Effects of Some Chlorinated Hydrocarbon Insecticides on Nematode Populations in Soils1

Abstract

DDT applied in the laboratory to a loatn soil at the rate of 600 and 1,000 Ibs./6' acre had no effect on nematodes 24 days after treatment, whereas lindane at 200 lbs./6' acre caused an 85% reduetion of the total population, a 99% reduction of Aphelenchus arenae and Acrobeloides spp, and an 85% reduction of Dorylaimus spp. These differences were all significant. Rhabditis spp. or Psilenehus spp. were not affected. Field investigatons with heptaehlor applied to a Carrington loam at 25 and 125 Ibs./acre and aldrin at 25 Ibs./acre showed that 5 weeks after treatment no significant effect on the nematode populations was obtained. Mimi silt loam plots were treated with aldrin, DDT, and lindane in 1954 and investigated in 1957 and 1958 to study the long-term effcets of these insecticides on nematode populations. Aldrin applied at rates up to 200 lbs./6' acre in 1954 (24.6 Ihs./acre present in fall of 1957) had no effect. Significant differences In nematode populations were found between the untreated soils and the plots that had been treated with DDT at a rate of 1,200 Ibs./6' acre in 1954 (604 Ibs./acre in the fall of 1957) and lindane at 100 lbs./6' acre in1954 (33.5 lbs. in the fall of 1957). The lower rates of application had no effect. A saprophagous species ChiloplaclIs symmetriclls was always signifieantly more numerous on both the DDT-treated (1,000 Ihs./acre) and lindane-treated (100 Ibs./acre) plots. Nematodes of the order Tylellchida were not numerous on the lindanctreated plot . From these investigations it seems that only some chlorinated hydrocarbon insecticides 01' their breakdown produets influenee nematode popnlations as a result of their direct or indirect effect on certain species or groups. Saprophagous species were often increased in number. Parasitic nematodes were often redueed slightly in numbers, hut as few were rounel it was impossihle to draw any condusion. Under field conditions, however, the nematode population was not seriously affected by the insecticides.