PROVISIONING SYRPHIDS WITH FLORAL RESOURCES: COUPLING ECOLOGICAL MECHANISMS WITH PEST CONTROL OUTCOMES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: NRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 0215106
• Grant No.: 2008-35302-04677
• Proposal No.: 2008-02358
• Project Start Date: Sep 1, 2008
• Project End Date: Aug 31, 2011
• Grant Year: 2008
• Program Code: [51.2A]- Arthropod and Nematode Biology and Management (A): Organismal and Population Biology

Recipient Organization
UNIVERSITY OF CALIFORNIA, BERKELEY
(N/A)
BERKELEY,CA 94720

Performing Department
INSECT BIOLOGY

Non Technical Summary
One strategy for improving biological pest control in agricultural systems is floral resource provisioning: the integration of flowering plants into the crop system with the intent of providing additional food to parasitoids and predators and enhancing pest control. Efforts to implement the floral resource provisioning strategy have met with failure as often as success. To increase the success rate of floral resource provisioning strategies, we must better understand how they work. Commercial growers of organic lettuce commonly integrate strips of flowering plants into their fields. The presence of flowering plants (i) appears to reduce or eliminate infestations of the lettuce aphid, one of the key pests in lettuce, and (ii) appears to increase the abundance of syrphid flies. Syrhpid flies are predators that consume dozens of aphids when they are larvae, but require nectar and pollen as adults. The goal of this project is to critically evaluate the floral resource provisioning strategy in lettuce. We will evaluate its success by measuring the effect of flowering plants on aphid densities, and we will understand its mechanisms by examining syrphid feeding and reproduction. Our work is expected to provide a mechanistic understanding of the role that floral resources can play in the practice of biological control, and thereby contribute to the success of future implementations.

Animal Health Component

30%

Research Effort Categories

Basic

70%

Applied

30%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
211	1430	1130	30%
215	1430	1070	70%

Knowledge Area
211 - Insects, Mites, and Other Arthropods Affecting Plants; 215 - Biological Control of Pests Affecting Plants;

Subject Of Investigation
1430 - Greens and leafy vegetables;

Field Of Science
1130 - Entomology and acarology; 1070 - Ecology;

Keywords

habitat management,

conservation,

bioloigcal control,

intercrop,

hoverflies,

aphids,

floral resources

nectar,

pollen,

lettuce

Goals / Objectives
We plan to test the hypothesis that the addition of flowering plants to an agroecosystem can improve pest control by providing parasitoids and predators with nectar and pollen as food sources. Floral resource provisioning appears to succeed in some agricultural systems but fail in others, and the reasons for success or failure are little understood. Floral resource provisioning programs have the potential to improve agricultural production while decreasing their reliance on synthetic pesticides; however, the uncertainty of success restricts implementation of these programs. We believe that to advance the state of the art, the mechanisms underlying successful floral resource provisioning must be identified. We propose to test an apparently successful system of floral resource provisioning. Working in organic lettuce, we will identify the mechanisms linking flower plantings to pest reductions. Aphids are the predominant pests of lettuce in the coastal areas of California. The primary aphid pest is the lettuce aphid (Nasonovia ribis-nigri); minor pest aphids include the green peach aphid (Myzus persicae) and the foxglove aphid (Aulacorthum solani). Aphids damage lettuce crops primarily through their presence, because the retail market holds an extremely low tolerance for insect contamination of vegetable crops. Growers cope with the aphid challenge in different ways. The primary tools available are systemic insecticides, contact insecticides, and biological control from beneficial insects. Growers that make beneficial insects their tool of choice have focused their attention on syrphid flies, also known as hoverflies. Adult syrphid flies lay eggs on plants with aphids. After an egg hatches, the syrphid larva steadily consumes dozens of aphids. Specific objectives are to: (1) test whether syrphids are limited by access to pollen and/or nectar, (2) test whether syrphids feed on pollen and nectar in the field, (3) test whether floral resources increase syrphid realized fecundity, (4) test whether floral resources increase syrphid predation rates, and (5) test whether floral resources reduce aphid densities. Our expect output is to provide a realistic evaluation of the floral resource provisioning hypothesis and learn more about the function of floral resources in agricultural food webs. Our project will mechanistically link the presence of flowers to syrphid and aphid population patterns.

Project Methods
The project objectives will be accomplished through a combination of field and laboratory studies. First, to determine whether syrphid longevity and fecundity is limited by access to flowers, we will rear syrphids in the greenhouse with and without flowers. Second, to verify that syrphids feed on flowers in the field, we will combine visual field observations of syrphids with dissection and chemical analyses that will quantify the syrphid pollen and nectar consumption. Third, we will test whether strips of flowers increase syrphid fecundity in lettuce fields by comparing the age and egg production of syrphid flies collected from fields with and without flowers. Fourth, we will test the effect of flowers on syrphid predation rates. Predation rates will be estimated in two ways (by measuring consumption and excretion) and compared between fields with and without flowers. Fifth, we will evaluate whether flower plantings fulfill their intended purpose of reduce pest densities by sampling aphid abundances in lettuce fields with and without flowers.

Progress 09/01/08 to 08/31/11

Outputs
OUTPUTS: In the three years of this project (August 2008 through August 2011) we conducted a series of experiments and observations to test five steps by which floral resources are hypothesized to reduce pest densities. We documented the links between supplemental flower plantings in lettuce fields, populations of predatory syrphid flies, and reduced densities of a key pest insect, the lettuce aphid. ACTIVITIES: Project results have been disseminated in manuscripts and in numerous talks. We presented our results to the community of growers and pest control advisors associated with the lettuce and spinach industries at conferences hosted by the California Leafy Greens Research Board and seminars hosted by the U.C. Cooperative Extension service. We presented our results to the community of researchers at the Western Regional Biological Control workshop and at national and branch meetings of the Entomological Society of America. PARTICIPANTS: This project supported the training of one graduate student (J. Hopper) and two postdoctoral scholars (E. Nelson and B. Hogg). TARGET AUDIENCES: Farmers of vegetable crops; researchers and practitioners of biological control and integrated pest management: IPM consultants and practitioners; entomologists; plant-insect ecologists. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
This project filled a knowledge gap in the field of conservation biocontrol. To aid and promote predatory insects, farmers in many crops have planted flowers in and around their crops. However, the hypothesized pathway by which flowers improve pest control has generally been left untested. This project demonstrated that flower plantings can aid in conservation biological control. Specifically, we found evidence to support each of the five assumptions of the floral resource provisioning hypothesis: (1) predatory syrphid flies are limited by access to pollen and/or nectar, (2) adult syrphids feed on pollen and nectar, (3) floral resources increase syrphid fecundity, (4) as a consequence of increased fecundity, more aphids are consumed by syrphid larvae when floral resources are present, and (5) floral resources reduce aphid densities. This represents a significant step forward in conservation biological control. Now that we have produced evidence that floral resource provisioning can work as hypothesized, biological control workers can better evaluate the likelihood of candidate crop systems benefiting from floral resource provisioning.

Publications

• B. N. Hogg, E. H. Nelson, K. M. Daane, and N.J.Mills, 2011. Floral resources enhance aphid suppression by a hoverfly. Entomologia Experimentalis et Applicata 414 (2): 138-144.
• J. V. Hopper, E. H. Nelson, K. M. Daane, and N.J.Mills, 2011. Growth, development and consumption by four syrphid species associated with the lettuce aphid, Nasonovia ribisnigri, in California. Biological Control 58(3): 271-276.
• Hogg, B. N., Bugg, R. L., and Daane, K. M. 2011. Attractiveness of common insectary and harvestable floral resources to beneficial insects. Biological Control 56: 76-84.
• E. H. Nelson, B. N. Hogg, K. M. Daane, and N. J. Mills, 2012. Syrphid flies suppress aphids in lettuce. BioControl, in review.

Progress 09/01/09 to 08/31/10

Outputs
OUTPUTS: In the second year of this project (August 2009 to August 2010) we supported our objectives with data from one lab study and several field studies. ACTIVITIES: We conducted a "Dome Cage Study" in the laboratory, which tested for the effect of sugars on the fecundity and longevity of adult syrphid flies. Our "Sugar Spray Study" compared flies from field plots sprayed with or without sugar water, in terms of the flies' attraction to the plots and in terms of the flies' gut sugar content. We performed a "Before and After Study" in crop fields to measure the effect of flowers on syrphid density and oviposition activity. We did an "Augmentation Study" to measure the effect of syrphid larvae on aphid population growth. We conducted a "Field Cage" study that measured the effect of alyssum on syrphid fecundity and aphid control. In our "Harvestable Hedgerows" study, we screened nine species of annual flowering plants (some of them marketable) in terms of their attractiveness to hoverflies. We collected "Feeding Observations" and "Movement Observations" of adult syrphids foraging in the field, and we recorded the flies' feeding behavior and movement rates. EVENTS: We presented our results to the community of growers and pest control advisors associated with the lettuce and spinach industries at a conference hosted by the California Leafy Greens Research Board. SERVICES: We answered questions from individual growers. We provided an interview to the California Academy of Sciences, which described our study system on their web site (URL: http://www.calacademy.org/sciencetoday/lettuce-insects/). We provided an interview to the Insect News Network. PARTICIPANTS: PARTICIPANTS: Eve Roubinet, lab assistant. Korey Kassir, lab assistant. Kevin Welzel, lab assistant. PARTNER ORGANIZATIONS: Earthbound Farm, San Juan Bautista, CA. Enza Zaden Research, San Juan Bautista, CA. California Leafy Greens Research Board, Salinas, CA. TARGET AUDIENCES: Researchers and practitioners of biological control and integrated pest management. Farmers of vegetable crops; IPM consultants and practitioners; Entomologists; Plant-insect ecologists. PROJECT MODIFICATIONS: Modification #1: In our grant proposal, some of our objectives were to be fulfilled using an approach that relied on finding organic lettuce fields with and without strips of flowers. As it turns out, most growers currently use flowers in their fields; the only flower-free fields we could find would not work for the project as described, either because they are sprayed with conventional pesticides or because they are planted with aphid-resistant varieties of lettuce. We considered other approaches that would allow us to compare syrphid activity and aphid control, and elected to use a field cage study to achieve our objectives. Modification #2: The flower strips that organic lettuce farmers plant in their fields displace the cash crop. We added a study to address two questions that are frequently raised: (1) Which plant species are most attractive to syrphid flies, and (2) Is it possible to attract syrphids with plants that have some market value, and could be harvested as a secondary crop As described above, we screened nine annual flowering plants for their attractiveness to syrphid flies. The screening study was primarily funded by the US EPA; this grant provided personnel support.

Impacts
The results of our studies provided new knowledge about syrphid flies in lettuce fields, or supported existing knowledge. Our "Dome Cage Study" and "Sugar Spray Study" showed that syrphids are attracted to sugar sources, that sugars can their gut sugar levels, and that sugars increase syrphid longevity. The "Before and After Study" suggested that syrphid activity is weather dependent as well as flower dependent. Our "Augmentation Study" showed that syrphid larvae suppress aphids in a field situation. The "Field Cage" study showed that the presence of alyssum increases syrphid fecundity and reduces aphid population growth. The "Harvestable Hedgerows" study identified several marketable plant species as inferior syrphid fly attractants. Our "Feeding Observations" showed that males and females have different diets, and our "Movement Observations" provided a lower bound for syrphid movement rates. Growers may use this information when making decisions such as: whether or not to plant floral insectaries; which plant species to use; or how to distribute the flowers in the field. Together, these results support our five project objectives. These results can be included in publications, and they may help the IPM community to identify elements of a crop system that permit insectary flowers to impact pest densities.

Publications

• Hogg, B.N., Bugg, R.L., and Daane, K.M., 2011. Attractiveness of common insectary and harvestable floral resources to natural enemies. Biological Control (in press).

Progress 09/01/08 to 08/31/09

Outputs
OUTPUTS: In the first year of this project, we initiated a research program that will provide a mechanistic understanding of how in-field floral resources can improve biological control. Our efforts in this review period focused on laboratory studies and field protocols. PARTICIPANTS: Erik Nelson (post-doc and assistant specialist) identified field space, coordinated the project, developed sampling techniques, collected data. Brian Hogg (post-doc) developed protocols for laboratory cage experiments. Julie Hopper (graduate student) measured consumption rates of syrphid fly larvae. Kent Daane and Nick Mills (co-PIs) advised on all aspects of the project. TARGET AUDIENCES: This project seeks to understand the apparent success seen in lettuce fields of an IPM strategy that has been applied with haphazard success in other crops. We will draw generalizable lessons from the lettuce system and present them to the community of IPM researchers and practitioners. The project will also yield specific information pertinent to lettuce production, which we will deliver to lettuce growers and pest control advisers. PROJECT MODIFICATIONS: Work during this reporting period indicates that the spatial scale of syrphid fly movement can exceed that of some of the experiments we originally planned. We have developed alternative studies to address our objectives.

Impacts
Preliminary data from laboratory experiments shows that flowers enhance the fitness of adult syrphid flies. Rearing methods were developed and we have measured the rates at which syrphid larvae consume aphids. Field sampling methods were developed. These results all support further work on the project objectives.

Publications

• No publications reported this period