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Title: FIELD EVALUATION OF DIFFERENT INSECTICIDE USE STRATEGIES AS RESISTANCE MANAGEMENT AND CONTROL TACTICS FOR BEMISIA TABACI (HEMIPTERA: ALEYRODIDAE).

Author
item Castle, Steven
item TOSCANO, NICK - UNIV OF CA, RIVERSIDE
item PRABHAKER, NILIMA - UNIV OF CA, RIVERSIDE DEP
item Henneberry, Thomas
item PALUMBO, J - YUMA AGRIC CTR. U OF A

Submitted to: Bulletin of Entomological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2002
Publication Date: 12/1/2002
Citation: CASTLE, S.J., TOSCANO, N.C., PRABHAKER, N., HENNEBERRY, T.J., PALUMBO, J.C. FIELD EVALUATION OF DIFFERENT INSECTICIDE USE STRATEGIES AS RESISTANCE MANAGEMENT AND CONTROL TACTICS FOR BEMISIA TABACI (HEMIPTERA: ALEYRODIDAE).. BULLETIN OF ENTOMOLOGICAL RESEARCH. 2002. v. 92: 449-460

Interpretive Summary: Although a variety of resistance management strategies have been devised and, to some extent, are supported by theoretical arguments, there is relatively little empirical support to point to a particular strategy as being more or less vulnerable to resistance development. Assumptions used in theoretical arguments often represent very simplified portraits of reality, and even the theoreticians accept that practical testing of theory is required to understand what works under a particular set of conditions. Hence, we were interested in finding out if the sweetpotato whitefly Bemisia tabaci would show variable levels of resistance to particular insecticides when they were applied in different spray regimens corresponding to specific resistance management strategies. We tested a spray rotation using 4 different insecticides (bifenthrin, endosulfan, amitraz, chlorpyrifos) representing 4 chemical classes (pyrethroids, cyclodienes, formamidines, organophosphates, respectively) vs. a continuous regimen that used each of these 4 insecticides week after week and independently in separate plots. A single mixture treatment was also used that combined 2 of the 4 insecticides. After 10 consecutive weeks of spray treatments, there was little difference in the responses of whiteflies collected from the field plots and tested in laboratory bioassays. Although disappointing that the rotation regimen failed to affect the resistance levels in B. tabaci, this study helped point to the importance of mitigating factors such as immigration into field plots that can substantially delay the onset of resistance through matings of resistant and susceptible genotypes. This study also demonstrated the superior control provided by the mixture treatment.

Technical Abstract: Various insecticide use strategies including rotations, sequential use, and mixtures were evaluated experimentally on Bemisia tabaci (Gennadius) in California and Arizona (USA) cotton fields. Toxicological responses of adult B. tabaci were measured along with preimaginal densities and cotton yields from plots subjected to different insecticide regimens. Weekly monitoring for susceptibility changes over ten consecutive weeks in four different trials failed to detect significant differences between sequential use and rotation regimens, nor in comparison to the control plots. There were, however, significant differences among study-site locations and between study years as well as significant within-season time effects. Relative infestations in insecticide-treated plots expressed as a percentage of preimaginal densities in control plots indicated that better control was obtained by all insecticide treatments in conjunction with higher susceptibility levels observed in the second year. Lower preimaginal densities of B. tabaci were measured in the rotation treatment in comparison to sequential treatments of endosulfan, chlorpyrifos, or amitraz, but all were less effective than sequential treatments of bifenthrin or the mixture of bifenthrin+endosulfan. Cotton lint yields were inversely related to B. tabaci densities, with highest yields in the bifenthrin and mixture plots and lowest yields in the control plots. Suppression of B. tabaci infestations in insecticide-treated plots relative to untreated control plots also improved under conditions of lower B. tabaci pressure. The increases in cotton yield and susceptibility to insecticides seen in the current study support the trend observed in the southwestern USA of improved management of B. tabaci despite continuing intensive use of insecticides.