Redheaded flea beetle (Systena frontalis) has become a serious insect pest of woody and herbaceous ornamental plants over the last several years. Research found larvae were active from 276 – 481 GDD50 and corresponded to black locust or azaleas being in bloom to full bloom. First generation adult emergence corresponded to 590 – 785 [607 average] GDD50, and Magnolia grandiflora was in bloom to full bloom. Second generation larvae were noticed about 1818 – 1856 GDD50 and plants such as Hibiscus and crape myrtle were in various stages of bud swell to full bloom. Second generation adults began emerging from pots about 2100 – 2140 GDD50; however, we were unable to locate suitable plant phenological indicators at this time in the summer. A third generation is possible but was difficult to document with an overlap of generations in our field populations.
Flea beetle larvae and pupae found in pots were reduced by about 60 percent when treated with S. carpocapsae; however differences were not significant from untreated controls in two field trials. Pots treated with the other nematode species had as many or more flea beetles than control pots.
This project has increased grower awareness about larval identification and proper timing of management efforts through the use of growing degree days and plant phenological indicators. Further work is needed to understand performance issues of nematodes in field containers. Results were presented to growers in a workshop, webinars, a poster and fact sheet.
Previous research by the Penn-DEL IPM group developed ranges of growing degree days (GDD) and plant phenological indicators (PPI) for many pests in southeast Pennsylvania, Delaware, New Jersey and Maryland (Penn-DEL 2005, unpublished). This data provides the green industry with the knowledge necessary to sustainably manage many insect pests and diseases; however when this project was underway, S. frontalis was not a pest. This project proposes to develop a range of growing degree days and annotate plant phenological indicators for this beetle. This will help inform growers when the time is ideal for treatments, thereby reducing the number of pesticide applications and reducing the cost of controlling this pest. Another goal is to demonstrate the effectiveness of entomopathogenic nematodes as a biological control agent to growers so they use them to help manage the flea beetle populations.
Knowing when nursery pests are most vulnerable to management effort requires scouting, identification of pest and beneficial arthropods, recognizing vulnerable life stages and proper timing of pesticide applications (Raupp et al. 1992, Mussey and Potter 1997). Calendar day prediction of insect activity is not reliable due to yearly variation in seasonal temperatures and regional differences. Since development of both insects and plants correlates with ambient temperatures, growing degree-days (GDD), a measure of the accumulation of heat throughout the year (Herms 2004) can be used to predict significant biological events of plants, such as bud break or bloom, and correlated with mite or insect biological events such as first emergence or peak activity. There are multiple ways to calculate growing degree-days, the simplest using average daily temperatures. However, using various identifiable plant phenological stages correlated with vulnerable stages of pests is easy to recognize as a laborer scouts the nursery (Mussey and Potter 1997). Herms (2004) discusses calculation of GDD, which varies for different insect pests and phenological stages of many indicator plants at similar GDD. Developmental degree-days were calculated for various flea beetles used as biological agents against leafy spurge and the lower development thresholds were found to be 45.5 or 48.7°F (7.5 or 9.3°C) depending on the species of beetle (Skinner et al. 2004). Preliminary data suggests adult S. frontalis begins activity around 585 GDD50 or when Magnolia grandiflora is in the flowering stage (Kunkel 2011, unpublished). These tools help nursery managers know when to first anticipate infestations, when insect populations peak and activity ends, and to plan control actions before damage is significant.
Entomopathogenic nematodes (Rhabditida: Steinernematidae or Heterorhabditidae ) are used as biological control agents against many soil-dwelling arthropod pests in turfgrass, greenhouse and nursery crops. The free-living stage of these nematodes enters a host through the mouth, anus or spiracles and releases its symbiotic bacteria. The host dies within 48 – 72 hours and the nematodes consume the bacteria and tissues of the dying insect. As resources are depleted, the wandering stage of nematode, called an infective juvenile, is produced in the next generation to continue the cycle. Foraging strategies and movement of different nematode species relates to nematode efficacy against arthropod pests. Cruiser-style nematodes excel at infecting sedentary insects and ambushers are effective versus mobile insects. Other nematodes have behaviors somewhere along this continuum (Lewis 2002). Little is known about S. frontalis larval behavior in soil or in containers; management strategies should evaluate efficacy of a variety of nematodes. Use of entomopathogenic nematodes to control the larvae of S. frontalis could reduce the amounts of foliar pesticides applied for this pest.
Success using entomopathogenic nematodes (EPNs) against difficult-to-manage arthropod pests comes from extensive knowledge about the pest and nematode biology. Black vine weevil is an important and difficult pest to control in a variety of situations, but thoughtfully choosing form of application increases chances for success. Shapiro-Ilan et al. (2003) found infective juveniles emerging from resource-depleted cadavers significantly reduced black vine weevil survival compared to infective juveniles applied in aqueous solution during a greenhouse trial. The ambusher-style nematode, Steinernema carpocapsae, was tested against immature wireworms, cucumber beetles and sweet potato flea beetles providing some control but poor environmental conditions may have limited efficacy (Schalk et al. 1993).
Preliminary work with entomopathogenic nematodes against S. frontalis has shown success. Field-collected larvae were exposed to three species of entomopathogenic nematodes, Heterorhabditis bacteriophora, Steinernema carpocapsae, and S. krauseii for 72 h in a lab bioassay. Steinernema carpocapsae caused about 95% mortality and the other two nematode species caused less than 30% mortality by the end of the experiment (Kunkel 2009, unpublished).
Growing Degree Day and Plant Phenological Indicators: Growing degree days (GDD)and plant phenological indicators were acquired for the various life stages of redheaded flea beetles whenever possible. After the second generation of flea beetle larvae, plant phenological indicators were very sparse for remaining beetle life stages. Goodness-of-fit analyses of the models are not as accurate as preferred and may be due to few data points. Nursery staff occasionally dislodged temperature recording probes and did not replace them to their proper locations (soil and pot sensors); thus temperatures were not as accurate for pot and soil readings.
Insect Phenology: Flea beetle life stages were found and recorded during the growing season. Caging peripheral areas and crop plants simultaneously was challenging due to movement of plant material. Therefore, we tried to determine if flea beetle populations could begin in ‘weedy locations’ by placing cages over various weeds along the periphery of the nursery. Complete information regarding the number of generations per year was difficult to obtain because of the overlap of life stages of field populations. Caging crop plants limits the overhead irrigation plants receive, which may reduce plant vigor.
Entomopathogenic nematodes (epns): A laboratory trial confirmed preliminary data that epns are able to cause significant larval mortality. Potted plants were used in two separate field trials with three and four replicates per trial. The number of epns used in field experiments were calculated based on a field rate of 2.0 billion/acre. Temperatures of containers and the amount of irrigation plants receive may be factors affecting epn efficacy.
Outreach: Poster and fact sheets have been printed and distributed as planned. The video has not been completed due to challenges with editing video clips for the principal investigator. Effort for developing the video continues. Scheduling a workshop during the growing season at a reasonable time for large attendance was difficult. Growers and employees at Holly Hill and Johnson Farms were shown how to scout for larvae and what they looked like so they could better time their management efforts. An additional workshop was scheduled in Virginia at a centralized location and five nurseries sent multiple representatives to attend. Multiple growers provided infested plants for others to view in field settings and under a microscope. The workshop led to the request of a Spanish version of the fact sheet.
Growing degree days and Plant Phenological Indicators: Data was recorded from the Delaware Environmental Observation System website for the Townsend, DE weather station for 1 March to 4 May 2012 to account for growing degree days before the project started. Hobo data logger stations were installed at Holly Hill Farms on 3 May and data started recording for the site at midnight 4 May 2012. Hobo stations were installed in a hoop house (Crops) and on a nearby maintenance shed (Periphery), and data was periodically collected using a data shuttle which was downloaded to a laboratory computer to calculate growing degree day data. Temperature data was collected until 1 November 2012. Hobos were reinstalled at Holly Hill 28 February 2013 with recording of temperature data beginning on 1 March 2013 until 22 May and a malfunction of the hobo weather station. The same weather station at Townsend was used to provide temperature data until adult emergence 12 June 2013. An additional Hobo data logger station was installed at Johnson Farms, Deerfield New Jersey on 7 March 2013. Temperature data from wunderground.com was used to provide temperatures for calculating growing degrees for dates prior to 7 March. Disturbed sensors were returned to their recording locations if disturbed between visits.
Plant phenology was recorded during visits to Holly Hill Farm when notable insect life stages were discovered among the crops. Plant phenological indicators were recorded for first generation larval activity, first generation adult emergence, and second generation of larvae. No plant phenological indicators were apparent on woody ornamentals when second generation adults were appearing at the nursery.
Insect phenology: Visits to our cooperator, Holly Hill Farms, Inc., began 1 May 2012 and continued until 1 September 2012. Scouting during the early growing season consisted of removing known host plants from their containers and examining root balls for flea beetle larvae. Thirty to sixty susceptible plants were examined for the presence of larvae before searching a different host plant. Two host plants were usually examined per visit from 1 May to 25 May and from 5 July to 20 July for larvae. Visits to the nursery after 25 May and 20 July revealed adult emergence had started for the respective generations. Flea beetle activity began to decline in August and scouting efforts were reduced to once per week until 1 September. Placing Bug-Dorms over weeds in the spring of 2012 was difficult to determine an ideal time to set up the cages since little information existed about adult flea beetle emergence. Cages placed over potted plants reduced the amount of irrigation plants received and caused additional stress upon saleable crops. The cages are netted so there was air flow through the cages and did not seem to be a source of concern, although caged plants could have been warmer (no data for temperatures of caged plants). Bug-dorm cages were placed over oxeye daisy, dandelion, white clover and broadleaf plantain found in peripheral areas during May 2013. These cages were observed for adults until flea beetle adults were found feeding on crops.
Entomopathogenic nematodes: Scouting trips to the nursery provided few pots to treat the first generation of larvae since we had little knowledge when to expect larval activity. Infective juveniles (IJs) were prepared in the laboratory for a lab efficacy trial 10 July 2013. Nematodes used in the experiment were Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae. Flea beetle larvae were exposed to 100 IJs/larva in 9.0 cm petri dishes lined with moistened filter paper until mortality was recorded at 72 h. Potted Salvia plants with 3 larva/root ball or more were used in the field experiments at two different nurseries (Holly Hill Farm and Johnson Farm, NJ). The same nematode species were applied at a rate of 2 billion/acre at dusk to reduce exposure to UV light and were watered into the pots. Applications were made 23 and 25 July 2012 at Johnson Farms and Holly Hill Farms respectively. Treated plants were kept in Bug-Dorms to determine if there were differences in the number of emerging adults. Pots were destructively sampled 14 d post application to count the number of live larvae and pupae remaining in pots. Data from separate field trials were analyzed and no differences between sites; therefore data was combined into one data set for analysis.
Setup of Hobos and accumulating missing temperature data for Holly Hill – 1 May
Scouting for redheaded flea beetle larvae – 1 May through 25 May (1st observed larva 4 May 2012)
Emergence of adult redheaded flea beetles – 25 May
Scouting for second generation flea beetles – 18 June through 14 July (1st observed larva, 2nd gen. 5 July 2012)
Laboratory trial – 10 July through 11 July 2012
Application of EPNs for Field trials – 23 & 25 July 2012 (Johnson Farm & Holly Hill Farm, respectively)
Webinar for General Biology of Redheaded flea beetle, NC State University, NC – 2 August 2012
Destructive sampling of Field trial – 7 August and 13 August 2012 (Johnson & Holly Hill Farm, respectively)
Poster discussing RHFB at Ornamental Meeting, Kanuga, Hendersonville, NC – 23 – 28 September 2012
NCERA-224 Meeting, San Jose, Puerto Rico – 29 October 2012
Presentation at Eastern Shore Agricultural Conference, Essex, VA – 4 January 2013
Webinar for Harrell’s – 21 February 2013
Fact sheets distributed (OK, MI, GA, NC, VA, MD, NJ, DE, NY) – April 2013
Grower workshop (VA) – 14 May 2013
Posters distributed (DE, MD, NJ, TN) – May 2013
Spanish version of the fact sheet – June 2013
Growing Degree Days & Plant Phenological Indicators: Growing degree days were calculated for the different life stages of redheaded flea beetles based upon temperature data from air, the pots or soil (Table 1 & 2). Temperature data can possibly be used to explain poor performance of entomopathogenic nematodes. Potting media temperatures sometimes exceeded 120?F (48.9?C) during July, but the average temperature of the media was frequently still less than 100?F (37.8?C) on those days. Some strains or species of epns are unable to tolerate such temperature extremes. Disturbance of sensors by nursery personnel may have caused some temperature data for the pot and soil readings to fluctuate more than they would have without the interference. Goodness-of fit-analyses were conducted using 50?F (10?C) and 48.7?F (9.3?C) expected values for predicting adult flea beetle appearance for the spring of 2013. Neither model provided accurate predictive timeframes for both cooperating nurseries. This may be due to too few data points for the model; therefore work continues towards this part of the project. Magnolia grandiflora phenology appears to be an excellent indicator of adult emergence because it was accurate for predicting emergence in VA, DE, MD and NJ this year. This aspect of the project continues to verify plant phenological indicators for second generation activity.
Insect phenology: Larvae were first found in pots at Holly Hill Farms on 4 May 2012 in a couple pots of Itea virginica. Unfortunately, there were too few infested pots for a meaningful nematode trial. Scouting techniques and larvae were shown to some of the staff at Holly Hill Farms. Our cooperator at Holly Hill first noted adults feeding on plants on 25 May 2012. Adult populations fluctuated during the spring until they were difficult to find in late June. Larvae were found consistently in pots beginning 5 July and collected larvae were used for a preliminary trial in the laboratory. A second generation of adults began to emerge from pots about 18 July at one nursery and 23 July at a separate nursery. Late July through the end of August, adults, larvae and pupae were found feeding on plants or found among roots of plants. Flea beetle adults were feeding on plants until the middle of October. Nursery operators are using these results to better time pesticide applications to coincide with vulnerable stages; thus protecting workers and reducing costs with fewer applications. Growers are now able to scout plants early in the spring looking for larvae to determine if pesticide applications targeting adults will be needed to protect their plants.
Entomopathogenic nematodes: The laboratory trial confirmed previous preliminary data that epns are able to successfully invade and kill flea beetle larvae. Steinernema carpocapsae caused greater mortality (76%) after 72 h compared to S. feltiae (60%), H. bacteriophora (25%); however there was no significant differences(P>0.05). Field experiments found fewer live flea beetles (larvae and pupae) found in S. carpocapsae treated containers than S. feltiae or H. bacteriophora; however only the number of pupae found was significantly reduced by the epns (F=3.9;df=3,9;P=0.0499). Bug-Dorms containing treated pots from immediately after treatment to before destructively sampling root masses had few adults inside (<6/treatment). This suggests that few beetles avoided nematode infection by completing development to the adult stage. Nematode efficacy can be affected by soil conditions such as excess moisture and extreme temperatures and warrants further investigation for nursery use. Field trials suggest nematodes could be a valuable tool in reducing flea beetle populations before adults emerge and damage plants.
Farmers attending the workshop were most interested in the insect phenology and growing degree day information. The work with entomopathogenic nematodes was received well but due to lack of significance of nematode treatments on flea beetle populations, many seemed reluctant to try this control method. Many farmers (7/9) stated they would like to see efficacy data with a bio-rational product available for controlling the larva stages (pers. comm.). Extension agents, extension technicians and other extension colleagues in other states have received the information on the flea beetles well and requested copies of our publications. Previously, growers knew little about how to scout for this insect, what the larva stage looked like or when the various stages occurred during the year. In the past, applications for controlling were made after significant damage had already occurred. The results of this project provide growers an opportunity to apply products at the appropriate time; thus potentially reducing the number of applications needed to manage this pest. Twenty-seven percent of growers spoken to this spring (3/11) said they were planning to implement the scouting techniques this year and 38% (3/8 remaining) said they planned to incorporate these changes next year (pers. comm.).
Publications/Outreach efforts: Our first scouting trips at Holly Hill involved our cooperator to give them hands-on practice at searching for larvae. We reviewed our techniques with him and some of his staff as the growing season progressed. We demonstrate our scouting techniques to personnel at each nursery we visit and provide them a fact sheet. Webinars seem to provide learning opportunities for professionals in the industry; thus when NC State and Harrell’s requested webinars to share our information we accepted. The NC State webinar had over 60 visits last fall and the Harrell’s webinar had about 100 people listen to the presentation this winter. Colleagues from other parts of the country have asked for copies of the fact sheet and other information about this pest as a result of the webinars and other presentations. Scheduling on-site workshops at the nursery was unable to be scheduled due to various complications during the season. However, growers did bring plants to a workshop we conducted in VA where we showed them what to look for, when to search, and how to do it successfully. Recording of the video was choppy and video editing of the video did not go well. Some of the issues were with the recording device used and that has changed, thus efforts continue in this regard. Growers have been thankful for the efforts directed at this seldom studied insect and most have stated they intend to follow the scouting techniques we have developed.
Education & Outreach Activities and Participation Summary
Posters and fact sheets provide some information provided by other projects and which are not fully detailed in this report (e.g., host plant preferences, insecticide trials).
Growers wanted to know what was available for controlling the various stages that worked well. Many growers have tried alternating between acephate, neonicotinoids and pyrethroids with varying degrees of success. Most liked the ideas of trying nematodes or other biological control options, if they could provide reliable and consistent control. Growers expressed some interest in products containing neem, Beauveria and Metarhizium as well as other traditional insecticides.
Areas needing additional study
Growers are concerned the flea beetles migrate in from adjacent corn or soybean fields during the summer. We told them that while flea beetles are able to move fairly well on their own; we were not sure how far this one is able to fly or is carried by the wind. Redheaded flea beetle is known to feed on corn and a number of different weed species, but little is known about their feeding preferences. Work with different flea beetle species has found success with trap cropping with other plants.
Trap cropping may work with this beetle, and host preference work would provide valuable insight into what would work best. Little is also known about moisture requirements for egg development which could be important due to the fact it was once considered a cranberry pest. Nurseries frequently irrigate their crops and this may increase their likelihood to attack by this particular flea beetle. Fate of nematodes in the containers would be useful information to relate towards persistence in pots and nematode efficacy.