Migratory and foraging movements in beneficial insects: a review of radar monitoring and tracking methods

Knowledge of flight movement is crucial to an understanding of the ecology, behaviour, genetics and evolutionary success of most insect species. However, all but the shortest flights will frequently take the insect beyond the range of both human vision and many optoelectronic devices, and thus radar technology has a valuable role to play in several distinct areas of movement research. In this review, we firstly consider the monitoring of high-altitude windborne movements of insect natural enemies, with emphasis on how novel vertical-looking radars are being employed to observe the migrations of aphid predators in the UK. Secondly, we discuss how scanning radars, with and without harmonic tags, have increased our understanding of the foraging flights of beneficial pollinators (bees), and how this technique might be applied to natural enemies. Lastly, we outline the use of harmonic direction-finders in studying the pedestrian and short flight movements of various beneficial insects, including predators. In each case we highlight the strengths and limitations of the techniques, and the prospects for future advances.