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Beneficial Insects on Lawns
编辑:郭海滨   出处:南京农业大学杂草研究室   时间:2011-1-13 15:06:07

Many insects which occur in lawns are beneficial insects. They provide a form of natural control of pest insects or assist in the breakdown of organic matter so nutrients can be returned to the soil.

Predators:

Predatory insects are relatively mobile insects that search out prey. Some predatory insects (like the assassin bug) have sucking mouthparts which penetrate the soft body of the victim and suck out the internal fluids, leaving only the outer shell behind. Other predatory insects (like ladybird beetles and ground beetles) have chewing mouthparts and feed on the entire body of the victim. Predators will feed on several victims during their lifetimes. Some of the more familiar predators which occur naturally in New England lawns include:

Ground beetles: These may be the most common predators on lawns in New England. The most common species are slightly smaller than Japanese beetles and are generally a shiny bronze or tan or green color. Both adults and larvae feed on soft-bodied insects and various caterpillars. Ground beetles usually are very quick moving and can "seek and destroy" their prey.

Rove beetles: Rove beetles may not be familiar to many people, but they do occur commonly in turfgrass areas. They are somewhat more elongated than other beetles, and the hindwings are not fully expanded. They feed on a variety of soft-bodied insects.

Spiders: Spiders are surprisingly common and active in turf areas and are very efficient predators. While they are not insects, many species of spiders are definitely beneficial in the garden or lawn, feeding on a wide range of immature insects and mites.

Ants: Some species of ants are carnivorous, and seek out insects and other soft bodied organisms with which to provision the nest. In addition, ant activity often can help in the general breakdown of organic matter and the formation of soil. However, if ant activity becomes excessive, the ants may become a nuisance or the soil may dry out and turf damage will result.

Parasites:

Another general group of beneficial insects is the parasites. These are small insects (generally smaller than the host) which develop inside or on the body of a single individual. The adult female finds a suitable host and lays her eggs on the outside of the body or inserts the eggs through the skin into the internal tissue of the host. The immature parasites feed on the organs and fluids inside the victim and gradually weaken and kill the host.

There are many parasitic wasps which occur naturally in New England and are active in lawn settings. Wasps such as Scoliid (family: Scoliidae) and Tiphiid (family: Tiphiidae) wasps are adapted to lay eggs in softbodied insects and do not bite or sting people. Scoliid wasps are about 16 mm (5/8 inch) long and blue-black, with blackish-purple wings. They have a yellow stripe on each side of the abdomen. Their bodies are fairly hairy and the back part of the abdomen is covered with reddish hairs. Tiphiid wasps are black and somewhat hairy with short, spiny legs. Both wasps are generally seen flying over the lawn during the day, leaving in early evening. Scoliids and Tiphiids are beneficial wasps in that they parasitize grub populations. They are not aggressive and generally do not attack humans. Adults are often seen on golden rod flowers in the late summer.

Final Thoughts:

Beneficial insects are very sensitive to insecticides, so whenever a general insecticide is applied to control a pest species (such as Japanese beetle grubs or chinch bugs), the material will usually have a detrimental effect on the beneficial organisms, often for at least a few weeks. Consider using alternate methods of pest management, biological control agents (if available and suitable) or providing optimum cultural conditions so that the lawn can tolerate higher levels of pest activity without visible loss of vigor. If an insecticide application is deemed necessary, make spot treatments rather than broad scale applications if at all possible.

Remember that the statement, "The only good bug is a dead bug," could not be further from the truth. Be sure you have an accurate identification of the insects in question and only attempt to control those which really warrant attention. There are in fact many "good bugs" out there! Let them help!


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