Terrestrial insects in water can often delay or escape drowning by floating and swimming. However, we observed that flooding of pitfall traps baited with rotting carrion results in high overnight mortality of captured beetles and reasoned that this risk may be enhanced by microbial respiration. By assessing carrion beetle (Coleoptera: Silphidae) response to flooding, tolerance to immersion, and swimming behavior, we offer insights to this cause of death and beetle behavioral physiology. Response of buried Nicrophorus orbicollis Say to soil flooding resulted in beetles moving to the soil surface. The lethal time to 50% mortality (LT50 (immersion); mean ± 95% CI) for Nicrophorus investigator Zetterstedt, Nicrophorus marginatus F., Necrodes surinamensis F., and Thanatophilus lapponicus Herbst was 14.8 ± 2.3, 9.0 ± 3.3, 3.2 ± 1.1, and 12.1 ± 2.5 h, respectively. Swimming behavior and survival time of N. investigator was tested using yeast:sucrose (Y:S) solutions to create a eutrophic, severely hypoxic aqueous environment. LT50 (swimming) for N. investigator was 7.5 ± 1.4, 6.0 ± 1.7, and 4.2 ± 1.2 h for the low, medium, and high Y:S solutions, respectively, and >24.0 h in control treatments. Nicrophorus investigator survived nearly twice as long when completely immersed in deoxygenated water, as might occur in flooded burrows, than when swimming on the surface. We document for the first time, the rapid induction of hypoxic coma and death for a terrestrial insect from enhanced microbial activity and CO2 production of an aqueous environment, as well as suggestions on trapping protocols related to the federally endangered Nicrophorus americanus Olivier.
Physiological stress from unfavorable environmental conditions can trigger a number of compensatory behavioral and biochemical processes that mediate survival (Sinclair et al. 2003). Under a typical environmental adversity such as high temperature or severe hypoxia, insects will enter a protective, reversible coma to conserve energy, prevent permanent tissue damage, and ultimately avoid mortality (Rodgers et al. 2010). This metabolic depression allows a variety of species to resist and survive stressful conditions (Hoback et al. 2000, Colinet and Renault 2012). Terrestrial invertebrates that burrow frequently face hypoxic and hypercapnic conditions in flooded soil with high microbial activity; many soil microhabitats develop hypoxia at varying rates depending on soil type, saturation, microbial community, and temperature (Hoback and Stanley 2001).
One group that likely encounters soil hypoxia regularly is burying beetles in the genus Nicrophorus. These species spend daily periods of inactivity buried in the soil (Scott 1998) and search the environment for small dead vertebrates. Upon finding a suitable carcass, a male and female Nicrophorus will bury it, remove fur or feathers, and shape it into a brood ball upon which they will rear their offspring (Scott 1998). Burrowing behaviors and use of dead animals likely expose these beetles to ambient oxygen levels as low as 1–2% saturation (Hoback and Stanley 2001). Because of their sensitivity to desiccation (Bedick et al. 2006), Nicrophorus beetles prefer soils nearing total saturation, with measured soil moisture preferences in Nicrophorusamericanus Olivier ranging from 75–100% (Willemssens 2015). When soils flood, microbial respiration can quickly decrease oxygen availability (Baumgärtl et al. 1994). Thus, adaptations for surviving floods and hypoxia are likely important life history traits for terrestrial invertebrates (Hoback et al. 2002), especially those that utilize wet meadow and floodplain habitats like Nicrophorus beetles (McPherron et al. 2012).
Among the carrion beetles in North America is the federally endangered American burying beetle, Nicrophorus americanus Olivier. This species is the largest North American member of the genus and has disappeared from >90% of its historic range (Bedick et al. 1999). Conservation assessment of N. americanus populations use variations of a baited pitfall trap design (Bedick et al. 2004) which can potentially flood. When traps flood, or beetles gain access to bait cups, trapped beetles often drown even though traps are checked within a few hours of rainfall events. Dead beetles are found floating at the surface (M. C. Cavallaro and W. W. Hoback, personal observation), and death has previously been speculated to result from blocked spiracles (USFWS 1991).
This observed mortality is unexpected as adult and larval insects from many terrestrial habitats can be submerged for hours or days by periodic or unpredictable flooding (Brust and Hoback 2009), and a variety of species have been found to survive immersion in severely hypoxic water for >24 h (Hoback 2012). Adult insects are likely to attempt to escape flood waters by crawling, flying, or if on the surface, by swimming. Moreover, most beetles possess hydrophobic hairs beneath their elytra or on abdominal sternites that can trap air, which may give the beetle buoyancy as it attempts to swim to a dry area. This trapped air can also potentially act as an oxygen reserve or a physical gill if it is in contact with the spiracles and air in the tracheal system (Balmert et al. 2011, Pedersen and Colmer 2012).
This study aimed to understand the cause of Nicrophorus mortality in flooded pitfall traps, which involved four experiments: 1) examine the behavioral response of Nicrophorus to flooding in simulated field conditions; 2) compare immersion tolerance in deoxygenated water among four Silphidae species: Nicrophorusinvestigator Zetterstedt, Nicrophorusmarginatus F., Necrodessurinamensis F., and Thanatophiluslapponicus Herbst; 3) measure the development of hypoxia in flooded pitfall traps with and without carrion bait (rotten rat); and 4) assess the swimming behavior and survival of N. investigator tested in eutrophic solutions designed to mimic the environment in flooded pitfall traps. Data generated from this study will help guide carrion beetle trapping protocol as it relates to N. americanus population monitoring. Furthermore, these results may offer insights to the reasons for terrestrial insect drowning in eutrophic standing waters despite the ability of most species to swim.
Materials and Methods
Experimental Animals
Beetles were collected using 18.9-liter buckets as pitfall traps baited with carrion (rotten rat) near Kearney, Nebraska, NE (40.7008° N, 99.0811° W); Alvena, Saskatchewan, Canada (52.5167° N, 106.0167° W); and Stillwater, Oklahoma, OK (36.0656° N, 97.0330° W). Trapping in Kearney, NE, yielded Ne.surinamensis and N.marginatus, whereas collection in Alvena, Saskatchewan, produced T.lapponicus and N.investigator; Nicrophorus orbicollis Say were captured near Stillwater, OK. Once captured, beetles were kept at a constant temperature of 22.0 ± 1.0°C and housed with moist coconut husk substrate for 24 h prior to experimentation. Each species of study was grouped in separate 37.8-liter aquaria. Prior to each trial, all beetles were assigned a treatment, weighed (g), and measured for pronotum width (mm; Table 1).
Mean (± 95% C.I.) lethal time to 50% mortality (LT50), average weight (± SD), and pronotum width (± SD) for adult beetle species immersed in hypoxic water (<0.2 mg/liter)
| Nicrophorinae | Silphinae | |||
|---|---|---|---|---|
| Species | N. investigatora,b | N. marginatusc | Ne. surinamensisc | T. lapponicusa |
| Weight average (g) | 0.49 (± 0.14) | 0.55 (± 0.10) | 0.31 (± 0.03) | 0.25 (± 0.02) |
| Pronotum width average (mm) | 12.3 (± 1.1) | 6.8 (± 1.2) | 6.1 (± 0.5) | 3.2 (± 0.2) |
| Hypoxic water LT50 (h) | 14.8 (± 2.3) | 9.0 (± 3.3) | 3.2 (± 1.1) | 12.1 (± 2.5) |
| Nicrophorinae | Silphinae | |||
|---|---|---|---|---|
| Species | N. investigatora,b | N. marginatusc | Ne. surinamensisc | T. lapponicusa |
| Weight average (g) | 0.49 (± 0.14) | 0.55 (± 0.10) | 0.31 (± 0.03) | 0.25 (± 0.02) |
| Pronotum width average (mm) | 12.3 (± 1.1) | 6.8 (± 1.2) | 6.1 (± 0.5) | 3.2 (± 0.2) |
| Hypoxic water LT50 (h) | 14.8 (± 2.3) | 9.0 (± 3.3) | 3.2 (± 1.1) | 12.1 (± 2.5) |
Species from the two Siphilidae subfamilies are represented: Nicrophorinae and Silphinae.
Collected in Saskatchewan.
Species used in swimming experiments.
Collected in Nebraska.
Mean (± 95% C.I.) lethal time to 50% mortality (LT50), average weight (± SD), and pronotum width (± SD) for adult beetle species immersed in hypoxic water (<0.2 mg/liter)
| Nicrophorinae | Silphinae | |||
|---|---|---|---|---|
| Species | N. investigatora,b | N. marginatusc | Ne. surinamensisc | T. lapponicusa |
| Weight average (g) | 0.49 (± 0.14) | 0.55 (± 0.10) | 0.31 (± 0.03) | 0.25 (± 0.02) |
| Pronotum width average (mm) | 12.3 (± 1.1) | 6.8 (± 1.2) | 6.1 (± 0.5) | 3.2 (± 0.2) |
| Hypoxic water LT50 (h) | 14.8 (± 2.3) | 9.0 (± 3.3) | 3.2 (± 1.1) | 12.1 (± 2.5) |
| Nicrophorinae | Silphinae | |||
|---|---|---|---|---|
| Species | N. investigatora,b | N. marginatusc | Ne. surinamensisc | T. lapponicusa |
| Weight average (g) | 0.49 (± 0.14) | 0.55 (± 0.10) | 0.31 (± 0.03) | 0.25 (± 0.02) |
| Pronotum width average (mm) | 12.3 (± 1.1) | 6.8 (± 1.2) | 6.1 (± 0.5) | 3.2 (± 0.2) |
| Hypoxic water LT50 (h) | 14.8 (± 2.3) | 9.0 (± 3.3) | 3.2 (± 1.1) | 12.1 (± 2.5) |
Species from the two Siphilidae subfamilies are represented: Nicrophorinae and Silphinae.
Collected in Saskatchewan.
Species used in swimming experiments.
Collected in Nebraska.
Response to Flooding
During periods of daily inactivity, Nicrophorus beetles burrow into soil with species-specific preferences for soil moisture and soil texture. In sandy-loam soils, N. orbicollis buries to ∼20 cm (Willemssens 2015). The response of buried N. orbicollis to flooding events was tested for two scenarios: 1) inundation from simulated rainfall on top of the burial location and 2) inundation from rising water. Test chambers (clear plastic cylinders 14 by 9 cm; 850 ml) were prepared by replacing the bottom of the container with a sponge. The test chambers were filled to a depth of ∼13 cm with loose loam soil and then were placed into an aquarium so that soil water levels could be monitored. Sets (n = 12) of three N. orbicollis were allowed to bury and become inactive. Ten minutes after burial, water was either added to the top of the containers to simulate a strong rainfall event at a rate of 4 cm per hour (n = 6) or added to the aquarium to raise the water level at a rate of 2 cm per 10 min. The response of buried N. orbicollis was recorded.
Immersion Tolerance
Beetles were immersed in hypoxic water following the methods of Hoback et al. (1998) and Whipple et al. (2013). Nitrogen gas was bubbled through an air stone into 5 liters of water at a rate of 5 min per liter. Measurements with a dissolved oxygen meter (YSI Dissolved Oxygen Meter Model: 55) confirmed oxygen concentrations were below 0.2 mg/liter. Sets of 20 individual beetles were placed in 25-ml screw cap glass vials followed by deoxygenated water. Vials were lightly tapped to remove air bubbles adhered to the beetle and underneath the elytra, and then were transferred to an environmental chamber at 20 °C and complete darkness. A set of 20 individuals from each species was removed from the water at 3, 6, 12, and 24 h and placed in plastic containers lined with paper towels. All beetles were given 24 h to recover. Mortality was confirmed by the inability of the beetle to roll over if placed on its back. Survival data were collected at each time point. Controls consisted of 10 individuals of each species housed in separate vials with a moist cotton ball and were observed for mortality at each time interval when subsets of immersed individuals were removed.
Flooded Pitfall Traps
Three different treatments were created to monitor microbial depletion of dissolved oxygen within a pitfall trap under environmentally relevant, semicontrolled conditions. Four 18.9-liter buckets were used per treatment and kept at a constant temperature of 22.0 ± 1.0°C. Treatments consisted of pure water, soil + water, and rotten rat + soil + water to simulate baited (rotten rat + soil + water) and unbaited (soil + water) traps. Soil (dark brown chernozem) was sieved through a 1-mm soil sieve to remove larger pieces and small rocks. All rats used were purchased frozen at a local pet store, placed in a closed plastic container, and left outside to decay until bloated (3–4 d). Approximately 250 g of sieved soil was added to each bucket followed by a rotten rat, depending on the treatment. Then, 1,000 ml of water was slowly added over top of the soil or soil + rotten rat medium to create roughly a 4:1 ratio of water:soil. Dissolved oxygen measurements were taken before the addition of microbial substrate (e.g., soil or rotten rat), after the addition of microbial substrate, and then 1, 3, 6, 12, and 24 h after the initial measurements.
Swimming in Eutrophic Water
To test the relationship between swimming survival time and hypoxic coma with increasing levels of microbial activity and subsequent production of CO2, N.investigator was exposed to three different treatments of a yeast:sucrose (Y:S) solution and three control treatments. The study species was chosen owing to its greater abundance during beetle sampling and greater relative size (Table 1). Using modified methods from Nelson (2012), sucrose (C12H22O11) was dissolved in water at a concentration of 5.0 g/liter. Control treatments included oxygenated spring water, deoxygenated water (bubbled with nitrogen gas at a similar rate as for immersion tests), and a sucrose solution with no yeast added (viscosity control). The nominal concentrations of yeast were 0.10, 0.33, and 1.0 g/liter. Approximately 150 ml of test medium was poured into a 250-ml plastic container, and an individual beetle was placed in the plastic container and monitored for the first 60 min of each test. To ensure no beetles escaped, a mesh cover was secured with a rubber band over the top of the plastic container. Over the first hour of the experiment, observations on beetle behavior were made on 40 beetles per treatment (n = 240 beetles; half of the total beetles used) every 10 min to assess activity (swimming) or inactivity (coma). After the initial swimming behavior assessment, we continued the experiment and evaluated mortality based on the same methods as outlined for the immersion tolerance trials. Twenty beetles were removed from each treatment at 3, 6, 12, and 24 h and survival was documented (n = 480 total beetles). Each beetle was quickly rinsed in clean, dechlorinated water to ensure yeast solutions did not dry and clog spiracles. Similar to immersion trials, beetles that appeared dead were given 24 h to recover. A separate set of plastic containers were used to measure dissolved oxygen at each time point that behavioral and survival observations were made. Dissolved oxygen was measured with a YSI Dissolved Oxygen Meter Model: 55.
Data Analysis
Beetles were selected at random from the population sampled in both regions for immersion and swimming tests. The sample size (n) for immersion trials followed the protocols outlined in previous studies (Hoback 2012). We designed swimming tests similarly to ensure data were comparable with immersion trials. Immersion survival data for N.investigator, N.marginatus, Ne.surinamensis, and T.lapponicus were analyzed using Toxstat 3.4 software (Western Ecosystems Technology, Inc., Cheyenne, Wyoming, WY). Mean lethal time to 50% mortality (LT50) was calculated using probit analysis; significant differences between survival times were determined by nonoverlapping 95% confidence intervals (Hoback et al. 1998). Statistical tests for N.investigator swimming behavior endpoints and dissolved oxygen measurements were performed using SigmaPlot Version 11.0 (Systat Software, Inc., San Jose, California,CA) with a 95% (α = 0.05) level of confidence. Significant differences among swimming test treatments and dissolved oxygen measurements were assessed using one-way analysis of covariance (ANCOVA) with time as a covariate followed by Holm–Sidak post hoc test for all pairwise comparisons, and one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test for all pairwise comparisons, respectively.
Results
When buried beetles were flooded from above, all 18 immediately moved to the surface and stayed at the tops of the containers. When water levels were higher than the soil in these containers, the beetles began to swim. Similarly, when containers were flooded from below, 17 of 18 buried beetles moved up in the soil column. Their movement mirrored the water level, with beetles moving up in the soil column in ∼2 cm increments while staying buried until water levels reached the soil surface. One of 18 beetles remained buried during soil flooding at a depth of 13 cm. This individual was initially unresponsive but later recovered when water dried.
Survival of immersion in severely hypoxic water differed among beetle species tested (Table 1). Mean lethal time to 50% mortality (LT50 ± 95% CI) values for N.investigator, N.marginatus, Ne.surinamensis, and T.lapponicus were 14.8 ± 2.3, 9.0 ± 3.3, 3.2 ± 1.1, and 12.1 ± 2.5 h, respectively. The mean LT50 value of Ne. surinamensis was significantly shorter than all other species tested. Based on nonoverlapping confidence intervals, N. investigator had a significantly higher LT50 than N. marginatus. No mortality was observed in the controls. Upon removal from the hypoxic water and swimming trials, all beetles initially appeared to be dead. If recovery occurred, beetles resumed movement within a period of several hours.
Mean (± SD) dissolved oxygen values (mg/liter) measured at 0.1, 3, 6, 12, and 24 h after combining all contents into 18.9-liter buckets (n = 4 buckets per treatment). Buckets containing rotten rat, soil, and water displayed significant dissolved oxygen loss after 3 h (P < 0.001;*). Significance was tested using a one-way ANOVA with Tukey’s post hoc test.
Percent of adult N. investigator actively swimming in six different aqueous solutions during the first 60 min of experiment (n = 40 beetles per treatment). Beetles were considered active (swimming) or inactive (coma). All control treatments beetle activity was statistically similar (P > 0.05). Beetles in the low yeast treatment displayed significantly less activity than all control treatments and significantly more activity than the medium and high yeast treatments (P < 0.001;***). Significance was tested using a one-way ANCOVA with a Holm–Sidak post hoc test.
Mean (± SD) dissolved oxygen values (mg/liter) measured at 0.1, 3, 6, 12, and 24 h during the N. investigator swimming trials in oxygenated water, deoxygenated water (bubbled with nitrogen), water and sucrose solution (5 g/liter sucrose), low yeast solution (0.10 g/liter yeast), medium yeast solution (0.33 g/ liter yeast), and high yeast solution (1.0 g/ liter yeast). All Y:S displayed significant dissolved oxygen loss after 3 h (P < 0.001;*). Significance was tested using a one-way ANOVA with Tukey’s post hoc test.
Discussion
The maintenance of internal Po2 (partial pressure of oxygen) by insects relies on diffusion and convection to meet oxygen demands (Pendar et al. 2015). This demand increases with body size and activity; large, active terrestrial insects require a ventilation process to meet oxygen demands (Greenlee et al. 2009). In hypoxic environments, insects may rely on anaerobic metabolism and metabolic depression to survive (Hoback et al. 2000). A potentially hypoxic and understudied environment is at the air:water interface. Terrestrial insects that fall into water commence swimming almost immediately. However, relatively few studies have tested the swimming abilities of terrestrial insects when compared with the number of experiments testing immersion tolerance and the physiology associated with survival of immersed individuals. To our knowledge, no studies have tested the effects of swimming in eutrophic water, conditioned by microbial respiration. Microbial respiration in eutrophic water lowers dissolved oxygen and raises dissolved CO2. We suspect that the rapid mortality of beetles swimming in eutrophic water may result from a combination of hypoxia and hypercapnia.
The effects of CO2 exposure in insects are well-documented given its application in several areas of entomology (e.g., medical, veterinary, and food storage). At low levels, CO2 can impair oxygen delivery to tissues and gradually decrease haemolymph pH, ultimately causing the dorsal aorta to stop pumping (Colinet and Renault 2012). Insects will respond to high external levels of CO2 within a few seconds of exposure (Badre et al. 2005), with rapid paralysis induced from inadequate synaptic transmission (Colinet and Renault 2012).
This is the first documentation of increasing microbial activity causing similar behavioral effects as complete immersion under water. Entering a hypoxic coma when immersed in water without any microbial activity allows the animal to maintain low rate metabolism and utilize oxygen reserves without any interference or rapid changes in haemolymph chemistry; however, in the presence of Y:S treatments, not only did yeast respiration potentially asphyxiate adult N. investigator, but it appeared to prevent induction of anaerobic metabolism to counter hypoxia and maintain internal ATP production. In this context, we acknowledge that yeast, soil microbes, and carrion-consuming bacteria would consume oxygen and produce CO2 and other volatiles at varying rates. In these trials, hypercapnia at the water surface potentially in conjunction with opening of spiracles is more lethal to swimming beetles than hypoxia associated with being beneath the water’s surface. Nielson and Christian (2007) found the mangrove ant, Camponotus anderseni McArthur & Shattuck, counters a hypercapnic environment by switching to anaerobic respiration. In this study, survival of immersion may be a result of metabolic depression and anaerobic metabolism, whereas swimming beetles may not be able to depress metabolism and maintain ATP levels through anaerobic metabolism (Hoback et al. 2000).
Any form of locomotion, such as swimming, elevates metabolic rates in insects (Chown and Nicolson 2004). A greater proportion of N. investigator ceased swimming in the sucrose solution before the individuals in pure water. Presumably, this is owing to the increased viscosity and greater expenditure of energy to continue searching for refuge. Studies examining the mobility of invertebrates with increasing water viscosity (sucrose solution) found both locomotive and behavioral differences with increasing dissolved solids (Hu and Bush 2010). Bohn et al. (2012) observed ants “running underwater” in the pitcher plant, Nepenthes bicalcarata Hook.f., whereas in the present study, beetles exhibited a swimming style that resembled walking, lacking any degree of speed.
The rapid mortality of beetles swimming in eutrophic water contrasts with the effects of immersion. Among the terrestrial insect taxa studied in immersion tolerance experiments (reviewed by Hoback 2012), beetles are the best-represented group, accounting for 85% (44 of 52) of the species tested. Previous studies have examined the immersion tolerance of beetle species from varying behavioral guilds but found that interspecies differences were of greater significance (Whipple et al. 2013). Here, we observed significant variation in survival among the four species tested (Table 1). Silphinae (T. lapponicus and Ne. surinamensis) mostly remain on the soil surface utilizing large carcasses for feeding and larval development; this subfamily is more likely to encounter anoxic or hypercapnic conditions in the body cavities of carrion that is putrefying, especially with large carcasses (Janaway et al. 2009). In contrast, Nicrophorinae (N. investigator, N. orbicollis, and N. marginatus) will bury and prepare a small vertebrate carcass to rear their offspring. Larvae from larger Nicrophorus spp. require 6–8 wk to develop into pupae (Scott 1998). Because of this extended subterranean portion of their life cycle, a greater immersion tolerance was anticipated. Compared with the other species tested, N. investigator and N. marginatus tended to survive immersion longer in hypoxic water than T. lapponicus and Ne. surinamensis. This may suggest that the selection pressure to survive immersion events and hypoxia is greater in the burrowing species (Nicrophorinae) as has been demonstrated in other invertebrate groups (Harrison 2015). Pétillon et al. (2009) found that among three wolf spider species tested for immersion tolerance, two of the salt-marsh species displayed significantly greater LT50 times, suggesting an adaptation based on the frequency of immersion through their evolutionary history.
Field observations of survival affected by hypoxia in terrestrial insects have primarily focused on wetland and riparian species (Pétillon et al. 2009, Pedersen and Colmer 2012), whereas the effects of elevated CO2 exposure are also documented in several taxa from diverse habitats (Nicolas and Sillans 1989, Nielson and Christian 2007). We found that N. investigator individuals can swim for >24.0 h in normoxic water and nitrogen bubbled hypoxic water, but die in Y:S hypoxic conditions in <4.2 h. In addition to consuming oxygen and releasing CO2, rotten rats in water release volatile organic compounds (VOCs) including dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide (von Hoermann et al. 2013). The gaseous by-products of carrion-consuming bacteria creating hypoxic water are the most likely cause of mortality for beetles that could otherwise escape by swimming until land was reached.
Few studies to date have assessed the potential impacts hypoxic environments have on the success of endangered or at-risk insect populations (Sei 2004, Brust et al. 2006, Cavallaro and Hoback 2014). Although many species possess adaptations to overcome physiological adversity, in some cases, these adaptations are insufficient in an artificial setting (e.g., pitfall traps). From laboratory trials that simulated flooding from precipitation and groundwater rise, most (35 of 36) N. orbicollis responded by avoiding the flood waters and moving to the surface. Burying beetles burrow into the soil during daily inactivity, when preparing a carcass to rear a brood, and to overwinter (Scott 1998, Willemssens 2015). Flooding could affect them during any of these periods and the response to flooding may vary based on the time of year and brooding status. Beetles in flooded pitfall traps leave the soil and begin to swim. The hypoxia and hypercapnia associated with microbial decomposition of bait results in mortality in the traps, while under natural conditions, active adult Nicrophorus can likely escape by swimming or climbing up vegetation. During winter diapause, adult burying beetles are likely to remain underground because freezing surface temperatures could be lethal. Additional investigation of the impacts of winter and early spring flooding events on burying beetles, including the endangered N. americanus, may aid in the identification of critical habitat for this species during periods of inactivity.
The federally endangered American burying beetle, N. americanus, is the largest species in the family Silphidae, and its greater size may place it at higher risk of pitfall trap mortality. Monitoring and collection of carrion beetles by means of pitfall traps is the main method for conservation measures for the American burying beetle. To safely document carrion beetle populations, additional protocols should be implemented. We suggest that when unresponsive N. americanus are discovered, that they be allowed a period of 12 h to recover. Measures to prevent beetles accessing the small bait containers and to prevent flooding of pitfall traps should be used. If spiracles are visibly coated with liquefied carrion, washing or wiping the material from the beetle’s abdomen with a damp paper towel may allow the beetle to recover. Furthermore, the provision of a float such as a block of Styrofoam would allow beetles to escape hypoxic waters and is recommended to reduce mortality from flooding events.
Acknowledgments
We thank Megan Congram, Camila Rosim, Ana Mijone, Silviane Santiago, and Stephanie Butler for their assistance in beetle collection. We also extend our appreciation to Bruce Noden and Phil Mulder for suggestions on an earlier version of this manuscript, and Iain Phillips for providing equipment resources. We thank Oklahoma State University Department of Entomology and Plant Pathology, the Oklahoma Agricultural Experiment Station, and the University of Saskatchewan Department of Biology for providing resources.
References Cited
Author notes
Subject Editor: Colin Brent
