Australian cattle researchers use organic management to deal with insect pest — ScienceDaily

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Few beef producers in the temperate climate of South Australia will have encountered the parasitic buffalo fly (Haematobia irritans exigua), a scourge of the livestock industry in the tropical and subtropical north of the country – but it has maintained this condition and also lifted a burden from the northern industry, is a A race against time and climate.

Buffalo fly is a serious challenge to animal health and production, costing the North Australian cattle industry nearly $ 100 million annually in treatments and lost production. However, combating the pest with insecticides is increasingly encountering resistance. In addition, the reputation of Australian beef as “clean green” must be protected, thus minimizing the need for pesticides.

In the last century, the buffalo fly has crept south across Queensland to northern New South Wales. The modeling shows that, with the help of climate change, it could extend to South Australia and Southwest Western Australia by 2030. The blood-sucking fly causes large, painful wounds, and desperate animals can be distracted from feeding to seriously affect growth.

The only obstacle on his way is a joint University, Industry, and Government biological control project using the insect-infecting bacterium Wolbachia – the same compound so successfully used to suppress mosquito-borne dengue fever in humans.

The project is led by Dr. Peter James, from the Queensland Alliance for Agriculture and Food Innovation (QAAFI) at the University of Queensland, who explains the key is using the Wolbachia bacterium to break the fly’s breeding cycle. If this can be sustained, there will be an opportunity to both suppress the buffalo fly population in the north and stop it from spreading south.

The buffalo fly is a formidable enemy introduced to the Northern Territory from Asia in the late 1830s, but the crack in its armor is that it weakens in cold weather. Its populations tend to shrink into localized pockets. Dr. James says if wolbachia can be used to further stress the buffalo fly in winter, a local eradication strategy will become a real possibility.

However, there are still some significant technical challenges to overcome. Since the bacterium spreads vertically from the mother to the offspring and is not transmitted laterally between the flies, buffalo flies must be artificially infected by microinjection. For mosquitoes, this is usually done by microinjection into the eggs. This approach couldn’t be used on buffalo flies because the eggs are extremely hard: “When we started microinjecting eggs, as we do with mosquitoes, we blunted needles and damaged the eggs in a way you wouldn’t believe. The needles even broke, “says Dr. James.

“From there we looked at adult flies or pupae with microinjection. The idea was that the bacterium was still spreading in the insect and getting into the germinal tissue of the female.”

He says the main thing is to establish the bacterium in the population because once flies are infected, three control scenarios open up. While Wolbachia is a maternally transmitted bacterium, male flies through eggs can still be used to manipulate this.

When a male infected with Wolbachia mates with a healthy female, the eggs are sterile and therefore no offspring. When a healthy male mates with an infected female, mating with eggs and offspring is successful, but they carry wolbachia and help spread it to the buffalo fly population. Dr. James says the benefit of this is that researchers no longer have to breed and release millions of infected or sterile flies.

“But Wolbachia has many other effects on the fitness of the fly population as well. We have shown that the very presence of the bacterium can shorten the life of the buffalo flies, reduce the number of eggs laid and the number of pupae hatching. These are likely other fitness- Punishments we haven’t identified yet, and when you start adding up all of these effects it can be a huge drag on survivability.

“And this is where the winter factor comes into play. In many areas, the buffalo fly only gets stuck in small numbers in winter, so even Wolbachia’s influence on the fitness of the population could be enough to eradicate these populations if the bacterium is used strategically.”

A second approach is to use Wolbachia to block transmission of the stephanofilaria nematode, which is transmitted by buffalo flies and has been linked to the development of buffalo fly lesions in cattle. Similar to how Wolbachia blocks transmission of dengue virus, Zika virus, and a number of other mosquito-borne viruses, it has also been shown to block transmission of some nematodes that are closely related to stephanofilaria. The spread of Wolbachia by the buffalo fly population could block the nematode and ease the development of lesions

A third option that is being investigated is to breed and release sterile males.

“Again, the idea is to strategize the sterile males by releasing them to the wintering areas, which are already in a weakened state. This could stop or slow the build-up of buffalo flies for the next season or stop them from spreading south or even form the basis for local repayment strategies. “

Dr. James says the challenge now is to improve the consistency and persistence of the Wolbachia infection. Since the beginning of the Wolbachia project in 2017, researchers have mastered the first major challenge of taking various Wolbachia strains from mosquitoes and also fruit flies and introducing them into a whole new species, the buffalo fly: “Wolbachia has been in several cases over generations transmitted, but we still have to produce a stably infected strain, “he explains.

“But we have reached the stage where we can start refining the approach. For example, we have a project that is looking for ways to make the fly immunosuppressive to promote Wolbachia infection.

“We have built a decent toolkit, so I am confident that we are on the verge of delivering sustainable biological control that will provide economic animal welfare to the northern livestock industry and save southern industries from ever having to bear the same burden.”