Abstract
Abstract Results are given of effects produced by application of acetone solutions of insecticides applied topically with a microloop delivering 0.36 µ1 to field-collected third instar larvae of Costelytra zealandica (White). The Median Effective Concentrations of DDT for mature larvae of the susceptible populations examined ranged from 0.74 µg to 3.00 µg per µl. The response to DDT of larvae collected from paddocks with a history of DDT treatment has revealed that tolerance to DDT exists in certain populations. In some instances separation of susceptible and tolerant populations at the E.C. 50 level was slight, but flatter and broken regression lines derived from heterogeneous d'ata indicated that mixed populations occurred. Soil analyses have shown the ability of DDT-tolerant larvae to thrive under treatment regimes which formerly gave control. The toxicity to third instar larvae of two carbamate, eight organophosphorus, and four organochlorine insecticides, in addition to DDT was examined, DDT was the least toxic of the organochlorine insecticides tested by this method.
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