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

Author
item DIEHL, JOHN - UNIV OF AZ, MAC
item Naranjo, Steven
item ELLSWORTH, PETER - UNIV OF AZ, MAC

Submitted to: University of Arizona Agricultural Experiment Station
Publication Type: Experiment Station
Publication Acceptance Date: 6/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: In 1996 two new insect growth regulators were granted an emergency registration in Arizona for use against the sweetpotato whitefly, a devastating pest of cotton in the southwestern US. In order to use these insecticides most effectively and extend their longevity in the field it will be necessary to carefully monitor pest density and time control efforts. We developed a sampling protocol for nymphs of the whitefly for timing the application of insect growth regulators. These plans require counting the number of large, visible nymphs within a 4 square centimeter disk on the fifth mainstem node leaf of a cotton plant. Use of insect growth regulators is recommended when pest densities from 30 plants averages 0.5-1.0 large nymphs per disk and 3-5 adults per whole leaf. We evaluated the protocols within a large-scale field experiment. Sampling precision was adequate for densities greater than or equal to 1.0 large nymph per disk. 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 variation while increasing efficiency and 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 3.88 cm sq leaf disk on the fifth main stem 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.O 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 1.0 large nymph per leaf and greater but sample sizes 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 efficiency and accuracy of decision-making.