Parasites get a leg-up on pest grasshoppers

An insect whose lifestyle sounds like something from a B-movie could be a godsend for the palm oil growers of Papua New Guinea, writes Caroline Davis.

The parasite, which lives and reproduces inside its host, has literally found the Achilles' heel of the long-horned grasshopper, the main pest of the palm grown for its oil.

The new species of Strepsiptera, discovered by Jeyaraney Kathirithamby, a zoologist at Oxford University, has a novel way of invading the fast-moving grasshopper that lives on palm fronds.

The female insect crawls into its host via the attachment pads at the end of the grasshopper's legs, Dr Kathirithamby reports in the journal Proceedings of the Royal Society Biological Sciences . The tiny larva, just 0.15mm long, then burrows into its host's abdomen, where it sheds its antennae, eyes and legs, mutates into a large bag of eggs and destroys the grasshopper's reproductive system.

"Structurally, it is absolutely stunning," Dr Kathirithamby said.

Female Strepsiptera live all their adult life inside other insects, including bees and ants. Males usually break out to mate. The parasite departs through the host's flank, leaving the abandoned host to die from the exit wound, then flies off on his stumpy wings to find a female.

The female simply lets her sex organs protrude from her host's side for the male to find. After mating, the male dies and the female produces up to 1 million larvae. These are scattered about as her host moves. This new species, however, can reproduce without males.

Dr Kathirithamby is working to introduce the bug as a biocontrol tool for oil palms, in collaboration with the Papua New Guinea Oil Palm Research Association.