The use of natural synergists to enhance pyrethrum activity against resistant insect pests
2015
Joffe, T. | Gunning, R. | Moores, G.
The insecticidal action of pyrethrum has often been enhanced by synergists since the mid-1940s. In recent years, the synergistic action has usually been provided by piperonyl butoxide (PBO). PBO is an excellent synergist as it inhibits both phase 1 metabolic enzyme systems (esterases and oxidases) that commonly detoxify insecticides. However, PBO is not accepted as compatible with organic agricultural practices in some countries, which may limit its use with natural pyrethrum in such cases. The use of a natural synergist was investigated to replace PBO in an organically-certifiable formulation of pyrethrum for use against insecticide-resistant pests. Inhibition of esterases and oxidases by the natural compounds using housefly enzymes were correlated to synergism shown in housefly bioassays using mixtures of the potential synergists with pyrethrum. This could indicate whether an enzyme assay could be used as a means of identifying potential pyrethrum synergists. Using bioassays, PBO showed the highest efficacy as a pyrethrum synergist, whereas dillapiole and parsley seed oils showed the highest efficacy as natural synergists. No esterase inhibition was found with the conventional assay with p-NPA as artificial substrate. Grapefruit, bergamot and dillapiole oils showed the highest blockade of esterases with the ‘esterase interference assay’. Esterase inhibition did not correlate with pyrethrum synergism. Dillapiole, PBO and parsley seed oil gave the highest inhibition of oxidases, all of which also showed synergism of pyrethrum. A significant correlation was found when PBO was removed from the analysis and the results indicate the possibility of oxidases playing a role in pyrethroid resistance in strain 381zb of houseflies.
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