WSU Extension

Hortsense

Predatory Bugs : Mirids
(revision date: 10/4/2018)


Biology
Plant bugs or mirids are small (1/4 inch) and black or brown, similar to big-eyed bugs (without the bulging eyes). Some species are omnivorous feeding on plants as well as insect prey but rarely cause significant plant damage. Like big-eyed bugs they are long-lived and spend their time searching for mites, thrips, insect eggs, leafhoppers and small caterpillars on leaves, buds and flowers. Deraeocoris brevis is the most common mirid seen in eastern Washington. It is oval, shiny black with paler markings, 1/10 to 1/5 inch long and approximately 1/12 inch wide. Nymphs are mottled whitish-gray with long gray hairs on the thorax and abdomen. A cottony secretion covers most of the body. Dark areas on the thorax and abdomen give it a spotted appearance. The eyes are dull red. Deraeocoris overwinters as an adult in protected places such as under bark or in leaf litter. Overwintered adults emerge from hibernation during March to April and feed on nectar of willow catkins and other early spring flowers. They seek out prey and begin laying eggs in late April or May. Nymphs of the first generation occur two to three weeks later. Nymphs develop through five stages in approximately 25 days at 70 ºF. Females lay up to 250 eggs during their lifetime and adults consume 10 to 20 aphids or mites a day. Nymphs can eat 400 mite eggs a day. Deraeocoris adults and nymphs prey on a wide variety of small insects and mites including aphids, thrips, leafhoppers, scale insects, small caterpillars, and spider mites.

Prey or Pest Targeted
  • Mites, aphids, leafhoppers, thrips, caterpillars, mealybugs, beetles, scale insects, insect eggs
     
Attracting and Keeping Natural Enemies & Pollinators in Your Yard
  • Avoid regular use of synthetic, broad-spectrum pesticides. Infrequent use of certain narrow-spectrum pesticides is more compatible with some beneficials but generally the less chemical inputs there are, the greater and more diverse the beneficial insect community will be. Extensive lawns are also not conducive to attracting and retaining a diversity of beneficial insects, mites and spiders. Minimize lawn areas and maximize shrub and bush plantings. Many beneficials reside naturally in riparian and other ‘natural’ areas near to many back yards. Natural dispersion from these refuges ensures that some beneficials will visit back yards but they will not stay unless food, host and shelter resources are available. Native plants have closer affinities with native insects and therefore provide most of these resources. A garden with a good diversity of local native flora in and around back yards, will improve the abundance and diversity of local, beneficial arthropods. Native flora also provides natural overwintering sites for many beneficial insects and it is useful to leave at least a small area of native vegetation undisturbed during fall and winter.
  • Some kinds of beneficial insects (e.g. lady beetles, lacewings, predatory mites) are available for purchase from commercial suppliers. However, benefits from introducing these beneficials are usually limited and short-lived. Upon release, commercially obtained lady beetles and lacewings often disperse and may rapidly leave your backyard despite the presence of prey and suitable nectar resources. Generally, it is more effective and sustainable to create a garden habitat that will be colonized by beneficials naturally.
     

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Caption: Adult predatory mirid (Deraeocoris brevis) (Miridae)
Photo by: D.G. James
Caption: Nymph of predatory mirid (Deraeocoris brevis) (Miridae)
Photo by: D.G. James