Conservation of Pollinators as a Yield Management Strategy in Sunflower

Gary J. Brewer
North Dakota State University
Dept. of Entomology, 202 Hultz Hall, 1300 Albrecht Blvd., Fargo, ND 58105
701-231-7908
701-231-8557
gary.brewer@ndsu.nodak.edu

Executive Summary

Although crops such as sunflower, Helianthus annuus L., support complex beneficial insect populations, many growers are solely interested in insects as pests. Often insect pest management is equated with using insecticides to kill insects, but the goal should be to protect yield in an environmentally benign manner. Insecticides are used to limit insect populations and preserve yield. However, even appropriately used insecticides may cause inadvertent yield reduction in crops such as sunflower by reducing pollinator populations.

Sunflower seed number, weight and oil percentage are positively affected by cross-pollination even though sunflower has been bred to be self-compatible. However, sunflower being worked by pollinating insects may also be infested with feed seeding insects. A grower responding by using an insecticide will limit insect damage but pollinator activity will also be reduced. Often, the yield reduction caused by seed feeding insects is less than the potential gain from pollinating insects. Therefore the yield gain from pollinator activity may offset or exceed the loss from seed feeders. If the cost of an insecticide and application is considered, the advantage of bee conservation is even greater.

This project will develop data showing the impact of native and honey bee pollinators on sunflower yield compared to losses from seed feeding insects. It is thought that in many cases the yield boost from vigorous pollinator activity will exceed the yield loss from seed-feeding, pest insects. Thus, no treatment may be the best option even if the current economic injury level guidelines suggest an insecticide treatment is warranted. Economic injury level determinations will be modified to include pollinator activity. Grower education will focus on pollinator conservation and how to use the modified economic injury level.

Objectives

Relate bee and pest populations to yield in commercial sunflower fields
Revise economic injury levels to include a pollinator factor
Demonstrate revised economic decision model in grower fields
Disseminate results

Justification

Relate bee and pest insect populations to yield in commercial sunflower fields
Ultimate success of this project will depend on grower integration of pollinator conservation practices into their sunflower production systems. To encourage adoption, it will be necessary to documenting the yield impact of pollinator cross pollination in commercial production fields and to demonstrate the net economic benefit to growers. Growers need to clearly see the benefits of pollinator activity to sunflower production and how the benefits may balance or exceed pest damage. Pollinator conservation will result in reduced pesticide use and as a consequence pollinator, environmental, and human health risks will be lessened.
Revise economic injury levels to include a pollinator factor
Appropriate insect pest management is based on sampling and economic decision making. The accepted approach is to develop science-based sampling protocols and economic injury levels. Typically the economic injury level incorporates terms for cost of management, crop value, insect injury, insect damage, and efficacy of the management technique. Economic injury levels have been modified to include terms for environmental costs and for insect resistant varieties. By modifying the banded sunflower moth economic injury level to include a term for pollinator activity, the economic injury level will be raised, and fewer insecticide applications will be made.
Demonstrate revised economic decision model in grower fields.
The best way to encourage adoption of a revised economic decision model is to demonstrate their use in grower fields. The demonstration trials will provide a nucleus of growers with experience in the use and benefits of pollinator conservation to sunflower production. These trials coupled with the extension education efforts of objective 4, will encourage adoption of pollinator conservation and result in less insecticide use in oilseed sunflower production fields. A better understanding of the grower decision making process will help us better design extension education programs and materials. As awareness of the monetary value of pollinators to sunflower production becomes more widely known, insecticide application will decrease, pesticide associated risks will be reduced, and crop value will be maintained.
Disseminate results
Grower understanding of a system to monitor and account for pollinator activity when making rational insect management decisions is critical to the project. An educational component is needed to encourage pollinator conservation and to increase awareness of their value in sunflower production. It will be necessary to demonstrate that strong pollinator activity is economically beneficial to sunflower growers. If pollinator conservation and promotion become integral to sunflower production, pesticide use and pesticide associated risks will be reduced, and economic returns to growers will be protected.

Literature Review

The major sunflower production areas include the Dakotas and the central High Plains of Colorado, Kansas, and Nebraska. Over last two years, North Dakota has averaged 47%, South Dakota 28.7%, and the central High Plains another 17.4% of the nations sunflower production. Together, these regions accounted for 96.2% of the nations total production (Nat. Sunflower Assoc. 2002).

Insects are important to sunflower as pollinators as well as pests. Although the development of self compatible sunflower hybrids has reduced the need for cross-pollination in sunflower hybrids (Free 1970, Furgula et al. 1979), there is variation in the levels of self-compatibility in sunflowers. Fick (1979) reported that even the hybrid varieties, which are as high as 80 to 90% self-compatible, benefit from cross pollination.

Honeybees, Apis mellifera L., are the most important pollinators of sunflower (Sosa 1988, Cirnue 1960). There is a body of literature showing that for sunflwoer hybrids grown in the 1970's honeybee pollination could increase seed production and oil content (Free 1970, Freund and Furgula 1982, Furgala et al. 1979, Krause and Wilson 1981, Langridge and Goodman 1974 and 1981, Mahmood and Furgula 1983, Parker 1981). However, none of those hybrids are still being grown.

A recent test of 47 sunflower hybrids grown in plot trials showed that in the presence of honeybees, sunflower yield increased. Of the different yield components for oilseed sunflower, on average seed set increased by 7%, 1000 seed weight by 7 g, and seed oil percentage was boosted by 3% (Jyoti and Brewer 1999a). The seed weight gain by itself is potentially valued at over $27 per acre for sunflower selling at $0.10/lb and at 18,000 plants per acre.

However, while honeybees and other pollinators can increase sunflower yield and oil content, use of insecticides to manage seed feeding insects can conflict with pollinator activity. In some cases the seed damage avoided by using insecticides may be less than the yield gain from pollinator activity. Thus, it may be to a growers net benefit to not treat for seed feeding insects if honeybees are working the field or if there is strong native bee activity in the field.

Several major insect pests are active in sunflower during pollen shed when pollinator activity is at a maximum. The banded sunflower moth, Cochylis hospes, oviposits on sunflower buds and later instars feed on pollen and developing seeds. It is distributed throughout the Great Plains (Charlet et al. 1995). The red sunflower seed weevil, Smicronyx fulvus, oviposits in developing sunflower seeds (Peng et al. 1997). Both species are major pests of sunflower in the Dakotas. A survey by the National Sunflower Association of 2001 production fields found that in field interiors, the percentage of banded sunflower moth damaged seed was 7.3% in North Dakota and 2.5% in South Dakota (Charlet 2002). The same survey also documented red sunflower seed weevil damage of 3.9 and 9.1% in North and South Dakota respectively. Insecticides are commonly used to manage both insects and are applied at early anthesis. The sunflower moth, Homoeosoma electellum, is a common pest of sunflower in Kansas, Colorado, and Nebraska. Those states experienced severe damage from the sunflower moth in 2001. Sunflower moth controls are applied during pollen shed.

Sunflower growers have not actively adopted honeybee and other pollinator conservation as part of their sunflower production system. The benefits of pollinator cross-pollination are not fully appreciated. This study will establish research and demonstration trials in grower fields to promote pollinator conservation as a component of sunflower production. It will develop a system to monitor pollinator activity and incorporate pollinator population levels into an economic injury level weighing pollinator and pest activity so that a rational treatment decision can be made.

Approach and Methods

1. Relate bee and pest insect populations to yield in commercial sunflower fields

Cooperating bee keepers have established relationships with sunflower growers and will recruit growers for the study. Growers will be supplied with sufficient sunflower seed to plant two separated 20 acre fields to a standard sunflower variety to allow comparison among fields. One field in the pair will have an associated honey bee yard. The other field will located away from the bee field to minimize the number of honey bees in that field. A minimum of 5 pairs of fields will be sampled. Five sites within each field will be sampled for bees and pest insects using an X pattern.

Populations of the banded sunflower moth will be sampled at late bud and early anthesis plant stages. Number of moths per 20 plants per site will be recorded using established methods (Charlet et al. 1995). Egg populations will be sampled at the same time using a sampling program developed by Peng and Brewer (1996).

At early and mid anthesis bee counts will be taken in each field on a sunny, warm day between 10 AM and 2 PM. Bees per 50 plants will be counted by walking an adjacent row so as to not disturb the bees. Honey bees and native bees will be counted separately. Samples of the native bee population will be collected for later species determination.

Red sunflower seed weevils will be sampled on the same dates that bee populations are sampled. Three plants per site will be sampled using the insect repellent sampling method described by Peng et al. (1997).

A second set of 10 plants at each sampling site will be covered with Delnet pollination bags before anthesis (Applied Extrusion Technologies, Middletown, DE) to exclude all pollinators. Data from these plants will be used to establish base-line levels for seed set, seed weight, and oil percentage without pollinator activity.

At plant maturity, the 10 bagged and 10 open plants per site will be harvested and the seeds analyzed for insect damaged seed (Peng and Brewer 1995a). Yield (seed number, seed weight, and seed oil percentage) will be determined using the procedures of Jyoti and Brewer (1999b). Multiple regression analysis will compare yield to pollinator numbers, pest populations levels, and seed damage.

2. Develop a revised economic injury level to include a pollinator tolerance factor

Multiple regression analysis outputs from objective one will used to modify the banded sunflower moth (Charlet et al. 1995) and red sunflower seed weevil (Peng et al. 1997) economic injury levels. Currently, the economic injury levels reflect the relationship between insect counts, injury, and seed damage; yield loss = number of insects X (injury/insect) X (damage/injury).

The modified economic injury levels will incorporate a term for pollinator yield enhancement; yield gain = (seed set x seed weight x oil percentage)/pollinator X pollinator number. The procedure will be similar to that used to modify the red sunflower seed weevil economic injury level to incorporate seed oil percentages (Peng and Brewer 1995b) and by Higley and Winersteen (1992) to develop an environmental economic injury level.

3. Demonstrate revised economic decision model in grower fields

Five or more growers in areas of risk to damage from the banded sunflower moth will be recruited for a demonstration trial. Prior to the field season growers will be provide with educational material and contacted to answer their questions about the pollinator study. Scouting crews will monitor each participating growers field for pollinator and banded sunflower moth population levels using the methods of objective 1. Timely reports will be provided to each grower regarding insect populations and recommendations based on the current and pollinator-adjusted economic injury levels for the banded sunflower moth. Growers will make control decisions and pay for any treatment that may be made. At plant maturity, fields will be sampled as in objective 1 for yield and insect damage in open and pollinator excluded plants.

End of season reports will be provided to growers regarding the yield components and insect damage levels. A discussion will be provided in context to the pest and pollinator population levels previously detected in that field. Approximately a week later, growers will be contacted to get their impressions of the two decision methods and their attitudes for future banded sunflower moth management decisions.

4. Disseminate results

Training materials will be developed for growers, crop consultants, and bee keepers explaining the revised methods. The training material will be shared with extension specialists and agents and used in grower meetings. The results will be presented at the National Sunflower Association Research Forum and published in Sunflower Magazine.

Educational materials suitable for use by crop scouts and growers will be developed that replace existing pest management guides for the banded sunflower moth and red sunflower seed weevil. The revised extension bulletins will be available as paper and web versions.

Impact Assessment

Impact will be assessed three ways.

Grower use of the pollinator-adjusted economic injury level in the demonstration trial will be determined. The economic value of the two approaches compared.
Participating grower attitude will reassessed after the field season and the outcomes compared.
Growers attending meetings discussing the pollinator-adjusted EIL and indicating they will adopt the new method will measured.

Literature Cited

Charlet, L. D. 2002. Insect damage in North and South Dakota sunflower fields in 2001: results from the National Sunflower Association crop survey. Proc. 24th Sunflower Res. Forum.

Charlet, L. D., P. A. Glogoza, and G. J. Brewer. 1995. Banded sunflower moth. North Dakota Extension Service E-823 (revised).

Cirnu, I. 1960. Results of bee pollination of sunflowers. Apicultra 33:18-20. In Romanian. AA-444/63.

Fick, G. 1979. Some factors to consider in the selection of a hybrid. The Sunflower. 5: 26-27.

Free, J. B. 1970. Insect pollination of crop plants. Academic Press, London.

Freund, D. E. and B. Furgala. 1982. Effect of pollination by insects on the seed set and yield of ten oilseed sunflower cultivar. American Bee J. 21: 648-652.

Furgala, B., D. M. Noetzel, and R. G. Robinson. 1979. Observations on the pollination of hybrid sunflowers. Proc. IVth Int. Symp. On Pollination, Md Agric. Exp. Sta. Spec. Misc. Publ. 1:45-48.

Higley, L. G. and W. K. Winersteen. 1992. A new approach to environmental risk assessment of pesticides as a basis for incorporating environmental costs into economic injury levels. Am. Entomol. 38: 34-39.

Jyoti, J. and G. J. Brewer. 1999a. Effect of honeybee (Hymenoptera: Apidae) pollination on sunflower hybrids. Proc. 21st Sunflower Research Workshop. Nat. Sunflower Assoc. Jan. 14-15, 1999. pp. 103-107.

Jyoti, J. and G. J. Brewer. 1999b. Honey bees as vectors of Bacillus thuringiensis for control of banded sunflower moth (Lepidoptera: Tortricidae). J. Environ. Entomol. 28(6): 1172-1176.

Krause, G. L., and W. T. Wilson. 1981. Honey bee (Hymenoptera: Apidae) pollination and visitation patterns on hybrid oilseed sunflowers in central Wyoming. J. Kans. Entomol. Soc. 54: 75-82.

Langridge, D. F., and R. D. Goodman. 1974. A study on pollination of sunflowers, Helianthus annuus L. Aust. J. Agric. Anim. Husb. 14: 201-204.

Mahmood, A. N., and B. Furgala. 1983. Effect of pollination on seed oil percentage of oilseed sunflowers. Amer. Bee J. 123:663-667.

National Sunflower Assoc. 2002. Research & statistics: USDA reports. http://www.sunflowernsa.com/research_statistics/usda/production.asp

Parker, F. D. 1981. Sunflower pollination: abundance, diversity and seasonality of bees and their effect on seed yield. J. of Apicultural Research. 20: 49-61.

Peng, C. and G. J. Brewer. 1995a. Description of achene damage by the red sunflower seed weevil, the banded sunflower moth, and the sunflower moth. J. Kansas Entomol. Soc. 68(3): 263-267.

Peng, C. and G. J. Brewer. 1995b. Economic injury levels for the red sunflower seed weevil (Coleoptera: Curculionidae) infesting oilseed sunflower. Can. Entomol. 127: 561-568.

Peng, C. and G. J. Brewer. 1996. Spatial distribution and sequential sampling plans for the banded sunflower moth (Lepidoptera: Cochylidae) eggs on sunflower. Entomol. Exp. Appl. 79(2): 235-239.

Peng, C., G. J. Brewer, L. D. Charlet, and P. A. Glogoza. 1997. Sunflower seed weevil management. North Dakota Extension Service E-817 (revised).

Sosa, M. A. 1988. Hymenoptera pollinators of sunflower in North Dakota. M. S. thesis. Department of Entomology, North Dakota State University, Fargo.

Timetable

Summer 1	Obj. 1) Field trial
Winter 1	Obj. 1) Analyze results Obj. 2) Revise EIL's Obj. 4) Hold educational meetings with growers and bee keepers
Summer 2	Obj. 3) Conduct demonstration trials
Winter 2	Obj. 3) Analyze demonstration trial results Obj. 4) Develop training and educational materials

Major Participants

Don Nelson and Mark Sperry, Bee keepers.
Don and Mark have bee yards in the sunflower production areas of North Dakota. They have extensive contacts with growers and will arrange grower partners and provide bees for the objective 1 field trials. They will assist in finding grower partners for objective 3.

Gary Brewer
Research Entomologist, Dept. of Entomology
202 Hultz Hall, North Dakota State University, Fargo, ND 58105.
Office: (701) 231-7908, Fax: (701) 231-8557
E-mail: gary.brewer@ndsu.nodak.edu

Project Budget

Budget Category	Grant Funding	Other Funding	Total Funding
Personnel	19,720		19,720
Fringe Benefits	197		197
Travel	7,500		7,500
Equipment	2,000		2,000
Supplies	2,360		2,360
Contractual
Other (publication)	664		664
Indirect Costs (23.3%)	7,559		7,559
Total	40,000		40,000