Comparison of two computer techniques and a visual technique for the estimation of wheat leaf consumption by cereal leaf beetle (Coleoptera : Chrysomelidae)

Three techniques for estimating wheat foliage defoliation by cereal leaf be etle, Oulema melanopus (L.), larvae were evaluated. The techniques were vis ual estimation, computer estimation with image capture through a flatbed sc anner (Lanalyze), and a commercially available Video computer image analysi s system (CIAS). Both computer-assisted techniques exhibited high levels of repeatability. Both consistently produced errors of less than 3 percent, a lthough each system exhibited different error patterns. The Lanalyze system tended to systematically underestimate actual defoliation of mock leaves, while the CIAS system tended to overestimate actual defoliation. Visual est imators exhibited greater Variation among estimates and, on average, greate r discrepancies from actual defoliation when compared with the computer ass isted techniques. The experience of the observer had a bearing on the accur acy and consistency of Visual estimates; more experienced observers had the best accuracy.