Question: I am seeing little clouds of flies that look like mosquitoes, hovering over areas of the yard. They don't seem to bite, however, so what are they?

Answer: There are many species of small flies known as midges that superficially resemble mosquitoes. Most are in the family Chironomidae and they are a commonly found in waters and very moist soil.

The larval stages of some of the most common species develop in ponds, feeding on dead plant matter, microorganisms, and organic debris. Often the adults emerge in masses, with spring emergence typically associated with the annual turning of waters that occurs when ponds warm. They then may produce striking swarms that usually hover over some prominent feature in the landscape. They may even move as this feature moves. For example, these non-biting midges may hover over your head and follow you if you walk slowly.

The non-biting midges are harmless. Adults may not feed at all or limit feeding to nectar or damp spots. Their superficial appearance to mosquitoes does not extend to blood feeding. Swarms typically dissipate after a couple of weeks.

Q: What is the best way to manage oystershell scale on my aspen?

A. Oystershell scale is probably the most serious scale insect pest of landscape plants. It is a very small brown or gray brown insect attached to the bark of trees and shrubs, with the overall appearance of an oyster's shell. During outbreaks it may form dense crusts on the bark. The insect can kill plant cells as it feeds on sap branches. Oystershell scale also may weaken plants, allowing disease organisms to invade. Aspen, ash, lilac and willow are among the most commonly infested of the hard wood plants oystershell may attack.

To help turn around a problem, scrape as many of the scales as possible off the plant with a nylon net "scrubby" or something similar. The scales pop off the plant readily. Once exposed, eggs dry out rapidly.

Horticultural oils have long been a staple for control of many scales. These are diluted and sprayed with the intention of smothering the insect. When applied in the dormant season, before eggs hatch, they can be moderately effective against oystershell scale. However, this insect produces a tough outer cover that protects many of the eggs housed underneath.

Things change dramatically when eggs hatch, usually in late May or early June. The newly hatched insects are tiny, pale yellow insects known as "crawlers." During this time they are vulnerable to several insecticides (e.g., malathion, permethrin). These sprays should be applied when crawlers are active - about two-weeks on most plants. Subsequently they settle on the bark and secrete a waxy cover that protects them from most sprays.

An exception, again, is horticultural oils. They can be sprayed after the crawler period to kill the young stages of scale during June. Be sure to use an oil that allows foliar or "summer" use and mix correctly to avoid plant injury.

Whitney Cranshaw is the Colorado State University Cooperative Extension Entomology specialist. For information on a variety of horticulture topics visit www.planttalk.org.