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An international team of researchers believes that the intra-cellular bacterium Wolbachia, could enable farmers to overcome the challenge posed by  African crop pests. Whilst investigating new affordable control measures to  tackle the African armyworm, researchers from Lancaster University, the  University of Greenwich and Tanzania-based Eco Agri Consultancy Services Ltd,  discovered that Wolbachia rendered the creatures vulnerable to the  biopesticide SpexNPV.

The African armyworm – a caterpillar  that feeds on staple cereal crops such as maize, wheat, millet and rice – can be  found in densities of up to 50,000 larvae per hectare, and can cause total crop  failure. As many farmers cannot afford the chemical pesticides currently on the  market, the armyworm poses a significant threat to food security.

Almost  three quarters of insect species carry Wolbachia, and some African  armyworms are amongst their number. Around 12 per cent of armyworms carry the  bacterium, but this varies between populations from as low as zero to as high as  56 per cent. As a recent study demonstrated that Wolbachia-carrying   mosquitoes are protected from viruses such as that which causes dengue in  humans, the Lancaster-led team decided to investigate whether this bacterium  offered armyworms any protection from biopesticides. To their surprise, however,  they discovered that the bacterium made the caterpillars more vulnerable to  SpexNPV than their Wolbachia-free counterparts.

I spoke to project  leader Ken Wilson, Professor of Evolutionary Ecology at Lancaster’s Environment  Centre, to find out more about this surprising discovery. I began by asking  Professor Wilson whether he understood how Wolbachia makes the  African armyworm more susceptible to SpexNPV.

"No, I don’t," he conceded.  "In many ways, we are still in the early stages of our investigations. This  wasn’t even the primary focus of our initial research. Our main focus was on the  baculovirus, and it was only when we found this that we decided to examine the  effects of Wolbachia on susceptibility.

"It could be that Wolbachia just triggers, or drains, the armyworm of resources that it  needs for fighting the virus. Maybe, the host is so busy fighting or interacting  with the Wolbachia that it has got fewer resources available for  interacting with the virus, rendering it more vulnerable. We really don’t know  at the moment. In mosquitoes, of course, a different strain of Wolbachia  has the opposite effect. It makes them more resistant to a different type of  virus. The reason our story is perhaps so newsworthy is because Wolbachia  has completely the opposite effect on armyworms than on mosquitoes."

I  went on to ask Professor Wilson whether this discovery came as a  surprise.

"It was a surprise because there are quite a few studies,  particularly on mosquitoes and fruit flies, that suggest particular strains of Wolbachia make insects more resistant to viruses," he replied. "One of  our initial concerns was that the bacterium might have a negative effect in  terms of using SpexNPV as a biological control agent. We expected Wolbachia to have either no effect at all, or to make the armyworm more resistant to the biopesticide.

"Our initial studies were  based on field data that we had collected over the course of a year. Wolbachia appeared to be making the armyworm more susceptible to the  virus, and we thought that this was quite unusual. We collected more data over  the next couple of years and it became evident that the bacterium was making the  creatures more susceptible to SpexNPV. It was at this point that we started to  conduct laboratory experiments. We used antibiotics to ‘cure’ the armyworms of Wolbachia before infecting them with the virus. Our previous results were  confirmed. The bacterium was making armyworms more susceptible to the  virus."

Professor Wilson and his colleagues found that Wolbachia-carrying armyworms were between six and 14 times more  susceptible to SpexNPV than caterpillars who had had their bacterial passengers  removed. Of course, these results seem to point to a simple solution. Simply  spread Wolbachia amongst the armyworm population and use SpexNPV to  protect crops. However, as Professor Wilson explained, due to the mobile nature  of adult armyworm moths, this is not an easy task.

"Wolbachia  makes mosquitoes more resistant to the dengue virus, so in Australia, scientists  have released mosquitoes carrying the bacterium into areas where dengue is  prevalent. The hope is that as the levels of Wolbachia increase, the  transmission of dengue from mosquitoes to humans will be  interrupted.

"However, these mosquitoes are fairly sedentary, which means  that you can concentrate the Wolbachia within a relatively isolated  population. The adult moths of African armyworms, on the other hand, migrate  across such large areas that we would probably need to release massive numbers  of them to sufficiently increase levels of Wolbachia.

I concluded  our interview by asking Professor Wilson about the further research that he  would like to conduct in this area.

"The research grant that we were  operating under has just ended, so we will be looking to apply for new funding  in order to take things forward," he explained. "As I said, we obtained these  results fairly recently, and unfortunately, the main project had already  finished by this point in time. I think that we are still in the initial stages  of our research. We haven’t even started to think about how we might apply our  newly gained knowledge in the field. Whilst there are potential challenges in  exploiting the effects of Wolbachia to control African armyworms, not all  major crop pests are as mobile. With more research, it might become possible to  apply our findings to other species."           

Read more: http://www.scienceomega.com/article/442/new-discovery-could-help-in-the-battle-against-the-armyworm#ixzz24xCl5eiO