  
Left: Zetzellia mali adult before feeding. J.Ogrodnick
Center: Zetzellia mali adult after feeding. J.Ogrodnick
Right: Mite eggs. From left, European red mite, phytoseiid, Zetzellia
mali. J.Ogrodnick
Zetzellia mali
(Acarina:
Stigmaeidae)
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.
Adapted 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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