Department of Entomology

Southeastern Apple Production ENTOMOLOGY

Predatory Mites

Neoseiulus fallacis, Zetzellia mali, etc.

Description

A variety of predatory mites occur on apple, potentially controlling populations of European red mites and two-spotted spider mites. The most commonly observed in North Carolina is the Phytoseiid mite Neoseiulus fallacis (formerly Amblyseius fallacis) and, to a much lesser degree, the Stigmaeid mite Zetzellia mali. Both are smaller than European red mites and range from clear yellow to deep red (after feeding).

Adult N. fallacis

N. fallacis with eggs

Adult Z. mali

Z. mali

Life History

Adult N. fallacis females may overwinter in tree bark. After emerging as early as bloom, populations increase rapidly until mid-summer. Each female lives approximately 20 days and will lay 40-60 oval, translucent eggs on the bottoms of leaves. Each egg hatches into a six-legged larval stage that lasts about 1 day and does not feed. It then molts into successive protonymph, deutonymph, and adult stages that all have eight legs. (The time from egg deposition to adult is about 5 1/2 days under normal summer conditions.)

Monitoring and Effectiveness

Several beneficial arthropods can help keep European red mite and twospotted spider mite populations below damaging levels. The most common in the Southeast are the phytoseiid mite (Neoseiulus fallacis) and the complex of generalist predators (e.g., black lady beetles (Stethorus punctum) and lacewings). However, recent research in North Carolina suggests that neither of these predators overwinters to any significant degree within orchards, so they must be reestablished in orchards in the spring. Hence, practices that delay the buildup of pest mites and enable predators to increase before mites become a problem will favor biological control. The two most effective practices are applying a delayed dormant oil spray and avoiding insecticides toxic to these predators.

Monitoring European or Two-spotted Spider Mite Populations: Use a regular monitoring program to follow the buildup of pest mite populations and to determine if and when supplemental applications of a miticide are necessary to avoid economic damage. Monitor each contiguous block of apples weekly beginning when adult mites first appear (which may vary from mid May to early July). Within each block, examine 5 leaves from each of 10 trees with a visor lens or hand lens. Rather than counting the total number of mites on each leaf, record the number of leaves infested with one or more mites, and estimate the mite density on a per-leaf basis from the table below.

Determining the Need for Miticides: When mite populations reach a density of 5 to 10 mites per leaf (80 to 90 percent infested leaves) decide whether to use biological control or a miticide to prevent mites from increasing to higher densities. Count the actual number of N. fallacis on sample leaves with a visor lens. If the ratio of N. fallacis to ERM is between 1 to 5 and 1 to 15, biological control is possible. For biological control with S. punctum to occur, the ratio should be 2.5 S. punctum to 1 ERM. S. punctum should be sampled by counting the number of adults and larvae observed during a timed 3-minute search around the periphery of mite-infested trees. S. punctum larvae must almost always be present if this predator is to control mites. If neither predator is present at sufficient levels for biological control to occur, and mite populations are between 5 to 10 mites per leaf, apply a miticide.

In areas where Alternaria blotch is a problem on Delicious apples, biological control is usually not an option. In the presence of Alternaria blotch, mite populations must be maintained at very low levels to avoid high levels of Alternaria and premature defoliation. If preventive control measures are not used, a modified threshold level of 1-2 mites per leaf should dictate the need for miticides.

Two N. fallacis mites feeding on a two-spotted spider mite

Insect and Mite Management Overview
Insect and Mite Index

Southeastern Apple Production
Mountain Horticultural Crops Research & Extension Center
455 Research Drive
Mills River, NC 28759
Phone: 828.684.3562 ~ Fax: 828.684.8715
Email: jim_walgenbach@ncsu.edu

Web Crafters: Anne S. Napier and Steve Schoof
Email: steve_schoof@ncsu.edu

Updated March 22, 2007