Scientists have long been warning us that with climate change can come expanding habitats for flying insects that transmit a host of potentially deadly diseases. In Europe, for instance, researchers are gearing up for the northward spread of arboviruses (insect-borne viruses), such as the one that causes African horse sickness (AHS, most often identified in Africa). In addition to preparing effective vaccines, they’re looking at controlling the source of the disease: biting midges.
Owners can protect their horses from midges by stabling them at night, using insecticide-drenched netting, and turning on blowing fans. But they can also reduce midge populations by treating both adults and larvae in the environment, said Cipriano Foxi, PhD, of the Experimental Zooprophylactic Institute of Sardinia “G. Pegreffi,” in Sassari, Italy.
“The control of Culicoides (midges) cannot disregard habitat management to reduce larval development,” he said. “The periodical application of insecticide to the walls and roofs of stables has been recommended as preventive measures. Habitat manipulation such as drainage and removal and/or alteration of breeding sites can reduce larval density and consequently also the abundance of adults.”
In their study, Foxi and colleagues tested different insecticide treatments—targeting both adults and larvae—on three farms in Central Italy. (The farms housed mainly sheep, goat, and cattle because midges also affect these animals. The deadly midge-borne diseases Bluetongue and Schmallenberg are already spreading in these areas, and while they doesn’t seem to affect horses, their spread acts as a model for how AHS could spread in the horse population.)
Specifically, they tested formulas based on diflubenzuron and Bacillus thuringiensis var. israelensis (H-14) to kill larvae and deltamethrin to kill adults. They used a blacklight trap to collect adult midges twice a week as a way to measure population numbers before and after treatments.
They found significant reductions in the numbers of three Culicoides species after each treatment compared to untreated control farms. This underlines the importance of not only protecting the animals from bites but also of killing the insects directly by treating their nesting areas, such as walls, roofs, and fences, Foxi said.
The goal isn’t to eliminate midges—which would appear impossible anyway, Foxi said—but to reduce their populations as much as possible. Fewer numbers mean reduced risk of viral spread, fewer bites, and lessened migration of midges to other neighboring farms.
“The management techniques are useful to control midge populations both on isolated farms and on large areas,” Foxi said. “The direct involvement of farm owners, with a good knowledge of the farm conditions that are often the main factor of Culicoides abundance, will be essential to optimize the vector control.”
That would involve recognizing and identifying midge breeding sites on farms, so as to focus treatment on those areas for maximum efficacy while reducing the ecological impact of such chemicals, he said.
“The spread of vector-borne diseases represents a growing global threat to human and animal health,” Foxi said. “Climate change as well as increased international travel and globalization of trade play an important role in the spread of arthropods and arthropod-borne pathogens worldwide.
“When a vector species moves in a new zone, it may bring pathogens into the range of other competent vectors, and climate change could increase their vector competence as well as the survival and establishment of pathogens,” he continued. “The continuing spread of pathogens in Europe (AHS virus, equine encephalosis virus, Bluetongue virus, Schmallenberg virus, West Nile virus, Chikungunya virus, to name a few) will probably be raised in the future.”
Efforts to control Culicoides midges should always be conducted according to integrated pest management principles, Foxi added.
The study, “Combined larvicidal and adulticidal treatments to control Culicoides biting midges (Diptera: Ceratopogonidae): Results of a pilot study,” was published in Veterinary Parasitology.