Tracking movement in small insect pests, with special reference to aphid populations

Abstract

Insects are among the greatest pests of agriculture, horticulture and forestry world-wide, inflicting damage and economic costs both directly and by transmitting plant viruses. Many kinds of insects are now resistant or cross-resistant to pesticides. In order to combat these pests, including for purposes of immediate control or to follow movements in order to better understand pest biology, tracking studies are important. In turn, such studies become useful for modelling and forecasting outbreaks. This is especially so for flying insects, which constitute the greatest threat in terms of the dissemination of plant pathogenic viral diseases. Tracking the aerial displacement of small insects over large spatial scales is difficult mainly because of their size. Dilution effects upon take off, together with displacement by air currents, makes the recapture of individuals tagged e.g. by fluorescent or radio-labelling, highly unlikely and hence estimates of flight direction, speed, duration and distance are hampered, more especially over larger distances. This is generally true also for larger insects. Consequently, molecular markers have been employed in attempts to resolve population structure and dynamics by inference from estimates of gene flow. In this article, we describe some of the methodologies devised that have provided invaluable information relating to the movement of small insect pests, particularly aphids, and explain how these techniques can be added to by detail gained from molecular marker studies. We outline a national survey-system that could be managed by specialist centres and involving members of the Public, that would enable invasive pest insect populations to be tracked efficiently. The logistics of such a survey are discussed along with the benefits. Overall, an insect tracking mandate is described that will promote the standardisation of population movement measurements. Adopting this approach should allow more accurate intra- as well as interspecies comparisons.