circle the targets. The results were similar for the two species of tsetse. When tested on their own, grey and vertically-striped targets caught similar numbers of flies and both caught significantly fewer than black or white targets (c. 36% as many). Horizontally-striped targets caught <10% as many flies as any other single target. Although there was no significant difference between the attractiveness of grey and vertically striped targets when they were presented together, when paired with the other targets, grey was as attractive as black or white, but the vertically-striped target was significantly less attractive than black or white (P < 0.001). In other words, a difference between grey and vertical stripes was found only in their attractiveness in relation to other targets. The horizontally-striped target, however, always caught the fewest flies, regardless of whether it was presented alone or alongside another target.     

First detection of endosymbiotic bacteria in biting midges Culicoides pulicaris and Culicoides punctatus,important Palaearctic vectors of bluetongue virus

Heritable bacteria have been highlighted as important components of vector biology, acting as required symbionts with an anabolic role, altering competence for disease transmission, and affecting patterns of gene flow by altering cross compatibility. In this paper, we tested eight U.K. species of Culicoides (Diptera: Ceratopogonidae) midge for the presence of five genera of endosymbiotic bacteria: Cardinium (Bacteroidales: Bacteroidaceae); Wolbachia (Rickettsiales: Rickettsiaceae); Spiroplasma (Entomoplasmatales: Spiroplasmataceae); Arsenophonus (Enterobacteriales: Enterobacteriaceae), and Rickettsia (Rickettsiales: Rickettsiaceae). Cardinium spp. were detected in both sexes of Culicoides pulicaris and Culicoides punctatus, two known vectors of bluetongue virus. Cardinium spp. were not detected in any other species, including the Culicoides obsoletus group, the main vector of bluetongue and Schmallenberg viruses in northern Europe. The other endosymbionts were not detected in any Culicoides species. The Cardinium strain detected in U.K. Culicoides species is very closely related to the Candidatus Cardinium hertigii group C, previously identified in Culicoides species in Asia. Further, we infer that the symbiont is not a sex ratio distorter and shows geographic variation in prevalence within a species. Despite its detection in several species of Culicoides that vector arboviruses worldwide, the absence of Cardinium in the C. obsoletus group suggests that infections of these symbionts may not be necessary to the arboviral vector competence of biting midges.     

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.     

In vitro culture of ovaries of a viviparous gall midge

Summary Ovaries of the viviparous pedogenetic gall midgeHeteropeza pygmaea can be cultured in hemolymph obtained from X-ray-sterilized larvae of the same species. In this culture medium, formation of follicles is essentially the same as in vivo, and sometimes female larvae develop from these follicles. The ovaries of such larvae, in their turn, have been cultured in vitro to produce larvae. In this way, in vitro development from oogonium to larva has been maintained for several generations. When using hemolymph obtained from larvae grown under different conditions, the in vitro cultured ovaries produce a second type of egg which probably is male-determined. Ovarian development in vitro has been studied with differential interference contrast optics and time-lapse cinemicrography. This work was supported by the Swiss National Science Foundation Grant No. 3.2010.73.     

Ecology of the biting midge Leptoconops albiventris in French Polynesia. I. Biting cycle and influence of climatic factors

Abstract. The diurnal biting cycle of Leptoconops albiventris de Meijere (Diptera: Ceratopogonidae) is described from beaches of Nuku-Hiva, French Polynesia. Biting activity increased during the morning, diminished during the afternoon and was sufficiently intense to constitute a nuisance throughout the whole day. Correspondence Analysis indicated that climatic factors influenced biting activity. Activity was initiated by and positively associated with sunshine, whereas high temperatures, increased wind speed and rainfall were factors limiting activity. Decreased density of females during the dry season and their low capacity for dispersal were considered potentially advantageous with respect to control.