Peter C Ellsworth

Judicious use of pesticides is generally accepted as an important pest-control tactic in integrated pest management programs, but not all pesticides are equally appropriate. When this project began, there was not an appropriate tool or set of criteria available to evaluate how well a proposed pesticide use fit within an IPM program. The Western Integrated Pest Management Center and Western Inter-Regional Project #4 (IR-4) collaborated to develop the IPM Compatibility Guidance Document—a set of criteria and instructions for evaluating the potential IPM fit of a proposed pesticide use. The IPM Criteria Guidance Document includes a set of instructions and examples to help IR-4 project requestors develop a ranking and a short narrative description (termed an IPM Fit Statement by the IR-4 Project) of a proposed pesticide use within an IPM program. The IPM Criteria Guidance Document lists 21 specific factors in eight categories—efficacy, economic benefit, nontarget effects, resistance concerns, environmental fate, worker risk, compatibility with monitoring, and utility as a preventative—with descriptors of affirmative, intermediate, and negative compatibility attributes. A survey of project requestors and their IPM Fit Statement submissions indicates that the IPM Criteria Guidance Document is helpful and its use increased the breadth of IPM factors addressed in IR-4 project requests. The IPM Criteria Guidance Document, as a model for formalizing pesticide ‘fit’ assessment, may have broader application in evaluating pest-management tools for their compatibility in IPM programs.

Abstract:

We tested enumerative and binomial sampling plans developed for Bemisia tabaci (Gennadius) in 3,240 ha of commercial cotton as part of the implementation of a community-wide integrated pest management (IPM) program in Laveen and Tolleson, AZ, in 1994. We compared new field observations to sampling distribution models developed previously for all lifestages, and validated and analyzed the performance of 5 sampling plans based on these models by resampling field data from 129 to 284 sites. Mean-variance relationships for the new data differed statistically from mean-variance models previously developed for adults, but not for eggs or nymphs. Resampling analyses indicated that desired precision (SE to mean ratio) was rarely achieved, on average, by fixed-precision sequential sampling plans. These enumerative sampling plans provided better precision than desired at moderate to high densities of eggs and adults and worse precision than desired at most densities of nymphs. An empirical model relating mean density to the proportion of leaves infested with 3 or more adult B. tabaci was accurate at mean densities 2 adults per leaf but over-predicted mean density at higher densities. Resampling analysis revealed that a sequential sampling plan based on this empirical model was accurate at classifying population density relative to an action threshold of 5 adults per leaf. At nominal α and β error rates of 0.10, population density was correctly classified ≈87% of the time. Accuracy was not improved by reducing nominal error rates to 0.05. Resampling analysis of a fixed-sample size plan based on n = 30 gave similar results and increasing sample size to 50 increased accuracy only 3%. Further resampling analyses that more closely approximated scouting protocols (15 sample units drawn from each of 2 quadrants in the field) resulted in an average accuracy of ≈70%. Accuracy declined when populations densities differed greatly among quadrants in a field. Most of this error was associated with making a decision to control when pest density was below the action threshold. Based on a robust validation technique using field observations representing a wide range of environmental and agronomic conditions, our sampling plans performed well and should be useful for estimating and classifying population densities of B. tabaci in cotton over a wide area.

CRC Press, Boca Raton

Pyriproxyfen has been an important insecticide used as part of an integrated pest management (IPM) program for the sweetpotato whitefly, Bemisia tabaci (Gennadius) (B biotype), in Arizona cotton. We used a simulation model to examine the effects of pyriproxyfen concentration, insecticide action thresholds, crop diversity, planting date, and pyriproxyfen decay on evolution of resistance to pyriproxyfen in B. tabaci. In the model, pyriproxyfen use was restricted to cotton with a limit of one application per season. Other model parameters were based on data from laboratory and field experiments. Whitefly population densities and the number of insecticide applications per year increased as resistance evolved. Resistance evolved slowest with a low pyriproxyfen concentration. Lower action thresholds for pyriproxyfen and higher action thresholds for insecticides other than pyriproxyfen also slowed the evolution of resistance. However, lower action thresholds for pyriproxyfen resulted in more insecticide sprays per year with a high pyriproxyfen concentration. Resistance to pyriproxyfen evolved fastest in cotton-intensive regions and slowest in multicrop regions. In regions with noncotton crops, increasing immigration to cotton slowed resistance. Resistance evolved faster with earlier planting dates, although fewer insecticide sprays were needed compared with fields planted later in the year. Faster rates of pyriproxyfen decay slowed resistance. In some cases, strategies that delayed resistance were effective from an IPM perspective. However, some strategies that delayed resistance resulted in higher population densities. Results suggest that modification of operational and environmental factors, which can be controlled by growers, could prolong the efficacy of pyriproxyfen.

doi: 10.1073/pnas.1117851109