麻豆传媒

PARASITIC wasps siphon off antifreeze from their fly hosts to protect them
from chilly winters鈥攁 discovery which could improve biological control of
pest flies.

Nasonia vitripennis wasps deposit their eggs in puparia, the
cocoon-like casings of developing flies. When the wasps hatch they feed on the
fly pupae. To survive the winter cold, both flies and wasps go into
diapause鈥攁 form of hibernation in which they accumulate antifreeze
compounds.

But the wasps don鈥檛 go into diapause until up to two months after the flies.
To try to explain this, David Rivers of Loyola College in Maryland and his
colleagues studied how the host鈥檚 diapause affects parasite hardiness. They
found that wasps reared on diapausing pupae could tolerate lower temperatures
longer than wasps reared on pupae of hosts that hadn鈥檛 entered diapause.

And diapausing pupae contained twice as much of the antifreeze glycerol as
non-diapausing pupae. Because glycerol levels in parasites correlated with those
in their hosts, Rivers thinks the wasps steal the flies鈥� antifreeze, timing
egg-laying to maximise the haul. 鈥淚t鈥檚 a slick strategy,鈥� he says.

鈥淭his is the first time this effect has been so clearly demonstrated,鈥� says
Jeff Bale, an expert in cold hardiness in insects at the University of
Birmingham. But Rivers has still to prove that the parasites get their increased
glycerol from the hosts.

No one yet knows whether similar exchanges happen in other host-parasite
pairs. 鈥淲e don鈥檛 know if it鈥檚 the rule or the exception,鈥� says insect expert
Michael Strand of the University of Wisconsin.

Widespread or not, it could be put to good use. Some farmers in the US use
parasitic wasps to eliminate flies in stables and chicken coops. But the wasps
often can鈥檛 survive the winter chill. If farmers reared wasps on antifreeze-rich
hosts, they could enjoy pest control all year round.