Roeder Lab

NEW PAPER OUT! A checklist of South Dakota bumble bees (Hymenoptera, Apidae)

1st pub for 2023 just came out in the Journal of Hymenoptera Research! This was a lovely collaboration between SDSU entomologists (Abigail Martens and Paul Johnson) and our bee group at USDA-ARS NCARL (Eric Beckendorf, Louis Hesler, Jesse Daniels, and myself). We compiled specimen and literature records for bumble bees collected over the past 130 years across South Dakota to create the first updated checklist in almost a century. In doing so, we found there have been at least 29 species in the state with ample opportunity to study both western and eastern bumble bees. We highlight additional areas that desperately need surveying, which is an important first step for any long term monitoring program. For an overall summary, the abstract sums up the results nicely…

“Several bumble bee species (Bombus Latreille) are declining and efforts to conserve populations will be strengthened by an improved knowledge of their geographic distribution. Knowledge gaps exist, however, especially in central portions of North America. Here we report 29 species of bumble bees from South Dakota in the north-central USA, based on 130 years of records from 1891 to 2021. Specimens or observations were available for >90% of the 66 counties, though they were not distributed evenly as most records came from Pennington, Lawrence, Custer, Brookings, and Day Counties. The five most commonly collected or reported bumble bee species were B. griseocollis (54 counties), B. pensylvanicus (41 counties), B. fervidus (39 counties), B. huntii (27 counties), and B. bimaculatus (25 counties). Twenty species were recorded from 10 or fewer counties. Despite differences in occurrence, 66% of the Bombus species in South Dakota were collected or observed since 2020, including six of the nine species of conservation concern (B. fraternus, B. pensylvanicus, B. fervidus, B. occidentalis, B. terricola, and B. morrisoni). However, the critically endangered B. affinis, B. variabilis, and B. suckleyi have not been collected or observed for over 50 years. While this checklist is the first for South Dakota bumble bees in nearly 100 years, data are still lacking as ~55% of counties had fewer than five species reported. We suggest future efforts should focus on these under-sampled areas to fill in baseline knowledge of the wild bee fauna towards completing a more holistic view of bumble bee distributions across the Great Plains.”

You can find the full manuscript by [CLICKING HERE].

NEW PAPER OUT! Importance of color for artificial clay caterpillars as sentinel prey in maize, soybean, and prairie

5th pub for 2022 just came out in Entomologia Experimentalis et Applicata! This was Matt Dorland’s summer project from an USDA Plains Area internship during our first field season here in South Dakota. We set out almost 2000 caterpillars in corn fields, soybean fields, and prairie near Brookings to test whether the color of sentinel prey (used to measure predation pressure) had any effect. Surprisingly the answer was yes! Green and terracotta caterpillars performed miles above any of the other colors and we offer a few thoughts on why in the discussion. For an overall summary, our abstract sums up the results nicely…

“The use of artificial clay caterpillars to measure predation pressure under real field conditions is one method that has garnered recent support for quantifying ecosystem services that beneficial insects provide. Here, we focus on color and ask whether it is an important variable that should be considered in studies using clay caterpillars as sentinel prey. We deployed a total of 1920 brown, cream, green, gray, terracotta, and white clay caterpillars onto maize, soybean, and prairie plants to test if lighter colored caterpillars will be attacked and retrieved more than caterpillars with darker colors. As hypothesized, color was a significant predictor with green and terracotta caterpillars performing best, whereas brown and gray caterpillars performed the worst. Interestingly, clay caterpillars were also attacked proportionally to the number of insects in the surrounding habitat. Combined, we suggest artificial clay caterpillars could be useful for rapid ecosystem function assessments, but only when their color is considered.”

You can find the full manuscript by [CLICKING HERE].

NEW PAPER OUT! Thermal tolerance of western corn rootworm: Critical thermal limits, knock-down resistance, and chill coma recovery

4th pub for 2022 just came out in Journal of Thermal Biology! This work is the first paper from USDA and contains ideas that I have been wanting for test for years. We measured how ramping rate, starting temperature, genetic line, and sex affected critical thermal limits. We then expanded these ideas to look at knock-down resistance and chill coma recovery. Overall, we found striking similarities between genetic line and sex across most of the physiological assays. But there were some surprising results. Our abstract sums up our results nicely…

Western corn rootworm, Diabrotica virgifera virgifera, is one of the most economically important crop pests in the world with estimates of damage and control approximating over $1 billion USD annually. Despite an abundance of research devoted to studying rootworm biology in the central Corn Belt of the United States, key aspects on their thermal ecology are still lacking. Here we address this knowledge gap by measuring critical thermal limits, knock-down resistance, and chill coma recovery. In doing so, we also address methodological questions surrounding measurements of thermal tolerance using a variety of dynamic and static assays. The average critical thermal maxima across all trials was 43.0 °C, while the average critical thermal minima was 2.5 °C. Critical thermal limits were relatively invariant across all treatments except at faster ramping rates. Knock-down resistance decreased with increasing temperature as survival dropped from 100% at 39 °C to 0% within 10 min at 44 °C. Recovery from chill coma increased by 1.62 min for each hour of exposure at 0 °C, while survival decreased by 50% after only 24 h. Combined, our results present the first composite picture of different thermal traits for western corn rootworm, which will be vital for predicting their survival and potential spread under future climate change scenarios.

You can find the full manuscript by [CLICKING HERE]. More rootworm thermal papers are on the way!

NEW PAPER OUT! Woody perennial polycultures increase ant diversity and ant-mediated ecosystem services compared to conventional corn-soybean rotations

3rd pub for 2022 just came out in Agriculture, Ecosystems, and Environment! This work is the first paper from my postdoc at UIUC with Dr. Alex Harmon-Threatt. We measured ants and how much insect prey ants were consuming in woody perennial polycultures and corn-soybean rotations monthly for an entire year! Our abstract sums up our results nicely…

The role plant diversity has played in regulating insect communities has been of interest for decades. Recent syntheses from agroecosystems suggest increasing plant diversity can positively affect beneficial insects like predators, reducing pest pressure and increasing yield. However, the agricultural landscape of the Midwestern United States is dominated by just two crops—corn and soybean—which cover approximately 180 million acres of arable land yearly. New ideas to conserve wildlife that additionally provide economic opportunities for farmers must be developed in order to promote sustainable and resilient ecosystems. Here we tested the capacity of an alternative cropping system to support more diverse insect populations than conventional cropping systems. We quantified differences in the diversity of an insect taxon, ants (Hymenoptera: Formicidae), over an annual cycle using pitfall traps in thirty-two 2-m2 plots of either woody perennial polycultures that contained apples, chestnuts, currants, hazelnuts, and raspberries or conventional corn-soybean rotations. In doing so, we found that woody perennial polycultures supported 2.4-fold more ant species and maintained a unique fauna of specialist and predatory ants. The observed differences in diversity were linked to higher levels of predation as 18.2-fold more sentinel prey were consumed during each month of the growing season. Combined, our results suggest that agricultural landscapes in the Midwestern United States can be modified to support important beneficial insects like ants while still producing commodities that can be economically beneficial to farmers.

You can find the full manuscript by [CLICKING HERE]. Also be on the lookout for more perennial polyculture papers in the near future!

NEW PAPER OUT! Thermal tolerance regulates foraging behaviour of ants

2nd pub for 2022 just came out in Ecological Entomology! This work was led by Dr. Diane Roeder and explores how temperature and physiological tolerances regulate foraging behaviour of harvester ants. We started this work many years ago as one of our first collaborations and I am excited to see this first paper out in press. Our abstract sums up our results nicely…

Theory suggests that performance increases with temperature up to an optimization point before rapidly decreasing as an animal approaches its upper thermal limit. Here, we use the red harvester ant, Pogonomyrmex barbatus, to test predictions about how daily temperature fluctuations and thermal tolerance combine to influence one metric of performance—foraging.
Over 2 years, we tracked 322 foraging trips from 15 colonies in a mixed grass prairie of southwestern Oklahoma. During each trip, we measured surface temperature, distance, time, worker mass, seed mass, and foraging tempo (i.e., running speed). To assess P. barbatus heat tolerance, we measured CTmax and knock-down resistance of field-collected workers in the lab.
Trip time, but not distance, decreased with increasing temperature, resulting in an increased foraging tempo as ants neared their CTmax of 50°C. Knock-down resistance trials confirmed that 50°C is an upper thermal limit, as individuals showed decreasing survival from 100% at 45°C to 0% at 50°C. Worker size and collected seed size were unrelated to temperature.
Our results highlight how daily temperature fluctuations drive activity, not only by limiting foraging but also by increasing foraging rates near the thermal limit. If temperatures continue to increase, the foraging ability of this and similar species may be restricted to an ever-narrowing window with effects potentially extending to the surrounding community.

You can find the full manuscript by [CLICKING HERE]. Also be on the lookout for at least two additional papers in the near future on harvester ant biology!

NEW PAPER OUT! Testing the role of body size and litter depth on invertebrate diversity across six forests in North America

Probably the last pub for 2021 or our first for 2022. This paper in Ecology is technically my last “official” dissertation chapter and it feels fantastic to get it out. To provide some background, I started working on this project in the summer of 2014 and spent almost a year measuring >40000 mites, springtails, and spiders from six forests in North America. Using the data from these measurements and species identifications from Brittany, we tested three hypothesis about body size, litter depth, abundance and species richness. Our abstract sums up our results nicely…

“Ecologists search for rules by which traits dictate the abundance and distribution of species. Here we search for rules that apply across three common taxa of litter invertebrates in six North American forests from Panama to Oregon. We use image analysis to quantify the abundance and body size distributions of mites, springtails, and spiders in 21-m² plots per forest. We contrast three hypotheses: two of which focus on trait-abundance relationships and a third linking abundance to species richness. Despite three orders of magnitude variation in size, the predicted negative relationship between mean body size and abundance per m² occurred in only 18% of cases—never for large bodied taxa like spiders. We likewise found only 18% of tests supported our prediction that increasing litter depth allows for high abundance; 2/3 of which occurred at a single deciduous forest in Massachusetts. In contrast, invertebrate abundance constrained species richness 76% of the time. Our results suggest that body size and habitat volume in brown food webs are rarely good predictors of variation in abundance, but that variation in diversity is generally well predicted by abundance.

You can find an open access version of our paper by [CLICKING HERE]

NEW PAPER OUT! Thermal traits predict the winners and losers under climate change: an example from North American ant communities

Our next pub for 2021 was just published in Ecosphere. This paper marks one of many papers from our group from our resampling events across the United States that took place in 2017 and 2018. In collaboration with Jelena Bujan, Kirsten de Beurs, Michael Weiser, and Michael Kaspari, we asked which ant genera are increasing or decreasing over the last ~20 years. Here is our abstract that sums up this work nicely…

“Across the globe, temperatures are predicted to increase with consequences for many taxonomic groups. Arthropods are particularly at risk as temperature imposes physiological constraints on growth, survival, and reproduction. Given that arthropods may be disproportionately affected in a warmer climate—the question becomes which taxa are vulnerable and can we predict the supposed winners and losers of climate change? To address this question, we resurveyed 33 ant communities, quantifying 20-yr differences in the incidence of 28 genera. Each North American ant community was surveyed with 30 1-m² plots, and the incidence of each genus across the 30 plots was used to estimate change. From the original surveys in 1994–1997 to the resurveys in 2016–2017, temperature increased on average 1°C (range, −0.4°C to 2.5°C) and ~64% of ant genera increased in more than half of the sampled communities. To test Thermal Performance Theory’s prediction that genera with higher average thermal limits will tend to accumulate at the expense of those with lower limits, we quantified critical thermal maxima (CT_max: the high temperatures at which they lose muscle control) and minima (CT_min: the low temperatures at which ants first become inactive) for common genera at each site. Consistent with prediction, we found a positive decelerating relationship between CT_max and the proportion of sites in which a genus had increased. CT_min, by contrast, was not a useful predictor of change. There was a strong positive correlation (r = 0.85) between the proportion of sites where a genus was found with higher incidence after 20 yr and the average difference in number of plots occupied per site, suggesting genera with high CT_max values tended to occupy more plots at more sites after 20 yr. Thermal functional traits like CT_max have thus proved useful in predicting patterns of long-term community change in a dominant, diverse insect taxon.”

You can find an open access version of our paper by [CLICKING HERE]

NEW PAPER OUT! Ant thermal tolerance: a review of methods, hypotheses, and sources of variation

Our 2nd pub for 2021 was just published in Annals of the Entomological Society of America. The idea for this review article started years ago at an annual meeting and we have been talking about topics to include ever since. In collaboration with Diane Roeder and Jelena Bujan, we put those ideas on paper. We spent about half a year going through published literature on ant thermal tolerance and found some interesting trends.

Over the past 30 years, there has been exponential growth in the number of ant thermal papers published. Many of these discuss 5 common metrics: critical thermal limits, lethal thermal limits, knock-down resistance, chill-coma recovery, and supercooling. We break down what we think are interesting patterns and hypotheses of thermal tolerance along spatial and temporal temperature gradients, focusing on relationships with latitude, elevation, urbanization, microclimate and ways ants cope with different temperatures like seasonal plasticity and acclimation. We further discuss other sources of variation including evolutionary history, body size, age, castes, and nutrition. To move the field further we highlight several topics that we think are interesting but currently lacking, ranging in scope from methods development to the impacts of climate change.

You can find an open access version of our paper by [CLICKING HERE]

NEW PAPER OUT! Testing effects of invasive fire ants and disturbance on ant communities of the longleaf pine ecosystem

1st pub for 2021 was just published in Ecological Entomology. This manuscript was a few years in the making as Julian Resasco and I originally talked about this back in ~2018. After a few job changes and moves, I am happy to say we finally finished it up!

Broadly, we were interested in how disturbance and invasive fire ant removal affected native ant communities. We took advantage of a framework proposed by MacDougal and Turkington that posited different ways invasive species could be characterized, either as “drivers” or “passengers” of change. The ‘driver’ model posits that species interact strongly and that native species are limited or excluded by competition with invasive species. Under this scenario, removal of an invasive species should increase native species richness and abundance. In contrast, the ‘passenger’ model posits that communities are primarily structured by factors other than interactions with invasive species (e.g. habitat disturbance) and that those factors are more beneficial to invasive species than native species. Under the ‘passenger’ model, removal of invasive species should have relatively little impact on native species.

But we also added a twist, an “interacting driver” model that was proposed as an alternative to the strict interpretations of “driver” and “passenger models” (Didham et al. 2005). The “interacting driver” model suggests additive or synergistic effects of habitat disturbance and invasive species that combine to reduce native species richness and abundance. Under this model, removal or reduction in abundance of invasive species should result in partial recovery of some native species.

To test these different hypotheses, we randomly assigned treatments of (1) unmanipulated, (2) soil disturbance, (3) fire ant removal and (4) soil disturbance + fire ant removal to experimental blocks and measured how ant communities changed over two years in thirty-six 15-m² plots. In doing so we found some interesting results. First, fire ant abundance in removal plots averaged 42% lower in pitfall traps and 95% lower on baits compared to unmanipulated, control plots (Fig. 1). No difference was found between disturbance and control plots though.

Second, species richness of co-occurring ants also decreased 42% in removal plots (Fig. 2), with significant changes in community composition. And again, no difference was found between disturbance and control plots.

Third, fire ant diet breadth—measured using carbon and nitrogen stable isotopes—increased up to 4.7‐fold in soil disturbance + removal plots. This last result is intriguing as it may suggest fire ants in removal plots consumed a greater variety of prey items and likely competed for resources with more co-occurring species.

Combined, our results suggest fire ants follow an alternative ‘interacting drivers’ model in which partial recovery of some species occurs when populations of an invasive species are reduced. However, further recovery of native ants may be limited by persisting, landscape‐level effects of fire ants suppressing co‐occurring ants below historical levels.

[CLICK HERE FOR PAPER]

NEW PAPER OUT! Bioenergy landscapes drive trophic shifts in generalist ants

The 6th and likely last pub for 2020 was just published in Journal of Animal Ecology. Led by Jackson Helms IV, this paper investigates isotopic and trophic relationships of ants in corn, switchgrass, and restored prairies in Michigan. A summary from Jackson in JAE…

Changes in trophic niche—the pathways through which an organism obtains energy and nutrients—are a fundamental way in which organisms respond to environmental conditions. But the capacity for species to alter their trophic niches in response to global change, and the ways they do so when able, remain largely unknown.
Here we examine food webs in three long‐term and large‐scale experiments to test how resource availability and nutritional requirements interact to determine an organism’s trophic niche in the context of one of the largest global trends in land use—the rise in bioenergy production.
We use carbon and nitrogen stable isotope analyses to characterize arthropod food webs across three biofuel crops representing a gradient in plant resource richness (corn monocultures, fields dominated by native switchgrass and restored prairie), and to quantify changes in the trophic niche of a widespread generalist ant species across habitats. In doing so, we measure the effects of basal resource richness on food chain length, niche breadth and trophic position. We frame our results in the context of two hypotheses that explain variation in trophic niche—the niche variation hypothesis which emphasizes the importance of resource diversity and ecological opportunity, and the optimal diet hypothesis which emphasizes dietary constraints and the availability of optimal resources.
Increasing plant richness lengthened food chains by 10%–20% compared to monocultures. Niche breadths of generalist ants did not vary with resource richness, suggesting they were limited by optimal diet requirements and constraints rather than by ecological opportunity. The ants instead responded to changes in plant richness by shifting their estimated trophic position. In resource‐poor monocultures, the ants were top predators, sharing a trophic position with predatory spiders. In resource‐rich environments, in contrast, the ants were omnivores, relying on a mix of animal prey and plant‐based resources.
In addition to highlighting novel ecosystem impacts of alternate bioenergy landscapes, our results suggest that niche breadth and trophic diversification depend more on the presence of optimal resources than on ecological opportunity alone.

Link: [CLICK HERE TO SEE THE PAPER]