Compatibility of selected insecticides with two steinernematid nematodes

Worthman, Marcus Glenn (1988) Compatibility of selected insecticides with two steinernematid nematodes. Masters thesis, Memorial University of Newfoundland.

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Abstract

The combination of insecticides with entomogenous nematodes in integrated pest management protocols could be an effective way of lowering environmental loads of harmful insecticides. The compatibility of two locally isolated steinernematid nematodes, (Steinernema sp. Newfoundland strain no. 1 (L1C) and Steinernema sp. Newfoundland strain no. 2 (5B)) with the organochlorine insecticides chlordane and methoxychlor, the organophosphates diazinon and malathion, the carbamates carbaryl (SevinR) and aminocarb (MatacilR), as well as the insect growth regulator diflubenzuron (DimilinR), was investigated. -- Direct exposure of infective juveniles to chlordane, methoxychlor, diazinon and carbaryl at a concentration of 1.0 mg/ml proved toxic. Exposure of nematodes to ≤0.1 mg/ml of these three and ≤1.0 mg/ml of malathion, carbaryl, Matacil and Dimilin did not cause significant mortality to the juvenile of both nematode. -- Efficacy of infective juveniles to the Greater Wax moth, Galleria mellonella was unaffected, except where nematodes were lethally affected by chlordane, methoxychlor a-and diazinon at 1.0 mg/ml. -- In vitro development of both nematodes was impaired by exposure to all tested insecticides. Toxicity appeared to be related to both direct toxicity toward adult and non-ensheathed nematode larvae as well as towards the associated bacterial symbionts. -- The doubling or generation time of the bacterial symbionts Xenorhabdus sp. L1C and Xenorhabdus sp. 5B, was found to be approximately 90 and 117 minutes respectively. Bacteria showed variable sensitivity to the tested insecticides but the carbamates and diazinon were particularly toxic at ≥0.1 mg/ml. -- The juveniles of both nematode strains demonstrated active seeking of hosts by migrating in soil towards G. mellonella larvae. -- Nematode migration in soil was not impaired by the organochlorine insecticide, chlordane. However the organophosphate diazinon reduced migration of both nematodes at ≥0.1 mg/ml. -- The data obtained suggest that compatibility of nematodes with insecticides in integrated pest management programs can be attained by lowering insecticide levels or altering timing of insecticide and nematode application.

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