Sample size and temporal variation effects on mortality of Colorado potato beetle (Coleoptera: Chrysomelidae) in a filter-paper bioassay
1993
Vencill, A.M. | Zehnder, G.W.
Filter-paper bioassays were performed on Colorado potato beetles, Leptinotarsa notarsa decemlineata (Say), collected from three commercial potato fields to determine the most cost-effective number of sample units (filter-paper disks, 10 larvae per disk). Relative net precision values from three different insecticide bioassays were used as an indication of sample-size efficiency and were based on variation in larval mortality and sample cost. Greatest sample-size efficiency in all insecticide bioassays was achieved from a sample of two to five filter-paper disk sample units (20-50 total larvae). Additional insecticide bioassays were done with Colorado potato beetle larvae collected at different times during the season (from a commercial potato field and from experiment-station plots) to determine whether the larval generation sampled or previous insecticide application affected results of the bioassay. Although trends in mortality were not always consistent among first generation larvae sampled on different dates (from insecticide-treated and untreated plots), first-generation larvae exhibited significantly greater mortality in the bioassay compared with second-generation larvae. Based on these results, it is recommended that bioassays to estimate the effectiveness of a particular insecticide against Colorado potato beetle be performed on the target generation immediately before the planned insecticide treatment.
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