Insecticidal screening tests

In the search for safe insecticides, hundreds of products have been prepared and subjected to screening tests against insects. This paper presents information on six materials related to piperonyl butoxide, tested in combination with pyrethrins. 

In the search for safe insecticides the authors have prepared hundreds of new products and subjected them to preliminary screening tests against insects. That part of their work dealing with methylenedioxyphenyl derivatives was prompted by the original fundamental studies of 0. F. Hedenburg, with whom they have collaborated in this field. Two materials of this type—piperonyl butoxide (I) and piperonyl cyclonene (II)—have recently been introduced commercially. These products have definite insecticidal properties in themselves, but show their maximum efficiency toward insects and other arthropods when used in combination with pyrethrins. Furthermore, they are at least as nontoxic... 

These tests not only represent different techniques, but also supply some basic information regarding the use of the insecticides under practical conditions. Because they are screening tests, it is desirable to use insects that are commonly employed by many different laboratories, in order to give a comparative evaluation of the materials. This pro-... 

Source USDA, Results of Screening Tests with Materials Evaluated as Insecticides, Miticides and Repellents at the Orlando, Florida Laboratory E-733, Bureau of Entomology and Plant Quarantine, United States Department of Agriculture, Orlando, FL, 1967... 

A recent method to screen the urine for alkyl phosphates as an indicator of exposure to organophosphate insecticides shows that the method can be used to determine environmental exposure to a specific organophosphate pesticide. The method was found to be sensitive, identifying low levels of exposure to insecticides in the environment by quantitation of urinary phosphates (Davies and Peterson 1997). The test is limited in that it is only useful for assessing recent exposure, due to the short half-life of the organophosphate pesticides. 

Experimental results obtained on these products by various screening procedures are summarized in Tables I to IV. Detailed description of these tests on insects and discussion of their relative practical usefulness for evaluating insecticides will be given in a subsequent publication (5). In this screening program on seven materials and the necessary standards of reference about 38,000 houseflies and over 5000 other insects were used. 

These discoveries led to the simple traps that are now used to monitor tsetse flies and to control them. A test operation in Zimbabwe in the late 1980s gave dramatic evidence of how potent such traps can be. Insecticide-impregnated screens, baited with acetone and octenol, were distributed at a density of four screens per square kilometer. These traps reduced tsetse populations by more than 99.99 percent over an area of 600 square kilometers (230 square miles). The screens are even more effective when the urine-derived phenols are added to the attractants employed. Their effectiveness having been clearly demonstrated, traps and screens have become important complements to insecticide-based measures for controlling tsetse flies. 

Synthesis and Screening. One of the key problems for industry is the question "How does one screen for new plant growth regulants " (8). In the case of herbicides and insecticides, they either work or they don t. The field effects of plant growth regulators are harder to see, predict or test for. 

Other groups of naturally occurring insecticides have been investigated, but without the same spectacular degree of success. Quassia, rotenones, sabadilla, ryanla, mamey, and several other plant products have been used as insecticides. The chemistry of the major groups is known, but many plant principles remain to be explored (25). Screening of natural products presents a problem and raises the issue of suitable bloassay in terms of insect species, the part of the plant that should be examined and the appropriate tests for activity. 

Acute dermal toxicity tests are an important method employed in assessing the safety of insecticides to workers. For dermal toxicity tests, typically, an albino rabbit weighing 2-3 kg is shaved around the abdomen and back, and the chemical in question is painted (dry power is moistened with isotonic saline to prepare a paste) over the area, which is then covered with either a rubber sleeve or cotton gauze held in place with a wire screen for up to 24 hr. The mortality is recorded and the median lethal dose obtained is referred to as dermal LD3(). 

---