II. Hosts: Zetzellia is primarily a predator of plant-feeding mites, but it will feed on pollen when mite population levels are low. The adults and the two nymphal stages (protonymph and deutonymph) can feed on all stages of mites, but most prey are eggs and young mites. The larvae of Zetzellia find it difficult to feed on the eggs of spider mites, but they will attack adult and immature apple rust mites.
III. Description: Adult Zetzellia (Plate 136) are smaller than European red mite or phytoseiid adults. They are slightly larger in the front than in the back. The adults are lemon-yellow to reddish-orange. They are primarily found on the lower surface of the leaf and they move very slowly. The immature forms (including the eggs) are also lemon-yellow and are predominately found near the mid-rib on the lower surface of the leaf.
IV. Biology: The predator overwinters as an adult beneath bark scales where they are often found in clusters of up to 150 females. They become active in spring when temperatures average above 41 degrees F (5 degrees C). There are 3-4 generations per year with succeeding generations overlapping. Populations normally increase in response to increasing phytophagous mite populations, but they usually peak in late July and August. A population can develop from egg to adult in an average of 16 days at 68 degrees F (20 degrees C).
V. Injury: This mite does not injure the