© 2007 Plant Management Network.
Helicoverpa zea Trends from the Northeast: Suggestions Towards Collaborative Mapping of Migration and Pyrethroid Susceptibility
Shelby Fleischer, Department of Entomology, The Pennsylvania State University, University Park 16802; Greg Payne, Department of Biology, State University of West Georgia, Carrollton 30116; Thomas Kuhar, Department of Entomology, Eastern Shore Agricultural Research & Extension Center, Virginia Tech, Painter 23420; Ames Herbert, Jr., and Sean Malone, Tidewater Agricultural Research and Extension Center, Virginia Tech, Suffolk 23437; Joanne Whalen, Extension IPM Specialist, University of Delaware, Georgetown 19947; Galen Dively, Entomology Department, University of Maryland, College Park 20742; David Johnson, Southeast Agricultural Research and Extension Center, Department of Crop and Soil Sciences, Pennsylvania State University, Landisville 17538; Jo Anna Hebberger, Pennsylvania State University, University Park 16802; Joe Ingerson-Mahar, Cooperative Extension, and Kristian Holmstrom, New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ 08901; and Doug Miller, Department of Geography, and Scott Isard, Department of Plant Pathology, Pennsylvania State University, University Park 16802 [* see Erratum]
Fleischer, S., Payne, G., Kuhar, T., Herbert, A., Jr., Malone, S., Whalen, J., Dively, G., Johnson, D., Hebberger, J. A., Ingerson-Mahar, J., Miller, D., and Isard, S. 2007. Helicoverpa zea trends from the Northeast: Suggestions towards collaborative mapping of migration and pyrethroid susceptibility. Online. Plant Health Progress doi:10.1094/PHP-2007-0719-03-RV.
In the northeastern US, sweet corn is attacked by three lepidopterans, two of which are primarily migrants from the south. Knowledge about when and where these immigrants arrive can dramatically reduce insecticide inputs. We discuss progress on monitoring for pyrethroid resistance in one of the migrants, Helicoverpa zea, and in developing interactive cartography for regional monitoring of migratory lepidopterans in the northeastern US.
In the northeastern US, sweet corn is attacked regularly by three lepidopterans: corn earworm, Helicoverpa zea (Lepidoptera: Noctuidae), European corn borer, Ostrinia nubilalis (Lepidoptera: Crambidae), and fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae). Growers typically spray insecticides (usually pyrethroids) multiple times to protect ears from damage. Corn earworm populations in the southern US have recently shown dramatic reductions in susceptibility (2), and we hypothesized that emigrants from southern populations showing increased tolerance to pyrethroids could affect insect pest control in the Northeast.
Two of these species, H. zea and S. frugiperda, are primarily immigrants from the south. Knowledge about when and where these immigrants arrive each season can dramatically reduce insecticide inputs. Unfortunately, because of the farm and crop diversity, spatial segregation of farms, and the smaller size of many farms in the Northeast, traditional Integrated Pest Management (IPM) monitoring programs such as field scouting can be a logistic and economic challenge. Moreover, a crop-consultant infrastructure does not exist in many areas. Regional monitoring may therefore provide advance warning of migration of the noctuid species.
Here, we discuss progress on monitoring for pyrethroid resistance in corn earworm, and in developing interactive cartography for regional monitoring of migratory lepidopterans in the northeastern US.
Corn Earworm Pyrethroid Susceptibility in the Northeast
Since 2001, we have evaluated corn earworm populations from five states (Delaware, Maryland, Pennsylvania, New Jersey, and Virginia) for susceptibility to the pyrethroid cypermethrin using the adult vial test (AVT) bioassay described for tobacco budworm, H. virescens (2,3). Moths were collected from pheromone traps (wire cone or Scentry traps baited with H. zea lures), or were reared from larvae collected from corn ears in the field. Adults were held in cages for 24 h with sugar water prior to the bioassay.
The insides of clean, borosilicate glass scintillation vials (20 ml) were coated with a residue of technical grade cypermethrin (94.4% pure, FMC Corp., Princeton, NJ). The concentrations were 5 µg and 10 µg of cypermethrin per vial. Control vials were treated with acetone alone. One moth was placed in each vial and the vials were capped loosely. The vials containing the moths were held at room temperature (about 24°C) and mortality recorded 24 h after the test was initiated.
More than 22,000 moths were bioassayed in the five states from 2003 to 2005. Data have been initially summarized as histograms showing moths collected from pheromone traps as the default histogram bars, and moths reared from field-collected larvae labeled as "larvae" in the histograms. Here, we present those histograms from the two geographic extremes of our survey: Eastern Shore of Virginia (Fig. 1) and Pennsylvania (Fig. 2), and briefly discuss patterns from all sites. Work currently underway includes final error-checking of the large database, and statistical analyses for spatial and temporal patterns of survivorship rates.
The graphical patterns suggest that survival of pheromone-trap-collected moths has been relatively low in the cypermethrin-treated vials. At the 5 μg rate, survivorship ranged from 0 to 17% in the Eastern Shore of Virginia (Fig. 1), and 0 to 8% in Pennsylvania (Fig. 2). However, at this low rate, most locations recorded survival during each of the three years, with the highest survival rates (33% in 2003, 17% in 2004, and 18% in 2005) occurring in the southernmost states sampled. Survival at the 10 µg cypermethrin rate was even lower: from 0 to 11% in the Eastern Shore of Virginia, and 0 to 3% in Pennsylvania (Fig. 2). However, at least some survival at the 10 μg rate has been consistently recorded throughout the southernmost states sampled (i.e., in Virginia, Delaware, and Maryland with 7 of 10 sites in 2003, 5 out of 9 sites in 2004, and 6 out of 9 sites in 2005).
Dramatic increases were evident in the survival of adults reared from field-collected larvae relative to those collected from pheromone traps. These increases are evident for both rates in Eastern Virginia (reaching 41% at the 5-μg rate in 2004, Fig. 1), and the 5-μg rate in Pennsylvania (reaching 27% in 2005, Fig. 2). Preliminary estimation using moths reared from field-collected larvae, averaged across locations and years, show 31% survival at the 5 μg rate and 11% survival at the 10-μg rate.
Our results suggest that pyrethroid-resistant corn earworms occur in the northeastern US each year. Monitoring for pyrethroid resistance in these populations should be continued, with methods modified to better understand the variation associated with dose and bioassay methods, and how they relate to field efficacy.
Mapping Migratory Lepidopterans in the Northeast
We organized monitoring data from state-level IPM programs, individual faculty research programs, and state Departments of Agriculture (Fig. 3) into a regional monitoring network. We focused on developing information technology products for interactive cartography of dynamic pest-density data. We started with information technology tools that required manual efforts to make text and graphic files from approximately 99 sites on a daily basis, and hyperlinked these files into a webpage. This resulted in classified postings of weekly average trap catch, with the points hyperlinked to a graph depicting the catch time series at that site (Fig. 4). Specifically, in the early part of the project, Delphi and Map Objects applications created maps and time-series graphics for each site and an automated web editor hyperlinked all into "clickable maps" web pages. Later, we re-designed the information technologies to support multi-scaling and dynamic querying and visualization. This was accomplished by moving from a technology that relied on hyperlinking independent text and graphic files to a MacroMedia Flash application (Fig 5). This was needed to grow geographically, improve spatial resolution, and integrate visualizations through animation. We initialized this migration in 2002 and fully implemented it in 2003.
By 2005, moth trap catch data were collected from eight states (Virginia, Maryland, Delaware, Pennsylvania, New Jersey, New York, Massachusetts, and Maine), and included approximately 250 sites. An Active Server Pages (ASP) application enables web-based data capture into MS Access relational databases. The current "PestWatch" (Fig. 9) ports the data into MySQL, and uses MacroMedia Flash to visualize changes over time as animations, while individual dates can be seen as still frames with linked time-series graphics. The default (Fig. 5) displays the last created corn earworm map and GIS functionality is provided through a small set of graphical function buttons. The website can be accessed at pestwatch.psu.edu. The "Interactive Maps" tab at this website brings the user to the Pestwatch visualization of the spatial and temporal data, and scrolling to the time points during July through August typically provides the most reporting data sites with the greatest spatial variation.
The major corn earworm moth migration into the Northeast has varied by as much as a month. For example, in 2002, the southern US experienced drought conditions in spring and summer, and we observed and reported in near real-time the much higher and earlier migration into the Northeast compared to other recent years, such as 2005 (Fig. 6).
We are hoping to expand this collaboration into the Midwestern states, and add an aerobiology modeling component such as that developed for soybean rust (1). A regional monitoring network coupled with an aerobiology modeling forecast system is similar to a "Pest Information Platform for Extension and Education (PIPE)" concept, which was originally proposed by Isard and Russo as an expansion of their USDA Soybean Rust Information System (1). In October 2005, Agriculture Secretary Johanns announced funding for a "Pest Information Platform for Extension and Education" (PIPE) (4). We can envision that a similar approach could help predict major immigration of migrant insect species of economic importance.
1. Isard, S. A., Gage, S. H., Comtois, P., and Russo, J. M. 2005. Principles of the atmospheric pathway for invasive species applied to soybean rust. BioScience 55:851-861.
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4. USDA. 2005. USDA expands national soybean rust risk management tool. News release no. 0465.05. USDA, Washington, DC.