The **Broad Mite** (*Polyphagotarsonemus latus*) is a microscopic pest of numerous economically important plants, including vegetables, fruits, and ornamental flowers. Unlike spider mites, they do not spin webbing. They are serious agricultural pests, particularly in greenhouses and tropical/subtropical climates, because their feeding injects toxins that cause severe distortion and bronzing of new plant growth, drastically reducing crop yield and quality.
Taxonomy and Classification
Broad Mites belong to the family Tarsonemidae (thread-footed mites) in the class Arachnida, subclass Acari (mites). They are part of the genus *Polyphagotarsonemus*, reflecting their wide host range. They are not insects but arachnids, characterized by their four pairs of legs. Their biology is unique in that the female’s last pair of legs are clawless, and the male uses his hind legs to carry the female pupa.
Physical Description
Broad Mites are among the smallest plant-feeding pests, measuring only 0.1–0.3 millimeters in length. They are translucent or pale yellowish-green and oval-shaped, making them nearly invisible to the naked eye; a magnifying lens is required for positive identification. Because they are so small, they are often confused with dust particles.
The eggs are highly distinctive: elliptical and colorless, covered with white, raised, circular tubercles (dots), giving them a diamond-dusted appearance. The damage they cause (plant distortion) is often the first and most obvious sign of infestation, not the mites themselves.
Distribution and Habitat
Broad Mites are cosmopolitan, but they thrive in warm, high-humidity environments, making them particularly problematic in greenhouses and tropical farming regions. They infest the most tender, actively growing parts of the plant: the terminal buds, new leaves, flowers, and developing fruit. This preference is due to their feeding style, which requires thin-walled plant cells.
They are spread primarily by human activity, moving on infested cuttings, clothing, equipment, and even carried by other flying insects (a process called phoresy) that visit infested plants.
Behavior and Life Cycle
The Broad Mite has an extremely rapid life cycle, sometimes completed in just 4–7 days under optimal conditions ($77^{\circ}\text{F}$ and high humidity). Females lay eggs singly on the undersides of young leaves or in crevices of terminal growth. The larvae hatch, feed briefly, and then enter a quiescent pupal stage.
A unique behavior involves the male mite. He carries the quiescent female pupa on his back, waiting for her to emerge as an adult. Mating occurs immediately upon her emergence, after which the male deposits the female on a fresh feeding site, maximizing the spread of the population.
Feeding and Damage
Broad Mites feed on the exterior cells of the plant tissue, but their saliva contains potent toxins that cause the characteristic damage. Symptoms of infestation resemble viral infections or herbicide damage: severe curling, cupping, and thickening of leaves; stunting of terminal buds; bronzing, browning, or purpling of the leaf surface; and distortion of flowers and fruits. In extreme cases, the growing tips may be entirely killed.
The severity of the damage is disproportionate to the number of mites present, as the toxic effect persists long after the mites have been eliminated. This damage severely impacts marketability and yield in crops like peppers, tomatoes, and citrus.
Management and Prevention
Control is challenging due to the mite’s rapid life cycle and its tendency to hide in terminal buds. **Biological control** using predatory mites (e.g., *Amblyseius swirskii*) is highly effective, especially in greenhouses. **Acaricides** must be applied, often requiring multiple applications due to the difficulty in eliminating the resistant eggs.
Cultural controls include removing infested plant parts and applying **sulfur dust or sprays** (where safe for the crop). Quarantine of new plant material and thorough sanitation of greenhouse spaces are the primary preventive measures.
Conservation and Research
Broad Mites are economic pests. Research focuses on their toxic saliva and methods to neutralize it, improving the effectiveness of biological controls, and understanding the genetics behind their extreme resistance to common chemical treatments.