Cruisers and ambushers: worms at work
The attraction of nematodes for insect control is that they are pesticides with the power of search.
"The worms are motile and can actively seek out an insect, in this case a sheep louse or fly maggot," Dr Peter James says. "We are looking primarily at lice control and strains that can work on sheep at body temperature, but we know the nematodes can also kill all stages of fly maggots."
The worms find an insect by either sitting up on their tail, waving around like a cobra and then jumping on when a potential host comes past - an 'ambush' strategy - or they actively follow insects along carbon dioxide or (perhaps) temperature gradients in the so-called 'cruise' strategy. Once they find a suitable host, they invade through an insect's mouth or anus, or sometimes directly through the cuticle and release a mutualistic bacteria that kills the insect. As the bacteria take over, the worm feeds on the replicating microbes to produce the next generation of worms.
"The tiny worms can be made to slow right down and can be formulated into pesticide powders with extended shelf life," Dr James says. "Once dissolved in water they revive and can be applied with normal spray equipment. We've applied one strain of nematode to sheep by jetting and have achieved up to 90 per cent reduction in lice numbers. We are now looking at different strains able to operate better at high temperatures and with different search strategies."
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