The broad mite, Polyphagotarsonemus latus, poses a challenge to agriculture globally, affecting a diverse range of plants. This microscopic pest is a widespread concern, especially within greenhouse environments where conditions often favor its rapid reproduction and spread.
Understanding the Broad Mite
Polyphagotarsonemus latus is also known as the broad mite, tropical mite, or white mite. These mites are exceptionally small, with adult females measuring approximately 0.2 to 0.3 millimeters in length, while males are about half that size. Their bodies are broadly oval and appear translucent, with a pale yellow or yellow-green hue. Females often exhibit a distinctive white stripe along their backs. They possess four pairs of legs.
This mite is polyphagous, feeding on over 60 plant families worldwide. Important agricultural crops include cotton, soybeans, peppers, strawberries, tomatoes, cucumbers, and eggplants. In tropical and subtropical climates, broad mites can reproduce year-round. In temperate regions, they are a serious pest in greenhouses, quickly reaching damaging population densities due to their high reproductive potential.
Signs of Infestation
Broad mite infestations often manifest through distinct visual symptoms on affected plants. Young, developing plant tissues, such as growing tips, new leaves, and flower buds, are particularly susceptible. Common indicators include stunting and twisting of leaves and flowers, which can also appear blackened. Affected leaves may become thickened, hardened, and brittle, sometimes exhibiting a bronze or rust discoloration, often starting from the undersides.
Damage from broad mites can easily be mistaken for other plant problems, such as viral diseases, micronutrient deficiencies, or auxin herbicide injury. Symptoms like leaf and fruit distortions, shortened internodes, blistering, shriveling, and leaf discoloration mimic these other issues. Severely infested plants may show dark brown edges at the base of young leaves or brown, collapsed spots. Fruit can also be deformed, split, or russeted, reducing its market value.
Life Cycle and Propagation
The broad mite has a rapid life cycle, progressing through egg, larval, quiescent (nymphal), and adult stages. Under favorable conditions, development from egg to adult can be completed in as little as 3 to 5 days. Females typically lay their elongated, oval eggs singly on the underside of young apical leaves or on fruit surfaces. These eggs are transparent with distinct white, circular projections, giving them a speckled or “jeweled” appearance under magnification.
Eggs usually hatch within two to three days. After another two to three days, the larvae transform into a quiescent nymphal stage. Male mites emerge from this quiescent stage slightly earlier than females and often pick up quiescent female nymphs, carrying them to new, younger plant tissues. This behavior aids in the dispersal of broad mite populations.
Once the female emerges, mating typically occurs immediately. An unmated female produces only male offspring. A mated female typically lays about four female eggs for every male egg, averaging 40 to 50 eggs over her lifespan of approximately 8 to 13 days. Optimal conditions for reproduction include temperatures around 25°C (77°F) and humid environments.
Effective Management Approaches
Managing Polyphagotarsonemus latus infestations requires a multifaceted approach due to their small size, rapid reproduction, and ability to cause damage at low densities. Removing and destroying visibly infested plants is an immediate step. Early detection is challenging, as plant injury often serves as the first indication, requiring careful examination of symptomatic plants, especially new growth, under magnification.
Chemical control can be effective. Abamectin has shown efficacy against broad mites, with other options including spiromesifen, azadirachtin, and neem oil. Foliar sprays targeting new plant growth are often recommended. Some chemicals, such as dinitrophenol compounds and synthetic pyrethroids, may not be as effective.
Biological control utilizes natural enemies of the broad mite. Predatory mites, such as Amblyseius swirskii, Neoseiulus barkeri, Neoseius californicus, and Amblyseius herbicolus, suppress broad mite populations. Releasing these predatory mites, for instance, at rates of 5 to 10 adults per plant, can reduce broad mite numbers within a week to several weeks.
Plant resistance also presents a long-term management strategy. Research indicates potential for resistance in certain plant cultivars. Some chilli and sweet pepper (Capsicum sp.) cultivars have demonstrated tolerance or resistance to P. latus infestations. Screening germplasm for these resistant traits can inform breeding programs for new crop varieties.