The pink hibiscus mealybug (PHM) has a dainty name, but don't let it fool
you. This insect pest can destroy more than 200 plant species by injecting them
with toxic saliva while sucking their sap. The exotic insect pest recently invaded
California and Florida, and has proven difficult to monitor. The mealybugs are
also hard to kill, partly because their waxy outer coating, or cuticle, resists
penetration by conventional insecticides.
But ARS scientists have now found a way
to lure male mealybugs, making them easier to detect. A team of researchers
led by chemist Aijun Zhang at the Chemicals Affecting Insect Behavior Laboratory,
in Beltsville, Maryland, has discovered two compounds that together make up
the female PHM's sex pheromone. The compounds provide a timely method with which
to monitor and ultimately reduce infestations.
The scientists carefully reared thousands of PHMs, using an insect growth regulator
that prevents development of males. Then they painstakingly isolated more than
6,000 virgin females from which they collected pheromone chemicals.
After pooling seven collections of airborne sex-chemical extracts from the
females, the scientists exposed them to male mealybugs' antennae, which consistently
responded to two attractant compounds. The previously unknown natural chemicals
were found to be (R)-lavandulyl (S)-2-methylbutanoate and (R)-maconelliyl (S)-2-methylbutanoate.
The researchers then prepared a synthetic version of the pheromone and further
demonstrated that the processed mixture was immensely attractive to PHM males.
They found the most potency when they mixed one part of the first compound with
five parts of the second.
"In many cases, just a few micrograms of the one-to-five blend placed
in a single sticky trap captured thousands of males," says Zhang. This
blend is effective for monitoring the mealybug's population densities and geographical
distribution to help scientists determine where to release natural enemies.
"Pheromones decompose relatively quickly, without leaving a harmful residue
or damage to the environment," says Zhang. Chemical insecticides, however,
break down at a very slow rate, so they tend to linger in soil for decades,
which can add to pollution. So biological control methodswhere natural
predators and parasitoids are "weaponized" against agricultural pestsare
Officials with USDA's Animal and Plant Health Inspection Service, headquartered
in Riverdale, Maryland, have introduced two exotic wasps to control PHM infestations
in the United States and Caribbean. But their efforts had been stalled by an
inability to detect the mealybug's presence and prevalence. Now, APHIS officials
are using the new pheromone blend as a sex lure to survey the degree of mealybug
pest infestations in Florida and California and to track the effectiveness of
biological control efforts against the pest.
USDA-ARS has applied for patent protection for the invention and has already
received requests to license the technology. The new blend of synthetic pheromones
could help crop producers safely manage the pests with either mass-trapping
or disruption of mating activity.
These natural compounds have good staying power: Just 1 microgram lures the
pest for 6 months, and 10 micrograms lures it for 1 year, Zhang says.
The discovery was published in the Proceedings of the National Academy of Sciences.By
Rosalie Marion Bliss,
Agricultural Research Service Information Staff.
This research is part of Crop Production, Product Value, and Safety, an
ARS National Program (#304) described on the World Wide Web at www.nps.ars.usda.gov.
Aijun Zhang is with the USDA-ARS
Chemicals Affecting Insect Behavior
Laboratory, 10300 Baltimore Ave., BARC-West, Bldg. 007, Room 312, Beltsville,
MD 20705-2350; phone (301) 504-5223, fax (301) 504-6580.
"Sex Potion Ensnares Mealybugs" was published in the April 2005 issue of Agricultural Research magazine.