Non-Pests (Beneficials) of the Month:
Other Important Predators

Two previous articles in this series have briefly discussed some of the predatory mites and ladybird beetles used in greenhouse biological control programs. Continuing in a similar manner, this article will cover some of the other predatory insects that are available from commercial suppliers.

Pirate bugs (Orius spp)

Pirate bugs (Hemiptera: Anthocoridae) are small (about 1/8-inch long), oval insects with black and white marking as adults (Figure 1). Two of the most common species in North America are O. insidiosus and O. tristicolor. Both adults and nymphs (Figure 2) are quite general predators. Pirate bugs will feed on many different pest groups, including aphids, spider mites, caterpillars and thrips. Most of their use in greenhouses is in biological control of western flower thrips - usually combined with predatory mites. Adults will eat 5 to 20 thrips per day. They occasionally will bite humans. Some people say that the bite is painful - especially for such a small insect. Others say that it is not so painful, but only irritating. You can decide for yourself.

Pirate bugs can survive without prey by feeding on pollen. They are very common insects on outdoor crops during warm weather months, and will invade greenhouses from surrounding areas. However, in greenhouses, pirate bugs are most effective if introduced as part of an organized pest management program.

The general life cycle is as follows: Adults insert eggs into plant tissue, usually on stems or near leaf veins. Eggs hatch into nymphs, which develop into adults in 9 to 25 days, depending on temperatures. When conditions are optimum, pirate bugs will develop from egg to adult in 20 days. The best conditions for pirate bug development are days longer than 11 hours and temperatures between 70º and 90º. At cooler temperatures and/or short days, pirate bugs will enter diapause (become inactive). Supplemental lighting will help keep these predators active during short days - as long as temperatures are above 50º. One 60W light per 60 foot radius is one suggested approach to this problem.

Lacewings (Chrysoperla, Chrysopa)

Lacewings (Neuroptera: Chrysopidae) are very common insects outdoors - particularly in late summer. The 1/2-1/3-inch long adults (Figure 3) are light green with long antennae and large wings containing numerous veins. The adults are not predators, but feed on pollen and nectar. Eggs are laid in groups on leaves. The eggs are on the ends of thin stalks off the leaf surface.

Lacewing larvae are general predators of pests such as scale crawlers, mealybugs and whiteflies. They will also be quite happy eating each other. However, they seem to be most useful against aphids. In fact, the larva (Figure 4) is called an aphid lion. Lacewing larvae have long curved pointed jaws with which they seize their prey. A venom is injected, which paralyzes the prey, and the prey's body fluids are sucked out. Not a pretty picture. The larval stage lasts for 2 to 3 weeks, with each larva able to eat as many as 200 aphids (or other prey) per week. They do best at temperatures between 67º and 89º and relative humidity greater than 30%.

Lacewings may not become established in greenhouses or interior plantscapes, so repeat introductions will be needed. They are usually obtained from commercial suppliers and introduced as eggs or larvae.

Aphid Midge (Aphidoletes aphidimyza)

These insects are midges in the gall midge family (Diptera: Cecidomyiidae). Unlike many other members of this insect family, Aphidoletes do not cause galls, but are insect predators as larvae. As the name implies, they are predators of aphids.

The adults are small fragile-appearing insects that look like fungus gnats. They feed on aphid honeydew. Females lay eggs near aphid colonies, which hatch in 2 to 3 days. Larvae hatching from eggs are orange (Figure 5) and about 3/16-inch long when fully developed. The larvae kill aphids by injecting a toxin into a leg joint which causes paralysis, and then making a hole in the aphids' thorax to suck out the body fluids. A single larva can kill from 4 to 65 aphids per day during their 3 to 7 day larval stage. When aphids are numerous the midge larvae will kill many more aphids than they can eat, an almost human-like quality, but beneficial to growers with aphid problems. When fully developed the larvae drop off the plants and burrow into the growing media or soil under benches to pupate. Because of this, control seems to be best in greenhouses with gravel or soil floors. Aphid midges do best at temperatures between 65º and 80º and a relative humidity of 70%. These insects will enter diapause when daylength is less than 12 hours and/or temperatures drop to 40º. As with pirate bugs, supplemental lighting can help keep them active during short days.

Aphidoletes will enter greenhouses from outside during the summer, but are much more effective when introduced on purpose in several introductions. Commercial suppliers ship them as pupae in small containers of vermiculite.

Spider Mite Predator (Feltiella acarisuga)

This is another gall midge predator (Diptera: Cecidomyiidae). The adults and larvae (Figure 6) are very similar in appearance to those of the aphid midge, with a similar life cycle, except that 1. They prefer spider mites to aphids; 2. Pupation occurs on leaves and not in the soil.

Adults apparently do not feed and live for only a few days. Females search out spider mite colonies to lay their eggs. Larvae hatch in 5 to 7 days and feed on spider mite eggs (300 eggs during larval development) as well as nymphs and adults. As mentioned, pupation takes place on leaves, making soil or gravel floors in the greenhouse less important. The best conditions for the midges are temperatures between 68º and 81º, with relative humidity above 60%.

Feltiella is used mostly by greenhouse tomato growers, because the predatory mite most often used for spider mite control, Phytoseiulus persimilis,is not very effective on tomato leaves, which tend to be hairy with glandular trichomes. However, despite these problems it is recommended that F. acarisuga be used in combination with P. persimilis.

References:

Cherim, Michael S. 1998. The green methods manual, Edition IV. The Green Spot Ltd. Nottingham NH. GrnSpt@cwixMail.com

IPM Laboratories, Inc. Locke, NY. ipmlabs@baldcom.net; http://www.ipmlabs.com

Midwest Biological Control News. http://www.entomology.wisc.edu/mbcn/mbcn.html

Koppert Biological Systems. The Netherlands. http://www.koppert.nl