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Title: Binomial sampling of western flower thrips infesting flowering greenhouse crops using incidence-mean models

Author
item UGINE, TODD - Cornell University
item SANDERSON, JOHN - Cornell University
item Wraight, Stephen
item SHIPP, LES - Agriculture Canada
item WANG, K. - Agriculture Canada
item NYROP, JAN - Cornell University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2011
Publication Date: 4/4/2011
Citation: Ugine, T.A., Sanderson, J.P., Wraight, S.P., Shipp, L., Wang, K., Nyrop, J.P. 2011. Binomial sampling of western flower thrips infesting flowering greenhouse crops using incidence-mean models. Environmental Entomology. 40(2):381-390.

Interpretive Summary: Pest population monitoring is an essential component of IPM programs, but the small size and cryptic habits of many insects makes them difficult to detect. Sampling of thrips, especially western flower thrips (WFT), a key pest of greenhouse vegetable and ornamental crops, is particularly problematic. Greenhouse growers and pest management scouts currently rely on yellow sticky cards for WFT monitoring. However, the relationship between sticky-card catches and thrips density in the crop are highly variable, and improved sampling methods are needed, especially methods effective across the great variety of ornamental crops produced in greenhouses. In this study our objective was to investigate the potential for using binomial sampling procedures for sampling WFT in mixed floral crops. Such methods greatly simplify the sampling procedure by requiring the pest manager to determine only that the sampled plant part is or is not infested based on a threshold number of insects. A mathematical model is then used to relate infestation rates to pest densities. When thrips infestation rates were determined by examining flower samples in the laboratory with the aid of a microscope, binomial sampling was found to provide accurate estimates of thrips densities across mixed crops. Investigations in the greenhouse revealed, however, that while using visual inspection to determine infestation rates produced reliable estimates of thrips densities in simple flowers (single impatiens), neither visual inspection nor flower tapping were reliable methods for assessing thrips infestations in complex flowers (marigolds). Results indicate that use of binomial sampling methods in mixed floral crops will require development of more accurate sampling techniques.

Technical Abstract: Accurate assessments of thrips density are important for effective thrips management programs. Complicating the development of sampling plans for western flower thrips (WFT) in greenhouse crops are the facts that these insects are small and difficult to detect and they attack a great variety of crops, which may be grown concurrently within the same greenhouse. Binomial sampling was therefore evaluated as an alternative to sampling plans based on complete enumeration. This work included comparison of incidence-mean models across diverse plant species (impatiens, cucumber, and marigold) to evaluate the possibility of using a generic model for sampling WFT in mixed crops. Data from laboratory-processed flower samples revealed that infestation rates calculated using a tally threshold of three thrips per flower provided best estimates of thrips population densities in each tested crop as well as in the combined crops (composite data set). Distributions of thrips populations were found similar across the three plant species, indicating potential for development of a generic sampling plan for mixed floral crops. Practical sampling methods for simple and complex flowers tested in the greenhouse (in situ) were evaluated via construction of binomial count operating characteristic functions. In the case of simple flowers (impatiens), visual inspections provided good estimates of thrips infestation rates at a low tally threshold, which ultimately enabled accurate estimation of thrips densities. On the other hand, neither visual inspection nor tap-sampling of complex flowers (marigold) provided reliable results. These findings indicate that use of binomial sampling methods in mixed floral crops will require development of more accurate sampling techniques.