In Search of Natural
Since its first detection in the Carribbean in 1994, the mealybug has
rapidly spread throughout the islands. It is now established there, as well as
in Belize, Costa Rica, Guatemala, and Mexico. Miller believes the scale is a
native of Mexico or Central America.
Because the species has been discovered recently in the United States and
because authorities on several Caribbean islands have asked for assistance in
controlling this pest, APHIS biological control specialist Dale E. Meyerdirk
has begun to investigate the possibility of finding natural enemies to serve as
biological control agents. Last June, APHIS sent Miller to Mexico, where he
spent 10 grueling days traveling nearly 3,000 miles in search of parasites.
"Actual collecting began on June 2 on the east coast near Veracruz and
ended on June 10 on the west coast near Colima and Uruapan," he says.
"We had little difficulty finding populations of the mealybug."
Miller and Mexican colleagues entomologist Juan Antonio Villaneuva (Colegio
de Postgraduados, Veracruz) and entomologist Héctor González
(Colegio de Postgraduados, Texcoco) collected 40 samples of parasites. They
included three wasps with potential as biocontrol agents.
Miller also asked his ARS colleague and parasitic wasp expert, entomologist
Michael E. Schauff at the SEL in Washington, D.C., to identify and classify the
wasps and other potential parasites in the 40 samples. Schauff, along with many
other ARS insect experts, works at the U.S. National Museum of Natural History,
where the national collection of insects is housed. He, in turn, requested the
help of the world expert on these parasites, British entomologist John S. Noyes
at the Natural History Museum in London, England.
Schauff identified the three wasps as:
- A tiny, 1/32nd-inch-long yellow wasp in the genus Acerophagus, which
attacks very young mealybug nymphs and lays one egg in each. It was the most
common parasite found in the 40 samples.
- A 1/8th-inch-long yellow and brown wasp with black markings on its antenna,
in the genus Anagyrus. It attacks larger nymphs and adult mealybugs,
laying one egg in each nymph. Members of this genus are known to be effective
- A 1/16th-inch-long black wasp in the genus Apoanagyrus. It attacks
large nymphs after 3 to 5 days.
"All three are from the same family," says Schauff. "Some may
be new to science. But all three cause the mealybug to mummify and blow up like
a cigar, killing it. And they all may play a role in controlling the papaya
Other Natural Deterrents
"Besides wasps, we observed a diversity of natural enemies that
included lady beetles, hover flies, and lacewings," Miller says. "In
several instances, the lady beetles and lacewings apparently had a significant
impact on mealybug populationsespecially when populations were high.
However, we decided to concentrate our efforts on the wasps.
"We collected as many mummiesparasitized mealybugs that had
turned brownas possible, since we knew that they contained wasps. We were
encouraged by the potential of these wasps as biological control agents,"
says Miller, "since they were present even when the density of the
mealybugs was low."
Several months before his trip started, Miller contacted ARS entomologist
Lawrence R. Ertle in the ARS Beneficial Insects Research Unit at Newark,
Delaware. Ertle is one of three entomologists there who conduct laboratory and
field tests on parasites and predators of problem insects. The scientists
import beneficial insects into the United States with a view toward
establishing them in areas where insect pests are abundant.
Once he had collected parasites and potential biological control agents of
the papaya mealybug, Miller sent live samples by overnight mail to Ertle at the
Newark quarantine facility, where the parasites could be reared.
In preparation for receiving the parasites from Mexico, Ertle established a
colony of papaya mealybugs on potato sprouts. "We've been mass-rearing
mealybugs for several months in anticipation of screening any potential
biocontrol agents that Miller might find," he says.
"The collected cultures arrived safely," says Ertle, who has
observed several different parasites emerging from the Mexican material.
"The small, yellow wasps are fairly abundant. We've seen them parasitize
the smaller, immature stages of the mealybug and probe the adults."
Now, Ertle is screening and studying the life cycle of these potential
parasites in living cultures. He is awaiting APHIS' approval to ship
populations of the wasps to St. Thomas, in the U.S. Virgin Islands, where they
will be released by APHIS in papaya fields for monitoring and studying their
Miller says that Ertle "also found six hyperparasitesparasites of
parasitesall small wasps that Schauff will eventually identify. These
parasites feed on beneficial wasps and interfere with effective biological
control. The hyperparasites must be eliminated from the cultures kept by Ertle
before they are sent to St. Thomas." Ertle says he will have more
information on all these biocontrol agents soon.
For the present, Florida state officials are encouraging residents to fight
infestations with a ladybug nicknamed the "mealybug destroyer."
However, Miller says that, based on past experience, the best control will
likely be to introduce wasps as natural parasites of the pest.
"If parasites cannot be located to effectively control this scale pest,
then it might be worthwhile to investigate insect predators of the
mealybug," says Miller. "In many instances, these predators were
quite common and appeared to have a significant impact on mealybug
Becker, Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at
Douglass R. Miller and
Michael E. Schauff are at the
USDA-ARS Systematic Entomology
Laboratory, 10300 Baltimore Blvd., Bldg. 005, Room 133, Beltsville, MD
20705; phone (301) 504-5895/5182, fax (301) 504-6482.