|ELLSWORTH, PETER - UOFA, MAC, MARICOPA, AZ
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2009
Publication Date: 12/15/2009
Citation: Naranjo, S.E., Ellsworth, P.C. 2009. The Contribution of Conservation Biological Control to Management of Bemisia tabaci in Cotton: A Life Table Analysis. Biological Control. 51: 458-470.
Interpretive Summary: The sweetpotato whitefly is a key pest of cotton and other crops in Arizona and many parts of the world. Natural enemies, primarily predatory arthropods, can cause high levels of mortality in whitefly populations but insecticides are routinely needed to control pest populations in cotton. Field life table studies were conducted to measure comparative mortality factors impacting whitefly populations when using different control methods. Regardless of the type of insecticide used, pest populations were immediately suppressed and life table analyses showed that insecticides were the main driving force. However, during periods 3-6 wks following these applications, predation returned to the high levels observed in untreated plots and were the main driving force affecting whitefly populations, but only when selective insecticides were used. Generally, only a single application of a selective insecticide was needed to achieve pest suppression throughout the season while as many as five applications of broad-spectrum materials were needed to achieve the same goal. We call this phenomenon the “bioresidual”, which is analogous to the term “residual” commonly used to describe longer term effects of insecticides, because it is the biological control components of the system that permits long-term pest control following the initial use of selective insecticides. This bioresidual is key to the success of whitefly management in cotton and has reduced insecticide use by nearly 90% since 1995.
Technical Abstract: Natural enemies in Arizona cotton can be conserved with the use of selective insect growth regulators (IGRs) for control of Bemisia tabaci. To examine the interaction of mortality forces, cohort-based life tables were constructed for B. tabaci populations subject to three different pest control strategies over a three year period. Immediately following the application of broad-spectrum insecticides or either of the selective IGRs (buprofezin or pyriproxyfen), insecticide mortality was high and assumed the role of key factor. Compared with an untreated control, this mortality generally replaced that provided by natural enemies and in all regimes. However, during periods 3-6 wks following initial insecticide application, natural enemy induced mortality, primarily predation, returned to the high levels observed in untreated plots and assumed the role of key factor in the IGR plots. Mortality by natural enemies remained depressed in plots receiving applications of broad-spectrum materials. Generally, a single application of either IGR was sufficient to suppress B. tabaci populations throughout the season. In contrast, as many as five applications of broad-spectrum compounds were needed to maintain the same level of season-long control. Because the chemical residual of the IGRs was limited to several weeks, results suggest a key role for mortality from conserved natural enemies. This effects, coined the “bioresidual”, allows for long-term pest control following the initial use of selective insecticides.