Peter C Ellsworth

Peter C Ellsworth

Professor, Entomology
Professor, Entomology / Insect Science - GIDP
Specialist, Entomology
Specialist, BIO5
Primary Department
Department Affiliations
Contact
(520) 374-6225

Work Summary

Peter Ellsworth is working to develop science-based solutions for integrated pest management through applied ecological investigations and organized outreach programs of Cooperative Extension, with principal focus on cotton; Integrated whitefly, Lygus, and pink bollworm management in cotton.

Research Interest

Peter Ellsworth, PhD, has broad interests in insect-crop interactions and applied insect ecology with particular emphasis on those aspects, which may be exploited for sound ecological and economical pest management. His responsibilities are to develop science-based solutions for integrated pest management through applied ecological investigations and organized outreach programs of Cooperative Extension, with principal focus on Bemisia tabaci, Lygus hesperus and Pectinophora gossypiella in the cotton agroecosystem, other field crops, and new crops as well as in cross-commodity interactions. In addition, Dr. Ellsworth is interested in insect phenology, diapause, insect-water relations, predictive modeling, pest biology, sampling, thresholds, and damage dynamics.As Director of the multi-disciplinary Arizona Pest Management Center, Dr. Ellsworth helps manage the institution's NIFA Extension IPM grant, serves as the state's federal IPM Coordinator and Pesticide Coordinator, and oversees and helps organize teams of research and extension faculty for the betterment of the science and application of IPM in Arizona.

Publications

Naranjo, S. E., Ellsworth, P. C., Chu, C. C., Henneberry, T. J., Riley, D. G., Watson, T. F., & Nichols, R. L. (1998). Action Thresholds for the Management of Bemisia tabaci (Homoptera: Aleyrodidae) in Cotton. Journal of Economic Entomology, 91(6), 1415-1426.

Abstract:

A 2-yr, multistate project was initiated in 1994 to determine action thresholds for management of Bemisia tabaci (Gennadius) Biotype B (=B. argentifolii Bellows & Perring) in cotton using chemical insecticides. Identical experimental designs and data collection protocols were used at sites in Brawley, CA, Yuma and Maricopa, AZ, and Weslaco, TX. The prescriptive application of insecticides based on 4 candidate action threshold levels (2.5, 5, 10, or 20 adult B tabaci per leaf) were compared with one another and an untreated control. In general, there were few differences in whitefly populations among action thresholds of 2.5, 5, and 10 adults per leaf at sites in Arizona and California. All insecticide treatments typically reduced population densities below those in untreated control plots. Insecticide applications were generally ineffective in Weslaco, possibly due to reduced insecticide susceptibility or the late onset of pest infestation, and there were few differences in population density among treatments. Yields were higher in sprayed treatments, but there was little difference among threshold levels. Yield differences were not detected among any treatments for Yuma and Weslaco in 1994 and for Maricopa in 1995. The levels of lint stickiness due to honeydew deposition, as measured by thermodetector, were not consistent among sites and were not generally related to pest densities in the different threshold treatments. Levels of stickiness tended to be higher in 1994. There were no treatment effects on other standard measures of lint quality. A simple budgeting analysis assuming $43.24/ha per application for insecticides and $1.59/kg for lint suggested that action thresholds of 5-10 adults per leaf provided the highest net return at most sites.

Naranjo, S. E., Ellsworth, P. C., & Hagler, J. R. (2004). Conservation of natural enemies in cotton: Role of insect growth regulators in management of Bemisia tabaci. Biological Control, 30(1), 52-72.

Abstract:

Field studies were conducted from 1997 to 1999 to contrast the effects of two insect growth regulators (IGRs) and conventional insecticides on natural enemy conservation in cotton within the context of alternative management strategies for Bemisia tabaci (Gennadius). Compared with an untreated control, insecticide regimes based on the initial use of the IGR buprofezin or pyriproxyfen reduced densities of eight predator taxa out of 20 examined in at least one year, including common species such as Geocoris punctipes (Say), Nabis alternatus Parshley, Chrysoperla carnea s.l., and the empidid fly Drapetis nr. divergens. Patterns of predator and pest population change relative to IGR application dates suggest that factors other than direct toxic effects, such as reduction in prey availability, were likely involved. In comparison, the use of conventional insecticides reduced populations of nearly all the predatory taxa examined in most years, including those affected by IGRs, with the impact being greater and more immediate in all cases. Predator:prey ratios were significantly increased by the use of IGRs compared with both the untreated control and a conventional insecticide regime in most instances. The application of conventional insecticides for suppression of Lygus hesperus Knight, another key pest in the system, in a split-plot design reduced densities of most predator taxa and diminished the selective advantage of the IGRs. Rates of parasitism by aphelinid parasitoids (Eretmocerus eremicus Rose and Zolnerowich and Encarsia spp.) were generally low and did not vary consistently due to B. tabaci or L. hesperus insecticide regimes over the three years. Our 3-year study demonstrates the more selective action of buprofezin and pyriproxyfen in an effective integrated control system for B. tabaci. The use of these IGRs could further facilitate biologically based management in cotton production systems.

Tabashnik, B. E., Sisterson, M. S., Ellsworth, P. C., Dennehy, T. J., Antilla, L., Liesner, L., Whitlow, M., Staten, R. T., Fabrick, J. A., Unnithan, G. C., Yelich, A. J., Ellers-Kirk, C., Harpold, V. S., Li, X., & Carrière, Y. (2010). Suppressing resistance to Bt cotton with sterile insect releases. Nature biotechnology, 28(12).
BIO5 Collaborators
Peter C Ellsworth, Xianchun Li

Genetically engineered crops that produce insecticidal toxins from Bacillus thuringiensis (Bt) are grown widely for pest control. However, insect adaptation can reduce the toxins' efficacy. The predominant strategy for delaying pest resistance to Bt crops requires refuges of non-Bt host plants to provide susceptible insects to mate with resistant insects. Variable farmer compliance is one of the limitations of this approach. Here we report the benefits of an alternative strategy where sterile insects are released to mate with resistant insects and refuges are scarce or absent. Computer simulations show that this approach works in principle against pests with recessive or dominant inheritance of resistance. During a large-scale, four-year field deployment of this strategy in Arizona, resistance of pink bollworm (Pectinophora gossypiella) to Bt cotton did not increase. A multitactic eradication program that included the release of sterile moths reduced pink bollworm abundance by >99%, while eliminating insecticide sprays against this key invasive pest.

Ellsworth, P. C. (2000). Insecticide efficacy and thresholds for Lygus hesperus in Arizona. 2000 Proceedings Cotton Conferences Volume 2, 1125-1128.

Abstract:

Changes in insecticide use, available pest control technologies, and local crop ecology together with severely depressed cotton prices place a renewed premium on Lygus control decision aids for Arizona cotton. As part of an on-going program to develop research-based Lygus management recommendations, we investigated the impact of various timings of chemical controls on Lygus population dynamics, number of sprays, costs of control, and net revenue as well as cotton heights, trash, lint turnouts, and yields. Once there were at least 15 total Lygus per 100 sweeps, sprays were made according to the number of nymphs in the sample (0, 1, 4, 8 or 16 per 100 sweeps). Up to 7 sprays were required (15/0 regime) to meet the needs of the target threshold. Lygus adult densities were largely unresponsive to the treatment regimes or individual sprays made. Three generations of nymphs, however, were affected by the treatments with the '15/4' regime harboring the fewest nymphs through July. This 'moderate' regime required 4 sprays and had the shortest plants, cleanest harvest, and highest lint turnouts. In addition, this regime out-yielded all other treatment regimes including the 6- (15/1) and 7- (15/0) spray regimes. Regression analyses of the data suggest that adult Lygus are less related to yield loss than nymphs and that large nymphs are best correlated with yield loss. Thus, spraying based on adults only would appear ill-advised. Returns were highest ($747/A) for the 15/4 regime with over $100 more than the more protective regimes. Thus, there is no economic advantage in advancing chemical control when nymph levels are low. Maximum economic gain was achieved by waiting for the 4 nymphs per 100 level (with 15 total Lygus/100) before spraying. However, waiting too long (beyond the 8 nymphs/100 level) resulted in significant reductions in yield and revenue. Our recommendations, therefore, are to apply insecticides against Lygus when there are at least 15 total Lygus, including at least 4 nymphs, per 100 sweeps. These recommendations are stable over a wide variety of economic conditions (market prices and insecticide costs). Continued work is necessary to verify these findings over a wider range of cotton developmental stages, varieties, and other environmental conditions.

Naranjo, S. E., & Ellsworth, P. C. (2010). Fourteen years of Bt cotton advances IPM in Arizona. Southwestern Entomologist, 35(3), 437-444.

Abstract:

The pink bollworm, Pectinophora gossypiella (Saunders), first invaded Arizona in 1926 and has been a key pest of cotton, Gossypium hirsutum L., since the early 1960s. A broad range of tactics has been developed to manage this pest including a variety of cultural methods, mating disruption via pheromones, sterile insect release, and plant resistance. Transgenic cotton producing the insecticidal proteins of Bacillus thuringiensis Berliner (Bt) was introduced in 1996 and was rapidly and widely adopted by producers in Arizona. Adoption rose to approximately 86% by 2006 and has been more than 93% since 2007 when the state was granted a U.S. Environmental Protection Agency exemption to eliminate required refuge plantings as part of a regional eradication program. The deployment of Bt cotton for selective control of caterpillars led to dramatic regional reductions in abundance of pink bollworm, and associated crop damage and insecticide use. Bt cotton has also been a key technology enabling more selective and biologically-based control approaches for sweetpotato whitefly, Bemisia tabaci (Gennadius), and western tarnished plant bug, Lygus hesperus Knight, two other keys pests of cotton in Arizona. Overall insecticide use (statewide average number of sprays per hectare) in cotton has dropped 88% since 1995. Some challenges ahead include re-invasion of eradicated zones, maintaining susceptibility of pink bollworm to Bt cotton, the economics of Bt cotton use in a post-eradication future, and a rapidly changing agroecosystem.