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Zetzellia mali Zetzellia mali is found throughout the United States and exists in most orchards to some extent.
Appearance Z. mali is smaller and less active than other predator mites. It is bright yellow, although its gut is visibly reddish after feeding. Its eggs are round, bright yellow, and approximately half the size of European red mite eggs. It completes about four life cycles per year, and it does not have the potential to build up as rapidly as the phytoseiid mites. However, it has the ability to persist utilizing various food sources, and so it can eventually reach high numbers.
Habitat (Crops) Apples orchards.
Pests Attacked Apple rust mite, European red mite, and two-spotted spider mite.
Life Cycle Z. mali overwinters as a mated female in crevices and under bark. It prefers to feed on rust mites but will prey on eggs and immature stages of tetranychid mites (European red mite and the two-spotted spider mite) as well as cannibalizing its own. It can survive on pollen, sap and fungal spores, but will not reproduce on this diet. It is slow to explore the tree in search of new prey, so as pest mites move from older leaves to new feeding sites on younger ones, they can escape predation by Z. mali.
Relative Effectiveness Z. mali is not likely to control pest mite infestations alone. It prefers to feed on the apple rust mite and does not eat many prey when it does feed on the tetranychid mites. In addition, it is slow to increase in population and may prey on other predator mite eggs. However, Z. mali can be beneficial over the long run in these ways: it can survive on several alternate foods when its preferred prey is not present and thus can live for long periods without prey; because of its feeding versatility, it can eventually reach population densities capable of controlling pest mites; it can complement biological control by other predator mites by feeding on stationary forms of pest mites such as eggs or immature stages (Neoseiulus fallacis and Galendromus pyri prefer the mobile forms); it can serve as another form of prey for N. fallacis and G. pyri.
Pesticide Susceptibility Pest mite problems are most common where pesticides are heavily used because predatory mite populations are killed along with target species. Although Z. mali has some resistance to organophosphate insecticides, it is susceptible to endosulfan.
Conservation Pesticides that are considered moderately toxic to predators may have little or no long term effect on their populations, as a whole, when applied sparingly, although if they are used too often they will have a negative effect. It may take up to three years to establish a population of predators high enough to control pest mites. Integrated pest management strategies, as outlined in the tutorial of this guide, can help establish colonies of predatory mites.
Commercial Availability Z. mali is not available commercially.
Acknowledgment Thanks to Jan Nyrop for reviewing this section.
Taken from: Kain, D. and Nyrop, J. (1995) Predatory Mites. Insect Identification Fact Sheet No. 23. Cooperative Extension, Cornell University, Ithaca, NY.
Additional References Beers, E.H., Brunner, J.F., Willett, M.J., and Warner, G.M. (Eds.) (1993) Orchard Pest Management: A Resource Book for the Pacific Northwest. Good Fruit Grower, Yakima, WA. 276 pp. Helle, W. and Sabelis, M.W. (Eds.) (1985) Spider mites: Their Biology, Natural Enemies and Control. Vol. 1B. Elsevier, Amsterdam. 458 pp.
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