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Evaluation of fixed sample-size plans for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli crops in Australia

Hamilton, A. J., Endersby, N. M., Schellhorn, N. A., Ridland, P. M., Rogers, P. M., Jevremov, D. and Baker, G. 2006, Evaluation of fixed sample-size plans for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli crops in Australia, Journal of economic entomology, vol. 99, no. 6, pp. 2171-2176, doi: 10.1603/0022-0493-99.6.2171.

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Title Evaluation of fixed sample-size plans for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli crops in Australia
Formatted title Evaluation of fixed sample-size plans for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli crops in Australia
Author(s) Hamilton, A. J.
Endersby, N. M.
Schellhorn, N. A.
Ridland, P. M.
Rogers, P. M.
Jevremov, D.
Baker, G.
Journal name Journal of economic entomology
Volume number 99
Issue number 6
Start page 2171
End page 2176
Publisher Entomological Society of America
Place of publication Lanham, Md.
Publication date 2006
ISSN 0022-0493
1938-291X
Keyword(s) broccoli
diamondback moth
fixed sample size
precision
sampling
Summary Fixed sample-size plans for monitoring Plutella xylostella (L.) (Lepidoptera: Plutellidae) on broccoli and other Brassica vegetable crops are popular in Australia for their simplicity and ease of application. But the sample sizes used are often small, ≈10–25 plants per crop, and it may be that they fail to provide sufficient information upon which to base pest control decisions. We tested the performance of seven fixed sample-size plans (10, 15, 20, 30, 35, 40, and 45 plants) by resampling a large data set on P. xylostella in commercial broccoli crops. For each sample size, enumerative and presence-absence plans were assessed. The precision of the plans was assessed in terms of the ratio of the standard error to the mean; and at least 45 and 35 samples were necessary for the enumerative and presence-absence plans, respectively, to attain the generally accepted benchmark of ≤0.3. Sample sizes of 10–20 were highly imprecise. We also assessed the consequences of classifications based on action thresholds (ATs) of 0.2 and 0.8 larvae per plant for the enumerative case, and 0.15 and 0.45 proportion of plants of infested for the presence-absence case. Operating characteristic curves and investigations of the frequency of correct decisions suggest improvements in the performance of plans with increased sample size. In both the enumerative and presence-absence cases, the proportion of incorrect decisions was much higher for the lower of the two ATs assessed, and type II errors (i.e., failure to suggest pest control upon the AT is exceeded) generally accounted for the majority of this error. Type II errors are the most significant from a producer’s standpoint. Further consideration is necessary to determine what is an acceptable type II error rate.
Language eng
DOI 10.1603/0022-0493-99.6.2171
Field of Research 010401 Applied Statistics
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©2006, Entomological Society of America
Persistent URL http://hdl.handle.net/10536/DRO/DU:30003634

Document type: Journal Article
Collection: School of Life and Environmental Sciences
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