CHAPTER 11 - Semi-field evaluation of arthropod repellents: emphasis on spatial repellents

Abstract

This chapter describes the attributes of topical and spatial arthropod repellents (SRs) and the use of semi-field environments to evaluate their efficacy parameters. Topical arthropod repellents are chemical compounds placed directly on the exposed skin and require either contact by the biting arthropods or very close proximity to stop them from biting at the very last stages of their feeding processes. In contrast, SRs are volatile compounds that become airborne and prevent/discourage blood-seeking arthropods from making physical contact or even entering a defined space occupied by a potential host, thus protecting it from bites. The SRs can reduce biting arthropod density and ultimately human-vector contact over a larger area as long as the active ingredient concentration in air is high enough to repel or kill the arthropod vectors. The focus of this chapter is on the use of semi-field environments to conduct efficacy testing of commercially available arthropod repellent products and the development of novel ones. Semi-field studies serve as a bridge between laboratory and field studies, and not a replacement for either. Not only are semi-field environments useful for understanding the biology and behavior of biting arthropods, but also for developing methods of control and disease mitigation. The structure and types of experiments that have been conducted in semi-field environments found worldwide are briefly summarized. While the dimensions of these screened enclosures varied, they were sufficiently large to reflect an area that SRs are intended to protect under local ambient environmental conditions. SR studies conducted at the USDA Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, United States, past, current, and future are presented in more detail.