How aphids find their host plants, and how they don't

There is a considerable interest in trying to understand how aphids find their host plants because they are a major cause of economic losses in agricultural and horticultural production systems. Indeed, the specific behavioural sequences during host finding by aphids are one of the main reasons for their prominent role as vectors of plant pathogenic viruses. This paper reviews the visual and olfactory stimuli involved in host-finding behaviour of aphids, both basic and applied aspects are covered. Although controlling aphids by manipulation of visual and olfactory stimuli involved in host finding and host selection can be highly successful, as shown by research, most of these measures can still be further optimised and adoption in practice is currently limited. Research therefore needs to address some critical open questions, including ( a) the effects of visual contrasts on aphid behaviour; (b) the specific responses of aphids to ultraviolet (UV) light during different stages in host finding; ( c) the quantification of behavioural sequences in the field and (d) the response of aphid behaviour to plant diversity at varying spatial scales; further, ( e) a much more comprehensive coverage of aphid taxa and aphid ecological groups is needed in host-finding related research to uncover ecological principles underlying this critical behaviour.