RECENT ADVANCES IN VETERINARY ENTOMOLOGY1

The advances during the last 15 years in our knowledge of the biology and control of arthropod pests of livestock and vectors of animal disease agents exceed those made in any similar period in past history. Before 1942 we relied mainly on rotenone, pyrethrum, the thiocyanates, and the arseni­cals for control of lice, ticks, mites, biting flies, and cattle grubs. While ef­fective against some pests under certain conditions, these materials were not practical for wide-scale use and did not meet the public demand for better insecticides. Today we have highly effective and low-cost insecticides such as DDT, lindane, TDE, toxaphene, methoxychlor, chlordane, and syner­gized pyrethrum for control of livestock insects. Their use has saved the live­ stock grower many millions of dollars annually and has benefited the con­ sumer by making more and better animal products available. Of almost equal importance to the development of the new insecticides are the contributions made to our knowledge of the biology and habits of several livestock insects and their transmission of agents of animal diseases. Many new ideas and approaches to studies on insect biology and control have been developed during the last few years. A good example of this is the unique method for the control of screw-worms by release of sterilized male flies over an area. The sterile males mate with the native females, but the eggs are infertile and thus reduce the numbers of screw-worms. Another ex­ ample of new trends is the promising research with insecticides that can be given internally to livestock for destruction of external pests. These studies will be discussed in detail in the following pages. Although great progress has been made in the use of insecticides, two disturbing factors have arisen to cause worry as to the future efficiency of chemical means of control. The first is the increasing and widespread de­velopment of resistance of insects to insecticides, particularly to the chlo­rinated hydrocarbons. House flies have developed such a high degree of re­sistance to DDT and related materials that satisfactory control is impossible in most areas. Organic phosphorus insecticides have so far performed in a creditable manner in controlling house flies, but there are indications that these chemicals may eventually fail. As yet no reports on resistance of horn flies, horse flies, deer flies, stable flies, sheep keds, or lice of livestock have appeared