Figure 1. Adult C. minuta are small beetles with a metallic bronze-black coloration and “flea-like” hind legs that allow them to jump when disturbed. Photos by Ben McGraw
As turfgrass managers gear up for the season, they typically forecast pest management needs based on the relatively stable pest complexes observed at the regional level. Variations usually manifest in the form of the intensity of familiar pests or localized
outbreaks. However, what is the course of action when an entirely unforeseen pest emerges and then rapidly vanishes thereafter? In 2018, a relatively small beetle, not previously known to be a pest of agricultural crops, much less turfgrass, was isolated
from damaged perennial ryegrass fairways in southern Utah (1). DNA analyses failed to match a species with those in genomic databases. Consequently, specimens were sent to the USDA Systematic Entomology Lab in Beltsville, Md., where taxonomists identified
the insect as Chaetocnema minuta Melsheimer, a native North American flea beetle within the Chrysomelidae family (the leaf beetles).
A review of existing literature revealed limited information on the ecology of C. minuta, other than its mention in annotated lists of flea beetles or in faunal surveys that identified the beetle in various habitats across North America. While some records
have linked the flea beetle with grasses in a general context, this instance marks the first report of a Chaetocnema species utilizing cool-season turfgrasses as hosts. Following its initial discovery, concerted efforts have been launched to monitor
populations in Utah, Nevada and Arizona to accumulate fundamental knowledge regarding the biology and ecology of the insect. Concurrently, there is an initiative to increase awareness among turf managers to aid in reducing turf damage. In this context,
we offer an overview of the insect's biology, seasonal ecology, host preferences and its currently known range.
Figure 2. Immature C. minuta are creamy white with irregular brown speckles occurring across their body. They possess three pairs of true legs and a darkened head capsule.
Identification
Adult C. minuta are relatively small oval-shaped beetles, approximately 0.1 inch long (2.5 millimeters) and metallic bronze to black in color. Their convex elytra, or hardened wings, are lined with a series of pits (Figure 1). The most distinguishing
characteristic of the adult beetle is its saltatorial or jumping hind legs. Their “flea-like” femurs on the hind legs allow them to spring across the turf when disturbed. Some turfgrass managers report observing adults entangled in spray
foam markers or resting on white surfaces. Additionally, their presence can be revealed through the application of a disclosing solution or soap drench to the turf, which brings them to the surface, or by laying a white sheet of paper on the turf
and walking around it to elicit movement. In cases of significant infestation, it is possible to collect them directly into cups by sweeping the cup across the turf surface, capturing them as they leap. We have also noticed adult beetles associating
with spotted spurge (Euphorbia maculate) during summer in areas of thin turf. These plants may provide shade for the adults during the heat of the day and provide a potential area to focus scouting efforts.
The larvae are minute, slender grubs that may resemble caterpillars to some. However, they do not possess fleshy prolegs on the abdomen, but rather have three pairs of true legs. They are creamy white with irregular brown speckles occurring across their
body. The head capsule is blackened, and the first thoracic sclerite behind the head is darkened (Figure 2). Three larval instars have been observed and range in length from 0.04 to 0.2 inch (1 to 5 millimeters). Larvae, particularly first instars,
are typically too small to be detected with the naked eye. Instead, they must be extracted from the turf by removing a sample and placing it in a lukewarm, saturated saline solution. Larvae are irritated by the solution, exit the plant and float to
the surface, where they may be detected with the aid of a microscope or hand lens. It may take 30 minutes to an hour to extract all larvae from a sample.
Figure 3. Adult C. minuta injure turf by skeletonizing the edges of leaves, leaving linear bands or strips along leaf edges. Photos by Adam Van Dyke
Diagnosing turf damage
Flea beetle turf damage appears to originate in roughs along edges of holes that may border native desert vegetation. Some superintendents have reported outbreaks near desert washes — a North American desert vegetation biome — occurring at
the bottom of canyons or other drainages that periodically lack water but are prone to periodic flooding events. Damage can develop rapidly, seemingly overnight, first appearing in small irregular spots and then coalescing into larger patches. Severe
outbreaks may extend into fairways and tees, where it is exacerbated by mowing and concentrated traffic.
Adult feeding may be the first signs of an infestation. Adult beetles skeletonize the edges of leaves, leaving linear bands or strips along leaf edges. This feeding activity imparts a grayish tint to the turf canopy, mimicking the appearance of disease
infection or a nutrient deficiency (Figure 3). As damage progresses, the symptoms resemble drought stress, but turf does not respond to irrigation. Adults are often observed jumping in symptomatic areas. As turf continues to decline, it becomes bleached,
or the stand collapses depending on the species affected. It is still unclear if feeding from the adult, larvae — or combination of both stages together — causes turf loss.
Figure 4. A battery-powered vacuum (modified to collect adult C. minuta into fine-mesh produce bags) has been an effective scouting tool for surveys and research. Photo by Adam Van Dyke
Host grasses
Information on the turfgrass hosts that can support C. minuta is limited. Infestations to date have been documented for perennial ryegrass (Lolium perenne), hybrid bermudagrass (Cynodon dactylon × Cynodon transvaalensis), Kentucky bluegrass (Poa
pratensis) and creeping bentgrass (Agrostis stolonifera) (2). Anecdotally, perennial ryegrass may be the least tolerant of the known hosts, with hot temperatures and high transpiration gradients in the region imposing additional physiological stress
on cool-season species that factor into their reduced feeding tolerance compared to warm-season species.
Utah superintendents have reported annual bluegrass (Poa annua) and tall fescue (Schedonorus arundinaceus) to be hosts, and we have observed adult beetles associating with seashore paspalum (Paspalum vaginatum) and fine fescue (Festuca spp.) in southern
Utah. Adults have also been found within mixed creeping bentgrass/annual bluegrass golf putting greens in southern Utah, but no damage has been reported to date, and no larvae have been recovered from a limited number of samples. Because adult flea
beetles are highly mobile, the presence of an adult on a particular species or playing surface (like a putting green) is not evidence that the insect can complete its development there. Putting greens may not support C. minuta development due to low
and frequent mowing. Laboratory choice tests are needed to identify potential hosts, flea beetle host preference and host plant tolerance to feeding.
Figure 5. Immature C. minuta are heat-extracted from turf-soil plugs in Berlese funnel traps and can be observed after dropping into collection cups.
Seasonal activity
History and early surveys
Beginning in the early 2000s, superintendents in southern Utah were perplexed by sudden and unexplained turf decline in July and August. Even more confusing was the abrupt disappearance of the problem in the fall. Superintendents reported seeing tiny
jumping insects in damaged turf, and therefore most presumed the culprit to be the dichondra flea beetle (Chaetocnema repens) — a close relative of C. minuta — which is known to damage dichondra and bermudagrass in California. The economic
impact of the problem was extensive. Copious amounts of money and time were spent on several insecticide applications that followed recommendations for controlling the dichondra flea beetle (some applied at weekly or biweekly intervals). These measures
were largely ineffective and resulted in the need to regrass damaged or dead areas in fall.
Surveys were initiated on two southern Utah golf courses in 2019 (Copper Rock in Hurricane and Entrada in St. George) and a third in southern Nevada in 2020 (Shadow Creek in Las Vegas) to better understand C. minuta population dynamics and time interventions.
Sticky-card traps were used to detect adults and determine the directional movement into and out of the turfgrass landscape. Cards were positioned along the borders of rough-fairways and directly above the turf canopy, with one side of the sticky
card facing the fairway and the other facing the desert surrounds. Two colors of card were used (yellow and white), and traps were replicated on various fairways and changed weekly.
Vacuum sampling was used to determine adult abundance and compare adult estimates with stick-card trapping. A battery-powered vacuum was modified to collect specimens from the canopy into fine-mesh produce bags (Figure 4). The vacuum method has been more
efficient for monitoring adult populations compared to the sticky card traps, so data listed in Table 1 do not include those from sticky card traps. Because larvae are small and suspected to reside within the turfgrass plant, we opted to sample immature
stages by removing turf-soil cores (plugs) and heat-extract (97 F/36 C) larvae using Berlese funnel traps (Figure 5). This method also extracts adults residing in the turf canopy. Stages drop into collection cups over several days and are counted
using a microscope or magnifying lens. The head capsules of larvae were measured to determine the larval age from samples in 2019 and 2020 (data not presented). Pupae cannot be extracted in Berlese funnels, and to date we have not observed this stage
or eggs.
Figure 6. Seasonal activity of Chaetocnema minuta flea beetle adults and larvae on perennial ryegrass at Copper Rock Golf Course in Utah from April to September during 2019 and 2020. C. minuta stages were collected from turf plugs after heat extraction in Berlese funnels. Adults were also collected from the turf canopy with vacuum sampling that began on July 24, 2019.
Minimal flea beetle activity was observed in southern Utah between April and June 2019, with only a few larvae recovered at Copper Rock. Traditionally, this was a period when many courses in Utah were being treated with insecticides for the insect. Larval
numbers increased in July, but few adults were found in turf samples during this time, and vacuum sampling had not been initiated. Adults were readily collected in the first vacuum sampling in late July, and subsequent vacuum sampling revealed a sharp
increase in adults throughout July (Figure 6). Greater numbers of adults were detected on sticky cards facing outward (toward the desert) prior to this first peak (data not shown), potentially indicating migration into the turf from the surrounds.
A second small increase of adults was detected with the vacuum in early August, before declining and then increasing sharply again three weeks later in late August.
High numbers of adults were also collected in vacuum samples at Entrada in southern Utah during this period (Table 1). At Copper Rock, larval abundance increased following the larger adult peak in August, then a sudden sharp decline of larvae occurred
in September. In 2020, the pattern of flea beetle activity at Copper Rock mirrored that of 2019, apart from a reduced initial surge in adult activity in mid-July, which was followed by two more pronounced spikes in activity during August (Figure 6).
Higher larval abundance also occurred around adult activity increases in 2020 before all activity declined again in September. Directional sticky trap data in August suggest that adults migrated out of the golf course (data not presented), perhaps
into protected areas in the surrounds/desert to overwinter.
Population structure and development in ryegrass fairways in southern Nevada differed from that which had been previously recorded in Utah, as high numbers of larvae were detected earlier in the year at Shadow Creek in Las Vegas in 2020 (Figure 7). Shadow
Creek differs from Copper Rock, as it overseeds ryegrass into bermudagrass during the fall. Larvae were detected in May as the stand was transitioning from perennial ryegrass to bermudagrass for summer. More larvae were detected in May and June in
Nevada than in Utah in either year. Furthermore, adult activity was reduced at Shadow Creek in summer, which may suggest that bermudagrass is a less optimal host.
Table 1. Distribution of C. minuta flea beetle stages collected from vacuum and heat-extracted turf-soil plug samples at several golf courses in the desert southwestern regions of Utah, Nevada and Arizona during 2019 to 2024.
Expanded surveys
Following the discovery that population dynamics differed in the region, further investigations were conducted across a broader range and over more years. Between 2021 and 2023, we sampled three additional courses in southern Utah (Coral Canyon and Sand
Hollow in Hurricane, and The Ledges in St. George), one additional course in southern Nevada (Coyote Springs in Moapa) and four courses in Arizona (Apache, Chiricahua, Renegade and Seven at Desert Mountain Golf Club in Phoenix). Our entire survey
dataset resulted from nearly 5,000 combined vacuum and turf samples from 12 golf courses across three states and includes four turf species (Table 1).
From these samples, more than 19,000 insect specimens have been collected, 86% of which have been from vacuum sampling, compared to just 2% of adults being heat-extracted from turf plugs. Vacuum sampling appears to be a practical way for both practitioners
and scientists to monitor adult flea beetle populations. This method provides real-time data, can be used to time an insecticide application and is the preferred method for surveys and research.
In 2023, seasonal activity on courses in Arizona with ryegrass was similar to surveys from southern Utah in 2019 and 2020. There was little activity, with low numbers of detections from April to June, followed by a steep increase in adult activity in
July. Several peaks in adult activity were observed into September before things quieted down in the fall (Figure 8). What was interesting from these courses was the difference in adult densities during the first peak. There were about 200 adults
in a vacuum sample of ~25 square feet (~2.3 square meters), at Renegade, compared to about 60 adults at Apache. This highlights the importance of regular scouting to determine population size before making application decisions.
Based on evidence from a series of laboratory experiments, the flea beetle can develop rapidly in high temperatures (McGraw and Van Dyke, in review), which may catch turfgrass managers unaware or cause confusion in timing insecticide interventions. Much
remains unknown, such as total fecundity, where oviposition occurs, and how many generations occur in a year. From our surveys, there appear to be several asynchronous generations that overlap in summer. Turf samples in July and August routinely contain
both adults and larvae of different instars that support this phenomenon. Based on adult activity peaks in surveys, there appeared to be two and three generations in Utah in 2019 and 2020, respectively, and two and four generations in Arizona in 2023,
depending on the course. The number of generations likely depends on temperature and other site factors like elevation and management.
Figure 7. Seasonal activity of Chaetocnema minuta flea beetle adults and larvae on hybrid bermudagrass that is overseeded with perennial ryegrass in the fall, at Shadow Creek Golf Course in Nevada, from May to August in 2020. C. minuta stages were collected from turf plugs after heat extraction in Berlese funnels.
Scouting practices
Weekly sampling should be done when the adults are expected to become active and continue until activity slows down. In our surveys of courses in the region with year-round cool-season grass, this has been June through September. In other months, biweekly
or monthly sampling is usually sufficient to monitor populations as activity generally slows down. The variability in seasonal activity of flea beetles may be more pronounced in courses that shift from cool- to warm-season grasses during the summer,
representing a significant gap in our current understanding of their behavior under such conditions. However, as outbreaks have occurred on courses we have surveyed since these surveys were initiated, the sampling period has been extended to include
months we previously thought insect activity had stopped.
Surprisingly, we have recovered adult and immature stages from samples in January and February 2024 in Utah, Nevada and Arizona (Table 1). Detections have been low like other off-peak activity months, with the exception being one course in Arizona (Apache),
where 40 larvae were recovered from three plugs — 31 larvae (mostly first instars) in a single plug. Adult beetles have not been detected in vacuum sampling this early, but adults have been forced from turf plugs with the heat-extraction method.
This new evidence shows at least a portion of the population overwinters in the turf, and the climate in the region supports year-round development. However, development is likely to be slower than that in summer due to cooler temperatures. No turf
damage has been reported in these early months, indicating insecticide applications are not warranted during this time.
These detections may just be “noise” in the overall seasonal activity of C. minuta. However, there have been late-summer outbreaks on courses in Utah that persisted at high levels going into winter and remained high into early spring because
they were not effectively controlled with insecticides. This suggests that scouting after a chemical application is also important to determine the effectiveness and perhaps understand why hot spots persist on particular areas of the course.
Control measures
Early management programs (early 2000s) adopted strategies prescribed for the dichondra flea beetle that recommended short-residual contact insecticide applications (e.g., organophosphates, carbamates and pyrethroids). These insecticides provided little
relief in summer, even with multiple applications. Thus, preventive applications, in particular neonicotinoids, were added to the program. Often these products were applied in spring (some as early as February) without knowledge of population structure
or seasonal phenology, and reapplied bimonthly. Different instars have occurred together in our samples in summer, and adults seem to come in waves over several weeks. This would help to explain, in part, why early efforts to control the beetle were
largely ineffective.
Recently, management has evolved to involve fewer, more-targeted applications based on information provided in surveys and the identification of effective scouting tools. Research must address concerns about past overuse of pyrethroids and neonicotinoids
potentially leading to resistant flea beetle populations. Insects that have a high reproductive potential, have limited movement, feed on few host plants and are subject to continuous exposure to the same chemicals have a higher probability of developing
resistance to insecticides. Although we do not know the reproductive potential or the full extent of host plant use, this may explain the inconsistency or lack of control from some insecticides (AVD unpublished data). At the very least, our observations
would suggest that insecticide applications prior to July will have little value.
The observed rapid development of populations in summer implies that timing an insecticide is paramount. Although it seems logical to apply a contact insecticide targeting adults when densities are increasing, this has not been effective in practice.
Long-residual systemic insecticides may be more appropriate at this time because larvae developing below ground are less likely to be affected by contacts, which also have a shorter residual. Incorporating new chemistries with different modes of action,
like anthranilic diamides, has proven effective against the flea beetle (AVD, data not presented).
Figure 8. Seasonal activity of Chaetocnema minuta flea beetle adults and larvae on perennial ryegrass at two Desert Mountain Golf Courses (Renegade [top] and Apache) in Arizona from April to December 2023 and in February 2024. C. minuta stages were collected from turf plugs after heat extraction in Berlese funnels. Adults were also collected from the turf canopy with vacuum sampling.
Knowledge gaps
Our understanding of C. minuta ecology and management is limited. An unsolved mystery is, where did it come from? Its recent pest status in turfgrass may be from being displaced from agricultural fields by population growth and urbanization of rural areas
in the region. The primary challenge for turf managers is determining effective controls. In order to control the flea beetle, one must have a sound understanding of behavior and biology, including which stage(s) cause turfgrass damage or where in
the landscape it overwinters. This requires effective sampling techniques to observe and study it, some of which we have presented here.
Preliminary data indicates most adults, similar to other flea beetles in agricultural crops, move away from feeding sites to overwinter. Although we have recently uncovered low numbers of adults and larvae capable of overwintering in the turf, this part
of the population likely contributes to a small portion of the adult population in summer.
More surveys from more courses will help fill the current knowledge gaps and help refine control measures. Finally, if you suspect the flea beetle is causing turf decline at your course, we encourage you to scout using the methods we have described here,
or reach out to us for assistance.
The research says
- Infestations to date have been documented for perennial ryegrass (Lolium perenne), hybrid bermudagrass (Cynodon dactylon x Cynodon transvaalensis), Kentucky bluegrass (Poa pratensis) and creeping bentgrass (Agrostis stolonifera).
- Weekly sampling should be done when the adults are expected to become active and continue until activity slows down. In our surveys of courses in the region with year-round cool-season grass, this has been June through September.
- Incorporating new chemistries with different modes of action, like anthranilic diamides, has proven effective against the flea beetle.
Acknowledgements
We could not present this information to the industry without the assistance of all the superintendents and assistants that helped collect samples or provided research space. Thank you, Landon White, Sean Streeter, Ross Laubscher, Todd Rummins, Greg Niendorf,
Wade Field, Ben Morris, Joshua Kent, J.P. Moore, Todd Bohn, Chris Gibson, Angel Gonzalez, Alex Miranda, Paul Dawson, Jeremy Jones, Albert McFadden, Ron Baker, Kristian Waagen, Andy Maxey and Kelly Grow. Your efforts and contributions are truly appreciated.
A special thanks goes to Haden Van Dyke for helping to process samples and count insects.
Literature cited
- Van Dyke, A., and B.A. McGraw. 2021. First report of Chaetocnema minuta (Coleoptera: Chrysomelidae) associated with turfgrass damage in the Desert Southwest United States. Journal of Integrated Pest Management 12(1),19:1–5 (https://doi.org/10.1093/jipm/pmab013).
- Van Dyke, A. 2023. New turfgrass host associations and regional detections for the flea beetle Chaetocnema minuta Melsheimer (Coleoptera: Chrysomelidae) in the Southwestern United States. The Coleopterists Bulletin 77(2):276-277 (https://doi.org/10.1649/0010-065X-77.2.276).
Adam Van Dyke (adam@proturfgrasssolutions.com) is owner, scientist and certified agronomist at Professional Turfgrass Solutions LLC, South Jordan, Utah; and Ben McGraw is an associate professor of turfgrass science at Penn State University, University Park, Pa.