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July 12, 2000

Biological Control Working Against Destructive Citrus Blackfly

Honolulu - The Hawaii Department of Agriculture (HDOA) has enlisted an army of two types of tiny wasps in a biological war against the citrus blackfly. So far, it looks like the biological control agents are winning. The battle is crucial, as the citrus blackfly is considered to be the most injurious insect affecting citrus trees and can rapidly cause a tree to stop bearing fruit.

The citrus blackfly, Aleurocanthus woglumi Ashby, is actually a type of whitefly and gets its name from the dark-colored adults, which measure about 1/16th inch. The adults can fly, but the juveniles appear as tiny black scales attached to the undersides of the leaves. Whiteflies injure plants by sucking out the sap and nutrients. Feeding by large numbers of adult and juvenile whiteflies weaken trees and may dramatically reduce or prevent fruiting.

The citrus blackfly was first found on Oahu in July 1996, and a month later on Maui and the Big Island. The first identification of the pest on Kauai, was reported a few months ago by a University of Hawaii county agent. In Hawaii, heavy infestations of this whitefly have been observed on the leaves of various citrus trees, such as pummelo (jabon), lemon, lime, orange and tangerine.

Soon after its discovery in Hawaii, the HDOA's Biological Control Program began surveying the state for pest infestations and plans began for exploration to search for biological control agents to attack this menacing whitefly. Several possible biological control agents were identified and two tiny parasitic wasp species were found and collected from Guatemala by the HDOA's exploratory entomologist. The tiny wasps were sent back to the department's quarantine facility, where they were screened to insure they were free of other pests.

After extensive research, the Biological Control Section received approval to release from quarantine, the two parasitic wasps, Amitus hesperidum and Encarsia opulenta. Release of the parasitic wasps began on Oahu in April 1999 and current surveys reveal that these wasps are effectively controlling this whitefly pest. After the discovery of the new infestation on Kauai, the HDOA immediately sent the parasitic wasps to be released on that island. Parasitic wasps are also being collected on Oahu to send to Maui where citrus blackfly infestations are well-established. Based on results on Oahu, HDOA entomologists are confident that this pest will be under control on Kauai and Maui.

These wasps are about the same size as the citrus blackfly and are known to parasitize only the citrus blackfly and will not harm plants or people. The wasps will eventually reduce citrus blackfly infestations, but time and patience is required before complete control takes place. Application of insecticides is not recommended because of the detrimental effect on existing natural enemies.

A native of India, the citrus blackfly also occurs throughout Asia and parts of Africa. In 1913, it spread to Jamaica, then to the West Indies, Mexico, Central America and South America. In the U.S., it has been established in Florida and Texas since the 1970s.

For more information about the citrus blackfly, call HDOA's Bio-Control Section at 973-9524.