Nootkatone Is an Effective Repellent against Aedes aegypti and Aedes albopictus.

Taylor C Clarkson,Ashley J Janich,William C Black Iv,Ken E Olson,Irma Sanchez-Vargas,Erin D Markle,Brian D Foy,John R Foster,Megan Gray

doi:10.3390/insects12050386

Abstract

Simple SummaryNootkatone, a natural organic compound in grapefruit and Alaskan yellow cedar, may have use as an insecticide and repellent against Aedes mosquito vectors of arboviruses. Here, we tested nootkatone against two medically important mosquito vectors, Aedes aegypti and Aedes albopictus. The insecticide potential of nootkatone was tested for both species using bottle bioassays and the repellency/irritancy and biting inhibition bioassays (RIBB) were used as tests for the A. aegypti strains only. We analyzed nootkatone’s insecticide potential against the New Orleans and Vergel strains of A. aegypti and ATM-NJ95 and Coatzacoalcos strains of A. albopictus. These strains were chosen because the New Orleans and ATM-NJ95 were permethrin susceptible (PERM-S) and Vergel was a confirmed permethrin resistant (PERM-R) strain. Coatzalcalcos was of unknown permethrin susceptibility. Permethrin is a commonly used insecticide to control mosquito populations, and permethrin resistance is becoming widespread in mosquito populations. We therefore wanted to compare nootkatone’s efficacy (and possible synergy) in the background of permethrin-susceptible and -resistant vectors. Bottle bioassays confirmed that the PERM-R Vergel strain was significantly less sensitive to nootkatone compared to PERM-S A. aegypti (New Orleans) and both A. albopictus strains were at least as sensitive to nootkatone as the New Orleans strain. We also showed that Zika virus (ZIKV)-infected New Orleans mosquitoes were as susceptible to nootkatone as the mock-infected controls. The infected Vergel strain was significantly less sensitive to nootkatone exposure than the New Orleans, ATM-NJ95, or Coatzacoalcos mosquitoes. In general, our studies concluded that as an insecticide, nootkatone was approximately 1000× less sensitive than permethrin, making it ineffective against A. aegypti and A. albopictus. However, RIBB analyses determined that nootkatone-treated arms of human subjects inhibited host-seeking and biting by A. aegypti mosquitoes. RIBB studies concluded that 20% nootkatone repelled mosquitoes at a rate comparable to commercially available N,N-Diethyl-m-toluamide (DEET; 7%) or picaridin (5%). Nootkatone has the potential to be an efficacious repellent against adult Aedes mosquitoes.We tested a nootkatone product for insecticide activity against the most prominent vectors of Zika virus (ZIKV), Aedes aegypti, and Aedes albopictus. We tested the permethrin-resistant (PERM-R) Vergel strain of A. aegypti and the permethrin-susceptible (PERM-S) New Orleans strain of A. aegypti to determine if insecticide resistance affected their susceptibility to nootkatone. Bottle bioassays showed that the PERM-S strain (New Orleans) was more susceptible to nootkatone than the confirmed A. aegypti permethrin-resistant (PERM-R) strain, Vergel. The A. albopictus strain ATM-NJ95 was a known PERM-S strain and Coatzacoalcos permethrin susceptibility was unknown but proved to be similar to the ATM-NJ95 PERM-S phenotype. The A. albopictus strains (ATM-NJ95 and Coatzacoalcos) were as susceptible to nootkatone as the New Orleans strain. Bottle bioassays conducted with ZIKV-infected mosquitoes showed that the New Orleans (PERM-S) strain was as susceptible to nootkatone as the mock-infected controls, but the PERM-R strain was less susceptible to nootkatone than the mock-infected controls. Repellency/irritancy and biting inhibition bioassays (RIBB) of A. aegypti determined whether the nootkatone-treated arms of three human subjects prevented uninfected A. aegypti mosquitoes from being attracted to the test subjects and blood-feeding on them. The RIBB analyses data calculated the spatial activity index (SAI) and biting inhibition factor (BI) of A. aegypti at different nootkatone concentrations and then compared the SAI and BI of existing repellency products. We concluded that nootkatone repelled mosquitoes at a rate comparable to 7% DEET or 5% picaridin and has the potential to be an efficacious repellent against adult A. aegypti mosquitoes.

Highlights

Aedes aegypti and Aedes albopictus are mosquito vectors that transmit medically important arthropod-borne viruses, infecting millions of people across the globe
Bottle bioassays were performed to verify that the PERM-S strains
Results from a previous study by Panella et al [9], showed that nootkatone and several of its derivatives, along with several other essential oil extracts, could be potential pesticide candidates for vector control against I. scapularis ticks, X. cheopis fleas, and A. aegypti mosquitoes based on the comparative LC50 /LC90 dose–mortality observations

Summary

Introduction

Aedes aegypti and Aedes albopictus are mosquito vectors that transmit medically important arthropod-borne viruses (arboviruses), infecting millions of people across the globe. Both vector species transmit dengue, chikungunya, and most recently, Zika viruses (ZIKV) [1]. No effective vaccines or antiviral therapies are available for widespread protection of humans from most arboviruses; the primary method of disease control is to target the vectors with insect repellents and insecticides [3]. There is a need for additional novel insect-control products that can be used as personal or household sprays, especially in areas where mosquitoes have developed resistance to insecticides and repellents [8]

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