Petrobia

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Petrobia is a genus of spider mites in the family Tetranychidae, with 34 described species, including several pests. They can be recognised by their reddish-brown cuticle, dark body contents, and a very long first pair of legs. Each leg ends in pad-like claws and a hooked empodium with more than one pair of tenent hairs. The prodorsum (front body) has three pairs of setae (ve, sci, sce), and there are no prominent lobes over the mouthparts. The ventral paranal setae (h2–h3) are on the underside.

The genus is usually divided into three subgenera: Mesotetranychus, Petrobia, and Tetranychina. Mesotetranychus has simple peritremes; Petrobia has anastomosing peritremes; Tetranychina normally has long dorsal setae on small tubercles (other subgenera may also have tubercles, but their dorsal setae are short).

Petrobia species can reproduce sexually (for example, P. harti) or asexually (parthenogenesis) (for example, P. latens). In P. harti, males make up 10% or less of field populations. Eggs are laid on the ventral surfaces of host plant leaves. Petrobia latens is all-female; females lay eggs parthenogenetically on soil and under stones.

Several Petrobia species are polyphagous pests, attacking a wide range of plants.