Biological Control of Citrus Pests
Worldwide, efforts to develop ecologically based approaches to arthropod, pathogen, and weed control for citrus production are producing diverse, effective, and economical alternatives to frequent, heavy applications of pesticides. Some of the methods noted below are well established, some are being rediscovered, and others are still in developmental stages.
Biological Control of Arthropods
Augmentation of Existing Control Organisms
In California, the California red scale (Aonidiella aurantii), one of the primary citrus pests, is now controlled by augmenting populations of Aphytis lingnanensis—a parasitoid of the red scale. Normally A. lingnanensis is more abundant in the summer, whereas adult female red scales accumulate in the spring. The control method is to release the parasitoid, commercially raised in grower-owned cooperatives, in the spring when the adult female red scale appears. The parasitoid is active against the female red scale before it can reproduce, thus eliminating the need for multiple applications of broad-spectrum scalicides (Graebner et al., 1984).
Commercially produced microbial pesticides that have been investigated for use in the citrus system include the fungus Hirsutella thompsonii, which is active against the citrus rust mite Phyllocoptruta oleivora, the most important citrus pest worldwide. Although problems with formulation of this product (Mycar®) limited the availability of this fungus in the 1980s, researchers continue to seek methods to solve these difficulties (McCoy and Couch, 1982). A commercial product currently in use for biological control of root weevils in Florida citrus is the entomophagous nematode Steinernema riobravis. This beneficial, soil-inhabiting nematode is cosmopolitan in distribution, but occurs naturally in soils at low levels, insufficient for effective management of the weevil larvae and pupae. Commercial fermentation culture has led to the marketing of a product (Biovector®) that is applied to the soil beneath citrus trees. The degree of success with this biological-control product remains to be determined, as the product has been in use for only 3 years (McCoy and Duncan, 1995). An acaricide (miticide) recently registered for use in citrus, Avermectin®, interferes with molting and transformation of mites from nymphs to adults. This growth regulator is an example of biologically based products that can be employed in pest management (Knapp, 1995).
Conservation of Existing Control Organisms
The importance of already existing natural processes of control is illustrated by the example of the bayberry whitefly, Parabemisia myricae, an introduced pest from Japan that became established in California citrus groves. Parasitoids of the whitefly were found in Japan, and several species were introduced into California, but without successful control. However, in 1982 populations of the whitefly declined