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Title: BEMISIA GROWTH REGULATORS: A FIELD SAMPLING PROTOCOL FOR NYMPHS

Author
item DIEHL, J. - DEPT. ENTOMO. UNIV OF AZ
item Naranjo, Steven
item ELLSWORTH, P. - DEPT. OF ENTOMO. U OF AZ

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sweetpotato whitefly has been a key pest of cotton and other crops in the southwestern US since the early 1990þs. High populations of this pest can reduce lint yields and contribute to degradation of lint quality through the deposition of honeydew. In 1996 Arizona growers were granted an emergency registration of two new insect growth regulators for whitefly control. In order for growers to use these materials most effectively and efficiently it was necessary to develop a field sampling method for whitefly nymphs. We developed and evaluated a sampling and decision-making plan within a large-scale field experiment. The plan consisted of counting large, visible nymphs within a quarter-sized disk on the underside of 5th mainstem node leaves. A sample size of 30 leaves was found adequate at an action threshold density of 1 nymph per disk. Variation between different samplers counting the same leaf disk was significant and could compromise accurate decision-making. A binomial (presence/absence) sampling plan was found to greatly diminish this sampler while increasing the accuracy of decision- making.

Technical Abstract: We developed a sampling protocol for nymphs of the sweetpotato whitefly for timing the application of insect growth regulators. These plans require counting the number of large, visible nymphs within a 4 square centimeter leaf disk on the fifth mainstem node leaf down from the terminal. Use of insect growth regulators for whitefly control is recommended when whitefly densities from 30 plants average 0.5-1.0 large nymphs per disk and 3-5 adults per leaf. We evaluated these sampling and decision-making plans within a large-scale field experiment. Precision was adequate for densities of 1 large nymph per disk over greater, but sample sizes of greater than 30 are needed for lower densities. The ability of samplers to detect and categorize nymphal instars and sampler-to- sampler variation in this ability were significant sources of variation. A binomial (presence/absence) sampling plan may diminish sampler-sampler variation while increasing the accuracy of decision-making.