Radar observations of individual desert locusts (Schistocerca gregaria (Forsk.) (Orthoptera, Locustidae))

Abstract

AbstractTechniques used in the radar detection and identification of individual flying insects are outlined, and laboratory and field measurements of the radar cross section of the desert locust, Schistocerca gregaria (Forsk.), are presented. The cross section was strongly aspect-dependent, and had an average value of approximately 1 cm2 at a radar wavelength of 3·2 cm. An example is given of the periodic fluctuation in radar cross section (the radar ‘signature’) produced by locusts in free flight, and the spectral contents of the signatures obtained from 35 laboratory-bred free-flying locusts are described. The fundamental components of the signatures, presumed to be at the wing beat frequency, were closely grouped about 23 Hz. It is suggested that the feasibility of using radar signatures as a means of insect identification will largely depend on the degree to which the species of interest are characterised by specific wing beat frequencies. Estimates of locust flying speed and heading deduced from photographs of locust and balloon radar tracks produced a mean value of 5·3 m s-1. Undetected small-scale flight manoeuvres may introduce negative errors in the estimation of flying speed. It is concluded that radar will provide unique observational facilities for the entomologist but that the limitations introduced by the problem of target recognition have yet to be defined.