The news of the invasion of Grand Cayman by the Pink Hibiscus Mealybug came as no real surprise. Despite every precaution, we seem unable to prevent pests from entering our islands - whether they be a plant-destroying insect or weapons for a gun-toting drug dealer.

What to do? Well, I'll leave the RCIP to try and deal with the weapons and the bad guys, and concentrate on the insects.

The Department of Agriculture has already imported thousands of predators in the form of ladybugs from Florida and has on order thousands of parasitic wasps. Between them, we're told, these two predatory species should destroy most of the Pink Hibiscus Mealybugs (PMH).

So what exactly is the PMH and how exactly does predator control work?

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 to 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 grow 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," says the DOACS. When fruits are infested, they are covered entirely in the white, waxy coating of the pest. The fruit will either drop off or remain on the tree in a dried and shrivelled 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 warmer climates like Cayman the insect reproduces year round.

Biological control

That's the pest. Now, how do the biological controls work? According to a recent article in Greenhouse Products News, the use of parasites which live on the mealybug is considered the most effective long-term solution to PMH infestation, far more so than the use of insecticides. According to the US Department of Agriculture (USDA) the parasites are "self perpetuating, persist even when the mealybug is at low population densities, and 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," according to the Greenhouse Products News.

"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, "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 to 60 mealybugs.

The ladybug beetle

"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 the citrus and long-tailed mealybug in greenhouses and interior plantscapes and has already been introduced in PMH biocontrol programmes to other islands in the Caribbean."

The adult female beetle lays an egg among the cottony egg sac of an adult female mealybug. The larvae of the beetle grow up to 1.3 cm in length and have woolly 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 to 400 eggs. It is capable of eating 3,000 to 5,000 mealybugs in various life stages," says the USDA.

According to the University of Georgia's Department of Entomology, the ladybug is considered a short-term solution to the mealybug infestation and can be used as it has in Cayman if rapid control of a large PMH population is necessary within a period of six to eight weeks.

All extremely interesting, but I begin to worry when we talk about bringing in one species to control another. Human beings have not had a very good track record in this regard.

Take the mongoose, for example. A carnivorous mammal that is native to South Asia and Africa, it was introduced in the Eastern Caribbean islands to control rat populations during plantation days. Of course, it was we humans (the exploring Europeans) who were responsible for bringing the rats in the first place! This controlling measure did not succeed because the mongoose hunts during the day and rats come out at night. Duh!

The mongoose's introduction to the islands was disastrous for the local bird and snake populations because it eats birds and their eggs, not to mention other mammals.

The cane toad in Australia has become the poster child for notorious failures in biological control that have turned into an ecological nightmare. It has also led to much public concern and caution about the introduction of new biological controls in that country.

Another example of a poorly researched introduced biological control is the sap-sucking lantana bug (Aconophora compressa) from South America, which was introduced into Australia in the 1995 to eat the lantana brought in by settlers. Unfortunately, the lantana bug also attacks other trees, including fiddlewood trees, which has caused serious problems for gardeners. Aconophora compressa was the 28th insect introduced into Australia to control lantana over a period about 80 years. None of them has been completely successful!

A Web search brings up many other examples of failed Australian attempts to control introduced species using more introduced species. The principle casualty has been the unique wildlife of that country, including such endangered species as the Tasmanian Devil and the Spotted Quoll.

An interesting paper by Daniel Simberloff and Peter Stiling, biologists at Florida State University and University of South Florida respectively, titled Risk of Species Introduced for Biological Control, questions the received wisdom that it's okay to bring in insects like the ladybug and parasitic wasp to control pests like the Pink Hibiscus Mealybug. The paper, which can be read in its entirety at
http://www.giriathrey.com/GSS/SimberloffStiling_1996.pdf, points out that we cannot predict the subsequent ripple effects of introduced biological controls on other populations, species, communities and ecosystems.

Do we really know for sure that the wasps and ladybugs we are bringing in to Cayman will die out along with the PMH? No, we don't. And if our track record in other countries is looked at closely, it's not very good. As on old teacher of mine used to say, "It's a choice between the devil and the deep blue sea."

Thank you for your e-mails. I would encourage everyone who feels strongly enough to contact the Hornet to send their opinions to the local news media as well. If you wish to contact the Green Hornet directly, you can e-mail me at: caymanhornet@yahoo.com. All messages will be treated confidentially.