Proactive Insecticide Resistance Monitoring and Management for Crucifer Flea Beetle
Daniel E. Waldstein, Ph.D.
Crop Protection Specialist
North Dakota State University
North Central Research Extension Center
Minot, ND 58701
(701) 857-7682
Introduction:
Insecticide resistance was first reported in 1914 by A. L. Melander. By 1991, there were 504 documented cases of insects species resistant to at least one insecticide (Georghiou 1986, Georghiou & Lagunes-Tejada 1991). Some insect species have become resistant to multiple classes of insecticides. Notorious examples of this include the Colorado potato beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) and the green peach aphid, (Hemiptera: Aphididae) which is resistant to more insecticides than any other insect (Vasquez 1995).
Insects become resistant to insecticides through three general mechanisms. These include changes in the target site of the insecticide, which prevents the insecticide from binding to the target site and exerting its toxic effect on the insect, metabolic resistance, which improves the ability of the insect to break down and detoxify the insecticide with enhanced enzymatic activity, and prevention of the insecticide from reaching the target site (e.g., decreased cuticular penetration, sequestration) (Plapp 1986).
Insecticide resistance occurs more rapidly when there is widespread adoption of one insecticide or insecticide class used year after year against an abundant pest. Crucifer flea beetles, Phyllotreta cruciferae (Coleoptera: Chrysomelidae) have been effectively controlled by neonicotinoid seed treatments (e.g., Helix, Gaucho, and Prosper) on canola for more than a decade. Seed treatments have an advantage over sprayer applications of insecticides because of decrease cost (for the active ingredient and the application cost), convenience, and decreased environmental impact on non-target species. Research conducted when many of these seed treatments were first used commercially showed that seed treatments typically protected canola seedlings from flea beetles for 21 days (Knodel 2005). Anecdotal evidence from some producers indicates that seed treatments are currently not providing 21 days of protection in some commercial canola fields.
Rationale and Significance:
Pesticide resistance has costly consequences. Pimentel (2005) estimates that $1.5 billion of agronomic losses occurs each year in the U.S. due to pesticide resistance. Waiting for new pesticides to replace older ones that have become ineffective due to resistance is not a stand-alone strategy. The estimated cost of discovering and bringing a new pesticide to market is approximately $180 million (Whitford et al. 2006). Because of the challenges agrichemical companies have recouping these costs, fewer new pesticides will be available in the future. In addition, newly registered pesticides are often more expensive than pesticides that have been registered for a number of years, especially when patents expire and lead to cheaper generic pesticides. It is therefore in our best interest to increase the useful life of the pesticides we currently have available.
Typically insecticide resistance management has been reactive rather than proactive. Once field failures of an insecticide are experienced by producers, scientists at land grant universities scramble to develop a plan to manage the problem. Like fighting with one hand tied behind our backs, this type of an approach makes it difficult to combat insecticide resistance, because once field failures occur the useful life of the insecticide is near its end.
A good example of proactive insecticide resistance management has occurred with transgenic crops expressing the Bacillus thuringiensis (Bt) bacterial product that is toxic to certain groups of insects. Originally resistance management was accomplished with a refuge strategy where a certain percentage of the field was planted with a susceptible non-Bt variety. More recently, multiple Bt expressing genes have been stacked to increase the useful life of these products. This strategy is successful much like using two different insecticide chemistries, because insect populations develop resistance to each insecticide independently. If the probability of an insect population developing resistance to one insecticide is 1 in 1 million, the probability of developing resistance to two insecticides with different modes of action that are not cross-resistant is generally multiplicative, in other words 1 in 1 million x 1 in 1 million = 1 in 1 trillion.
Typically cross-resistance occurs between insecticides with the same target site or a similar chemistry acted on by increased enzymatic detoxification in resistant insects. However, just because an insecticide has a new chemistry and new mode of action does not necessarily guarantee it will not be cross-resistant to a currently used insecticide. An example of this occurred in the 1990’s with obliquebanded leafroller, Choristoneura rosaceana (Harris) populations from commercial apple orchards in New York that exhibited cross-resistance to the newly registered, tebufenozide, which had a novel chemistry and mode of action (Waldstein et al. 1999). It is important for canola producers to have multiple classes of seed treatments available for effective insecticide resistance management of canola flea beetles. This study will establish if insecticide resistance to currently used flea beetle seed treatments is present in field populations of crucifer flea beetles and the effectiveness of a new seed treatment for insecticide resistance management of this ubiquitous pest of canola.
Objectives:
This study will be conducted to see if insecticide seed treatments on canola are currently as effective against crucifer flea beetle populations in North Dakota and in adjacent states as they were when they were first introduced commercially. In addition, bioassays will be conducted on a new insecticide seed treatment for canola with a unique mode of action. Monitoring of pest populations response to currently registered and new insecticides prior to commercial release is a useful starting point in forming a plan for insecticide resistance management (Waldstein and Reissig 2000).
Approach:
Flea beetles will be collected in the spring in canola fields with a history of insecticide seed treatments with a minimum of two fields each from northeastern, north central, northwestern, and southwestern North Dakota, Minnesota, and Montana. Flea beetles will be transported from field sites in coolers to minimize mortality before arrival at the research center. Separate flea beetle populations will be maintained in a climate controlled insect growth chamber prior to conducting bioassays. Bioassays will be conducted with commercially available insecticide treated canola seed (e.g., Helix Extra and Prosper FX). These neonicotinoid insecticides will be compared with canola seed treated with the new insecticide, Cyazypyr (cyanthraniliprole). Unlike the neonicotinoid seed treatments that act as an acetylcholine agonist and influence sodium flow in insect cells, Cyazypyr modulates the ryanodine receptor and influences calcium flow in insect cells.
Flea beetle bioassays will be conducted to determine the rate of mortality to beetles and damage to canola seedlings at 7, 14, and 21 days after planting. The bioassays will be conducted by planting 5 canola seeds in 4 inch pots and placing 25 flea beetles from the various collected populations in the pots surrounded by no-see-um/mosquito netting at 7, 14, or 21 days after planting. The mortality of flea beetles and the damage to canola seedlings will be assessed 7 days after flea beetles are first put in contact with the canola seedlings. Bioassays with untreated seed will be used as a control. Bioassays will be replicated a minimum of three times for each treatment, population, and exposure time (i.e., 7, 14, 21 days). The three exposure regimes will allow for modified dose response curves and toxicological probit analyses to be generated so that different populations of flea beetles can be statistically compared. This newly generated data can be compared with baseline data generated by Knodel (2005) and Antwi et al. (2007) approximately ten years ago when these insecticide seed treatments were first introduced to commercial canola fields.
Outreach/Extension Activities:
Research results from this study will be communicated to producers, consultants, and other members of the agricultural community through summer field days, winter meetings, and through publication in the annual farmer’s report produced by the research extension center. In addition, the results of the study will be put on our website.