Control of Hippelates Gnats with Soil Treatments Using Oregano-chlorine Insecticides 1

Abstract

The initial and long-term effectiveness of six organochlorine insecticides applied to soil were determined in the field against Hippelates gnats. The field trials were aimed mainly at controlling H. collusor (Townsend), the predominant species in California and the Southwest. Other species controlled were H. hermsi Saurosky, H. pusio Loew, and H. dorsalis Loew. But the latter two species maintain very low population densities in the Coachella Valley of southern California, where these investigations were carried on, and consequently are not a problem in that area. H. hermsi is not considered pestiferous. In a young citrus grove, aldrin, dieldrin, endrin, toxaphene, DDT, and DDT+toxaphene sprays were applied on the basis of equal cost per acre and effectiveness of these materials was ascertained over a period of 4 seasons. Excellent control of Hippelate collusor was obtained for 2 seasons with the DDT and DDT+toxaphene treatments, but the other materials provided only poor-to-fair control. In the third season, only the DDT treatment still gave significant reduction of the eye gnats. During the fourth season, DDT produced no appreciable control of the gnats. In other tests also, DDT sprays were effective against H. collusor , as well as against H. pusio and H. hermsi . In trials in two date gardens, endrin, applied at rates of 2 to 6 pounds per acre in both spray and granular forms, yielded erratic results and poor control of Hippelates collusor . Various concentrations of DDT granules produced poorer control of H. collusor and H. hermsi , 3 months after treatment than the sprays of approximately the same dosage. As the concentration of DDT in the formulation increased, the degree of control decreased. Shell Development Company compound SD-4402 (1,3,4,5,6,7,8,8 octachloro 3a,4,7,7a-tetrahydro-4,7-methanophthalan) applied as sprays (2 to 10 pounds per acre) gave good-to-excellent initial control of Hippelate collusor and H. hermsi but less control after 3 months. Only the 10-pounds-per-acre teatment yielded excellent control of H. collusor 3 months after application. Twelve months after treatment the 10-pounds-per-acre treatment produced excellent control of H. collusor . The 5-pounds-per-acre treatment also resulted in good control of this species 12 months after treatment. Both these dosages yielded moderate-to-good control of H. hermsi 12 months after treatment. Sixteen months after treatment the 10-pounds-per-acre rate of SD-4402 yielded excellent control of H. collusor and moderate control of H. hermsi . However, the emergence of both species was low and the residual activity of SD-4402 cannot be assessed clearly after this period.