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Impact of Grasshopper Control Tactics on Biological Control Agents of Leafy Spurge

 Nelson Foster

Question 1. What major problem or issue is being resolved and how are you resolving it?

Many leafy spurge infestations occur in areas that have a history of grasshopper problems. Flea beetle populations established to control leafy spurge may be in jeopardy in areas of western rangelands where damaging populations of grasshoppers require chemical insecticide treatments. The impact of traditional uniform aerially applied spray grasshopper treatments on flea beetles is undetermined. New grasshopper strategies that rely on substantially less insecticide in combination with alternating treated and untreated swaths of applied insecticide may mitigate the impact on flea beetles, but are untested. Direct exposure of flea beetles during grasshopper treatments will probably cause some mortality. However, at the time when grasshoppers should be treated, sufficient flea beetle eggs may have been produced and deposited to minimize or alleviate suppression in the flea beetle population the next year. The land manager needs to know which grasshopper treatments would impact the established populations of leafy spurge biological control agents the least and how long that impact will last.

Laboratory bioassays and replicated field studies are being conducted to determine the immediate impact of seven different grasshopper treatments on flea beetles and the long term impact of those treatments on subsequent flea beetle populations respectively.

Question 2. How serious is the problem? Why does it matter?

Leafy spurge infests about 5 million acres, much of which occurs in western states where there is a history of grasshopper outbreaks. Grasshopper infestations may occur over even larger areas as illustrated by rangeland acreage’s of 4.8 million, 13.8 million and 20 million which required federally sponsored treatments in 1972-73, 1979-81 and 1985-86, respectively. Even in non-outbreak years hundreds of thousands of acres can harbor damaging populations of grasshoppers that require treatment. Many land managers are required to deal with both leafy spurge and grasshoppers at the same time. When extremely serious grasshopper problems occur, the land manager has little option but to treat to protect the forage and prevent long term damage to the rangeland. Where leafy spurge biocontrol agents have been established, one to several years of effort may have been invested. If both investments for the rangeland are not optimized, land managers incur a short and long-term economic loss from reduced agricultural production of these lands.

Question 3. How does it relate to the National Program(s) and National Program Component(s)?

The TEAM Leafy Spurge project is a part of the USDA/ARS Area-Wide Management Program. It is a component of Crop and Commodity Pest Biology, Control and Quarantine (304). TEAM Leafy Spurge complements efforts to develop new and improved pest control technologies and assess component technologies for integrated pest management (IPM) systems.

Question 4. What was your most significant accomplishment this past year?

Previously non-existent protocols were developed for laboratory bioassays of grasshopper treatments on Aphthona flea beetles. Bioassays of seven different grasshopper treatments were conducted in the laboratory with A. lacertosa caged on leafy spurge. Some treatments were bioassayed with A. nigriscutis to provide bridging data between species. Levels of mortality to A. lacertosa that could be expected from direct treatment or exposure to treated vegetation were developed from the laboratory bioassays.

Adult beetle survey protocols were established for estimating field populations of adult flea beetles. Three acceptable areas were located for the initiation of field plot studies. Nine field plots each containing 16 specific sample sites were established in each of the three areas. Seven grasshopper treatments were applied by air and one treatment was applied by ground to established populations of Aphthona beetles on leafy spurge. In the season of treatment, pre and post treatment counts were conducted and initial summarization and analysis of data was performed.

Question 5. Describe your major accomplishments over the life of the project, including their predicted or actual impact.

The project was initiated during 2000. Laboratory bioassays of seven different grasshopper treatments were conducted on Aphthona beetles caged on leafy spurge. In those bioassays different doses of the same treatment performed in dose rank order. Both spray and bait treatments of carbaryl resulted in mortalities of 85% to 96%. Malathion treatments resulted in intermediate mortalities ranging from 22% to 41%, while Dimilin treatments showed only very slight mortality if any at all. Field plots were established and treated with the same seven grasshopper treatments to determine the immediate and long term effect on established populations of flea beetles. Pre and post treatment field population estimates of flea beetles were collected from all of the treated plots and the untreated plot in each of the three locations. Field data indicate that Dimilin may not cause an immediate reduction in flea beetles but that other treatments do and those levels of reduction are directly related to the dose applied.

Population estimates collected before and after treatments in 2000 will allow for comparison with population estimates to be collected in 2001. These will show the comparative impact of the different grasshopper treatments on established populations of flea beetles which are exposed to grasshopper treatments.

The data developed in this study will identify the grasshopper treatments with the least impact on biocontrol agents established on leafy spurge and will allow the land manager to optimize investments made when both leafy spurge and grasshoppers require control at the same time and place.

Question 6. What do you expect to accomplish year by year, over the next three years?

In 2001, monitoring of the flea beetle populations in all of the treated and untreated plots will continue. This will determine which grasshopper treatments had an impact and the level of that impact on established populations of flea beetles. Subsequent population monitoring of the populations which did not return to pretreatment levels at one year after treatment will be conducted to determine how long is required for those populations to return to pretreatment levels.

Information will be provided to the land manager that will enable them to make the best treatment decision when required to treat grasshoppers where biological control agents are established for leafy spurge.

Question 7. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology?

This project was initiated during 2000 and analysis of the first year data is incomplete. Complete first year summaries and analysis of data will be available in the next few months. The majority, if not all, of the data analysis and evaluation should be completed by the end of 2001 and available to land managers, industry and scientists very shortly thereafter. As the data is developed it will be presented at appropriate meetings such as the National Grasshopper Management Board Annual Meeting. The data will be submitted for publication upon completion of the project.

Question 8. List your most important publications in the popular press (no abstracts) and presentations to non-scientific organizations, and articles written about your work (NOTE: this does not replace your peer-reviewed publications which are listed below).

None to date. Project started June 2000.

Question 9. Scientific publications

None to date. Project started in June 2000.

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