An IPM Synthesis

The practice of IPM over the years has generated substantial criticism for its continued heavy reliance on pesticides to curtail pest infestations. New paradigms have been proposed in an effort to correct the persistent skew towards chemical control. For example, "biologically intensive IPM'' that relies on host-plant resistance, biological control and cultural control was introduced as an alternative to chemically intensive IPM.126 A similar emphasis was expressed in "ecologically based pest management" that emerged from a committee convened by the National Research Council's Board of Agriculture, but one that was criticized21 for having essentially the same goals of IPM, but with a loftily stated focus on safety, cost-effectiveness, sustainability and ecosystems. There have been other elaborations of IPM, e.g. "IPM implementation at three levels of integration''21 that really only obfuscate the simple elegance contained in the principles of the integrated control concept.16 These principles have endured at the very core of IPM because they provide a robust methodology for determining if and when a pesticide application should be made. It was the solid linking of this methodology to the economic bottom line of the grower that makes the integrated control concept so powerful, so easily adoptable. It also included, however, the compelling argument regarding the potential of environmental resistance to limit pest populations, and how efforts should be made to preserve biological control and not upset it. It is these underlying values of the integrated control concept, and by extension IPM, that get lost in the more familiar and oft-quoted instructions to apply pesticide when the ET has been reached, which if practiced in the context of the whole of the integrated control concept is laudable. Where it too often comes up short, however, is that the ET has almost certainly been arbitrarily and comfortably defined on the side of safe rather than sorry.

There are very few examples of IPM programs that are true to the fundamentals of IPM that include the empirical determination of ET and EIL, the development of a statistically based sampling program, or the incorporation of selective insecticides to better conserve natural enemies. It can require many years and much effort to develop each one of these components to a level where they can be brought together into a cohesive and complete IPM program. An outstanding example of tying all components together into a comprehensive IPM program is one that was developed in Arizona for control of B. tabaci in cotton. Research had begun in the early 1990s at a time when perennial outbreaks of B. tabaci were severely disrupting agricultural production in the southwestern USA. Early studies were concerned with identifying spatial distributions of B. tabaci on a cotton plant to identify a representative leaf posi-

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tion to serve as a sample unit. - In addition, insect growth regulator (IGR) insecticides not yet registered for commercial use were being evaluated for their efficacies and selectivity towards natural enemies.130,131 Action thresholds were determined empirically132,133 and refined over time to configure to different treatment regimens. The compelling event that brought it all together was a resistance crisis that occurred during the 1995 cotton season.134 Putting together an IPM program in time for the 1996 season required pushing through emergency registrations on the two IGRs, buprofezin and pyriproxyfen (see Figure 9.6), to the U.S. Environmental Protection Agency, and then training growers in workshops conducted around the state on how to most effectively

Figure 9.6 Structures of buprofezin (IRAC group 16: Inhibitors of chitin biosynthesis, type 1) and pyriproxyfen (IRAC group 7C: juvenile hormone mimics).

use the IGRs. The training was required as a condition of the emergency registration and provided the opportunity to familiarize growers with the different elements of the IPM program including how to sample for whiteflies and how to know when an economic threshold (ET) had been reached.

Implementation of the new IPM program beginning in 1996 produced almost immediate results, as whitefly populations were kept under control with fewer insecticide treatments. This began a pattern of decreasing insecticide use each year until a low point was reached in 2001, after which other new insecticides became available that tended to disrupt the integrity of the IGR-based IPM program. In the meantime, further research that examined differences in fields where conventional broad-spectrum insecticides were sprayed to those that were treated with the IGR insecticides began to reveal a crucial component of the program's success. Life table studies performed in the field were able to partition and identify the different sources of whitefly mortality in the conventional versus IGR-treated fields. The findings that were most evident and consistent through all comparisons were that treatments with either IGR supported more natural enemies than the conventional treatments, and that a single application of a broad spectrum insecticide could significantly affect the beneficial arthropod community for up to 7 weeks.135 In contrast, predator : prey ratios in the IGR-treated cotton recovered relatively quickly following applications, as the beneficial insects continued to supply a significantly larger component of mortality relative to the conventional-treated cotton. This phenomenon of a decline in immature whitefly numbers soon after a treatment with an IGR, but then persisting at depressed levels beyond the time when a chemical residual would still be effective, gave rise to the concept of bioresidual activity as the beneficial insects rapidly re-colonized and continued to suppress whitefly numbers. The bioresidual finding is a powerful example of how chemical and biological controls can be integrated to produce a stable and sustainable IPM. Since 1996, a 70% reduction in foliar insecticides has been realized along with a >$200 million saving in control costs.135

The whitefly IPM program in Arizona demonstrates that when the core principles of IPM are observed and put into practice, a reduction in insecticide use and an increase in natural enemy effectiveness are not only possible for a single season, but can become a stable and persistent outcome. Another important change that occurred in Arizona cotton was the large-scale adoption of Bt cotton for control of the pink bollworm that began in 1996 and increased to 60-80% of total cotton acreage over the next decade.135 The reduction in insecticide applications against the pink bollworm also benefitted the natural enemy populations in cotton, possibly advancing the breadth of biocontrol in conjunction with the IGRs used against whiteflies. Perhaps the most impressive aspect of this IPM success story is that we have a thorough understanding of why it has been successful. The research that first went towards the development of the IPM methods, and then into the determination of what was working and why, is both exceptional and exemplary of what can be achieved in pest management. Further understanding and knowledge like that gained from the

Arizona experience will be needed to support sustainable intensification3 and increase food production to the levels required to meet the growing human demand.

These lessons may also prove valuable in the fight against insects that serve as vectors of infectious agents that cause diseases such as malaria in humans. Managing mosquitoes and other disease vectors is a challenging endeavor due to the involvement of aquatic habitats that are often intricate parts of natural habitats. Maintaining eco-balance to encourage natural control of both immature and adult stages is of obvious importance for avoiding vector outbreaks and spillover to populated areas. The use of IPM methodologies against vector species is more realistic in populated areas, where avoidance measures must be emphasized to curtail breeding sites for mosquitoes across the landscape. However, the much more dispersed nature of micro-breeding habitats for mosquitoes is a significant departure from the concentrated nature of crop pests that can be easily targeted using biological or chemical control tactics. Vector control agencies play vital roles in managing mosquitoes in aquatic habitats that are dispersed through rural and urban settings, but also rely on an educated public to contribute to the management effort by preventing ephemeral breeding habitats from forming during rainfall events. As with crop protection, effective management of vector insects requires an informed workforce to be aware of the pest and disease potential and to take appropriate action when required. More than just the farmer that faces the consequences of insufficient pest management in crops, every person within endemic disease zones potentially pays the price for inadequate vector control.

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