Attacking Flies With Wasps
Tachinaephagus zealandicus wasp
(male shown here), a promising
parasitoid for fly control.
Females of this species,
common in the southern
hemisphere, lay eggs inside
House flies and stable flies are not only a nuisance on livestock and
poultry farms, but they also transport disease-causing organisms. Certain
native parasitic wasps are used as biological control agents of fly
populations, reducing use of insecticides while saving farmers time
To give farmers even more options, scientists in the ARS
Mosquito and Fly Research Unit in Gainesville, Florida, have collaborated
with scientists at the University of Campinas in Brazil for about 2
years to evaluate exotic wasp species that may complement the native
species in controlling pest flies.
Currently, farmers can buy native parasitic wasps, such as Muscidifurax raptor, Spalangia endius, and S. cameroni, from commercial insectaries. These wasps emerge into adulthood from the pupal stage, where they develop wings. They fly from the release stations in which they have been held, hung from barn ceilings or other out-of-reach places and away from rodents looking for a savory meal. Female wasps swoop down onto the farm in search of their prey. They are single-minded; they choose only muscoid flies on which to feed and release their progeny.
Muscidifurax raptor wasp
on a fly puparium. Once the
female chooses a suitable
puparium host, she lays a
single egg in it. The egg
hatches, and the wasp
larva feeds on the fly pupa.
The parasitic wasps (also known as parasitoids) target only flies in their pupal stage, in which a layer of skin remaining from the fly's larval stage hardens and forms a protective case known as a puparium. When the wasp finds a pupa in soil or litter, she inserts her stinger and withdraws it, drawing blood and paralyzing the pupa. After she ingests some blood, she might allow the stingerless male to feed. If the sting doesn't eventually kill the pupa, the feeding will. If the female wasp decides the pupa would make a suitable host for her progeny, she inserts one egg into the air space under the puparium. The egg hatches after 1 day, and the larva feeds on body fluids and organs for 2 to 4 weeks. Eventually, the wasp chews its way out of the dead host's puparium and flies away as an adult.
As if farm flies didn't have enough to worry about with these American-bred wasps, a new threat has emerged from south of the border. One such species, Tachinaephagus zealandicus, attacks flies earlier, while they are still in the larval, or maggot, stage. T. zealandicus has a mode of operation different than that of native parasitoids. Not only does the female lay multiple eggs in the maggot, she lays them inside its body cavity. Her eggs hatch after 1 day, but they leave their prey alive as they slowly devour it from the inside out, saving the brain and eyes for last. Their host actually continues to metamorphosealmost into adulthoodbefore it succumbs.
Despite being native to South America, T. zealandicus does not thrive in the hot summer months. ARS entomologist Christopher J. Geden says these wasps do not perform as well when the temperature gets in the mid or upper 90s. But they could be used in cooler months in the South or all summer in northern states.
Unlike their native counterparts, these adult exotic wasps do not derive
energy from feeding off their fly hosts, according to Geden. Whereas
natives must feed to develop their eggs, T. zealandicus wasps
have eggs when they emerge from the fly puparium as adult females. But
they don't have energy remaining for future attacks after they lay the
eggs in a host.
Aggressor Becomes the Victim
Parasitoid wasps are vulnerable themselves to nature's cruel forces
and are sometimes infected with a microsporidium in the genus Nosema.
Infected wasps take longer to develop into adults and then lay far more
male eggs. This is bad news for commercial insectaries, because only
female wasps attack.
The Gainesville and Brazilian researchers also discovered in 1999 a
new Nosema disease infecting T. zealandicus. Geden says
the disease is transmitted from females to their offspring and is spread
among wasp larvae when they share the same fly host.
"A drug test showed us that transmission from mothers to progeny can be interrupted by feeding the mothers honey treated with the antibiotic rifampicin," Geden says. "After treatment, a clean colony was established from family lines of uninfected females. Because they don't crave honeythough they will eat itnative wasps are harder to treat for Nosema disease."
Separated at Birth
Different species of parasitic wasps look so similar that telling them
apart can be difficult. If species get mixed up in rearing factories,
it can damage or ruin a whole program. ARS chemist David A. Carlson,
in the Gainesville unit, applied a method known as gas chromatography
to identify them by chemical analysis of the waxes wasps use to waterproof
themselves. The waxes, known as cuticular hydrocarbons, may also be
used in mate recognition. A hexane solvent removes the wax components
from the exoskeleton, and a tiny sample is vaporized and its properties
analyzed. They found reliable differences on cuticular hydrocarbons
on four closely related species of parasitoids.
T. zealandicus is currently being evaluated for use in muscoid
fly control. The wasp doesn't sting people or livestock. Although it
is under quarantine, Geden says it has made it into the United States
before and does not appear to be any kind of threat if released.
"Ideally, we would like to see T. zealandicus used in natural
biological control," Geden says. "After thorough testing,
we have more work to do to ensure there are no undesirable nontarget
effects, meaning it doesn't attack beneficial insects. If everything
works out, we would seek permission to use this species to control muscoid
Core, Agricultural Research Service Information Staff.
This research is part of Arthropod Pests of Animals and Humans,
an ARS National Program (#104) described on the World Wide Web at http://www.nps.ars.usda.gov.
Geden is in the USDA-ARS Mosquito
and Fly Research Unit, Center for Medical, Agricultural, and Veterinary
Entomology, 1600 S.W. 23rd Drive, Gainesville, FL 32608; (352) 374-5919,
fax (352) 374-5922.
|"Attacking Flies With Wasps" was published in the August 2002 issue of Agricultural Research magazine.|