minx
07-10-2003, 03:18 AM
Hannibal Lecter couldn't imagine a more cunningly macabre way to dress for dinner - a tiny insect parasite cloaks itself in its host's skin to avoid detection, researchers have found.
Fooled into thinking that the parasite is part of its own body, the host leaves the intruder to feast in peace. "The host thinks: 'It's my tissue so I won't do anything about it'," says entomologist Jeyaraney Kathirithamby of the University of Oxford, who discovered the bizarre tactic1. The trick is unique to a group of tiny insects called twisted-wing parasites (Strepsiptera), she thinks.
The larva of a twisted-wing parasite punches a hole through its host's tough outer skeleton - in this case a type of grasshopper called a katydid. It then pushes into the soft skin-like layer underneath, creating a pouch. Natural healing causes the hole to close behind it, forming a bag inside which the larva feeds and develops.
It's not just the parasite's dress-sense that is bizarre. Initially less than 0.1 millimetres long, the grub eventually grows to fill its host's body. Females spend their entire lives inside, pumping out new larvae. Fly-like males hover around, looking to mate with the small part of a female's body that protrudes from her host's abdomen.
Many insect parasites eat other insects from within. If an insect detects an invader, it builds a tough capsule around it, cutting off its food supply and killing it. But Kathirithamby has never seen a twisted-wing parasite suffer this fate.
"Strepsipterans are very weird, and this is another example of them doing something weird," says evolutionary biologist Charles Godfray of Imperial College, London. "It's a nice example of a parasite's mechanism for avoiding host defences." Other insects seem to mimic their host's tissue, rather than borrow it, he adds.
Skin-stealing might be the reason why the 596 species of twisted-wing parasites can infect a wide variety of hosts. For example, in some species, males target ants, but females develop inside grasshoppers.
Most parasites are much more specialized. Disguising oneself in a host's tissue might be a more versatile strategy than overcoming the specialized defences of many different hosts.
Fooled into thinking that the parasite is part of its own body, the host leaves the intruder to feast in peace. "The host thinks: 'It's my tissue so I won't do anything about it'," says entomologist Jeyaraney Kathirithamby of the University of Oxford, who discovered the bizarre tactic1. The trick is unique to a group of tiny insects called twisted-wing parasites (Strepsiptera), she thinks.
The larva of a twisted-wing parasite punches a hole through its host's tough outer skeleton - in this case a type of grasshopper called a katydid. It then pushes into the soft skin-like layer underneath, creating a pouch. Natural healing causes the hole to close behind it, forming a bag inside which the larva feeds and develops.
It's not just the parasite's dress-sense that is bizarre. Initially less than 0.1 millimetres long, the grub eventually grows to fill its host's body. Females spend their entire lives inside, pumping out new larvae. Fly-like males hover around, looking to mate with the small part of a female's body that protrudes from her host's abdomen.
Many insect parasites eat other insects from within. If an insect detects an invader, it builds a tough capsule around it, cutting off its food supply and killing it. But Kathirithamby has never seen a twisted-wing parasite suffer this fate.
"Strepsipterans are very weird, and this is another example of them doing something weird," says evolutionary biologist Charles Godfray of Imperial College, London. "It's a nice example of a parasite's mechanism for avoiding host defences." Other insects seem to mimic their host's tissue, rather than borrow it, he adds.
Skin-stealing might be the reason why the 596 species of twisted-wing parasites can infect a wide variety of hosts. For example, in some species, males target ants, but females develop inside grasshoppers.
Most parasites are much more specialized. Disguising oneself in a host's tissue might be a more versatile strategy than overcoming the specialized defences of many different hosts.