Signal-Sending Plants Identify Their AttackersBy
When caterpillars attack, some corn, cotton and tobacco plants release
chemical SOS signals to recruit help from friendly parasitic wasps. But the
wasps may not answer unless the caterpillar in question is a species they
To avoid "no-shows," scientists recently found, plants customize
their signals, advertising their attackers' identity and ensuring that the right
wasp comes calling.
The finding refutes an earlier belief that wasp-calling plants emit an all-purpose
signal, regardless of the caterpillar species. So say entomologist Joe
Lewis and chemist James Tumlinson,
of the Agricultural Research Service,
and University of Georgia graduate student
Consuelo DeMoraes. ARS is the U.S. Department
of Agriculture's chief scientific arm.
Their work aims to curb insecticide use through integrated pest management
and breeding crops with stronger signaling traits. DeMoraes led the study under
the guidance of Tumlinson, in Gainesville, Fla., and Lewis, at ARS'
Insect Population Management
Research Laboratory in Tifton, Ga.
In Georgia field trials, they saw Cardiochiles nigriceps wasps
flying to plants signaling an attack by tobacco budwormsa host these wasps
prefermore often than to plants chewed by corn earworms, a related
caterpillar species. Budworm-infested plants accounted for 164 of 198 total wasp
The team also monitored plants after removing any leaves that caterpillars
had chewed on. This ensured the wasps weren't homing in on chemical cues in
their caterpillar host's saliva or in feces, rather than the plant's own signals
Indeed, the Cardiochiles wasps visited budworm- damaged plants 32 of 48
Gas chromatography revealed consistent differences in concentrations of
about 12 chemical volatile compounds rising from the plants. The differences
depended on which caterpillar species was attacking.
An article about the research, in this month's Agricultural Research
magazine, is also on the World Wide Web at:
Scientific contact: Joe Lewis, ARS Insect Biology and Population
Management Research Laboratory, Tifton, Ga., phone (912) 387-2348, fax (912)