Volatile Cues Influence Host-Choice in Arthropod Pests

Abstract

Many arthropod pests of humans and other animals select their preferred hosts by recognising volatile odour compounds contained in the hosts' 'volatilome'. Although there is prolific literature on chemical emissions from humans, published data on volatiles and vector attraction in other species are more sporadic. Despite several decades since the identification of a small number of critical volatiles underpinning specific host-vector relationships, synthetic chemicals or mixtures still largely fail to reproduce the attractiveness of natural hosts to their disease vectors. This review documents allelochemicals from non-human terrestrial animals and considers where challenges in collection and analysis have left shortfalls in animal volatilome research. A total of 1287 volatile organic compounds were identified from 141 species. Despite comparable diversity of entities in each compound class, no specific chemical is ubiquitous in all species reviewed, and over half are reported as unique to a single species. This review provides a rationale for future enquiries by highlighting research gaps, such as disregard for the contribution of breath volatiles to the whole animal volatilome and evaluating the role of allomones as vector deterrents. New opportunities to improve vector surveillance and disrupt disease transmission may be unveiled by understanding the host-associated stimuli that drive vector-host interactions.

Keywords: VOC; allelochemical; allomone; host–parasite interactions; kairomone; non-host volatile; vector; volatilome.

Figure 1

Relative proportion of volatile organic compounds (VOCs) in different chemical classes that have been documented from domestic animal emissions, and across all species reviewed. Numbers in parentheses are the total number of unique compounds reported for the species. Percentages indicate the relative abundance of chemical entities described in each compound class, not their relative concentrations.

Figure 2

Olfactory attractants of tsetse flies (Glossina) from bovine volatile emissions. Broken outlines delineate the different odour compartments from which the analytes are emitted. Solid boxes identify chemical structures that have been shown to demonstrate both electroantennographic and behavioural activity.

Figure 3

Number of bioactive volatiles from bovine rumen odour that have been shown to stimulate electrophysiological and/or behavioural activity in tsetse fly (39), stable fly (31), and tick (13) species. Numbers in parentheses indicate the total number of allelochemicals in rumen emissions for each pest type; numbers in compartments of the figure show the chemicals with allelochemical function that are shared by different arthropod taxa [138].

Figure 4

Volatile organic compounds derived from microbial metabolism of hoopoe uropygial secretions [86]. Generation of malodorous fatty acid shows similarities to the compounds produced by cutaneous bacteria on human skin [156].