Assessment of the repellent effect of citronella and lemon eucalyptus oil against South African Culicoides species

The use of insect repellents to reduce the attack rate of Culicoides species (Diptera: Ceratopogonidae) should form part of an integrated control programme to combat African horse sickness and other diseases transmitted by these blood-feeding midges. In the present study the repellent effects of a commercially available mosquito repellent, a combination of citronella and lemon eucalyptus oils, on Culicoides midges was determined. The number of midges collected with two 220 V Onderstepoort traps fitted with 8 W 23 cm white light tubes and baited with peel-stick patches, each containing 40 mg of active ingredient, was compared with that of two unbaited traps. Two trials were conducted and in each trial the four traps were rotated in two replicates of a 4 x 4 randomised Latin square design. Although more midges were collected in the baited traps, the mean number in the baited and unbaited traps was not significantly different. This mosquito repellent did not influence either the species composition or the physiological groups of Culicoides imicola Kieffer. The higher mean numbers in the baited traps, although not statistically significant, may indicate that this mosquito repellent might even attract Culicoides midges under certain conditions.http://www.jsava.co.zaam201

The suitability of the Triple trap for the collection of South African livestock-associated Culicoides species

The relatively large number of Culicoides midges (Diptera: Ceratopogonidae) that can be collected with a light trap makes it the most widely used tool for this purpose. However, the majority of these traps were originally designed for collecting mosquitoes. The evaluation and improvement of traps to increase their effectiveness in collecting Culicoides midges will unavoidably form part of research on these insects. In the present study the efficiency of the Triple trap for collecting livestock-associated Culicoides midges was compared with that of the Onderstepoort 220 V, the BG-sentinel and the mini-CDC traps. A unique feature of the Triple trap is that selected surfaces are coated with TiO2 (titanium dioxide) which, in the presence of ultra violet light, acts as a photo-catalyser to produce CO2, which in turn may attract blood-feeding insects. Overall, the Onderstepoort trap collected significantly higher numbers of midges than the others. Relative efficiency varied between different occasions and under some conditions, for example periods with low midge abundance during the winter, the mean numbers collected with the Triple trap did not differ significantly from those of the Onderstepoort or BG-sentinel traps. By replacing the collection chamber of the Triple trap with a sock and beaker, similar to that of the Onderstepoort trap, it can effectively be used for the collection of Culicoides midges.The South African Equine Veterinary Association of the South African Veterinary Associationhttp://www.jsava.co.zaam2014ab201

Influence of carbon dioxide on numbers of Culicoides midges collected with suction light traps in South Africa

To implement risk management against diseases transmitted by Culicoides species Latreille, 1809 (Diptera: Ceratopogonidae) it will be essential to identify all potential vectors. Light traps are the most commonly used tool for the collection of Culicoides midges. Taking into account the indiscriminative artificial attraction of light, these traps will collect all night flying insects and not only livestock associated Culicoides midges. Factors that could increase the efficacy of these traps for especially livestock associated Culicoides midges need to be investigated. In the present study, results obtained with CDC- and Onderstepoort light traps baited with CO2 were compared to those of unbaited traps. Comparisons were done in two replicates of a 4 x 4 randomized Latin square design. With both traps, the mean numbers of Culicoides midges collected in 16 baited collections were higher than those in 16 un-baited collections. Despite exceptionally low numbers collected with the CDC traps, the increase in the numbers and frequency of collection of Culicoides imicola Kieffer, 1913 was more pronounced in the CDC compared to that in the Onderstepoort trap. These results indicate that the addition of CO2 could increase the efficiency of these traps for the collection of C. imicola, and other livestock associated Culicoides species.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-29152017-03-30hb201

Attraction range of the Onderstepoort 220 V light trap for Culicoides biting midges as determined under South African field conditions

Despite some limitations suction lighttraps are the primary tools used for the collection of Culicoides species (Diptera: Ceratopogonidae). The range of attraction of the Onderstepoortlighttrap is not known but an insight into the range of a trap will determine where the trap must be positioned relative to the hosts present, possible breeding sites and environmental structures in the trapping vicinity. It will therefore contribute to a more meaningful interpretation and comparison of results between trapping events. In the present study the number of Culicoidesmidges collected in a single trap was compared to those of traps made with an additional trap respectively 1 m, 4 m and 8.5 m away from the first. Treatments between sites were rotated in three replicates of a 4 × 4 Latin square design. While interactions were found in traps 4 m apart no statistically significant interactions were found when they were 8.5 m apart. The range of attraction, indicated by the interaction between two traps, will be between 2 m and 4 m. In interpreting lighttrap results the limitations of this collection method needs to be taken into consideration.http://www.elsevier.com/locate/vetparab201

Culicoides species abundance and potential overwintering of African horse sickness virus in the Onderstepoort area, Gauteng, South Africa

In South Africa, outbreaks of African horse sickness (AHS) occur in summer; no cases are reported in winter, from July to September. The AHS virus (AHSV) is transmitted almost exclusively by Culicoides midges (Diptera: Ceratopogonidae), of which Culicoides imicola is considered to be the most important vector. The over-wintering mechanism of AHSV is unknown. In this study, more than 500 000 Culicoides midges belonging to at least 26 species were collected in 88 light traps at weekly intervals between July 2010 and September 2011 near horses in the Onderstepoort area of South Africa. The dominant species was C. imicola. Despite relatively low temperatures and frost, at least 17 species, including C. imicola, were collected throughout winter (June–August). Although the mean number of midges per night fell from > 50 000 (March) to < 100 (July and August), no midge-free periods were found. This study,using virus isolation on cell cultures and a reverse transcriptase polymerase chain reaction (RT-PCR) assay, confirmed low infection prevalence in field midges and that the detection of virus correlated to high numbers. Although no virus was detected during this winter period,continuous adult activity indicated that transmission can potentially occur. The absence of AHSV in the midges during winter can be ascribed to the relatively low numbers collected coupled to low infection prevalence, low virus replication rates and low virus titres in the potentially infected midges. Cases of AHS in susceptible animals are likely to start as soon as Culicoides populations reach a critical level

Repellent effect of organic fatty acids on Culicoides midges as determined with suction light traps in South Africa

The efficacy of a 15% (w/w) mixture of octanoic, nonanoic and decanoic acids in light mineral oil to repel Culicoides biting midges (Diptera; Ceratopogonidae) was determined in three replicates of a 4 × 4 Latin square design under South African field conditions. The fatty acids were applied to ±0.07 m2 polyester meshes with a mesh size 2–3 mm fitted to 220 V 8 W Onderstepoort downdraught light traps. To reduce the relatively strong attraction of the light trap, the black light tubes in the Onderstepoort trap were replaced with 8 W 23 cm white light tubes. The traps were operating overnight next to cattle. Two traps treated with the mixture of fatty acids collected 1.7 times fewer midges than two untreated traps. Although this mixture of fatty acids had shown a repellent effect against a number of blood-feeding insects this is the first indication that it also has a significant repellent effect against Culicoides species and especially Culicoides (Avaritia) imicola Kieffer when applied to polyester mesh.Afrivet (Pty) Ltd.http://www.elsevier.com/locate/vetparab201

Possible over-wintering of bluetongue virus in Culicoides populations in the Onderstepoort area, Gauteng, South Africa

Several studies have demonstrated the ability of certain viruses to overwinter in arthropod vectors. The over-wintering mechanism of bluetongue virus (BTV) is unknown. One hypothesis is over-wintering within adult Culicoides midges (Diptera; Ceratopogonidae) that survive mild winters where temperatures seldom drop below 10 °C. The reduced activity of midges and the absence of outbreaks during winter may create the impression that the virus has disappeared from an area. Light traps were used in close association with horses to collect Culicoides midges from July 2010 to September 2011 in the Onderstepoort area, in Gauteng Province, South Africa. More than 500 000 Culicoides midges were collected from 88 collections and sorted to species level, revealing 26 different Culicoides species. Culicoides midges were present throughout the 15 month study. Nine Culicoides species potentially capable of transmitting BTV were present during the winter months. Midges were screened for the presence of BTV ribonucleic acid (RNA) with the aid of a real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) assay. In total 91.2% of midge pools tested positive for BTV RNA. PCR results were compared with previous virus isolation results (VI) that demonstrated the presence of viruses in summer and autumn months. The results indicate that BTV-infected Culicoides vectors are present throughout the year in the study area. Viral RNA-positive midges were also found throughout the year with VI positive midge pools only in summer and early autumn. Midges that survive mild winter temperatures could therefore harbour BTV but with a decreased vector capacity. When the population size, biting rate and viral replication decrease, it could stop BTV transmission. Over-wintering of BTV in the Onderstepoort region could therefore result in re-emergence because of increased vector activity rather than reintroduction from outside the region

Evaluation of radiation sensitivity and mating performance of Glossina brevipalpis males

BACKGROUND : Area-wide integrated pest management strategies that include a sterile insect technique component have been successfully used to eradicate tsetse fly populations in the past. To ensure the success of the sterile insect technique, the released males must be adequately sterile and be able to compete with their native counterparts in the wild. METHODOLOGY/PRINCIPAL FINDINGS : In the present study the radiation sensitivity of colonised Glossina brevipalpis Newstead (Diptera; Glossinidae) males, treated either as adults or pupae, was assessed. The mating performance of the irradiated G. brevipalpis males was assessed in walk-in field cages. Glossina brevipalpis adults and pupae were highly sensitive to irradiation, and a dose of 40 Gy and 80 Gy induced 93% and 99% sterility respectively in untreated females that mated with males irradiated as adults. When 37 to 41 day old pupae were exposed to a dose of 40 Gy, more than 97% sterility was induced in untreated females that mated with males derived from irradiated pupae. Males treated as adults with a dose up to 80 Gy were able to compete successfully with untreated fertile males for untreated females in walk-in field cages. CONCLUSIONS/SIGNIFICANCE : The data emanating from this field cage study indicates that, sterile male flies derived from the colony of G. brevipalpis maintained at the Agricultural Research Council-Onderstepoort Veterinary Institute in South Africa are potential good candidates for a campaign that includes a sterile insect technique component. This would need to be confirmed by open field studies.The Research was done in collaboration with the Joint Food and Agriculture Organization/ International Atomic Energy Agency Division of Nuclear Techniques in Food and Agriculture under the coordinated research project 17753/R0.http://www.plosntds.orgam2017Veterinary Tropical Disease

Culicoides species abundance and potential overwintering of African horse sickness virus in the Onderstepoort area, Gauteng, South Africa

In South Africa, outbreaks of African horse sickness (AHS) occur in summer; no cases are reported in winter, from July to September. The AHS virus (AHSV) is transmitted almost exclusively by Culicoides midges (Diptera: Ceratopogonidae), of which Culicoides imicola is considered to be the most important vector. The over-wintering mechanism of AHSV is unknown. In this study, more than 500 000 Culicoides midges belonging to at least 26 species were collected in 88 light traps at weekly intervals between July 2010 and September 2011 near horses in the Onderstepoort area of South Africa. The dominant species was C. imicola. Despite relatively low temperatures and frost, at least 17 species, including C. imicola, were collected throughout winter (June–August). Although the mean number of midges per night fell from > 50 000 (March) to < 100 (July and August), no midge-free periods were found. This study, using virus isolation on cell cultures and a reverse transcriptase polymerase chain reaction (RT-PCR) assay, confirmed low infection prevalence in field midges and that the detection of virus correlated to high numbers. Although no virus was detected during this winter period, continuous adult activity indicated that transmission can potentially occur. The absence of AHSV in the midges during winter can be ascribed to the relatively low numbers collected coupled to low infection prevalence, low virus replication rates and low virus titres in the potentially infected midges. Cases of AHS in susceptible animals are likely to start as soon as Culicoides populations reach a critical level.http://www.jsava.co.zatm201

The efficiency of light‐emitting diode suction traps for the collection of South African livestock‐associated Culicoides species

Culicoides biting midges (Diptera: Ceratopogonidae) are vectors of a range of orbiviruses that cause important veterinary diseases such as bluetongue and African horse sickness. The effective monitoring of Culicoides species diversity and abundance, both at livestock and near potential wildlife hosts, is essential for risk management. The Onderstepoort 220‐V ultraviolet (UV) light trap is extensively used for this purpose. Reducing its power requirements by fitting low‐energy light‐emitting diodes (LEDs) can lead to greater flexibility in monitoring. A comparison of the efficiency of the 220‐V Onderstepoort trap (8‐W fluorescent UV light) with the efficiency of the 220‐V or 12‐V Onderstepoort traps fitted with red, white, blue or green LEDs or a 12‐V fluorescent Onderstepoort trap demonstrated the 220‐V Onderstepoort trap to be the most efficient. All the results showed nulliparous Culicoides imicola Kieffer females to be the dominant grouping. Despite the lower numbers collected, 12‐V traps can be used in field situations to determine the most abundant species.The ARC Climate Change Collaboration Centre, Pretoria.https://onlinelibrary.wiley.com/journal/136529152019-12-01hj2018Veterinary Tropical Disease