A time-efficient method of counting insects caught on yellow sticky traps was developed for use in greenhouses. The distributions of trapped insects were examined with three-way G tests using log-linear models on 344 yellow sticky traps (11.5 by 14 cm) used to monitor three commercial greenhouses in 1986. Four taxa, Diglyphus begini (Ashmead), Frankliniella occidentalis (Pergande), Liriomyza trifolii (Burgess), and Trialeurodes vaporariorum Westwood, tended to cluster along the vertical trap plane but each tended to be uniformly distributed along the horizontal trap plane. These results suggested that the number of insects caught on a trap could be estimated accurately by counting a 2.3-cm-wide vertical strip of the trap. This hypothesis was tested in four commercial greenhouses monitored with 586 yellow sticky traps in 1987 and 1989. Trap-catch estimates from vertical strip counts were not significantly different from whole-trap counts (paired t tests) for six of the seven taxa caught on traps in these greenhouses. All regression coefficients obtained from least-squares linear regressions were significantly >0.2, and column counts (independent variable) explained >90% of the observed variation in wholetrap counts (dependent variable) in 12 of the 23 cases examined. We concluded that 2.3-cm-wide vertical strip counts accurately predict insect densities on an entire trap. Because only 20% of the trap area is counted, the technique presented reduces counting time by 80% compared with whole-trap counts.
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Heinz et al. (1992) studied this question.