New research suggests that fungi could be used to control insect-borne diseases common in livestock. The study shows for the first time that a fungus can effectively kill adult midges in the family of insects that carry bluetongue virus (BTV). Bluetongue outbreaks have caused significant losses on European farms in recent years, and the study indicates that using the fungus as a means of biological control could help reduce reliance on chemical insecticides, in the absence of effective vaccines.
Bluetongue disease mainly affects sheep and cattle and can lead to death. The disease is caused by a virus that is transmitted by Culicoides biting midges and is of growing importance in Europe under the influence of climate change and globalisation of trade. Recent outbreaks have had economic impacts in northern European countries. In addition to livestock losses from clinical disease, restrictions imposed by Directive 2000/75/EC 1 of the European Council on cattle movements to limit BTV spread also inflict substantial losses.
In the current study, the researchers, based in the UK and Netherlands, exposed adult Culicoides midges to different types of a fungus to investigate their potential for controlling the insects. Perceived negative impacts of insecticides on humans and the environment have encouraged the search for other means of controlling bluetongue. Biological control methods are those that use one species, such as fungi, to target another problem species. In the case of bluetongue, attempts have been made to target the disease-carrying midges with fungi, but previous studies have focused on insect larvae rather than adult midges. Control of adults, in particular, is crucial because it is the adult insects that are responsible for transmitting BTV.
The researchers found that one fungus, called Metarhizium anisopliae V275, was particularly effective at killing the midges in the lab, and under semi-field conditions (in cages in a greenhouse). This type of fungus has been also used successfully to control African locusts and separate research suggests it can also control mosquitoes. The researchers also found that increasing the dose of fungus reduced the number of midges that survived, and that the fungus worked quickly - within 24 hours - to kill the insects. The most effective fungus formulations were 'dry' as opposed to 'wet' formulations. The dry fungus killed 100 per cent of adult midges after 5 days, however, the researchers point out that it may be more susceptible to environmental conditions, such as UV radiation, humidity and high temperatures, when the same formulations are applied in the field.
According to the authors, fungi represent a potential method for targeting bluetongue-carrying midges and may form part of an integrated pest control programme. Fungi could be applied to places where midges rest, such as animal housing and livestock. So far, the fungi tested in the study appear to present little risk to the environment, or people. However, the researchers say that the success of control programmes using fungi will depend on rigorous field trials to establish the best formulations and methods of delivery, and to evaluate wider potential risks.