Improved Management of the Egyptian Alfalfa Weevil in California Alfalfa to Protect Environmental Quality

Larry D. Godfrey

University of California-Davis

Dept. of Entomology
One Shields Ave
Davis, CA 95616

530-752-0473

530-752-1537

ldgodfrey@ucdavis.edu

Executive Summary

Alfalfa is the most commonly grown crop in California with 1 million acres per year and hay production of nearly $1 billion per year (number one valued field crop). Several insect pests injure alfalfa fields and reduce crop yields and quality. The alfalfa weevil complex, comprised of the Egyptian alfalfa weevil (EAW), Hypera brunneipennis and alfalfa weevil, Hypera postica, is the most damaging arthropod in California alfalfa. Weevil larvae are well-controlled with insecticides primarily organophosphates and carbamates. However, the occurrence of organophosphate insecticides in surface waters, particularly chlorpyrifos (Lorsban®) and diazinon, coinciding with the timing of treatment for EAW larvae, has placed added emphasis on finding alternative means to manage this pest. Pyrethroid insecticides and indoxacarb were recently registered in alfalfa but have drawbacks of being non-selective for natural enemies and only marginally cost-effective, respectively. These insecticides, particularly pyrethroids, are not without their environmental concerns as well. Therefore, it appears that alternative, refined measures are needed for EAW management in alfalfa in California. A considerable amount of work was done on alfalfa pest management in the 1980's and before in California, but research efforts have waned during the last 15 years for various reasons including competing priorities, funding limitations, etc. Through this project, we propose to re-establish an alfalfa research program by re-evaluating the status of biological control of EAW larvae and studying the EAW treatment threshold under current production practices. Ten parasitoid species were released in CA for EAW from 1957-1988 and three were reported as established, but incidence of these organisms has not been studied recently. Observations by Godfrey in 2002 and 2003 indicated relatively high natural mortality of EAW larvae at one study site. The second area that could facilitate EAW management in California is a re-evaluation of treatment thresholds for EAW under the current production regime.

Objectives

Monitor Egyptian alfalfa weevil larval populations in California alfalfa fields and determine incidence of naturally-occurring mortality agents.
Re-assess the treatment threshold for Egyptian alfalfa weevil larval populations in California alfalfa fields under current production practices.
Extend results to growers through appropriate field days, symposia, newsletter articles, etc.

Justification

Objective 1. Alfalfa is the most commonly grown crop in California with approximately 1 million acres per year and hay production of nearly $1 billion per year (number one valued field crop). Much of the alfalfa hay goes to support the milk and dairy industry in the state which is the number one agricultural commodity (in gross value) produced in California. Several insect pests injure alfalfa fields and reduce crop yields and quality. The alfalfa weevil complex, comprised of the Egyptian alfalfa weevil (EAW), Hypera brunneipennis and the alfalfa weevil, Hypera postica, is the most damaging arthropod pest of alfalfa in most areas of California. In the Central Valley of California, intermountain areas, and coastal areas (comprising over 80% of the alfalfa acreage), these weevil larval pests damage the first alfalfa cutting of the production year from February to June (depending on location in the state). Aphids, including spotted alfalfa aphid, blue alfalfa aphid, pea aphid and a recent pest, the cowpea aphid, damage the second cutting alfalfa in March to July. Host plant resistance is used to partially manage the first two of these aphid species, but naturally-occurring biological controls, i.e., lady beetles, lacewings, etc., are imminently important for aphid management. Lepidopterous larvae (beet armyworm, alfalfa caterpillar, and others) move into alfalfa and are significant pests during the summer and early fall months. An insecticide application per cutting cycle is not uncommon to control these worm pests. Biological control, primarily wasp parasitoids, is also important in fields unperturbed by insecticides for controlling these pests.

Management of the alfalfa weevil, being the first insect pest of the season, often highly influences the management actions in an alfalfa field for the entire year. If biological control of aphids and lepidopterous larvae is upset with insecticides, consequences of this often persist throughout the season. The alfalfa weevils are well-controlled with insecticides; organophosphate and carbamate materials have been applied for several years for this purpose. In fact, in 2001, four of the most commonly used six insecticides in alfalfa were either an organophosphate and carbamate material (#1=chlorpyrifos, #4=dimethoate, #5=methomyl, #6=carbofuran) and 50% of all applications were of materials from these two insecticide classes. However, the occurrence of organophosphate insecticides in surface waters, particularly chlorpyrifos (Lorsban®) and diazinon, coinciding with the timing of treatment for Egyptian alfalfa weevil has placed added emphasis on finding alternative means to manage this pest. New regulations (http://www.cdpr.ca.gov/docs/pressrls/april10.htm) have recently been released primarily aimed at ground water but surface waters are also a concern in California (http://www.cdpr.ca.gov/docs/sw/surfdata.htm). The federal Clean Water Act and CA Dept. of Pesticide Regulation actions are mandating changes in pesticide use patterns through TMDL and other criteria (Prichard 2002). Pyrethroid insecticides (Warrior®, Mustang®, Baythroid®, and others) have recently been registered in alfalfa and effectively control EAW. Long et al. (2002) demonstrated the fit of pyrethroid insecticides for this use and the positive attributes for reduction in run-off in irrigation tailwater. These insecticides, however also have their associated environmental concerns, and also have the additional consideration of having broad-spectrum activity and destroying populations of beneficial organisms in alfalfa. These natural enemies are very important in alfalfa for the management of aphids and lepidopterous larvae. Recently, indoxacarb was registered for use in alfalfa; EAW control at cost-competitive rates is moderate to good but appears to be less than with organophosphate and carbamate insecticides. Therefore, it appears that alternative, refined measures are needed for EAW management in alfalfa in California.

A considerable amount of work was done with biological control of the alfalfa weevil pests starting in the 1930's and was highlighted by the release of ten separate hymenopterous species from 1957-1988. The later years of this work were part of the National Alfalfa Weevil Biological Control Project, ARS and APHIS phases. The goal was to establish a suite of parasitoids that would positively impact populations of alfalfa weevil larvae in California as has occurred in the northeastern and midwestern U.S. (Kingsley et al. 1993, White et al. 1992). Evaluations done in CA in the 1980's (Kingsley et al. 1993, Pitcairn and Gutierrez 1989) showed establishment of three species of parasitoids but only at low levels. I am unaware of more recent surveys to ascertain the status of biological control of EAW in California. One of us (Godfrey) conducted studies on efficacy of registered and experiential insecticides against EAW in 2002 and 2003. Larval populations were slow to develop and never exceeded the exceeded threshold value for treatment even though fields were located in areas with known severe EAW pressure. Several larvae were observed in a sluggish, discolored state and larval mortality appeared high. The reasons for this mortality were not determined. It is hypothesized that a biological agent (parasitoid) or fungal disease could be exerting an effect on the population. This could be an important, unrealized control agent of EAW and if more information was available this could entice growers to reconsider treatment or at least more closely evaluate the population before treatment.

Objective 2. The second area that could facilitate EAW management in California and could perhaps reduce insecticide usage is the area of treatment thresholds for EAW. The published threshold of 20 larvae per sweep (http://www.ipm.ucdavis.edu/PMG/r1300511.html) is dated and growers lack confidence in this threshold. One obvious criticism of this threshold is that it is static, whereas it should float according to hay values (which vary significantly from $70 to $170 per ton) and with costs of controls. If insecticides are the primary control option, it is unrealistic to say they have not changed in price over the last 30 years, the tenure of this threshold. In addition, alfalfa cultivars and production practices have changed significantly since this threshold was developed in the 1970's.

Overall Summary

Alfalfa fields, as a short-term perennial agroecosystem, support a wide range of arthropods, most of which have neither positive nor negative effects on the crop. van den Bosch and Stern (1969) estimated approximately 1000 species of arthropods in the typical alfalfa field in California. These organisms contribute to the biodiversity of agricultural systems. A few of these insects can be significant competitors with the crop for resources and as such can reduce yields. As in many systems, the most important alfalfa insect pests were accidentally introduced from other countries. The alfalfa weevil complex, Egyptian alfalfa weevil (EAW), Hypera brunneipennis and the alfalfa weevil, Hypera postica was introduced from the Mediterranean region/Mideast area on three separate occasions; 1904 near Salt Lake City, 1939 near Yuma, AZ, and 1951 near Annapolis, MD (Radcliffe and Flanders 1998). The designation of these insects as two species has been under debate (see Hsiao and Hsiao 1985), but there are some biological/behavioral differences that suggest speciation.

Biological control efforts against these pests by U.S. agencies began in 1911 when the insect was still in Europe. Isolated efforts were undertaken in Utah in the 1920's, California in the 1930's, Arizona in the 1940's and the northeastern U.S. in the 1950's (Radcliffe and Flanders 1998). As the complex became a nation-wide pest, USDA coordinated biological control efforts and millions of parasitoids from approximately 10 species were released. These organisms adapted quickly in the northeastern, midwestern, north central U.S. In fact, in the northeast, weevil populations declined within 10 years of the releases (Day 1981) and insecticide use on alfalfa dropped 73% (Radcliffe and Flanders 1998). White et al. (1995) showed economic benefits of $2,200,000,000 to producers in the northeast, which was 25 times the cost of the program. However, in other regions, the parasitoid species released were less effective. Kingsley et al. (1993) and (Radcliffe and Flanders 1998) reported that insecticide usage on alfalfa through the 1980's in the West was unaffected by the program. Some additional releases were done in California in the 1980's (new species or strains better adapted to western conditions). Pitcairn and Gutierrez (1989) summarized the history of these releases and stated that three species had established in CA. The larval parasitoids Bathyplectes curculionis, B. anurus, and Tetrastichus incertus were reported as "widely established", "recently recovered", and "established central California", respectively from the 1982-83 surveys. Systematic, more recent studies have not been done in order to re-evaluate the incidence of these organisms.

The economic threshold is central to any integrated pest management system. Lacking this threshold value, or lacking a reliable, grower accepted value, management efforts resort to preventative treatments. Koehler and Rosenthal (1975) published results of work supporting a threshold of 20 per sweep for EAW. The threshold has been effectively used for numerous years such that an insecticide application prior to the first cutting for EAW is routine in the Central Valley. The research in the 1970’s assumed hay values of $50-$70 per ton and treatment costs of $6-8 per acre (these values are approximately doubled in today’s alfalfa economy). In addition, alfalfa cultivars such as ‘Lahontan’, ‘El Dorado Improved’, and Caliverde 65’ were used in this study; these are not grown to any extent in the Central Valley today. First harvest yields averaged about 2500 lbs/A in this work conducted in the 1970’s whereas yields today for the first harvest are commonly 4000-4500 lbs/A.

Approach and Outcomes

Objective 1. Naturally-occurring biological control will be assessed in several areas of the state. Kuhar et al. (1999, 2000) reported on similar efforts conducted in Virginia. Studies will be conducted in four areas of the Central Valley (from south to north - Bakersfield, Fresno, Davis, and Willows) and one intermountain location (Yreka). Two approaches will be used. The first will evaluate the incidence of biological control from about 10 fields per location. Near the time of peak larval population (but before insecticide treatment), 200 EAW larvae will be collected per field and held in the laboratory on alfalfa bouquets at room temperature. Parasitoid cocoons will be collected and any larva dying will be assayed for fungal conidia or resting spores of the entomopathogenic fungus Zoophthora phytonomi. These data will allow us to evaluate the incidence of biological control in several areas of the state. For the second approach, two fields per area (the intermountain area will be excluded from this aspect) will be sampled every 10-14 days starting in January and continuing through EAW pupation (about May). EAW adults and larvae will be collected from sq. ft. samples of alfalfa foliage; specimens will be dislodged from the clipped stems and counted. Eggs will be recovered by the blender - flotation method of Pass and Van Meter (1966) and quantified. Pupae (at the appropriate time) will be enumerated by counting the number per sq. ft. samples (pupae are often on the soil surface). Recovered adults, eggs, larvae, and pupae will be held in the laboratory for natural enemy expression (although larval parasitoids are apparently most common some parasitoids of the egg, adult, and pupae stages have been released). The densities, timing, and mortality of all life stage will be summarized.

Objective 2. Plots will be established on the UC-Davis campus for this objective. Two approaches will be used. Separate plots will be treated for EAW at 5-7 day intervals as the larval population builds for a total of five timings; the final treatment will be untreated. An effective EAW product such a Warrior will be used. For the second approach, five insecticide treatments (plus an untreated) will be used. The goal is to establish a gradient of EAW larval populations near the time of the peak population. Warrior (3.8 oz./A), Lorsban 4E (2 and 1 pt./A), Steward SC (2.6 and 1.3 oz./A) will be used. The goal is not to compare insecticides but rather to remove various percentages of the EAW population. Each treatment timing or treatment insecticide will be replicated four times and plots (20 x 50’ each) will be in a randomized block design. EAW larval populations will be quantified in each plot every 7 days using the standard sweep net sampling method. Plots will be harvested and yields and nutrient quality (% crude protein, % IVDDM) will be determined. Based on current hay prices, an economic analysis will be conducted.

Objective 3. Results will be extended to growers through newsletter articles, the UC Alfalfa Workgroup, the Alfalfa Symposium which attracts ~500 participants annually, the Annual Alfalfa Field Day in May, and other appropriate outlets.

Impact Assessment

The one-year tenure of this project will make it difficult to assess impacts. However, I believe if good information is developed on the availability of biological control of EAW and on treatment decision/timing, unnecessary applications will decrease and this will promote protection of the water resources. Over time, a positive impact will be incurred. Our intention is to pursue additional funding and to extend the project for a second year, which will make the results more robust.

Literature Cited

Hsiao, C. and T. H. Hsiao. 1985. Rickettsia as the cause of cytoplasmic incompatibility in the alfalfa weevil, Hypera postica. J. Invert. Path. 45: 244-6.

Kingsley, P. C., M. D. Bryan, W. H. Day, T L. Burger, R. J. Dysart, & C. P. Schwalbe. Alfalfa weevil (Coleoptera: Curculionidae) biological control: spreading the benefits. Environ. Entomol. 22: 1234-50.

Koehler, C. S. and S. S. Rosenthal. 1975. Economic injury levels of the Egyptian alfalfa weevil or the alfalfa weevil. J. Econ. Entomol. 68: 71-75.

Kuhar, T. P., R. R. Youngman & C. A. Laub. 1999. Alfalfa weevil (Coleoptera: Cuculionidae) pest status and incidence of Bathyplectes spp. (Hymenoptera: Ichneumonidae) and Zoophthora phytonomi (Zygomycetes: Entomophthorales) in Virginia. J. Econ. Entomol. 92: 1184-9.

Kuhar, T. P., R. R. Youngman & C. A. Laub. 2000. Alfalfa weevil (Coleoptera: Cuculionidae) population dynamics and mortality factors in Virginia. Environ. Entomol. 29: 1295-1304.

Long, R. F., M. Nett, D. H. Putnam, G. Shan, J. Schmierer, & B. Reed. 2002. Insecticide choice for alfalfa may protect water quality. Cal. Agric. 56(5): 163-9.

Pass, B. C. and C. L. VanMeter. 1966. A method for extracting eggs of the alfalfa weevil from stems of alfalfa. J. Econ. Entomol. 59: 1294.

Pitcairn, M. J. and A. P. Gutierrez. 1989. Biological control of Hypera postica and Hypera brunneipennis (Coleoptera: Cuculionidae) in California with reference to the introduction of Tetrastichus incertus (Hymenoptera: Eulophidae). Pan-Pac. Entomol. 65: 420-8.

Prichard, T. 2002. Total maximum daily loads (TMDLs) in alfalfa: the implications for alfalfa irrigation management. Proc. 2002 Western Alfalfa and Forage Conf. pp. 23-29.

Radcliffe, E. B. and K. L. Flanders. 1998. Biological control of alfalfa weevil in North America. Integrated Pest Man. Rev. 3: 225-242.

van den Bosch, R. and V. M. Stern. 1969. The effect of harvesting practices on insect populations in alfalfa. Proc. Tall Timbers Conf. on Ecol. Animal Control by Habitat Man. 1: 47-51.

White, J. M., P. G. Allen, L. J. Moffet, & P. C. Kingsley. 1992. A method for economic evaluation of regional pest control programs. Dept. of Resource Econ., Univ. of Mass., Amherst, Working Paper.

Timetable

Objective 1.
Jan to June - sample EAW eggs, larvae, pupae and adults and evaluate incidence of biological control
July to Sept. - summarize and analyze data

Objective 2.
March to May - treat plots, evaluate EAW populations and harvest plots
June to July - summarize and analyze results

Objective 3.
May (field day), Oct. to Dec. - extend results

Major Participants

Larry Godfrey, Extension Entomologist/Entomologist in Agricultural Experiment Station, Dept. of Entomology, Univ. of California-Davis
Godfrey will coordinate the project and advise the GSR on the day-to-day operations the project. He will provide laboratory and greenhouse facilities as well as environmental chambers, computers and other needed equipment. Godfrey has responsibilities for IPM of field crops.
Dan Putnam, Agronomist and Cooperative Extension Specialist, Dept of Agronomy and Range Science, Univ. of California-Davis
Putnam as the state-wide Alfalfa Agronomy Specialist will provide expertise on alfalfa production issues. He will assist with yield and nutrient quality evaluations. Putnam annually sets up Field Days and organizes the other key outreach efforts in alfalfa. He is active in environmental and political issues that could impact alfalfa production in CA. He is active in the California Alfalfa and Forage Association (CAFA) which represent producers in the state.
Univ. of California Cooperative Extension Farm Advisors will be involved to liaison with growers in the counties. Steve Orloff (Yreka), Rachael Long (Davis), David Haviland (Bakersfield) have active programs in alfalfa and grower contacts in the alfalfa industry. With the large number of grower fields involved in the study (~50), growers have not been selected yet but the key personnel are in place to do so. All the personnel in this project have worked with alfalfa growers previously, so getting access to fields should be achievable.

Project Budget

Funding Request
Funding Requested	Other Funding	Total Funding
$40,000	0	$40,000

Project Period: 1/04 – 12/04