I offer the following comments in amplification of Jerry Bromenshenk's recent note about harmonic radar and bees, which appeared under the subject 'Research Funding' The hand held 'skier' units to which Jerry refers are often loosely called radars, but in fact they are actually harmonic direction finders - they tell you roughly in what direction the target is, but crucially, NOT its range; (RADAR = RAdio Direction And Ranging). So to locate a target you have to walk (or run!) along the direction of strongest signal until you can actually see it. By contrast, the system that we designed and built, and used with Beth Capaldi is a true, scanning radar that gives instantaneous position fixes (target range and bearing) once every three seconds, and so yields dynamic and geometrically accurate records of the insects' actual flight paths. You don't have to guess where a bee is when it's out of sight, you KNOW its actual position (and ground speed). The maximum range of our radar is currently about 900m, so it gives coverage over a 1.8 km diameter circle, i.e. over an area of about 2.5 square kilometres. We first described it in 1996 (Riley et al. "Tracking bees with harmonic radar", Nature 379, 29-30) An interesting summary of radar and bee studies is given in Norman Carreck's 1993 article in Bee World, 80 (3), 124-131. Harmonic radar has proved particularly useful in investigating flight by bumble bees: (Riley et al 1999, "Compensation for the wind by bumble bees", Nature 400, 126); (Osborne et al., 1999 "A landscape-scale study of foraging range and constancy, using harmonic radar" J. Appl. Ecol 36, 519-533). We have also used it successfully to track night-flying moths (Riley et al. 1998, "Harmonic radar as a means of tracking the pheromone-finding and pheromone-following flight of male moths", J. Insect. Behav. 11, 287-296). For a more general overview of radar entomology, see Alistair Drake's excellent Radar Entomology Web Site (http://www.ph.adfa.edu.au/a-drake/trews/). Jerry correctly draws attention to the need to keep the weight of the transponder as low as possible, and we have produced operational devices that weigh just less than one milligram (equivalent to about a single grain of sugar) with this in mind. However, these lightweight transponders were mechanically rather fragile, and were often bent and damaged when being fitted to the bees. It was for this practical reason that we often choose to use the heavier and more robust versions described in Beth's paper. Unfortunately, all our transponders are 16mm long (but about 1 tenth of the optimal required for the hand-held direction finders), so (as Jerry points out) they have to be removed before returning bees can actually re-enter their hive. This is inconvenient, but has not proved an impossible obstacle in our studies so far. -- Prof. Joe Riley, M.A., D.Phil., FIEE, C.Eng. NRI Radar Unit, University of Greenwich, Malvern, UK Tel: +44-(0)1684-582193 Fax: +44-(0)1684-582984 [log in to unmask] / [log in to unmask]