Bioassays for attractants, to what end: aiding identification, measuring adaptive value, or verifying orientation mechanisms?

R.T. Cardé

Department of Entomology, University of California, Riverside, CA, USA.

Laboratory bioassays of insect attractants serve many masters. In identification, laboratory bioassays are used to monitor fractionation procedures for active components and ultimately to verify correct identification. Some identification bioassays, such as those commonly employed in wind tunnels, attempt to mimic most aspects of field behavior, whereas others rely on selected responses as being representative of the full behavioral repertoire. Do such truncated laboratory bioassays fall short, either by failing to reveal active components or by claiming behavioral activity for odors that in the field seem inactive? A second issue, measuring the adaptive value of attraction and attractive odorants, often involves simple, two-choice bioassays. These can produce valuable insights into an organism’s behavioral capabilities, but they also can present artificial choices that would rarely, if ever, be encountered in the field. Comparisons using no-choice assays and choice assays with positive controls offer complimentary approaches. Varying the duration of assays also can influence their outcome. A third area of inquiry is establishing the maneuvers and multiple sensory inputs that culminate in location of the odorant’s source. The term “attractant” conveniently denotes the ‘end point’ of displacement, and this level of analysis may be sufficient for understanding the ecological and evolutionary value of attractants. Several very different orientation mechanisms, however, can modulate finding of odorant source in wind and still air. To date, in-flight maneuvers have been documented mainly with video in 2-D planar view; however, a 3-D perspective can be critical to understanding orientation maneuvers. These principles will be illustrated with selected examples with moth and beetle attraction to pheromone and female mosquito attraction to host odorants.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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