Evaluation of Metarhizium anisopliae for the control of Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae), the principal vector of bluetongue virus in Australia

Comparative laboratory and field study of biorational insecticides for Culicoides biting midge management in larval developmental sites

An appropriate management strategy of bluetongue vectors should include larvicidal treatments in their larval development sites utilizing active substances with low environmental impact. A selection of biorational insecticides with potential against dipteran larvae was assayed in the laboratory against field collected Culicoides larvae including C. cataneii, C. circumscriptus, and C. imicola, determining their median lethal concentrations in water and mud/water substrate. The efficacy of formulations containing the insect growth regulators pyriproxyfen and cyromazine, the botanical insecticide azadirachtin, and the entomopathogenic bacteria Bacillus thuringiensis israelensis and Brevibacillus laterosporus, was also assessed in field conditions in a comparative study conducted in sheep farm larval development sites, including treatments with the organophosphate temephos. Significant larvicidal properties were associated with the various insecticides evaluated in the laboratory assays and in field trials, although with different levels of effectiveness. While temephos was confirmed to be an effective broad spectrum larvicidal substance, B. laterosporus appeared to be the most effective among entomopathogens, while insect growth regulators combined a good efficacy to a long-lasting residual effect in the field. Everything considered, the use of these biorational insecticides alone or in combination with larval habitat manipulation techniques appears to be a promising method to complement integrated biting midge management programs.

Projected economic losses due to vector and vector-borne parasitic diseases in livestock of India and its significance in implementing the concept of integrated practices for vector management

Broadly, species of arthropods infesting livestock are grouped into flies (biting and non-biting), fleas, lice (biting and sucking), ticks (soft and hard), and mites (burrowing, non-burrowing, and follicular). Among which, biting and non-biting flies and ticks are the potent vectors for many bacterial, viral, rickettsial, and protozoan diseases. Vectors of livestock are having economic significance on three points (1) direct losses from their bite and annoyance, worries, and psychological disturbances produced during the act of biting and feeding, (2) diseases they transmit, and (3) expenditure incurred for their control. Flies such as Culicoides spp. and Musca spp. and various species of hard ticks play important role in disease transmission in addition to their direct effects. For control of vectors, recent concept of integrated pest management (IPM) provides the best solution and also addresses the problems related to acaricide resistance and environmental protection from hazardous chemicals. However, to successfully implement the concept of IPM, for each vector species, estimation of two monitory benchmarks, i.e., economic injury level (EIL) and economic threshold level (ETL) is essential prerequisite. For many vector species and under several circumstances, estimation of EIL and ETL appears to be difficult. Under such scenario, although may not be exact, an approximate estimate can be accrued by taking into account several criteria such as percent prevalence of vectors in a geographical area, percent losses produced, total livestock population, and current prices of livestock products such as milk, meat, and wool. Method for approximate estimation is first time described and elaborated in the present review article.

Application of an embryonated chicken egg model to assess the vector competence of Australian Culicoides midges for bluetongue viruses

Culicoides biting midges (Diptera: Ceratopogonidae) are vectors of a number of globally important arboviruses that affect livestock, including bluetongue virus (BTV), African horse sickness virus and the recently emerged Schmallenberg virus. In this study, a model using embryonated chicken eggs (ECEs) was utilized to undertake vector competence studies of Australian Culicoides spp. for 13 laboratory-adapted or wild-type virus strains of BTV. A total of 7393 Culicoides brevitarsis were reared from bovine dung, and 3364 Culicoides were induced to feed from ECEs infected with different strains of BTV. Of those, 911 (27%) survived the putative extrinsic incubation period of 9-12 days. In some trials, virus was also transmitted onward to uninfected ECEs, completing the transmission cycle. This model does not rely on the use of colonized midges and has the capacity to assess the vector competence of field-collected insects with strains of virus that have not previously been passaged in laboratory culture systems. There is also potential for this model to be used in investigations of the competence of Culicoides spp. for other arboviruses.

Bluetongue: control, surveillance and safe movement of animals

The performance of different bluetongue control measures related to both vaccination and protection from bluetongue virus (BTV) vectors was assessed. By means of a mathematical model, it was concluded that when vaccination is applied on 95% of animals even for 3 years, bluetongue cannot be eradicated and is able to re‐emerge. Only after 5 years of vaccination, the infection may be close to the eradication levels. In the absence of vaccination, the disease can persist for several years, reaching an endemic condition with low level of prevalence of infection. Among the mechanisms for bluetongue persistence, the persistence in the wildlife, the transplacental transmission in the host, the duration of viraemia and the possible vertical transmission in vectors were assessed. The criteria of the current surveillance scheme in place in the EU for demonstration of the virus absence need revision, because it was highlighted that under the current surveillance policy bluetongue circulation might occur undetected. For the safe movement of animals, newborn ruminants from vaccinated mothers with neutralising antibodies can be considered protected against infection, although a protective titre threshold cannot be identified. The presence of colostral antibodies interferes with the vaccine immunisation in the newborn for more than 3 months after birth, whereas the minimum time after vaccination of animal to be considered immune can be up to 48 days. The knowledge about vectors ecology, mechanisms of over‐wintering and criteria for the seasonally vector‐free period was updated. Some Culicoides species are active throughout the year and an absolute vector‐free period may not exist at least in some areas in Europe. To date, there is no evidence that the use of insecticides and repellents reduce the transmission of BTV in the field, although this may reduce host/vector contact. By only using pour‐on insecticides, protection of animals is lower than the one provided by vector‐proof establishments.

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1182/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1171/full

Insight on the larval habitat of Afrotropical Culicoides Latreille (Diptera: Ceratopogonidae) in the Niayes area of Senegal, West Africa

BACKGROUND

Certain biting midges species of the genus Culicoides (Diptera: Ceratopogonidae) are vectors of virus to livestock worldwide. Culicoides larval ecology has remained overlooked because of difficulties to identify breeding sites, methodological constraints to collect samples and lack of morphological tools to identify field-collected individuals to the species level. After the 2007 unforeseen outbreaks of African horse sickness virus (AHSV) in Senegal (West Africa), there is a need to identify suitable and productive larval habitats in horse farms for the main Culicoides species to evaluate the implementation of vector control measures or preventive actions.

METHODS

We investigate twelve putative larval habitats (habitat types) of Culicoides inside and outside of three horse farms in the Niayes area of Senegal using a combination of flotation and emergence methods during four collection sessions.

RESULTS

Among the three studied horse farms, three habitat types were found positive for Culicoides larvae: pond edge, lake edge and puddle edge. A total of 1420 Culicoides individuals (519♂/901♀) belonging to ten species emerged from the substrate samples. Culicoides oxystoma (40 %), C. similis (25 %) and C. nivosus (24 %) were the most abundant species and emerged from the three habitat types while C. kingi (5 %) was only retrieved from lake edges and one male emerged from puddle edge. Culicoides imicola (1.7 %) was found in low numbers and retrieved only from pond and puddle edges.

CONCLUSIONS

Larval habitats identified were not species-specific. All positive larval habitats were found outside the horse farms. This study provides original baseline information on larval habitats of Culicoides species in Senegal in an area endemic for AHSV, in particular for species of interest in animal health. These data will serve as a point of reference for future investigations on larval ecology and larval control measures.