The swarming behaviour of the Scottish biting midge, Culicoides impunctatus (Diptera: Ceratopogonidae)

Abstract.

• 1 Swarms of Culicoides impunctatus males were examined in the field in Scotland. Most swarms were close to midge emergence/breeding grounds over a variety of vegetation, some of which clearly acted as swarm markers. Low light (0–1000 lux) and still/humid conditions favoured swarming.
• 2 Swarm size ranged between less than 10 and more than one thousand midges. The modal size was 200 individuals. The smallest swarms were usually columnar in shape and the larger swarms ovoid.
• 3 Midges behaved individually within swarms, moving in an elliptical manner characteristic of other dipterans in swarms.
• 4 Swarms were classified as either ‘persistent’ or ‘transient’ in terms of their shape, size and stability. Wind was the most influential factor in disrupting swarms.
• 5 Swarms were confirmed as mating sites for C.impunctatus.

     

Detrimental effects of Haemoproteus infections on the survival of biting midge Culicoides impunctatus (Diptera: Ceratopogonidae)

The effects of Haemoproteus belopolskyi, Haemoproteus fringillae, and Haemoproteus lanii on the survival of their vector the biting midge Culicoides impunctatus were examined. Wild-caught females were infected experimentally by allowing them to feed on naturally infected birds. A group of flies, which fed on an uninfected bird, was used as a control. There was a highly significant difference in the survival rate between the noninfected group and all groups of infected flies for postfeeding (PF) periods 1-2, 3-4, 5-6, and 7-8 days. For days 7-8, the percentage of noninfected surviving flies was 4.4 times higher than the percentage of infected surviving flies, testifying to the detrimental effects of avian Haemoproteus infections on the longevity of C. impunctatus. The mortality rates of the infected flies were highest for days 1-2 and 3-4 PF, indicating possible negative effects of ookinetes and early oocysts on the vector.     

Electrophysiological and behavioural studies of the biting midge, Culicoides impunctatus Goetghebuer (Diptera, Ceratopogonidae): interactions between some plant-derived repellent compounds and a host-odour attractant, 1-octen-3-ol

Abstract. Electroantennogram (EAG) and y-tube bioassays have been used to demonstrate the repellent properties of five plant compounds with host-seeking parous female Culicoides impunctatus Goetghebuer. The compounds were methyl salicylate and allyl-, butyl-, phenyl- and 2-phenylethyl isothiocyanate. EAG thresholds were 1 times 10^-3 to 1 μg. In the bioassays, maximal repellencies occurred with 1 times 10˜² to lOug. When each compound was combined with 1-octen-3-ol, a confirmed host-odour attractant for C.impunctatus females, additive effects were recorded in EAG assays and in bioassays, all of the compounds either reduced or reversed the attractancy of l-octen-3-ol. Of the isothiocyanates, allyl isothiocyanate was the most potent and when combined with 1-octen-3-ol in field trials, the attractant effect of l-octen-3-ol was reduced.     

Oogenesis and laboratory survival in the Scottish biting midge Culicoides impunctatus

Abstract.  Oogenesis is investigated in Culicoides impunctatus to provide information useful for the laboratory culture of this species. The first mature follicles in individuals held at 15, 20, 25 and 30 °C appear at 132, 120, 108 and 96 h, respectively, after a blood meal, whereas mature follicles are present in 50% of individuals by 156, 132, 120 and 108 h. Potential fecundity is low and the production of mature follicles is not synchronized closely with digestion of the blood meal. Adult survival is both temperature- and density-dependent. These results are interpreted in terms of the species' adaptation to a Northern climate and recommendations are made for future laboratory colonization attempts as well as future studies.     

Heterogeneity of ITS1 sequences in the biting midge Culicoides impunctatus (Goetghebuer) suggests a population in Argyll, Scotland, may be genetically distinct.

Ribosomal DNA (rDNA) internal transcribed spacer 1 (ITS1) is a useful genomic region for understanding evolutionary and genetic relationships. In the current study, variation in ITS1 from eight Culicoides species was analysed by PCR, DNA restriction analysis, cloning, and sequencing. ITS1 variants were essentially homogenized within a species, as sequences were identical or closely related. However, Culicoides impunctatus ITS1 sequences derived from one (Argyll) of five populations contained considerable genomic diversity. The secondary structure of each ITS1 was computed. The structure aided the production of an accurate alignment and the identification of a large indel. A phylogenetic analysis was performed. Some of the sequences from the diverse Argyll C. impunctatus population were more related to Culicoides imicola, a vector of animal pathogens in the Old World, than they were to the other C. impunctatus sequences. Thus, the rDNA ITS1 regions of individuals in the Argyll C. impunctatus population were not conforming to the general theory of rDNA homogenization through molecular drive.     

Abundance and host-seeking activity of the biting midge,Forcipomyia taiwana (Diptera: Ceratopogonidae)

The abundance and host-seeking activity of the biting midge, Forcipomyia taiwana (Shiraki), were measured in Central Taiwan at 418 locations with low, medium, and high densities using a human-bait method. Abundance estimates at 10 min after sampling commenced were comparable to longer sampling periods of 20 min, allowing a shorter 10 min sampling period to be used throughout. Host-seeking F. taiwana females were only active during daylight and biting activity did not occur after sunset. The diurnal activity of host-seeking females changed seasonally, beginning at around 07:00–08:00 during the spring equinox, summer solstice, and autumnal equinox, whereas activity began an hour later in winter. Most females were collected during 10:00–16:00, with a peak abundance during 13:00–15:00. Blood-sucking activity of female F. taiwana were positively correlated with ambient temperature with a minimum threshold of 18 °C. When different years, seasons, trapping times, environmental factors, and female adults trapped were analyzed using multiple regression model, the results showed that all these factors contributed to the regression model and the determination coefficient (R²) of this multiple regression model was 0.81.     

Toward development of neem-based repellents against the Scottish Highland biting midge Culicoides impunctatus

Oil of neem, from the tree Azadirachta indica A. Juss (Meliaceae), was evaluated for repellent and antifeedant activity against Culicoides biting midges (Diptera: Ceratopogonidae), by three complementary methods with serial dilutions. Electroantennograms revealed the sensitivity of Culicoides nubeculosus (Meigen) females to neem > or = 0.10%. Culicoides impunctatus Goetghebuer females were repelled by > or = 1% in a Y-tube olfactometer, Using a membrane feeder for wild-caught parous females of C. impunctatus, the proportion blood-feeding was significantly reduced by topical applications of neem oil > or = 0.10% concentrations, with blood-feeding completely prevented by > or =1%. On the basis of these response data, we developed 2% neem-based formulations for personal protection against biting midges.     

Identification of bloodmeals of the Scottish biting midge, Culicoides impunctatus, by indirect enzyme-linked immunosorbent assay (ELISA)

Abstract. An indirect enzyme-linked immunosorbent assay (ELISA) has been developed to identify the bloodmeal sources of Culicoides impunctatus Goetghebuer. Nightly light trapping in Scotland, between April and September 1992, caught a total of 344 blood-engorged female C. impunctatus , all in May, June and July. The insects were stored in 70% ethanol and tested 5–7 months later. Bloodmeal sources were positively identified for 246 (71.5%). Bovine hosts were most common (38.4%), followed by deer (23.0%) and sheep (9.9%). Only one midge had fed on human blood. Relatively freshly fed (<24h), fully engorged females gave the clearest results. The wider applications of the technique to the study of Culicoides host preferences is discussed.     

Diel flight periodicity of the biting midge Culicoides impunctatus and the effects of meteorological conditions

Abstract The hourly flight periodicity of adults of the biting midge Culicoides impunctatus was sampled at a site in Western Scotland, using suction traps over 18 days in July/August 1994. In addition, meteorological conditions were logged continuously. Female but not male C. impunctatus had a bimodal pattern of activity, with peaks at dawn and dusk. The dawn peak (05.00–07.00 hours) was most distinct. Correlation analysis revealed significantly positive relationships between catches of female midges and both relative humidity and rainfall, and negative relationships with wind velocity. The calculation of partial correlation coefficients reinforced the influence of relative humidity on female activity, and highlighted a further positive relationship with air temperature. Male C.impunctatus activity was negatively correlated with air temperature, although the total male catch was relatively small (15% of total trap catches) and further data would be required to confirm this result. Overall, the results help to clarify previous confusion as to whether C.impunctatus has a circadian rhythm of activity, with the data matching closely predictions of a bimodal pattern. Clearly, this pattern will be damped by meteorological conditions, which may vary greatly on a local scale.     

Fine structure and sporogonic development of a Vavraia sp. (Microsporida: Pleistophoridae) in the biting midge Culicoides edeni (Diptera: Ceratopogonidae)

A microsporidium with ultrastructural characteristics of the genus Vavraia was found in the fat body of an adult specimen of Culicoides edeni (Diptera: Ceratopogonidae) collected in northern Florida. The sporogonial stages developed within sporophorous vesicles, which contained variable numbers of oval spores at maturity. The wall of the sporophorous vesicle was composed of two electron-dense outer layers and an electron-lucent intermediate layer. Sporonts contained haplokaryotic nuclei and divided by rosette formation. Mature spores had anisofilar polar filaments and measured 3.8 +/- 0.28 microns in length and 2.2 +/- 0.16 microns in width in thick sections of resin-embedded material. This is the first report of a Vavraia sp. from a species of Culicodes.     

The transmission of Haemoproteus belopolskyi (Haemosporida: Haemoproteidae) of blackcap by Culicoides impunctatus (Diptera: Ceratopogonidae)

Haemoproteus belopolskyi of blackcap, Sylvia atricapilla, underwent sporogony in wild-caught female biting midges, Culicoides impunctatus, which were experimentally infected by feeding them on naturally infected birds. The engorged flies were held for 8-12 days to allow development of sporozoites and then aspirated and triturated in 0.85% saline. Seven uninfected nestlings of blackcap at the age of 20-21 days were inoculated into the pectoral muscle with 0.3 ml of the slurry containing approximately 45 sporozoites. Parasitemia of H. belopolskyi developed in 6 nestlings, with a prepatent period of 11-12 days. The maximum parasitemia varied between 0.9 and 16% of erythrocytes in different experimental hosts. Culicoides impunctatus is an experimental vector of H. belopolskyi. It is likely to be the important natural vector of Haemoproteus spp. of passerine birds in Europe.     

Efficacy of the Entomopathogenic Fungus, Culicinomyces clavisporus against Larvae of the Biting Midge, Culicoides nubeculosus (Diptera: Ceratopogonidae)

Culicinomyces clavisporus, a fungal pathogen of a wide range of mosquito species, was investigated in relation to potential pathogenicity against Culicoides nubeculosus biting midge larvae. Seven different C. clavisporus strains were assayed. Each showed some degree of activity against C. nubeculosus larvae with LC₅₀ values of between 3.2×10^-5 and 1.1×10^-6 spores/mL; these effects occurred in dose-dependent manners and tended to be delayed until 72-96 h post treatment. The results are discussed in relation to incorporation of C. clavisporus into biocontrol programmes for Culicoides spp.     

Herpetomonas ztiplika n. sp. (Kinetoplastida: Trypanosomatidae): a parasite of the blood-sucking biting midge Culicoides kibunensis Tokunaga, 1937 (Diptera: Ceratopogonidae)

Herein, we describe the first case of a natural infection of biting midges by a kinetoplastid protozoan. Flagellates from a female Culicoides kibunensis captured in a bird's nest were introduced into culture and characterized by light and electron microscopy. However, because the morphological data were inconclusive, the novel endosymbiont-free trypanosomatid was assigned into Herpetomonas primarily on the basis of the 18S and 5S ribosomal RNA (rRNA) gene sequences.     

Two new species of larval mites (Acari: Trombidioidea: Microtrombidiidae and Johnstonianidae) parasitising Culicoides impunctatus,the highland midge (Insecta: Ceratopogonidae), in Scotland

The larval stage of the trombidioid mites Parafeiderium stuarti n. sp. (family Microtrombidiidae Thor, 1935) and Centrotrombidium blackwellae n. sp. (family Johnstonianidae Newell, 1957) are described. Both species were found parasitising Culicoides impunctatus Goetghebuer, the highland midge (Diptera: Ceratopogonidae), in Scotland. A revised diagnosis for Parafeiderium Vercammen-Grandjean & Cochrane, 1974 and a key to the world species of larval Centrotrombidium Kramer, 1896 are given.