Williams is also evaluating a parasitic ant, S. daguerrei, under
quarantine. It is found only on fire ants in Argentina and Brazil. The
parasite doesn't produce workers, so it relies on its host, taking resources
from the queen while the colony feeds and maintains its brood. Mound
densities were 33 percent less in sites with the parasitic ant, and
the number of fire ant queens was 47 percent less in parasitized colonies.
Terror from Above
Fire ant decapitating phorid flies, from the genus Pseudacteon,
are natural enemies of imported fire ants. Just their presence keeps
frightened ants from leaving their mounds. That alone is good news because
it forces a shift in when the fire ants forage and allows native ants
to compete better.
A female fly hovers over a mound before she pinpoints a victim, dive-bombs
it, and deposits one of her eggs inside it. The egg, as researchers
at the center discovered, eventually produces a larva that eats its
way to the head and causes it to fall off. Entomologist Sanford Porter
estimates there are about 20 types of Pseudacteon flies that
attack fire ants. They could be used to complement each other in control
So far, two phorid fly speciesP. tricuspis and P. curvatushave
been released and established in the United States. P. tricuspis
took hold and is expanding at the rate of 10 to 20 miles a year. P.
curvatus works better on black imported fire ants and the hybrid
than on red ones. It was imported from Argentina and is being used in
Alabama, Mississippi, and Tennessee. A third species, P. litoralis,
works especially well on the red ants and has been approved for release
in field studies.
Porter and colleagues at ARS' Biological Control and Mass Rearing Research
Unit, located near Starkville, Mississippi, developed an attack box
that has greatly improved their ability to mass-rear phorid flies. The
boxes are held under environmental conditions that strictly mimic the
flies' natural habitat. Specially designed cups are alternately raised
up and down within the box in a cycle every 10 minutes, causing the
ants to run from one cup to the other. This action allows the phorid
flies to easily attack and parasitize them. New flies are continually
released into the main attack box from an attached holding box at one
end to maximize the amount of eggs deposited.
Because CMAVE reached its capacity to rear the phorid flies, an initiative
to mass-produce them was launched with ARS, USDA's Animal and Plant
Health Inspection Service (APHIS), and Florida's Department of Agriculture
and Consumer Services. The new facility in Gainesville will eventually
produce 6,000 to 12,000 flies a day.
Social Insects Suffer Uninvited Guests
Chemist Robert Vander Meer studies semiochemicals, such as pheromones,
in an effort to modify ant behavior and control the pests. Social insects
like fire ants use semiochemicals to communicate with each other and
influence activities. Vander Meer wants to see how the ants use these
compounds and then disrupt the processes.
One reason fire ants are so troublesome is that they commonly short-circuit
electrical equipment of all kinds. Of course, they electrocute themselves
in the process, and large numbers of dead ants are sometimes found piled
up in electrical mechanisms. Vander Meer and Porter discovered that
electrocution causes the ants to release alarm pheromones that attract
other ants as well as phorid flies. In response to these pheromones,
phorid flies lay more eggs in ants, and fly production increases by
15 to 20 percent. This knowledge will help them develop new ways to
use alarm pheromones in biological control programs.
Vander Meer is involved in other fire ant pheromone projects. He found
that fire ants use their stinger not only for defensive purposes but
also for pheromone dispersal. His knowledge of how fire ants use semiochemicals
to recognize intruders enabled scientists to decipher how two parasites
(a beetle and a wasp) are able to infiltrate aggressive colonies. Pioneering
work revealed how fire ants locate food and recruit other workers to
the source with pheromone trails.
An ARS-funded areawide project began in March 2001 to demonstrate how
to keep fire ant populations at very low levels by combining strategic
pesticide applications with phorid flies and T. solenopsae. Diverse
demonstration sitesas large as 300 acresin five states were
chosen for the project to represent the fire ant's infestation range,
according to Williams. ARS is coordinating the major activities of four
land-grant universities and other organizations associated with the
project for 4 to 5 years.By Jim
Core, Agricultural Research Service Information Staff.
This research is part of Arthopod Pests of Animals and Humans, an
ARS National Program (#104) described on the World Wide Web at http://www.nps.ars.usda.gov.
is with the USDA-ARS Imported
Fire Ant and Household Insects Research Unit, CMAVE, 1700 S.W. 23rd
Drive, Gainesville, FL 32608-0000; phone (352) 374-5903, fax (352) 374-5818.
"Update: Hot on the Trail of Fire Ants" was published
in the February
2003 issue of Agricultural Research magazine.