DR. MacDANIELS: Thank you, very much, sir. We will take a few minutes recess now.
(Whereupon, a short recess was taken.)
Editor's Note: The following paper which was delayed, was originally scheduled for our 1949 Report.
Insecticides for Nut Insects
E. H. SIEGLER United States Department of Agriculture Agricultural
Research Administration Bureau of Entomology and Plant Quarantine
Fortunately, the growers of nuts do not have to combat a large number of injurious insect species. However, some species do at times cause a heavy loss of nuts and may also damage the vegetation growth of the trees. Injury by insects will vary from year to year, due to various causes, and insects frequently show varietal host preferences. Timely use of insecticides is the most effective means of combating many harmful species.
Until the beginning of World War II a rather limited number of insecticides was available, such as lead arsenate, cryolite, nicotine, mineral oil emulsions, and rotenone. Some injurious insects were satisfactorily controlled through the timely application of one or the other of these materials, or combinations of them; others survived in damaging numbers in spite of all attempts to suppress them.
During and since World War II, both in the United States and abroad, work on insecticides has been stepped up markedly. As a result, many new insecticides have been developed and are available for general use.
The first of the new insecticides about which we heard was DDT. Actually, the compound itself was not a new one, since it was prepared by a German student chemist in 1874. However, no use was found for it until 1939, when a Swiss chemist found it promising as an insecticide against the Colorado potato beetle. It was first tested in the United States a few years later.
Since the successful introduction of DDT, promising new insecticides have become available more frequently and in greater numbers than ever before. Among these materials are certain chlorinated hydrocarbons related to DDT. These include methoxychlor and TDE, neither of which is, on the whole, as useful as DDT but both of which are of value and have an important advantage over DDT in that they are reported to be less toxic to warm-blooded animals. Other new chlorinated hydrocarbons include benzene hexachloride, synthesized in 1828 and first tested against insects in France in 1941 and discovered about the same time in England; chlordane, developed in the United States a few years ago; and toxaphene. Several organic phosphorus compounds, including hexaethyl tetraphosphate, tetraethyl pyrophosphate, and parathion, have also been developed.