Black and Sichuan pepper constituents significantly enhance the neurophysiological effects of natural pyrethrins in Aedes aegypti

Authors: Norris, Edmund; BLOOMQUIST, JEFFREY - University Of Florida

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/5/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: With insecticide-resistant mosquito populations becoming an ever growing concern, new vector control technologies are needed. With the lack of available new chemical classes of insecticides to control mosquito populations, the development of novel synergists may allow improve the performance of already utilized insecticides We have identified two plant extracts, black pepper and Sichuan pepper, that significantly synergize the effects of natural pyrethrins when applied topically to Aedes aegypti females. Black pepper extract (SR = 17) and Sichuan pepper (SR = 15.3) synergized the effects of natural pyrethrins on Aedes aegypti when applied topically in combination with piperonyl butoxide, a commercially available synergist. This synergism of natural pyrethrins was also observed directly on the mosquito central nervous system, indicating that this synergism is mediated via action directly on the nervous system. Piperine, the primary active constituent of black pepper extract, and a-hydroxysanshool, the primary active constituent of Sichuan pepper extract, were purchased and screened as synergists of natural pyrethrins. Both piperine and a-hydroxysanshool were shown to be synergists of natural pyrethrins both topically (SR = 13.9 and 8.5, respectively) and in vitro. Interestingly, only piperine was capable of synergizing natural pyrethrins on a pyrethroid-resistant strain of mosquitoes, indicating that both molecules possess a slightly different mechanism of action. To probe this question further, we evaluated the effects of both compounds on American cockroach giant axons. Both piperine and a-hydroxysanshool applied at 10 µM produce continually diminishing action potential amplitudes after continual stimulation when axons are stimulated at 10 Hz. However, a-hydroxysanshool produces marked depolarization in axon resting membrane potential, whereas piperine dose not. This activity-dependent block of action potentials in both compounds, but the differences in their ability to depolarize nerve membranes, may provide valuable information allowing for better understanding pf how these two pepper constituents synergize pyrethroids on both a pyrethroid-susceptible and pyrethroid-resistant strain. It is our hope that the identification and characterization of the effects of target-site synergists may lead to the development of more selective and potent pest control chemistries in the future.