The silverleaf whitefly,
Bemisia argentifolii, is only about one-sixteenth-inch long. Click image
for additional information.
Scientists Identify Wasp's Chemical Cue for
Marking Whiteflies By
Alfredo Flores and
September 24, 2003
A tiny wasp that parasitizes silverleaf whitefly nymphs has
surprised scientists with its chemical communiqué.
Service scientists found that female Eretmocerus mundus wasps
produce specialized lipids for marking whitefly nymphs they've chosen as
suitable egg hosts. The discovery lends biochemical evidence to earlier
observations on E. mundus' reproductive behavior and could foster
greater success in mass-rearing it to battle silverleaf whiteflies, a worldwide
Insecticide use problems, including whitefly resistance, have
necessitated alternative measures such as biocontrol, according to James
Buckner, an insect biochemist at the ARS
Red River Valley Agricultural Research
Center in Fargo, N.D.
E. mundus' heat tolerance, host-specificity and fecundity
are appealing biocontrol attributes. It's also a team player. After choosing a
nymph, a female wasp chemically marks its back with lipids, alerting her
compatriots: "I put my egg beneath this one; find another!" Such cues avoid
double-parasitizing of the host, making the wasp a proficient whitefly
parasite, according to Walker Jones, who leads the ARS
Beneficial Insects Research
Unit in Weslaco, Texas.
These lipids, known as marking pheromones, are highly unusual,
according to Jones. The female detects the marks with her antennae. That's how
she knows whether a nymph has been touched by another wasp.
In Weslaco, Jones designed an experiment enabling Buckner to use
gas chromatography (GC) techniques to identify lipids extracted from the
cuticles of whitefly nymphs in four groups: those with wasp eggs beneath them;
those without; 10-day-old nymphs with wasp larvae feeding inside them; and an
older group, called fourth instars, with eggs beneath them.
In the first group of whitefly nymphs, Buckner's GC analysis
revealed two foreign lipids, known as C31 and C33 dimethylalkanes. Neither
lipid is produced by whiteflies. When Buckner checked for these lipids in the
wasps, however, he found a match. No dimethylalkanes appeared in the third
groupeven though those nymphs had been parasitizedbecause they had
shed their skins before GC testing. Lipids also appeared in fourth instars that
had been parasitized after molting.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.