Biological Control of Pink Hibiscus Mealybugs
USDA Sentinel Survey inspectors collected samples from infected hibiscus plants at four residences in St. Petersburg’s Greater Pinellas Point, Fla. The samples were shipped to the division of plant industry headquarters in Gainesville, where they were tested and confirmed as by an entomologist as pink hibiscus mealybug. This is the first confirmed report of PHM on the west coast of Florida.
What is PHM?
According to the Florida Department of Agriculture and Consumer Services (DOACS), PHM is a tiny (3 mm) sap-sucking insect that attacks fruit trees, vegetables and ornamental plants and occurs in most tropical areas of the world. The insect has a life cycle of 24–30 days, and there could be as many as 15 generations each year. PHM can kill more than 200 plant species, including ornamentals such as chrysanthemums, roses, ginger lily, oleander, palm and hibiscus; food-producing plants such as tomatoes, cucumbers, lettuce, asparagus, cabbage and peppers; and fruit-bearing trees such as oranges, mangos and papayas.
The insect forms colonies on the host plant, which grows into large cotton-like masses of white, waxy deposits on branches and leaves. As it feeds, it pierces into the soft tissues of the plant, injecting a toxic substance that results in malformed leaf and shoot growth (commonly called “bunchy top”), stunting and possibly death. When fruits are infested, they are covered entirely in the white, waxy coating of the pest. The fruit will either drop off or remain in a dried and shriveled condition. If flower blossoms are attacked, the fruit will set poorly.
In the egg and crawler stages, PHM is most easily spread by wind. The wax, which sticks to each egg, can also be transported by ants and other small insects, by a person’s clothing or by an animal’s fur. It can be identified from other mealybug insects by its reddish-brown, smooth body and pink-to-red body fluid. In cooler climates, the pest overwinters on the host plant, either in the egg stage or as an adult. In warmer climates, the insect may stay alive and reproduce year round.
Geography of PHM
According to the USDA, PHM is a serious pest of many plants in tropical and subtropical regions, including Africa, southeast Asia, and northern Australia. The insect arrived in Egypt from India in 1912 and in Hawaii in 1984. It was found in Grenada, Trinidad and St. Kitts in 1994, and it has spread to other islands in the Caribbean, where it attacks many hosts of economic importance.
In Florida, it was first discovered on the east coast in Broward County in June of 2002, and then in Dade County later that year. Lance Osborne, entomologist at University of Florida’s Institute of Food and Agricultural Services (UF/IFAS) recently reported that the pink hibiscus mealybug has been found in Clearwater, Fla. This is the second area in Pinellas County that the mealybugs have been spotted. Although it has not been detected in central Florida, Osborne warns that it may already be in central areas. The popularity of hibiscus growing on the coast has allowed PHM to be easily detected.
Biological control is considered the most effective long-term solution to the mealybug infestation. According to the USDA, the parasites are self perpetuating, persist even when the mealybug is at low population densities, and they continue to attack the mealybug, keeping populations below economic-injury levels.
Anagyrus kamali is a parasite from China provided by the International Institute of Biological Control. It has already been released in the Caribbean to control the PHM. After five months, the USDA found an 80 to 90 percent reduction in population density of the PHM at release sites.
This small, parasitic wasp is the most important natural enemy currently used to manage PHM. It attacks the mealybugs in two ways. The adult wasp will puncture a mealybug, extracting fluid from the wound. The female wasp will feed on the fluid of the dying mealybug, which acts as a nutrient to help mature the wasp’s eggs.
The female wasp can also kill the mealybug by laying an egg inside of it. The egg will hatch inside the mealybug and the larva will feed internally, killing the mealybug. When the fully developed adult wasp comes out of what is now called the “mummy” of the mealybug, it cuts a circular hole in the end of the mummy and crawls out. The process can take place in half the time it takes for the entire life cycle of the mealybug. According to the USDA-APHIS, “The beetle will feed on parasitized mealybugs and significantly reduce the parasites’ population density if released at the same time and place.”
A. kamali typically has a 15-day life cycle in tropical climates. During its lifetime, the female wasp can lay a single egg inside 40-60 mealybugs.
Cryptolaemus montrouzieri, commonly called the redheaded ladybird beetle or the mealybug destroyer, is a black lady beetle imported into the United States in 1891 from Australia to control citrus mealybug in California. It is considered a predator of citrus and long-tailed mealybug in greenhouses and interior plantscapes and has already been introduced in a biocontrol program in the West Indies to control PHM.
The adult female beetle lays an egg among the cottony egg sack of an adult female mealybug. The larvae of the beetle grow up to 1.3 cm in length and have wooly appendages of wax, which makes them superficially resemble the mealybug. The larvae feed on mealybug eggs and young crawlers.
The lifespan of the Cryptolaemus montrouzieri is two months. During this time, the mealybug destroyer can lay up too 400 eggs. It is capable of eating 3,000-5,000 mealybugs in various life stages.
According to University of Georgia’s department of entomology, The mealybug destroyer is considered a short-term solution to the mealybug pest infestation and can be used if rapid control of a large mealybug population is necessary within a 6- to 8-week period.
More information about PHM is available at www.doacs.state.fl.us/pi/enpp/ento/pink.htm and http://aphisweb.aphis.usda.gov/oa/pubs/phmpaler.pdf.