The pink hibiscus mealybug (PHM) is a native of Southeast Asia. But wherever
it goes, it can inflict serious damage to ornamental plantsnotably hibiscusand
important crops such as bean, beet, cabbage, citrus, corn, cotton, cucumber,
grape, lettuce, peach, pear, pepper, pumpkin, okra, squash, and tomato.
Oval, pink, wingless adult PHM females are just 1-3 mm in length. But when
they feed, their saliva leads to malformation of fruit, leaves, and shoots,
stunting the plant and eventually killing it. Crop losses in the United States
could reach $750 million per year if ways to control the pest are not found.
Fortunately, ARS scientists in Fort Pierce,
Florida, and Beltsville, Maryland, have made key advances that will help win
the battle against PHM.
This species of mealybug, Maconellicoccus hirsutus, has spread throughout
the Caribbean region since first being detected on the island of Grenada in
1994. It later spread to Mexico, Central America, and in 2002, Florida. USDA's
Animal and Plant Health Inspection Service (APHIS) and the Florida Department
of Agriculture and Consumer Services responded together to the Florida infestation
by releasing two effective parasites (Anagyrus kamali and Gyranusoidea
indica) and a predatory ladybug (Cryptolaemus montrouzieri) to control
the mealybug, which has resulted in over 98 percent reduction in PHM population
density. Despite these efforts, plants from an infested ornamental nursery in
Florida were shipped last year to 36 other U.S. statesand PHM may have
been hiding in some of these shipments and may become established in these states.
APHIS is therefore expanding production of PHM natural enemies in preparation
for release in other states.
Scientists in ARS's Subtropical Insects Research Unit, headed by David Hall
at the U.S. Horticultural Research Laboratory in Fort Pierce, have been key
in PHM research. Their efforts began long before the pest came into Florida.
Working in St. Croix, U.S. Virgin Islands, ARS scientist Stephen Lapointe discovered
that female PHM emitted a powerful pheromone that attracted males. This ultimately
led to creation of a synthetic equivalent, or analog. (See "Sex
Potion Ensnares Mealybugs" in this issue.) To assist with the development
of this chemical, Lapointe used a hormone analog to eliminate male PHM from
a colony, leaving only females for pheromone analyses.
Lapointe also developed a simple diet for rearing the mealybug. While those
raised on the diet were not as fit as ones reared on some plants, the research
showed that PHM could easily be reared on an artificial diet.
For release of biocontrol insects like A. kamali and C. montrouzieri,
they must be available in sufficient supply. Since it's very time consuming
and inefficient to catch them in the wild, scientists rear the biocontrol agents
in captivity on their host insect. But successful mass-rearing of insects like
PHM requires an environment and a diet conducive to their successful development
Faced with an expanding infestation range and the need to increase production
of the mealybug's natural enemies, APHIS requested help from ARS in developing
an artificial diet for the bugs. Lapointe's earlier work on this problem would
therefore pay off.
Lapointe is developing a new artificial diet that should, in time, eliminate
costly greenhouse rearing of PHM. He began by feeding the mealybugs an assortment
of crops in test greenhouses and verified that a particular variety of Japanese
pumpkin was their favorite.
"We were able to successfully rear generations of PHM, and more importantly,
we achieved complete development of parasitoids on mealybugs reared on the artificial
diet based on canned pumpkin and sugar," says Lapointe.
The diet requires further refinement to produce quality mealybugs in the large
numbers required. The goal is to formulate an inexpensive diet based on readily
available materials and supplemented with nutrients required for complete mealybug
development and successful production of parasitic wasps.
Developing insect diets is laborious because of the many nutrients that must
be tested to determine the quantities required for normal and complete development.
"It would be prohibitively expensive and time consuming to test each diet
component individually," says Lapointe. So he and ARS plant physiologist
Terence Evens are applying a sophisticated statistical approach to the problem
of solving multiple equations simultaneously. The approach, called Response
Surface Methodology, has only recently become feasible for such applications
because of the tremendous increase in computing power now widely available.
Lapointe and Evens hope to show how this method can be applied to development
of insect diets in general and to the particular problem of designing an effective
diet for PHM.
By raising healthy, well-fed mealybugs, researchers will be best able to produce
the quantities of A. kamali wasps and C. montrouzieri ladybugs
needed for successful PHM-control programs.
"Our studies have shown that the quality of the parasitoids and predators
we raise is directly related to the quality of the mealybug host they're grown
on," says Lapointe. Once the new formulation is perfected, this artificial
diet will, ideally, produce a new generation of adult mealybugs every 21 days.
"APHIS came to us with their research needs," says Hall, "and
we've responded with some great results so far. We're excited that we're able
to work hand-in-hand in this effort to get rid of this invasive and troublesome
Flores, 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.
"Mealybugs May Have Met Their Match: Insect predators and parasites home in on this growing menace" was published in the April 2005 issue of Agricultural Research magazine.