methodology-for-developing-life-tables-for-sessile-insects-field

Methodology for Developing Life Tables for Sessile Insects in the Field Using the Whitefly, <em>Bemisia tabaci</em>, in Cotton As a Model System

Life tables provide a means of measuring the schedules of birth and death from populations over time. They also can be used to quantify the sources and ...

USDA-ARS, Arid-Land Agricultural Research Center

Four sampling methods that included A-Vac, D-Vac, pole-bucket, and beat-net devices were evaluated for estimating relative densities of glassy-winged sharpshooter, Homalodisca vitri-pennis (Germar) (Hemiptera: Cicadellidae) nymphs and adults on citrus (Citrus spp.) trees. All four methods produced similar temporal and spatial distribution profiles, although significant differences in quantities of H. vitripennis adults and nymphs caught by each device were observed. The four sampling methods also showed a consistent male bias in adult populations across a range of densities, suggesting that previously reported male-biased sex ratios in H. vitripennis adult populations are real and not a product of sampling bias. A strong relationship (R2 = 0.95) between the monitoring methods we evaluated and yellow sticky trap catches of female H. vitripennis adults suggest that yellow sticky trap catches may provide a good relative index of infestation levels in citrus trees. Based on quantitative analyses examining precision and cost, the pole bucket was the most efficient method for sampling nymphs, and it was as efficient as the beat-net method for sampling adults and both stages combined. In addition to these analyses, consideration of other sampling characteristics such as added flexibility in sampling and higher sensitivity in detecting infestations within individual trees helped to fortify the conclusion that the pole bucket was the best overall sampling method of those tested.

Comparison of sampling methods for determining relative densities of Homalodisca vitripennis (Hemiptera: Cicadellidae) on citrus.

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.

Fifty years of the integrated control concept: moving the model and implementation forward in Arizona.

Transgenic cotton that produced one or more insecticidal proteins of Bacillus thuringiensis (Bt) was planted on over 15 million hectares in 11 countries in 2009 and has contributed to a reduction of over 140 million kilograms of insecticide active ingredient between 1996 and 2008. As a highly selective form of host plant resistance, Bt cotton effectively controls a number of key lepidopteran pests and has become a cornerstone in overall integrated pest management (IPM). Bt cotton has led to large reductions in the abundance of targeted pests and benefited non-Bt cotton adopters and even producers of other crops affected by polyphagous target pests. Reductions in insecticide use have enhanced biological control, which has contributed to significant suppression of other key and sporadic pests in cotton. Although reductions in insecticide use in some regions have elevated the importance of several pest groups, most of these emerging problems can be effectively solved through an IPM approach.

Impacts of Bt transgenic cotton on integrated pest management.

Lesquerella, Physaria fendleri (A. Gray) S. Watson, is a mustard native to the western United States and is currently being developed as a commercial source of valuable hydroxy fatty acids that can be used in a number of industrial applications, including biolubricants, biofuel additives, motor oils, resins, waxes, nylons, plastics, corrosion inhibitors, cosmetics, and coatings. The plant is cultivated as a winter-spring annual and in the desert southwest it harbors large populations of arthropods, several of which could be significant pests once production expands. Lygus spp. (Hemiptera: Miridae) are common in lesquerella and are known pests of a number of agronomic and horticultural crops where they feed primarily on reproductive tissues. A 4-yr replicated plot study was undertaken to evaluate the probable impact of Lygus spp. on production of this potential new crop. Plant damage and subsequent seed yield and quality were examined relative to variable and representative densities of Lygus spp. (0.3-4.9 insects per sweep net) resulting from variable frequency and timing of insecticide applications. Increasing damage to various fruiting structures (flowers [0.9-13.9%], buds [1.2-7.1%], and seed pods [19.4-42.5%]) was significantly associated with increasing pest abundance, particularly the abundance of nymphs, in all years. This damage, however, did not consistently translate into reductions in seed yield (481-1,336 kg/ha), individual seed weight (0.5-0.7 g per 1,000 seed), or seed oil content (21.8-30.4%), and pest abundance generally explained relatively little of the variation in crop yield and quality. Negative effects on yield were not sensitive to the timing of pest damage (early versus late season) but were more pronounced during years when potential yields were lower due to weed competition and other agronomic factors. Results suggest that if the crop is established and managed in a more optimal fashion, Lygus spp. may not significantly limit yield. Nonetheless, additional work will be needed once more uniform cultivars become available and yield effects can be more precisely measured. Densities of Lygus spp. in unsprayed lesquerella are on par with those in other known agroecosystem level sources of this pest (e.g., forage and seed alfalfa, Medicago sativa L.). Thus, lesquerella production may introduce new challenges to pest management in crops such as cotton.

Impact of Lygus spp. (Hemiptera: Miridae) on damage, yield and quality of lesquerella (Physaria fendleri), a potential new oil-seed crop.

A concern with Bt-transgenic insect-resistant plants is their potential to harm non-target organisms. Early studies reported that Cry1Ab-producing Bt maize and purified Cry1Ab harmed larvae of the green lacewing, Chrysoperla carnea. Although these effects could not be confirmed in subsequent studies, some authors still refer to them as evidence that Bt maize harms beneficial species. We provide a comprehensive review of the studies evaluating the effects of Bt (Cry1Ab) maize on C. carnea. The evidence indicates that this important predator is not affected by Bt maize or by the produced Cry1Ab protein. We discuss how conceptual models can assist environmental risk assessments, and we emphasize the importance of robust and reproducible studies.

The end of a myth-Bt (Cry1Ab) maize does not harm green lacewings.

Biological control is an underlying pillar of integrated pest management, yet little focus has been placed on assigning economic value to this key ecosystem service. Setting biological control on a firm economic foundation would help to broaden its utility and adoption for sustainable crop protection. Here we discuss approaches and methods available for valuation of biological control of arthropod pests by arthropod natural enemies and summarize economic evaluations in classical, augmentative, and conservation biological control. Emphasis is placed on valuation of conservation biological control, which has received little attention. We identify some of the challenges of and opportunities for applying economics to biological control to advance integrated pest management. Interaction among diverse scientists and stakeholders will be required to measure the direct and indirect costs and benefits of biological control that will allow farmers and others to internalize the benefits that incentivize and accelerate adoption for private and public good.

Economic value of biological control in integrated pest management of managed plant systems.

Crops producing insecticidal crystal (Cry) proteins from the bacterium, Bacillus thuringiensis (Bt), are an important tool for managing lepidopteran pests on cotton and maize. However, the effects of these Bt crops on non-target organisms, especially natural enemies that provide biological control services, are required to be addressed in an environmental risk assessment. Amblyseius andersoni (Acari: Phytoseiidae) is a cosmopolitan predator of the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae), a significant pest of cotton and maize. Tri-trophic studies were conducted to assess the potential effects of Cry1Ac/Cry2Ab cotton and Cry1F maize on life history parameters (survival rate, development time, fecundity and egg hatching rate) of A. andersoni. We confirmed that these Bt crops have no effects on the biology of T. urticae and, in turn, that there were no differences in any of the life history parameters of A. andersoni when it fed on T. urticae feeding on Cry1Ac/Cry2Ab or non-Bt cotton and Cry1F or non-Bt maize. Use of a susceptible insect assay demonstrated that T. urticae contained biologically active Cry proteins. Cry proteins concentrations declined greatly as they moved from plants to herbivores to predators and protein concentration did not appear to be related to mite density. Free-choice experiments revealed that A. andersoni had no preference for Cry1Ac/Cry2Ab cotton or Cry1F maize-reared T. urticae compared with those reared on non-Bt cotton or maize. Collectively these results provide strong evidence that these crops can complement other integrated pest management tactics including biological control.

The interaction of two-spotted spider mites, Tetranychus urticae Koch, with Cry protein production and predation by Amblyseius andersoni (Chant) in Cry1Ac/Cry2Ab cotton and Cry1F maize.

Steven E. Naranjo

USDA-ARS, Arid-Land Agricultural Research Center

Methodology for Developing Life Tables for Sessile Insects in the Field Using the Whitefly, Bemisia tabaci, in Cotton As a Model System