Several chemical agents will kill the eggs and larvae of monoxenous worm parasites in stable manure. None, to our knowledge, has been specifically demonstrated to be effective against the eggs and larvae of the heteroxenous worms. Some of the agents do kill ascarid eggs, which are thick-shelled, and the means for killing chemically all types of worm eggs and larvae in manure probably are at hand. Investigation to prove this is needed, however. Stable or poultry manure which has not been processed in some manner ought not be used on the farm for fertilizer.

The destruction of breeding places and direct attacks against insects and their larvae are weapons that can be applied generally to control these vectors. Usually both lines of attack should be employed, but the habits and life histories of insects are so diverse that the weapon of choice habitat destruction or larvicide or destruction of the adult may differ with the insect to be fought.

Attacks against the house fly can be directed most feasibly and easily against the larvae. DDT has been reported to be effective against the maggots of this fly when used in a water emulsion. Such an emulsion was found to be effective also against certain other species of flies breeding in poultry manure. DDT, methoxychlor, chlordane, lindane, and other insecticides are recommended as residual sprays directed toward the control of the adults. Important supplemental measures include disposal of manure, chemical treatment of manure, the use of properly baited fly traps, and the use of pyrethrum fly sprays.

The stable fly likewise is most vulnerable to attack in its larval stage. A principal measure for its control applicable also in the case of the house fly is the destruction of its breeding places. When it is impossible to locate and eliminate all of these, insecticides as recommended for controlling the housefly are distinctly useful against the adult stable flies.

Mosquitoes, biting midges, and black flies breed in water, and the elimination of their breeding places is not always feasible or desirable. Ponds, small pools, and useless swampy areas may often be filled in or drained. Since the maintenance of large ponds and streams is desirable, treating the water with oils to kill the larvae mechanically and with such larvicides as paris green long has been one of the approaches to the problem of mosquito control. DDT when incorporated into an oily vehicle for application to the water surface is effective for the destruction of the mosquito larvae. This insecticide also is of value in killing the adults of mosquitoes, biting midges, and black flies. Tests have indicated that the larvae of black flies are susceptible to DDT, TDE, and other new chlorinated insecticides.

Cat and dog fleas in and around buildings may be controlled effectively by the use of DDT sprays or dusts. One to two gallons of 5 percent DDT in oil sprayed lightly over areas of 1,000 to 2,000 square feet has been found effective in the complete eradication of adult fleas. Five percent DDT powder, applied with a dust can, is recommended for the destruction of fleas on dogs. The application of the dust to the building will destroy the larvae and adults as they emerge.

Methods are available for the control of grasshoppers, earwigs, and cockroaches. Beetles frequenting poultry manure likewise may be controlled chemically. The use of insecticides against these beetles probably would not be practical in seeking to control worms in poultry flocks having access to large areas, but the confinement of birds, as presently widely practiced, favors the feasibility of measures for beetle destruction in accumulated manure.

In theory, beetles frequenting manure on pastures no doubt also may be dealt with by means of insecticidal dusts or sprays, but we know of no work demonstrating that this is practical. Since it has been demonstrated that the feeding of small amounts of drugs, such as phenothiazine, to cattle prevents the development of horn flies in their dung, it would seem advisable to investigate the possibility that beetles might be controlled as worm vectors by the routine incorporation of suitable insecticidal materials into the diet of farm animals and birds. Manure deposits on pastures may be broken up and spread to reduce the attractiveness of the manure to insects. The maximum adverse effects of dryness and sunlight on worm eggs and larvae may also be had by this step. The chemical destruction of beetle mites on pastures and grazing land apparently has not been investigated, but even were it possible, its practicability seems doubtful. It seems probable that other means will have to be sought for the prevention of tapeworm infections transmitted by these mites.

EVERETT E. WEHR is a parasitologist doing research in parasitology in the zoological division, Bureau of Animal Industry, at Beltsville, Md. He has been associated with the division since 1928 and has been in charge of its investigations on the parasitic diseases of poultry since 1936. He is the author of numerous papers on the worms and other parasites of livestock and poultry. He has particularly investigated the nematodes of birds. Dr. Wehr is a graduate of the University of Idaho, University of California, and George Washington University.

JOHN T. LUCKER is a parasitologist and has been associated with the zoological division since 1930. He also is stationed at Beltsville. The identification of nematodes has been one of his chief assignments since 1940. He is a graduate of the University of Washington and George Washington University.