By Jawwad A. Qureshi
Natural enemies are the beneficial organisms that control insect and mite pests. Citrus trees produce most of their young shoots (flush) for the year in spring and will continue to produce more in summer and fall.
Arthropod activity has already started in citrus groves. For example, overwintering Asian citrus psyllid (ACP) adults have started reproducing. Other pests such as citrus leafminer (CLM), aphids, mites, scales, thrips and weevils also colonize citrus during the growing season.
Flushing groves attract natural enemies, so several are already actively suppressing pests. There are more species of natural enemies in the groves than pests that colonize citrus. The decades-long role of natural enemies in managing citrus pests in Florida is critical to the development of integrated and sustainable pest management.
PREDATORS
Predators are the organisms that hunt, kill and consume their prey. Predatory insects, spiders and mites significantly suppress citrus pests. As generalists, they can consume a wide range of pest species. They may feed on any or all stages of a pest and complete their life cycle on a single prey type.
Predatory groups — such as lacewings, spiders, syrphid flies, mites, assassin bugs, etc. — also colonize citrus groves and consume psyllids, aphids, leafminers, mites, scales and other pests. In recent years, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers have observed three species of lacewings and 29 species of phytoseiid mites in Florida citrus groves, most of which have predatory potential against multiple pests. Five species of phytoseiid mites were also observed in citrus under protective screen (CUPS).
PARASITOIDS
Parasitoids are tiny wasps that attack different life stages of a pest (egg, nymph or larvae). Most parasitoids are specialists against specific pests. Several pests of citrus — such as ACP, CLM, scales, mealybugs, whiteflies, root weevils, etc. — are attacked by parasitoids, which are indigenous to Florida or introduced from other regions of the world and established.
For example, the Tamarixia radiata parasitoid of ACP, introduced from Asia, is now well established in Florida and is being augmented through mass-rearing facilities. Researchers have observed 30% to 40% or more parasitism of ACP nymphs by this parasitoid. Feral populations of several parasitoids suppressing CLM, mealybugs and scales have also been observed in recent years, including in CUPS, suggesting their significant role in pest suppression.
ENTOMOPATHOGENIC FUNGI
Entomopathogenic fungi also regulate multiple pests of citrus. Hirsutella citriformis, which commonly attacks ACP, is not available commercially. Recently, a lower incidence of Hirsutella-infected ACP has been observed in citrus groves than a decade ago, possibly due to the heavy use of insecticides against ACP in previous years. Commercially available Beauveria bassiana and Cordyceps fumosorosea effectively suppress mealybugs and ACP.
CRITICAL FACTORS
The contributions of natural enemies, along with other factors, largely depend on the use of insecticides, which negatively impacts them. Therefore, the selection of products and the timing of application are critical.
Jawwad A. Qureshi is an associate professor at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
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