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Southeastern Apple ProductionENTOMOLOGY |
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Black Lady Beetle
Stethorus punctum
Description
Stethorus punctum (SP) adults are similar in shape to the better-recognized complex of reddish orange lady beetles attacking aphids, but are much smaller with a diameter of approximately 1 1/2 mm. The shiny, black surface is sparsely covered with fine whitish hairs. The pupal stage is black and teardrop shaped. Young SP larvae are dark gray but turn reddish as they mature, and eggs are white, 1/2 mm long, ovoid, and are usually laid on the undersides of leaves.
 Adult |
 Adult |
 Pupa |
 Larva |
Life History
SP may overwinter as adults in dead leaves and other debris in or near the orchard. Emergence begins around the tight cluster stage and peaks from pink to bloom. Adults remain active for the remainder of the growing season. Eggs are laid in late spring to mid summer, and larvae usually hatch within 5 days. They feed on mites for about 12 days before entering a pupal stage that lasts about 5 days. There are usually three generations per year.
Monitoring and Effectiveness
Several beneficial arthropods can help keep European red mite and two-spotted spider mite populations below damaging levels. The most common in the Southeast are a 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 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.
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% Mite-infested leaves (1+ mite/leaf) |
Expected number of mites per leaf |
|---|---|
| 40 | 0.7 |
| 45 | 0.9 |
| 50 | 1.1 |
| 55 | 1.3 |
| 60 | 1.6 |
| 65 | 2.0 |
| 70 | 2.6 |
| 75 | 3.4 |
| 80 | 4.7 |
| 85 | 6.8 |
| 90 | 11.4 |
| 95 | 26.4 |
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 pest mites 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 pest mite. 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.
 Adults and larvae |
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 |
Updated March 12, 2007