Peter B. Goodell

Plant compensation, natural biological control, and herbivory by Aphis gossypii on pre‐reproductive cotton: the anatomy of a non‐pest

Crop plant compensation for herbivory and the population dynamics of herbivores are two key elements in defining an herbivores pest status. We studied the dynamics of natural, unmanipulated populations of the aphid Aphis gossypii on seedling plantings of cotton, Gossypium hirsutum and Gossypium barbadense, over a 4‐year period in Californias Central Valley. Aphid populations colonized all plantings, but reached densities in excess of 0.5 aphids/leaf during only one year (1991), when outbreaks occurred. Outbreak populations were, however, ephemeral; predation and parasitism suppressed aphid populations prior to the initiation of flower bud production, when cotton plant growth may become photosynthate‐limited. Effective natural biological control was observed despite the action of hyperparasitoids and the heavy mortality of immature parasitoids that occurred when predators consumed parasitized aphids.

Effects of Local and Landscape Factors on Population Dynamics of a Cotton Pest

Background Many polyphagous pests sequentially use crops and uncultivated habitats in landscapes dominated by annual crops. As these habitats may contribute in increasing or decreasing pest density in fields of a specific crop, understanding the scale and temporal variability of source and sink effects is critical for managing landscapes to enhance pest control. Methodology/Principal Findings We evaluated how local and landscape characteristics affect population density of the western tarnished plant bug, Lygus hesperus (Knight), in cotton fields of the San Joaquin Valley in California. During two periods covering the main window of cotton vulnerability to Lygus attack over three years, we examined the associations between abundance of six common Lygus crops, uncultivated habitats and Lygus population density in these cotton fields. We also investigated impacts of insecticide applications in cotton fields and cotton flowering date. Consistent associations observed across periods and years involved abundances of cotton and uncultivated habitats that were negatively associated with Lygus density, and abundance of seed alfalfa and cotton flowering date that were positively associated with Lygus density. Safflower and forage alfalfa had variable effects, possibly reflecting among-year variation in crop management practices, and tomato, sugar beet and insecticide applications were rarely associated with Lygus density. Using data from the first two years, a multiple regression model including the four consistent factors successfully predicted Lygus density across cotton fields in the last year of the study. Conclusions/Significance Our results show that the approach developed here is appropriate to characterize and test the source and sink effects of various habitats on pest dynamics and improve the design of landscape-level pest management strategies.

Establishment of Peristenus digoneutis and P. relictus (Hymenoptera: Braconidae) in California for the control of Lygus spp. (Heteroptera: Miridae)

Abstract Lygus hesperus Knight is native to the western United States and is a perennial pest of numerous crops in California. It is responsible for triggering the early season application of insecticides on cotton, Gossypium hirsutum L., and strawberries, Fragaria L. Despite several surveys conducted in alfalfa (Medicago sativa L.) grown in central California, nymphal parasitoids associated with L. hesperus and L. elisus have not been found. Two exotic parasitoids were released into California beginning in 1998. Peristenus relictus (Ruhte), formerly P. stygicus Loan, and P. digoneutis Loan were collected from several locations in southern Europe and released at up to six locations over a 6-year period. At the original release site in Sacramento, a 0.25-ha plot of alfalfa, parasitism by P. digoneutis and P. relictus combined increased from zero to 90%, 3 years after the last releases were made. Parasitoids have been recovered from vacant fields of weedy annuals within 2 km of this site. Recoveries at more southerly release sites in central California have been poor.

Implementing principles of the integrated control concept 50 years later--current challenges in IPM for arthropod pests.

1 INTEGRATED CONTROL CONCEPT The 1959 publication of the article ‘The Integrated Control Concept’ by Stern and colleagues1 established a new philosophical framework for pest management that eventually provided a foundation for IPM to develop. Considered within the context of pest control approaches 50 years ago, the integrated control concept radically departed from the undisciplined and at times unrestrained use of pesticides for controlling pest populations. Stern and his California colleagues had been concerned about the deleterious, broad-spectrum effects of pesticides in agriculture for some years,2 – 4 but with no framework available to address the critical issue of when to treat with an insecticide if pest infestations were inadequately suppressed by natural control. It was through the development of dual theoretical constructs, economic injury level (EIL) and economic threshold (ET), that Stern et al.1 devised a pragmatic and sensible means of integrating chemical and biological control. However, the enduring impact of the integrated control concept is also due to other novel perspectives that these authors brought to pest management in their historic article. Their broad experience in the field and innovative insights into landscape ecology contributed to a unique understanding of pest dynamics and also provided a practical knowledge of the challenging decisions faced by growers concerned with protecting their crops. By combining a theoretical basis of insect management, represented by EIL and ET, with a realistic view of pest populations as potentially destructive agents of crops and ultimately grower livelihoods, Stern and colleagues1 formalized the integrated control concept into a robust theory of pest management that continues to serve modern IPM in both theory and practice.

Second International Lygus Symposium Asilomar Conference Grounds, Pacific Grove, California, April 15–19 2007

The Second International Lygus Symposium brought together 52 entomologists from six nations and 11 states representing universities, public agencies, and private entities to discuss the latest research on Lygus species and their relatives. Symposium topics included Lygus biology, behavior and ecology, IPM, insecticides and resistance, and biological control. Papers and posters dealt with Lygus as a pest of several crops, including cotton, strawberries, seed alfalfa, canola, dry beans, cucumbers, cereals, peaches, and new crops guayule and lesquerella. Intercrop movement of Lygus2008200820082008 species was another important topic of many presentations. In the capstone session, participants identified needs and priorities for ongoing Lygus research and education (available at http://ag.arizona.edu/apmc/Arid_SWPMC_RAMP.html). The conference was sponsored in part by FMC Corporation, the University of Arizona Arizona Pest Management Center, the University of California Statewide IPM Program, and a grant to Ellsworth et al. (CRIS# 0207436) from the USDA-CSREES, Risk Avoidance and Mitigation Program (RAMP).

Strategic and tactical modeling: cotton-spider mite agroecosystem management

We discuss the development of two simulation models, a mechanistic cotton crop model and a spider mite population model. In a strategic mode, the simulation models are used to address basic hypotheses involving the interaction of cotton with its environment, and with the spider mite population, and to develop general strategies for managing the crop and its herbivores. In a tactical mode, these models are used to provide estimates of the anticipated severity of a spider mite population. Tactical modelling is made possible by using a statistically-based adaptive interface. The departure of simulated patterns of growth from observed patterns is used to ‘adapt’ several crop parameters including rate of photosynthesis, rate of vegetative growth, and metabolite allocation priority for fruit. For the spider mite population model, fecundity, predator-mediated mortality, and acaricide-induced mortality are adapted to specific field conditions.

Strip Cutting Alfalfa for Lygus Management: Forage Quality Implications

Strip cutting is used to limit lygus migration from alfalfa into susceptible neighboring crops. Hay growers are concerned that the uncut strips negatively impact quality and marketability of alfalfa from subsequent cuttings. The objective of this trial was to determine if blending the hay from the uncut strips with the new growth could mitigate reductions in quality and improve marketability. There were negative impacts of mixing old hay with the new growth alfalfa in both 2000 and 2001. As old growth was added in 25% increments to the new forage in the bale, crude protein values declined by 1 to 2% and ADF values increased by 1 to 3.5%. Since ADF is used to calculate TDN, increases in ADF will have a significant impact on the value of the forage. There was no significant reduction in crude protein value when 7 or 14% old growth alfalfa was present in bales as compared to bales containing 100% new growth. With respect to ADF, the only significant difference was between the new hay and the hay containing 14% old growth. When visually evaluating hay, there appear to be subtle changes in appearance when old growth is blended with new growth that can be detected. The most sensitive characteristics are color and overall quality. Growers need to assess the requirements of their market, and determine the best strategy for managing the alfalfa strips left in fields for the purpose of lygus management based upon the expected reductions in quality reported here.