What was once the most popular hedge plant in Los Angeles is making a comeback – thanks to a minuscule wasp and Mickey Mouse.
Syzygium paniculatum, commonly known as Australian brush cherry or eugenia, forms a hedge that can grow to well over 10 feet tall. Its leaves are soft, diamond shaped, and 1 to 2 inches long; the color of young foliage is somewhere between red and bronze. Eugenia possesses an elegance lacking in other plants such as boxwood, photinia, pittosporum, oleander and Indian laurel fig, which also are used as hedges.
During the last decade or so, leaves of eugenias all over town have been puckered and pitted by diminutive locustlike insects known as psyllids. The only treatment successful at thwarting the eugenia psyllid has been application of highly toxic insecticides at short, regular intervals and, even then, control has not been complete.
If you visited Disneyland several years ago, you might have wondered what was wrong with those thousands of feet of sickly looking eugenia hedges, especially in the parking lot. You happen to have been looking at the sad result of the largest infestation of eugenia psyllids in the history of plants.
Not willing to abandon his beloved eugenia to the ravages of an insect pest, Mickey Mouse was determined to take whatever steps were necessary to stop the blight. Soon enough, Disney Imagineering became the financial backer of research conducted by the University of California for the purpose of controlling eugenia psyllid.
Australia is the country that the eugenia plant calls home. Although psyllids are found there, they cause no damage to eugenias due to the presence, in Australia, of the psyllid’s natural enemies. One of these enemies is a parastic wasp called Tamarixia.
In 1992, Tamarixia wasps were trapped in Australia and sent to California. Later that year, these wasps were released in Disneyland, where they became fruitful and multiplied exceedingly, living off the fat of the land in the form of eugenia psyllids.
This spring, only three years after the initial release of Tamarixia, new growth on eugenia hedges throughout Southern California is looking healthy again.
Parasitic wasps are the most important group of beneficial insects. Although related to yellow jackets and hornets, they are harmless to humans. Most are barely visible, often no larger than the size of a pencil tip, though some reach a length of 1-1/2 inches. They typically make up 10 percent or more of all the insects in a given area. Were it not for parasitic wasps, insect pests would destroy our gardens, orchards, fields and farms. These wasps parasitize every kind of insect pest, including aphids, ants, white flies, scales, mealy bugs, thrips and larvae (caterpillars and grubs) of all kinds. Worldwide, there are more than a quarter million species of parasitic wasps.
This is not the first time parasitic wasps have been imported to combat a pest problem in Southern California. Several years ago, the ash white fly was a major problem in our area until its natural predators – parastic wasps from Israel and Italy – were imported and released in Los Angeles County. Within a year, the ash white fly was less visible and, today, it seems to have disappeared altogether.