Dragonflies as potential biological control on farms: prey assessment using a DNA approach

Progress report for GNE21-257

Project Type: Graduate Student
Funds awarded in 2021: $15,000.00
Projected End Date: 08/14/2022
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Graduate Student:
Faculty Advisor:
William Lamp
University of Maryland, College Park
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Project Information

Project Objectives:

The overall goal of this study is to better understand Odonata community composition, prey selection and their potential for pest suppression in agroecosystems. This goal can be divided into two research objectives:

  1. To compare richness and abundance of assemblages of adult species of dragonflies and damselflies among farms and crops.
  2. To compare prey composition using next generation sequencing (NGS) of feces from multiple dragonfly species between upland farm habitat and near water habitat.
Introduction:

The purpose of this project is to determine whether dragonflies and damselflies (Odonata) eat insects that are pests of agricultural crops. Odonata provide humans with ecosystem services in several ways, with one primary contribution being their ability to eat large quantities of arthropods often considered pest species. It is well understood that adult dragonflies are generalist and opportunistic insectivorous predators. Dragonfly and damselfly diet analyses consistently show small Diptera as primary prey, but they are known to eat a wide range of insects. Most prey capture occurs in flight, but damselflies and one family of dragonflies can glean prey from surfaces (Corbet 1999), which broadens the range of potential prey species. Historic diet studies consist of field observations and gut content identification. Both of these techniques are problematic due to observer bias and labor intensive, time-consuming methods. New molecular technology using fecal metabarcoding can provide a more complete analysis of predator diet. This rapid and comprehensive methodology for analysis of dragonfly diet can help future researchers understand the importance of dragonflies and damselflies as ecosystem service providers in both agricultural and urban habitats.

 

Chemical insecticides, though widely used, pose several challenges to farmers. They can be costly, incite concern from the public regarding safety, and induce insect resistance leading to pest outbreaks. Predatory insects used as biological control in agriculture are an alternative to chemical pesticides and can indirectly improve soil and water quality by reducing chemical inputs into the environment. Dragonflies are good candidates for conservation biological control in agroecosystems. Oftentimes, farmers augment water flow in their fields and, when necessary, retain water for later irrigation in on-farm retention ponds. These water sources can be areas of high adult dragonfly activity and possible breeding and oviposition habitat for subsequent generations of dragonflies. The theory of conservation biological control is to improve survival, fecundity, longevity, and behavior of a natural enemy through such activities as reduction of pesticide use and habitat enhancement (Holland et al. 2016; Landis et al. 2000). By showing the importance of dragonflies as natural enemies of agricultural pests, we can then begin to help farmers create conservation biological control plans inclusive of dragonflies on farms, as well as outline actions for improving the quality of on-farm water bodies.

 

Preliminary research performed during the summer of 2020 included surveys of alfalfa, soybean and corn crops at four University of Maryland farms in central and western Maryland. These surveys indicated the presence of 21 species of Odonata encompassing six families across the four farms, with the most speciose farm having 18 species present and the least speciose farm having only 4. Many of the species were found in high abundance at most (3 out of 4) farms throughout the cropping season. Feces were collected over a 24-hour period from several species of dragonflies. These samples will be analyzed by GENEWIZ in early May 2021. These preliminary data will help to optimize the protocol for the 2021 sampling season and DNA processing projected to take place in late 2021.

Research

Materials and methods:

Objective 1: To compare richness and abundance of assemblages of adult species of dragonflies and damselflies among farms and crops.

 

Quantifying dragonfly and damselfly richness and abundance in agroecosystems will help farmers and researchers better understand the specific species assemblage associated with farmlands. To date, no research has focused on precisely which dragonfly species are utilizing farmland as foraging habitat. To address this objective, visual encounter surveys (VES) were conducted in multiple crop fields and water bodies at different farms to assess whether different dragonfly communities occur across agroecosystems. This will allow us to determine the most common and widespread dragonflies on farmland and to pinpoint any shared attributes among these species. The four University of Maryland farms used for this study were in central and western Maryland and included the Western Maryland Research and Education Center in Keedysville (KV), and three Central Maryland Research and Education Center locations in Beltsville (BV), Clarksville (CV), and Upper Marlboro (UM). Timed VES were conducted in three crops at each farm and a water body at CV and UM. Clakrsville and Upper Marlboro were selected for water body surveys because they had large, well-established on-farm water retention ponds and livestock waste lagoons. Alfalfa, soy and corn were used because they are important cash crops throughout the eastern United States and dragonflies have historically been observed as predators of pests in soybean. Twice a month from June 2021 through September 2021, 30-minute VES were conducted at each farm in crop fields and water bodies twice a day, once in the morning and once in the afternoon. These surveys were conducted over several days, with one farm being visited per day. Each VES field was approximately 60 m x 60 m. During the VES, the number of novel dragonfly and damselfly encounters were recorded as well as identified to species whenever possible. Most dragonflies are easily identified to species using binoculars; However, when necessary, individuals were collected and photographed for later identification. Crop height, cloud cover, temperature, wind speed, time, behavior at time of sighting, sex, and, if applicable, maturity of dragonflies were also recorded. The behavior of the dragonfly was described as flying, perching, foraging, aggression or tandem flying. A one-way ANOVA was performed to determine differences in dragonfly species abundance among farms.

 

Objective 2: To compare prey composition using next generation sequencing (NGS) of feces from multiple dragonfly species between upland farm habitat and near water habitat.

 

To answer this objective, dragonfly individuals of multiple species and both sexes were collected once a month on three of the four farms were visual encounter surveys took place: Clarksville, Beltsville and Upper Marlboro. Dragonfly fecal samples were collected both in the upland crop fields as well as at on-farm water bodies as a control, because many dragonflies exhibit differential foraging in upland versus near water habitats. Fecal sampling was performed at the farm level, not the crop level, to ensure the collection of a large enough sample size. Sampling was not timed but rather at least ten individuals were collected per month at each farm for a minimum monthly total of five dragonflies from upland crop fields and five from on-farm water bodies. Dragonflies were captured using an aerial net and transported back to the lab for 24-hour fecal sampling. To sample feces, the dragonfly was placed in a sterile 50 mL Eppendorf tube for 24 hours during which time they defecate membrane bound pellets in the tube. Sterile micropipette tips were used to remove feces every three hours to a sterile microcentrifuge tube and placed on ice in the field or freezer in the lab (Fig. 1). Feces were processed in a molecular genetics lab at the University of Maryland using the Qiagen DNeasy Blood and Tissue Kit for DNA extraction. After DNA extraction, polymerase chain reaction (PCR) was conducted to amplify the DNA (Fig. 2). The target region was the cytochrome c oxidase subunit I mitochondrial gene (COI) using universal primers. During PCR, the DNA sample was mixed with PCR PreMix, primers and ddH2O and incubated in the thermocycler at 96˚C for 3 minutes followed by 35 cycles of 94˚C for 30 seconds, 50˚C for 30 seconds and 72˚C for 45 seconds. Lastly, the sample was incubated at 72˚C for 10 minutes. PCR products were purified using the ExoSAP-IT Express reagent in preparation for next generation sequencing (NGS) by the genomics company GENEWIZ using their Amplicon-EZ NGS service. During PCR cleanup, the post-PCR reaction product was mixed with ExoSAP-IT Express and incubated in a thermocycler at 37˚C for 4 minutes followed by incubation at 80˚C for 1 minute. NGS will give a broader profile of the prey DNA in the feces compared to Sanger sequencing. GENEWIZ provides clients with DNA sequences as well as gel electrophoresis images. Sequences provided by GENEWIZ are currently being compared to the NCBI GenBank database to determine the proportion of the diet composed of agricultural pests.

Fig. 1. Capture and fecal sampling of dragonflies for fecal DNA analysis.
Fig 2. DNA extraction and amplification were performed on dragonfly fecal samples.

 

Additionally, five sticky traps were deployed and arranged in an “X” configuration twice a month in each crop at each of the three farm locations to compare the available prey to the prey DNA found in the feces. These sticky traps were collected after one week of field exposure. Poles for the sticky traps were three-foot dowel rods early in the season when plant growth is low, then progressed to six-foot bamboo rods as corn and soy grew taller. The goal is to sample prey slightly above the canopy as this is where many species of odonates have been observed to forage. Sticky traps are currently being processed by visually identifying and counting insects to order level. Specific crop pest species will be identified to family and genus and compared to the results of the fecal DNA analyses.

Research results and discussion:

Of the 26 species of dragonflies and damselflies were surveyed across all farms, seven at Keedysville, 17 at Beltsville, 15 at Clarksville, and 22 at Upper Marlboro (Table 1; Fig. 3). Of the total 26 odonates, 20 were dragonflies and 6 were damselflies. The five most abundant species were in the family Libellulidae and included the common whitetail (Plathemis lydia), widow skimmer (Libellula luctuosa), blue dasher (Pachydiplax longipennis), Eastern pondhawk (Erythemis simplicicollis), and Eastern amberwing (Perithemis tenera). The habitat preferences of the most abundantly surveyed species are similar. They are common, cosmopolitan species found in all counties in Maryland and they are associated with slow-moving, lentic water bodies (Maryland Biodiversity Project 2021). Average daily abundance at Upper Marlboro (36 ± 49) was significantly greater than at Keedysville (0.4 ± 0.6), Beltsville (6 ± 5), and Clarksville (7 ± 9)  (ANOVA, p < 0.001).

 

Table 1. The species of dragonflies and damselflies surveyed at four University of Maryland farms from May through September 2021. The farm codes are Keedysville (KV), Beltsville (BV), Clarksville (CV) and Upper Marlboro (UM).
Fig. 3. The total species richness of dragonflies and damselflies surveyed from May through September 2021 at four University of Maryland farms. The farm codes are Keedysville (KV), Beltsville (BV), Clarksville (CV) and Upper Marlboro (UM).

 

A total of 97 odonates were sampled for fecal material across 13 species at three farms. During a 24-hour period, dragonflies produced an average of 20 fecal pellets, with a minimum of 1 and maximum of 53. Most of the fecal material was sampled during the first 12 hours post capture. Preliminary results from NGS sequencing shows individuals eat a wide variety of prey including species from Hemiptera, Ephemeroptera, Coleoptera, Diptera, Hymenoptera, and Lepidoptera. The most prevalent prey is in the order Diptera, or true flies.

Participation Summary

Education & Outreach Activities and Participation Summary

1 Published press articles, newsletters
2 Webinars / talks / presentations

Participation Summary:

60 Farmers
10 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

Providing farmers with information about dragonflies and damselflies as beneficial predators is a priority for this project. Many people believe dragonflies are primary predators of mosquitoes, though there is little scientific research confirming their diet composition. It is therefore important that more empirical data, rather than conjecture, about dragonflies be included in extension articles and presentations. Since there is such limited peer-reviewed literature about dragonflies in agriculture, it is vital to release our findings to other scientists and researchers through presentations at professional meetings and publications. This is an important first step in generating interest in continued research on dragonflies in agroecosystems.

 

We plan to communicate the importance of dragonflies as predators for biological control with stakeholders in Maryland and throughout the region in several ways. Presentations at the National and Eastern Branch Entomological Society of America, Society for Freshwater Science and Dragonfly Society of the Americas meetings through both poster and oral presentations are planned for 2022. A main outlet for local outreach to farmers will be through publications, meetings and workshops hosted by the Maryland Organic Food and Farming Association and University of Maryland Extension. Publishing pamphlets and fact sheets in both local agricultural publications, such as Agronomy News, and on the University of Maryland Home and Garden Information Center website, as well as preparing manuscripts for peer-reviewed journals will be prioritized. My personal interest and passion for dragonflies will ensure I continue to discuss their importance through outreach and extension well beyond my projected graduation date. 

Project Outcomes

Project outcomes:

My project will contribute to future sustainability by informing farmers and other agricultural stakeholders of the value of dragonflies as predators in agroecosystems. This project is one step in helping farmers understand odonates and their biological control function on their farms. In the next year, I will present my findings at several meetings such as the Eastern Branch Entomological Society of America and the Joint Aquatic Sciences Meeting as well as find opportunities to educate Maryland farmers at the local level. 

Knowledge Gained:

Throughout the course of this project, my advisor and I have gained knowledge about the prevalence and community composition of odonates on farms. Farmers are aware and know there are dragonflies and damselflies on farms, but knowledge is lacking on how to encourage dragonfly populations. However, preliminary findings suggest active breeding populations on the farm may increase abundance and species richness of dragonflies in upland crop habitats. Implementing management practices for conservational biological control of dragonflies, wherein farmers encourage populations on the farm by creating and maintaining favorable habitat, is one strategy to increase dragonfly predation in your crops. Varied structural complexity in the agricultural landscape that includes both high perches and bare ground is also an important consideration for encouraging dragonfly predation. Dragonflies often use tall perches, such as corn stalks or sticky trap posts, while foraging (Fig. 4).

 

Fig. 4. Dragonflies are observed perching during foraging. A black saddlebags (Tramea lacerata) is perching on a sticky trap post on the left and a great blue skimmer (Libellula vibrans) is seen perching high atop corn on the right (Photos by Muinot Anamashaun).

 

Assessment of Project Approach and Areas of Further Study:

The next step is helping understand how on-farm retention ponds and lagoons can be managed to increase the health and habitat suitability for dragonflies and other beneficial aquatic taxa. Managing water sources on farms that can sustain dragonfly populations may increase the net ecosystem services provided by the water body, which will result in economic benefits from biological control, pollination and increased soil and water quality (Fig. 5).

 

Fig. 5. The water retention pond at Upper Marlboro was frequently inundated with dragonflies and damselflies. Five dragonflies are pictured in the inset photo (Photo by Muinot Anamashaun).

Information Products

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.