Pestology Blog
NPMA BugBytes Live at Pestworld 2024 in Denver, Colorado!
Denver, CO – October 25, 2024
The November 2024 episode of NPMA BugBytes was a special LIVE episode recorded with attendees at PestWorld 2024 in Denver Colorado! Cohosts Ellie, Laura, and Mike were joined by a live audience in this special episode as the BugBytes team discussed new research. In this episode, Laura reviewed an article on paper wasps, Ellie gave a spooky summary of an article on bed bugs, and Mike covered a recently published article on using caffein to enhance insecticidal baits for Argentine ants. As an additional special surprise, a new podcast trophy was unveiled at the live taping! Mike, Ellie, and Laura hold the new BugBytes trophy (shown left).
Featured Article Summaries
Paper Wasp Sociality
Personality and Body Mass Impact Social Group Formation and Function in Paper Wasps
Paper wasps, or Polistes fuscatus, are well-known for their extensive cooperative systems upon which they build their nests. However, prior to “settling down” to build their house and home, paper wasps will engage in a behavior known as “shopping”. This entails nest-founding queens interacting with other nest-founding queens to determine if they would be good social partners, and additionally searching for good roosts for their nests. Paper wasp queens can either go at their nest-building endeavors solo, or they may choose to join a group of up to five other paper wasp queens. However, if a queen joins a group, she risks the chance of becoming a “subordinate” queen who still will lay eggs, but largely will be forced to do work for the nest, while the “dominant” queen will take up the mantle of the most eggs laid. But on the other hand, it’s hard to take a go at nest building as a single mother.
To understand the dynamics behind these various interactions, the researchers sought to understand how the individual characteristics, specifically body mass and both social and nonsocial traits of these paper wasp queens would affect both the formation of these grouped nests, and how these nests operated.
Queens were collected, marked with colors identifying who they were, and were assessed for their nonsocial and social personalities. To test nonsocial personality, the researchers placed the wasps in a 10-chambered maze, which measured how exploratory the individuals were. To test social personalities, the wasps were individually presented with a dummy wasp in a chamber for 10 minutes, and the researchers measured how aggressive, nonaggressive, or investigative the wasps were. Once their personality tests were complete, they were released into a vespiary with all of the other collected wasp queens. The wasps were then allowed to “shop” for nestmates, and their interactions were recorded, along with how the subsequent nests performed over the course of the season.
Wasps that were more exploratory from the outset assessed more individuals as potential partners, joined groups later, and were less likely to become the dominant queen on nests. In addition, the nests by these exploratory wasps were not always the most successful, meaning that it didn’t always pay off to “shop around”, and doesn’t always translate to successful partnerships.
Individuals that had less exploratory personalities were more likely to become aggressive once the nests were formed and were also more likely to become the dominant queens in the nest if they happened to group up. These individuals also sampled fewer social partners and chose faster compared to the more exploratory wasps. Therefore, because these individuals chose their nests so early, it may lead to them being the dominant queens, as they’re the ones who “staked their claim” first. However, as a trade-off, the nests that featured more aggressive individuals often saw less offspring produced and featured smaller nests overall. Dominant wasps that featured more nonaggressive personalities and the wasps that decided to build their nests on their own built the largest nests.
Interestingly, body mass was not linked to whether the wasp would become the dominant queen. Instead, body mass was correlated with the number of roosting sites sampled, as those with a larger body mass sampled more sites. This makes sense, as these sampling trips come with a large energetic cost to the wasp queens. However, the researchers also found that the more nonaggressive wasps sampled fewer roosting sites, potentially because they were more tolerant of other wasps coming into their areas.
Overall, the researchers discovered that nonsocial and social traits, and body mass all played a role in how the wasps assessed potential nestmates, nest foundation, and how these chosen social groups interacted with each other.
While there are a lot of complicated factors at play in this study, it appears that the personality of the individual wasps impacted many different factors of the “shopping” and nest building experience, including how individuals sampled potential partners, the timing of joining a group, and how aggressive the wasps were within groups. This study provides new context on how paper wasps form their nests, as well as their behavior after the nest is built.
Article by Laura Rosenwald, BCE
References
Emily C. Laub, Noa Pinter-Wollman, Elizabeth A. Tibbets. Animal Behavior, 213 (2024), 207-218, https://doi.org/10.1016/j.anbehav.2024.03.020.
DEET Repellent and Bed Bugs
Repellency of DEET During Host-Seeking Behavior of Bed Bugs in Binary Choice Olfactometer Assays
We are all familiar with the bed bug. They are challenging pests that can be difficult to control. While they do not transmit diseases, they are a public health threat. They produce allergens, disturb customers, and can cause itchy bites. Researchers are constantly looking to understand their biology further and work towards more control solutions.
In this study, the researchers were looking to use a binary choice olfactometer, which is a fancy way of saying they gave the bed bugs a two-way choice based on difference chemical cue smells. They wanted to prove that this method was viable was of testing bed bug preferences.
They prepped the bed bugs by keeping them under standard conditions and then used females as they are more inclined to find blood for their egg development. They were starved for 10-14 days and then moved to ensure there were no eggs on their bedding.
For the choice tubes, they put human odor in both sides. The human odor used was from a test subject who avoided anything that might alter their scent for a day or so and then filter paper was swabbed over their body to collect the odor to be used. They placed this on each end of the y-tube.
Basically they had human odor both ways and one had DEET so it was to tell if the DEET did anything to dissuade them.
The researchers looked at the relationships between repellency of varying concentrations of DEET and found that bed bugs largely avoided the DEET. If you combined more host cues such as more odor or more co2, the bed bugs overcame their aversion to the DEET to the more attractive host cue. This puts doubts in whether DEET would be an effective repellent because the bed bugs will overcome if the host cues are strong enough as would be the case with an actual human nearby.
Another interesting relationship that you may not be aware of is that of pyrethroid resistant bugs and sensitivity to repellants. This varies across species so it was explored here in how resistant vs susceptible bed bugs would respond to the repellants comparatively. They found that at high concentrations of DEET in the air, the insecticide susceptible bugs were repelled and less so with lower concentrations. It took much less DEET to repel them by contact instead of in the air. But the crazy thing is that the insecticide resistant bed bugs were actually repelled much more by the DEET at much lower concentrations. For reference, pyrethroid resistant bed bugs represent what you actually run into in the field. Susceptible strains really only exist in labs for study purposes as far as we are aware.
The conclusion here was that the olfactometer worked and could be used in future experiments with bed bugs and repellents. The researchers were careful to make the point that they DO NOT conclude that DEET can save you from the bed bugs. This was a proof of concept that shows that this method could be used to study other repellents in the future.
Article by Ellie Sanders, BCE-Intern
References
Christopher C Hayes, Coby Schal, Repellency of N,N-diethyl-3-methylbenzamide (DEET) during host-seeking behavior of bed bugs (Hemiptera: Cimicidae) in binary choice olfactometer assays, Journal of Medical Entomology, Volume 61, Issue 4, July 2024, Pages 1016–1025, https://doi.org/10.1093/jme/tjae073
Caffeine and Ant Foraging
Acute Exposure to Caffeine Improves Foraging in an Invasive Ant
Ants are among the most difficult pests for PMPs to manage. This is especially true when we’re up against invasive ants, like the Argentine ant. These non-native invaders often have no natural predators to keep them in check, allowing foragers to locate and secure resources without much competition. Which means colonies can grow to plague-like numbers. And even if they do encounter resistance from native ants, invasive species often use their overwhelming numbers to their advantage and simply beat native species into submission. Which usually means displacing those species and causing serious ecological damage.
Luckily, the development of insecticidal ant baits revolutionized the ant management game, helping to tip the scales in the PMPs favor. Working like ant-seeking missiles, baits allow PMPs to target and eliminate reproductives without ever having to locate the nest. While there is a wide variety of ant baits on the market today, they all share a few similar traits. First, the baits incorporate a slow-acting, non-repellent active ingredient that allow hungry foragers enough time to consume and share the bait with other nestmates before dying. And second, the bait is formulated with a food attractant, like sugars or fat, that encourage the ants to consume the bait and toxicant.
Traditional research efforts aimed at improving ant bait performance usually focused on enhancing the bait itself by tweaking formulations, developing new active ingredients, or incorporating more enticing food attractants. Well, one group of researchers decided to go in a completely different direction and explore ways to enhance the ants rather than the baits! And, their method involved the incorporation of an active ingredient that I think we are all familiar with the effects of…our early morning friend, caffein!
Working with the invasive Argentine ant, Linepithema humile, researchers wanted to see what would happen to the foraging efficiency of hungry workers when caffeine was added as a food additive at different concentrations. This wasn’t the first time researchers have tried tempting insects with caffein to improve foraging. A previous study feeding caffein to honeybees noted an increase in foraging frequency, and another study looking at feeding caffein to Argentine ant workers to explore impacts on olfactory memory, but this study only looked at caffein exposure using a single concentration.
For this study, researchers wanted to see what happened to foraging behavior when caffein was added to foods at different concentrations They hypothesized that caffeine would serve as a neuroactive modulator to manipulate foraging behavior by improving homing behavior, increasing foraging speed, and decreasing overall foraging time. To test this hypothesis, the researchers exposed Argentine ant workers to a range of caffeine concentrations and measured their foraging time and foraging pathway, both to, and from a food resource using an open foraging arena. Here’s what they found:
- Without caffeine, the amount of time it took foragers to reach a food resource didn’t significantly change over consecutive visits. Meaning that once foragers found food, they weren’t getting any faster at returning to the same food source over time.
- And caffeine had no impact on the amount of time it took foragers to initially find a food source.
- However, under low (25ppm) to intermediate (250ppm) caffeine concentrations, ants were, on average, 38% faster at returning to the resource with each consecutive visit. That increase was due to ants returning to the food in a straighter line on each return visit, demonstrating higher location recall and implying that caffeine could have positively boosted learning.
- Interestingly, these same learning improvements were not observed at high (2,000ppm) caffeine concentrations.
So, what does all this mean? Well, these data suggest that caffeine at low to intermediate concentrations could serve as an effective food additive to enhance the overall effectiveness of ant baits when used against Argentine ants by increasing their ability to remember where baits are located and decreasing return trip time. Meaning that this could be an interesting way to improve bait performance by making the ants better at finding and recruiting to the baits!
Of course, this study was only conduced with Argentine ants, and in a laboratory environment, so there is a lot of room for follow up studies to measure these effects across different species and in more ecologically relevant field conditions. Nevertheless, this study showed that caffeine isn’t just for keeping us going through those late nights and early mornings, it may also hold the key to unlocking new tools in the never-ending fight against invasive ants.
Article by Mike Bentley, PhD, BCE
References
Acute exposure to caffeine improves foraging in an invasive ant.Galante, Henrique et al.. iScience, Volume 27, Issue 6, 109935
Listen to the Episode!
Have questions or feedback for the BugBytes team? Email us at training@pestworld.org, we'd love to hear from you!
