Exploiting Synergies

Tawny Mole Cricket

Tawny Mole Cricket Photo: Ilona Loser

In some cases, application of 2 insecticides to an insect will have effects that are greater than the additive effects of each insecticide alone. The greater than additive effects are called “synergistic”. Treatments that combine neonicotinoids and pyrethroids have synergistic effects on insects and ticks, both in pest control trials and in physiological experiments. Kostromytska, Buss & Scharf* measured effects of the pyrethroid bifenthrin and the neonicotinoid imidacloprid on mole crickets. Together, the insecticides had a synergistic effect, both in toxicity tests with mole crickets and on the increase in nervous system activity. Imidacloprid is an agonist (stimulator) of acetylcholine receptors in insects. Holding the receptors open increases the rate of nerve action potentials in the nerve axon. Bifenthrin and other pyrethroids act on the sodium channels in the nerve axon that are responsible for the rising phase of the action potential by blocking open the channels and preventing their closure. At the nerve level, the bifenthrin turns each action potential into multiple action potentials. The imidacloprid generates additional action potentials. Thus the two acting together could have a multiplicative effect. Both imidacloprid and pyrethroids have low toxicity to mammals. A synergistic effect on insects, but not on mammals can increase the safety ratio and allow reduction in the total amount of pesticide applied.

*Olga S. Kostromytska, Eileen A. Buss, Michael E. Scharf. 2011. Toxicity and neurophysiological effects of selected insecticides on the mole cricket, Scapteriscus vicinus. Pesticide Biochemistry and Physiology, 100:27-34.
http://dx.doi.org/10.1016/j.pestbp.2011.01.012

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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