Pestology Blog
Ant Amputations, Termite Death Zones, and New Cockroach Control Tools
Fairfax, VA – September 1, 2024
In the September 2024 episode of NPMA BugBytes, the team discusses the benefits of ant amputations, we dive into the phenomena of termite death zones, and we share new research on novel active ingredients used to control cockroaches. We're joined in this episode by special guest Sara Cromwell of Abell Pest Control!
Featured Article Summaries
Ant Amputations
Wound-dependent Leg Amputations To Combat Infections in an Ant Society
Many species use antimicrobial secretions from certain glands in an attempt to combat pathogens. However, some species, such as the Florida Carpenter Ant (Camponotus floridanus), have lost this gland over evolutionary time, and they now must find other ways to combat the problems that open wounds can cause to a colony. We now have evidence that the Florida Carpenter Ant is the first non-human animal to use amputations to treat infected individuals and can adapt the type of treatment depending on the wound location.
Florida Carpenter Ant (Camponotus floridanus)
Enter, amputations. Or, ant-putations.
The researchers noticed that in response to workers with injuries to their legs, nestmates would often perform amputations. Further experiments revealed that the decision to amputate the leg was dependent on where the injury occurred on the leg. For example, 76% of individuals who had an injury to the femur experienced amputation by nestmates, but those that were injured on their tibia never experienced amputations by their nestmates, but did receive longer wound care.
On average, amputations occurred around the four-hour mark post-injury and generally followed the same behavioral pattern for the amputation. The nestmate would begin to lick the wound, and then would move up the leg to the trochanter, which is the connection point between the femur and the coxa, which connects to the thorax. The nestmate would then use their mandibles to bite repeatedly until the leg was cut off.
The researchers also assessed the survival rates and bacterial loads of ants that had experienced either a femur injury or a tibial injury, and then were exposed to a pathogen. The researchers either left the ant by itself, induced the amputation by their own hands, or returned the ant to the nest. Infected individuals with femur injuries that were isolated without an amputation had a lower survival rate and a higher bacterial load compared to the other treatments. Interestingly, infected individuals with femur injuries that received manual amputations at the trochanter one-hour post-infection from the researchers had similar survival rates and bacterial loads as those that were returned to the nest. This means that the amputations can be the make it or break it factor that allows the ants to survive. In addition, this also means that they are also potentially bringing back less pathogens into the nest.
However, ants with tibial injuries were a completely different story. Infected individuals with tibial injuries who received amputations from the researchers at the trochanter one-hour post-infection had the same survival rates and bacterial loads as those that were infected and isolated. This means that amputation is not an effective tool for tibial injuries, which is what the researchers observed from the ants to begin with. However, ants that experienced tibial injuries, but were allowed to return to the nest had similar survival to the control ants, but featured an in-between bacterial load to the control ants and those that were infected but isolated. This indicates that nestmates are extremely important in management of potential disease entering the colony.
The researchers additionally physiologically examined these ants to determine why amputations were so effective for femur injuries, but not tibial injuries. Using micro-CT scans, they examined the structure of the trochanter, femur, and tibia, and determined that the femur features a larger amount of muscle tissue. The destruction of muscles in the femur could potentially lead to less effective hemolymph circulation, which gives the ants more time to make their cuts, as it may be. The researchers additionally examined effectiveness of amputations in tibia injuries, and only those that were made immediately after pathogen exposure proved to be beneficial for those injured ants.
This study emphasizes just how adaptable ants are as a species. With a couple of snips of their mandibles, they’re able to keep their fellow nestmates on the move and relatively healthy. With this kind of resourcefulness when it comes to injuries, it does bring to mind how resourceful they can be when faced with our tools and tricks of the trade when it comes to managing them.
Article by: Laura Rosenwald, BCE
References
Frank ET, Buffat D, Liberti J, Aibekova L, Economo EP, Keller L. Wound-dependent leg amputations to combat infections in an ant society. Curr Biol. 2024 Jul 22;34(14):3273-3278.e3. doi: 10.1016/j.cub.2024.06.021. Epub 2024 Jul 2. PMID: 38959879.
Termite Death Zones
Death Zone Minimizes The Impact Of Fipronil-treated Soils On Subterranean Termite Colonies By Negating Transfer Effects
When it comes to treating subterranean termite infestations of existing structures, the two most common control approaches include applying a liquid termiticide to the soil and installing termiticide bait stations around the foundation of the structure. In post-construction treatments, the liquid termiticide is applied to the soil directly against the foundation of the structure while the bait stations are installed a few feet to a few meters away from the foundation. Both control options work similarly by incorporating slow-acting active ingredients that allow termites to survive long enough after exposure to pass the active ingredient onto colony mates through trophallaxis (sharing of food through regurgitation) or through social contact.
Decades ago, liquid termiticides were formulated with repellent insecticides under the premise that the repellency of the products would help to deter termites. Unfortunately, the repellent nature of the products also meant that termites could more easily find breaks in the barrier treatment that may unintentionally occur when soil is disturbed after application, such as when a homeowner decides to build a new deck or re-landscape one side of the home. A major breakthrough in the liquid termiticide game came with the development of non-repellant active ingredients such as fipronil. The absence of repellency meant that subterranean termites who encountered treated soil would not know when they were in a treated area and would be less likely to find any possible gaps in treatment coverage.
As is the case with other non-repellent liquid termiticide chemistries, fipronil is intended to go undetected by hungry termites as they forage through treated soil. Additionally, fipronil should be slow acting enough to allow termites enough time to leave the treated area and share the active ingredient with other colony mates before succumbing to the effects of the toxicant. In a recently published study, Dr. Thomas Chouvenc is challenging the full extent of fipronil’s non-repellent nature in an interesting way…through what he’s calling the death zone!
In a series of laboratory experiments, Thomas used specially constructed, 3x15 meter foraging arenas to measure how far subterranean termites would travel after encountering fipronil-treated soil before they started to die off. This die-off effect is significant because termites are “necrophobic” meaning they will actively avoid dead nestmates. So, areas where the dead start to pile up…the death zone...could have repellent effects on foraging termites.
Using the foraging arenas, Dr. Chouvenc introduced termite colonies to arenas where soil was treated with fipronil (0.06% concentration) at either 1.5m, 7.5m, and 12.5 meters away from the colony central nest (See Figure 1). Then he measured if they started dying, and how far that death zone would be away from the treated area. What he found was the “death zone” for colonies set at the shortest 1.5m distance from the treated area averaged just over 1 meter away from the from the treatment. For colonies set at 7.5m and 12.5m away from the treated area, the “death zone” averaged about 2.56 meters away from the treatment. He also noted that mortality was low across all three treatment distances over a 200+ day span, with most of the mortality being recorded in the first few days of the experiments. The low mortality was largely assumed to be a result of the death zone cutting other termites off from accessing the treated soil once the dead started to pile up.
Dr. Chouvenc’s conclusions from the study are that, despite fipronil’s non-repellent chemistry, the faster rate of kill of the active ingredient could lead to the establishment of a death zone around structures that would act to repel termites from continuing to access the treated soil. And, that does seem to be the case in his study.
But, as is the case with all experiments, there are always some considerations to take into account. First, Dr. Chouvenc is the protégé of, and works out of the same lab as, Dr. Nan Yao Su who is known for his development of Sentricon, a well-known commercial termite baiting system.
And second, this study was done in a laboratory setting using experimental foraging arenas which inherently impart limitations on the study and influence termite behavior. While Dr. Chouvenc does an excellent job at trying to minimize other variables, it’s nearly impossible for foraging arenas to replicate real world environments. So, more work needs to be done in the field to fully evaluate this death zone effect on subterranean termites in the field.
Having said all that, I find this research very compelling and have had several conversations with Thomas about this work over the past year. What’s most interesting to me is his hypothesis of how the death zone effect could impact overall treatment efficacy of structures that utilize both a liquid termiticide and a bait station treatment. Essentially, Thomas’s laboratory experiments suggest that the distance of the death zone from the treated foundation of a structure could fall in line with the distance where bait stations are typically installed away from a structure. That would mean stations could be installed in this repellent area, potentially having negative impacts on the efficacy of bait stations. He plans to follow up this study with field work to continue testing this hypothesis, so stay tuned for future updates!
Article by Mike Bentley, PhD, BCE
References
Thomas Chouvenc, Death zone minimizes the impact of fipronil-treated soils on subterranean termite colonies by negating transfer effects, Journal of Economic Entomology, 2024;, toae150, https://doi.org/10.1093/jee/toae150
New Cockroach Control Tools
Toxicity of Isocycloseram, an Isoxazoline Insecticide, Against Laboratory and Field-Collected German Cockroaches (Blattodea: Ectobiidae)
German cockroaches are one of the top pests PMPs face on a very regular basis. These are known not only for being unwanted house guests, but also for their ability to mechanically vector pathogens and trigger allergies in the people they live with. Control of these unsanitary pests can be accomplished using several products in a PMP’s IPM toolkit.
Buckle up to get excited about insecticide modes of action because I promise this is really cool. Isocycloseram is part of a new insecticide class called isoxazolines which target GABA-gated chloride channels as allosteric modulators. This is a new IRAC group 30 that targets the insect’s nervous system. If you have heard of the human medication gabapentin, you may be familiar with it as a treatment for nerve pain or it calms down overactive nerves. GABA is the thing that calms your nervous system down so think of this insecticide as the opposite of this. It messes with GABA and overexcites the nervous system leading to the eventual death of the insect.
A new IRAC group is a huge deal. Insecticide resistance with urban and structural pests can cause persistent infestations of tough-to-kill pests. German cockroaches have shown resistance to some insecticides in some populations but with this new product, the hope is that nothing will be resistant yet since nothing has seen it. A world of opportunity! Now, this isn’t yet commercially available but with continued research, we get closer every day. German roaches are however known to develop resistance quite quickly even against new chemicals. Keep all that in mind. 
Cut to the research scene. In this case, they got the insecticide to use as the active ingredient 1% solution in a gel bait.
The researchers collected a susceptible lab-reared strain and several field-collected populations so the real ones were out on the streets. For these 6 total strains, they ran a series of tests to see which baits were the most effective which meant the highest mortality rate. In the tests, the isocycloseram bait performed comparably meaning it was similarly effective in some tests to the other baits tested which included several commonly used baits on the market. The resistant and susceptible strains reacted similarly to the iso bait which indicates that cross resistance was not found.
Meaning that resistance to some other baits didn’t carry over and work against this new one. This is a good thing! It is important to note that another common ingredient, fipronil is also related to the GABA channels and the resistance to fipronil did not carry over to any resistance to isocycloseram. They also found that PBO, a synergist, added to the efficacy of the product against the one strain it was less effective against. It is important to note that bait performance is also affected by other ingredients in the bait such as the parts that make it tasty.
Adding another active ingredient and another IRAC group that can be used against these pests will help reduce resistance overall as we can use each group less frequently, and have another weapon at the ready for tough infestations.
As is always the case with science, there are other factors to consider. I think the key takeaway here is the last sentences of the paper which say that with its consistent positive performance against other baits, the researchers conclude that it is a “promising bait toxicant for the control of the German cockroach”
This is a study that will be discussed at one of our Pestworld educational sessions! Come see us in Denver and hear more about Dennis Lee's exciting new research.
Article by Ellie Sanders, BCE-Intern
References
Shao-Hung Lee, John So, Gregory S Kund, Jun-Yin Lum, Ethan Trinh, Emily L Ta, Rattanan Chungsawat, Dong-Hwan Choe, David L Cox, Michael K Rust, Chow-Yang Lee, Toxicity of isocycloseram, an isoxazoline insecticide, against laboratory and field-collected German cockroaches (Blattodea: Ectobiidae), Journal of Economic Entomology, Volume 117, Issue 3, June 2024, Pages 1086–1094, https://doi.org/10.1093/jee/toae079
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!
