Novel pesticide formulations for locust and grasshopper control

Abstract

The primary question addressed was one of whether advanced fonnulation techniques, and more specifically microencapsulation, could be used to produce efficient fonnulations tailored for locust control. The key benefits of microencapsulation sought were an increase in persistence of a non-cumulative synthetic insecticide while reducing the toxicity to beneficial arthropods. In the first phase of the investigation a number of insecticides of different chemical classes were assessed for suitability in microencapsulation. Emphasis was placed on developing oil based fonnulations appropriate for application with the controlled droplet application (CDA) sprayers commonly used for locust control. A novel oil based fonnulation of the organophosphorus insecticide malathion was selected and variants developed for efficacy testing. Since it is clear that synthetic insecticides are unsuitable for all possible control situations, a novel oil based fonnulation of fungal conidia was also developed. Malathion microcapSUle fonnulations were tested for efficacy against nymphs of Schistocerca gregaria (Forskal) (Orthoptera: Acrididae) in the laboratory. The contact toxicity of dried malathion microcapsule residues on a glass substrate was found to be comparable to non-encapsulated malathion but having the benefit extended persistence. A single variant of the malathion microcapsule fonnulation was tested for oral toxicity to S. gregaria nymphs and found to be between six and seven times less toxic than non-encapsulated malathion. Finally, the same microcapsule fonnulation was assessed for toxicity to the indicator beneficial insect, Aphidius colemani (Viereck) (Hymenoptera: Braconidae), using a laboratory test in which the insects were exposed to dried microcapsule residues on glass. In this worst case scenario of continuous contact microencapsulation of malathion significantly increased the median lethal time to death. Overall it was demonstrated in the laboratory that microencapsulated malathion has potential utility in locust control operations, future research should be aimed at optimising the wide range of microcapsule parameters to give the correct balance of persistence and toxicity to locusts while reducing the toxicity toward beneficial arthropods.

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