Entomology, Department of


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E. A. Heinrichs, C. J. Southards. 1970. Susceptibility of the sod webworm Pediasia trisecta to biological control agents. Tennessee Farm and Home Science Progress Report Number Progress Report Number 73 January, February, March 1970: 30-32.


Homeowners in Tennessee have observed complete destruction of their lawns by the sod webworm a few months after applying an insecticide to control sod webworms or white grubs. The reason for this increase rather than a decrease in the webworm population is not perfectly understood. We believe, however, that the natural enemies of the webworm may be reduced to such low population levels that they exert very little control on the webworm. Thus, once the natural enemies are destroyed in a lawn, it may require several months or even years for them to increase to a population level necessary to exert a satisfactory control on the webworms. In the absence of their natural enemies, which serve to control their population, the webworms, because of their high reproductive potential, increase rapidly and lawn destruction follows.

Insecticides which cause an increase of webworm numbers are the chlorinated hydrocarbons such as dieldrin and chlordane. These are excellent insecticides for the control of soil insects such as white grubs which feed on grass roots but have not been satisfactory in webworm control in Tennessee.

Insecticides that are recommended by the Institute of Agriculture for webworm control (Sevin and Diazinon) have not been implicated in causing webworm increases, but they probably do have an adverse effect on the natural enemy population. There is also a possibility that webworms may develop resistance to these chemieaIs. In addition, these chemicals have the disadvantage of having to be applied every 3 weeks during the summer because of their short activity period. Because of the above-mentioned disadvantages of chemicals, we are searching for new means of sod webworm control.

Biological control, which involves the dissemination of large numbers of parasites, predators, and/or insect pathogens, may offer promise in sod webworm control. We have conducted preliminary studies utilizing biological control agents which are non-toxic to humans, birds, wildlife, and fish. Some of these agents are so specific as to insects attacked that certain ones can be selected that destroy the target insect pest but leave unharmed other insects and mites which are predators and parasites. Biological control agents cause no phytotoxicity at high rates as some insecticides do.

Insect pathogens, which were the subject of this study, are manufactured in various formulations such as wettable powders, dusts, baits, and aqueous suspensions, and can be applied with the same equipment as insecticides. Costs for those whic

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