Current and Future Repellent Technologies: The Potential of Spatial Repellents and Their Place in Mosquito-Borne Disease Control

Abstract

Every year, approximately 700,000 people die from complications associated with etiologic disease agents transmitted by mosquitoes. While insecticide-based vector control strategies are important for the management of mosquito-borne diseases, insecticide-resistance and other logistical hurdles may lower the efficacy of this approach, especially in developing countries. Repellent technologies represent another fundamental aspect of preventing mosquito-borne disease transmission. Among these technologies, spatial repellents are promising alternatives to the currently utilized contact repellents and may significantly aid in the prevention of mosquito-borne disease if properly incorporated into integrated pest management approaches. As their deployment would not rely on prohibitively expensive or impractical novel accessory technologies and resources, they have potential utility in developing countries where the burden of mosquito-borne disease is most prevalent. This review aims to describe the history of various repellent technologies, highlight the potential of repellent technologies in preventing the spread of mosquito-borne disease, and discuss currently known mechanisms that confer resistance to current contact and spatial repellents, which may lead to the failures of these repellents. In the subsequent section, current and future research projects aimed at exploring long-lasting non-pyrethroid spatial repellent molecules along with new paradigms and rationale for their development will be discussed.

Keywords: DEET; biorational; contact; disease; mosquito; para-menthane-3,8-diol; pyrethroid; repellent; resistance; spatial.

Figure 1

Equation describing the vectorial capacity of a particular vector population. m = mosquito abundance, a = interaction describing the man-biting rate, p = probability of daily mosquito survival, n = extrinsic incubation period (EIP) in days [30].

Figure 2

The relative spatial repellency of various plant essential oils at points immediately after treating a surface and after a five hour waiting period. Adult mosquitoes are placed in a closed 2-ft × 90-mm diameter cylinder, with one side containing a filter paper treated with the plant essential oil of interest. Relative mosquito abundance on both sides is quantified throughout the experimental interval to calculate percentage repellency. (a) Corresponds to the repellency caused by the plant essential oils if mosquitoes are immediately exposed to the filter paper after treatment and (b) corresponds to the repellency caused by various plant essential oils if mosquitoes are exposed to the treated filter paper after it is allowed to dry for 5 h. Oils that are predominantly composed of monoterpenoids (citronella and thyme oil) cause rapid, high levels of repellency in the short-term assay, with relatively lower values of repellency in the long-term assay. Oils that are composed primarily of repellent sesquiterpenoids cause lower immediate repellency, but maintain a higher level of repellency in the long-term assay (amyris oil).