Peter C Ellsworth

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Fifty years ago, Stern, Smith, van den Bosch and Hagen outlined a simple but sophisticated idea of pest control predicated on the complementary action of chemical and biological control. This integrated control concept has since been a driving force and conceptual foundation for all integrated pest management (IPM) programs. The four basic elements include thresholds for determining the need for control, sampling to determine critical densities, understanding and conserving the biological control capacity in the system and the use of selective insecticides or selective application methods, when needed, to augment biological control. Here we detail the development, evolution, validation and implementation of an integrated control (IC) program for whitefly, Bemisia tabaci (Genn.), in the Arizona cotton system that provides a rare example of the vision of Stern and his colleagues. Economic thresholds derived from research-based economic injury levels were developed and integrated with rapid and accurate sampling plans into validated decision tools widely adopted by consultants and growers. Extensive research that measured the interplay among pest population dynamics, biological control by indigenous natural enemies and selective insecticides using community ordination methods, predator:prey ratios, predator exclusion and demography validated the critical complementary roles played by chemical and biological control. The term 'bioresidual' was coined to describe the extended environmental resistance from biological control and other forces possible when selective insecticides are deployed. The tangible benefits have been a 70% reduction in foliar insecticides, a >$200 million saving in control costs and yield, along with enhanced utilization of ecosystem services over the last 14 years.

Abstract:

Natural mortality is an important determinant of the population dynamics of a species, and an understanding of mortality forces should aid in the development of better management strategies for insect pests. An in situ, observational method was used to construct cohort-based life tables for Bemisia tabaci (Gennadius) Biotype B (Homoptera: Aleyrodidae) over 14 generations on cotton in central Arizona, USA, from 1997 to 1999. In descending order, median marginal rates of mortality were highest for predation, dislodgment, unknown causes, egg inviability, and parasitism. The highest mortality occurred during the 4th nymphal stadium, and the median rate of immature survival over 14 generations was 6.6%. Predation during the 4th nymphal stadium was the primary key factor. Irreplaceable mortality was highest for predation and dislodgment, with the absence of these mortality factors leading to the greatest increases in estimated net reproduction. There was little evidence of direct or delayed density-dependence for any mortality factor. Wind, rainfall, and predator densities were associated with dislodgment, and rates of predation were related to densities of Geocoris spp., Orius tristicolor (White), Chrysoperla carnea s.l. Stephens, and Lygus hesperus Knight. Simulations suggest that immigration and emigration play important roles in site-specific dynamics by explaining departures from observed population trajectories based solely on endogenous reproduction and mortality. By a direct measurement of these mortality factors and indirect evidence of adult movement, we conclude that efficient pest management may be best accomplished by fostering greater mortality during the 4th stadium, largely through a conservation of predators and by managing immigrating adult populations at their sources. © 2005 The Netherlands Entomological Society.

Abstract:

Lygus management has become more important in Arizona cotton in the last few years due to a series of factors. Two of these factors, widespread availability of insect growth regulators (IGRs) for whitefly control and transgenic 'Bt' cotton for lepidopteran control, have resulted in a drastic reduction in the number of Lygus-active insecticides sprayed in our cotton systems (see Ellsworth, this volume). In 1995, an average of 12.5 foliar insecticide sprays for all insects (1.26 directed at Lygus) were made in Arizona cotton, many of which had some degree of Lygus activity (see Williams, 1996-1998). In 1997, this was reduced to 5.33 applications (2.10 directed at Lygus), and about 0.5 of these were IGRs which have no Lygus activity. This reduction in use has effectively opened a window during which Lygus can cause damage and promoted this pest to major status. Another factor that has also raised the prominence of this pest in our landscape is the substantial increase in alfalfa acreage, including some seed alfalfa, in Arizona. When any 'old' pest comes into prominence, there are often complaints about insecticide spectrum, residual, and performance. In addition, in spite of the reduction in overall foliar insecticide use, resistance to insecticides is an ever-present threat which may be present and may or may not be impacting insecticide performance in each area of production (Dennehy, this volume; Pacheco, this volume). Whatever the causes that have elevated Lygus pest status, we must consider susceptibility management of this and all other pests when constructing sustainable integrated pest management strategies. While this paper was invited to address the problem over the entire West and over multiple crops, my focus will be on Arizona cotton only. The necessity of this approach becomes obvious after considering the large differences in management and chemical efficacy between California (Godfrey, this volume) and Arizona (Pacheco, this volume). Nonetheless, the tenets of susceptibility management are equally relevant across all regions and all crops. They are in their simplest forms: 1) limit insecticide use to the lowest practical level; 2) diversify insecticide use patterns; and 3) partition insecticides among crops and pests such that modes of action are segregated as much as is practically possible.