Whiteflies are tiny, moth-like insects that pose a significant challenge to gardeners and agricultural producers globally. These sap-sucking pests, belonging to the order Hemiptera, weaken plants by extracting phloem and excrete a sticky substance known as honeydew, which encourages the growth of black sooty mold.
The widespread use of chemical insecticides has led to whitefly resistance and environmental concerns, prompting a shift toward biological control methods. This approach involves using the whitefly’s natural enemies—its predators, parasites, and pathogens—to regulate its population, offering a more sustainable and long-term solution.
Generalist Insect Predators
Generalist insect predators actively hunt and consume whiteflies across various life stages, but they also feed on a wide range of other small pests. Their broad diet makes them a constant presence in a garden ecosystem, providing consistent pest management.
The larvae of Green Lacewings are particularly effective, often called “aphid lions,” and readily consume whitefly eggs and nymphs with their piercing mouthparts. Minute Pirate Bugs (Orius) are tiny, yet formidable, hunters that pierce and drain the fluids from whitefly nymphs and adults.
These bugs are often sustained by feeding on pollen when pest populations are low, helping them remain present when whiteflies arrive. Lady beetle species, including their larvae, also feed on whitefly eggs and nymphs. While most lady beetles are generalists, the Delphastus catalinae beetle specializes in whiteflies and can consume hundreds of eggs daily.
Specialized Parasitoid Wasps
Parasitoid wasps are specialized biological control agents that focus primarily on the immobile nymph stage. The female wasp locates a suitable whitefly nymph and uses her ovipositor to lay a single egg inside or directly beneath the host’s body. The developing wasp larva then consumes the whitefly internally, killing it before it can mature into an adult.
The tiny Encarsia formosa wasp is widely utilized, particularly in greenhouse settings, and is most effective against the greenhouse whitefly (Trialeurodes vaporariorum). When successfully parasitized, the whitefly nymph turns black, creating a visible “mummy” from which a new adult wasp will eventually emerge by chewing a small, circular exit hole.
Another commercially available species is Eretmocerus eremicus, which is favored for controlling the sweet potato whitefly (Bemisia tabaci) and is more tolerant of warmer temperatures. Eretmocerus females also engage in “host feeding,” where they sting and consume the body fluids of whitefly nymphs to gain protein for egg development.
Microbial and Fungal Control Agents
Microbial control agents are fungi that act as insect pathogens, providing an alternative to insect predators and parasites. These agents are typically applied to plants as a spray, similar to a chemical pesticide, but their mode of action is entirely biological. Two prominent examples are the entomopathogenic fungi Beauveria bassiana and Isaria fumosorosea.
For these fungi to be effective, their spores must attach to the whitefly’s outer layer, or cuticle, and then germinate. Once a germ tube is produced, it penetrates the whitefly’s body, and the fungus grows internally, leading to the insect’s death.
Successful fungal infection requires a period of high relative humidity, which is necessary for the spores to germinate. These fungal applications are useful in controlling dense whitefly populations across both nymph and adult stages.
Supporting and Releasing Natural Enemies
Successfully using natural enemies requires a proactive approach that combines the strategic introduction of beneficial organisms with cultural practices that sustain them. Predators and parasitoids can be purchased from commercial suppliers and should be released early in the season, ideally before a whitefly population explodes.
The correct timing and density of release are determined by monitoring the pest population, often using yellow sticky traps to count the number of adult whiteflies present. To encourage natural enemies to stay and reproduce, gardeners should avoid the use of broad-spectrum pesticides, which kill beneficial insects alongside the pests.
Planting diverse flowering species, known as farmscaping, provides necessary pollen and nectar for adult predators and parasitoids, which helps maintain their population even when whitefly numbers are low. Maintaining appropriate environmental conditions, such as temperature and humidity, is also important, as the efficacy of both insects and fungal agents is dependent on these factors. For example, Encarsia formosa performs optimally in a temperature range of 68 to 77 degrees Fahrenheit.