So, You Want to Study Termite Control? Step 1: Raise a Few Million Termites
By Thomas Chouvenc, Ph.D.
Social insects are fascinating for many good reasons. Scientists who study them will each give you their own long personal list of marvelous things social insects can do, one being their complex social organization, which can result in magnificent nest architectures. How many young kids who observed (and destroyed) an ant mound, followed foraging honeybees, or collected abandoned paper wasp nests were actually impressed enough to become an entomologist? By the age of 10, I did all of these things, and by 12 I knew that I wanted to study social insects. Alternatively, how many kids living in a temperate climate were exposed to termites and got excited enough about them to turn it into a career? Not so many. Termites are cryptic by nature, which makes them hard to find and observe (unless you live in the tropics, but this is another story).
Social insect scientists often have access to whole nests of their model insect, which is convenient when you want to study colony-level aspects of their societies. For many ant species, a colony with a centralized nest structure can be collected, brought back into the lab, and reared indefinitely. A honey bee hive setup by a beekeeper is the poster child for a social-insect model that can easily be studied at the colony level. For most termite species, however, not so much. This is especially true for pestiferous subterranean termite species for which a colony can easily reach a million individuals and the subterranean nest and galleries are a diffused amoeba-like structure spread over a residential block. Good luck if you want to find the primary queen and king and their massive brood.
As a consequence, the study of subterranean termite pests within the Coptotermes genus has historically been limited to observations using small subgroups of termites collected from field foraging populations. More critically, the assays aimed at testing control methods against pest termite species were restricted to small petri dishes using less than 50 termites at a time. Forget the large termite population, forget the queen and king, forget the brood, forget the foraging distances along a residential block in the soil, and forget any behaviors that would emerge from an established field colony. As a result, most of the past—and present—scientific literature about termite control is essentially an accumulation of studies that could be summarized as “We killed bugs in a jar.” These studies bear little to no biological relevancy, and for the most part they present unrealistic experimentation strategies (not to mention the horrendous mortality of the control groups usually associated with such assays).
If you do a quick search, you would be amazed by how many studies have tested “wannabe” pesticides (synthetic, extracted from plants, pathogens, etc.) that have been labeled as “extremely promising candidates” for termite control, with no follow-up beyond the petri-dish assay and without producing any viable candidates for commercial products. Many have realized, often too late, that the issue with subterranean termite control research is not the lack of candidate pesticides; rather, the challenge primarily resides in limitations with the evaluation protocol—i.e.,its scale. Of course, any quick preliminary assay may initially rely on “killing a bug in a jar,” but far fewer are realistically or biologically scalable.
Currently in the United States, to prevent or stop structural damage by subterranean termites, two different approaches exist: liquid termiticides (primarily fipronil formulations) and chitin synthesis inhibitor (CSI) baits. The preferential use of one control method over the other has long been the source of a vigorous debate (and, for some, still is). The fact that you cannot monitor a whole colony in the field limits your ability to claim termite colony elimination. You can only infer using proxies. However, back in 2005, a study using extended foraging arenas (10,000 termites per replicate within 50 meters of foraging distances in soil) by my University of Florida colleague Nan-Yao Su, Ph.D., provided robust evidence that liquid termiticides kill subterranean termites only in close proximity to the treatment and do not affect the foraging population beyond a few meters away from the treatment. Alternatively, CSI baits can eliminate all the termites within the arena system, regardless of the distance.
This study was a major milestone in showing the importance of distance and secondary repellency in the efficacy—and limits—of termite control methods. However, despite using more than 90,000 termites in the experiment (which was more termites than any previous study in the laboratory by several orders of magnitude), it still fell short of proving the “colony-wide” effects of either treatment. The termites were originally collected from a foraging population from the field, which means only a fraction of the colony, with only old foragers, no young workers, no brood, and no queen and king were used in the experiment.
Then came 2013 with its massive swarms of Asian subterranean termites (Coptotermes gestroi) in Florida (see video above). Following Jacques Monod’s Chance and Necessity, I happened to be at the right place at the right time to start something that would, unbeknownst to me, be the foundation of my research for years to come. Having in the past been a vocal critic of minimalistic approaches to studying termite pathology, I also had experienced the frustration of looking only at the tip of the iceberg, never to look underwater. So, I thought, how about changing all of this by starting colonies from scratch and growing them up, so that I got to see the whole picture in the lab? I knew I needed time, space, and resources. What I did not know, is that I needed a lot of time, a lot of space, and a lot of manpower.
I took the opportunity to collect large numbers of alates (termites in their winged form) during the termites’ dispersal flight, brought them back into the lab, and started colonies simply by pairing males and females in vials that would contain all their needs for at least a year. From a lousy colony-foundation success rate of less than 25 percent in the first year, we quickly were able to improve the rearing conditions to now having more than 80 percent colony survival rates. And so then we were in business.
At the beginning, all of this lab rearing of termite colonies could fit on one shelf. However, as colonies grew bigger, they needed to be transferred to larger containers. I also scaled up the number of incipient colonies every year after 2013, so I could have enough material for the needs of graduate students’ experiments and also for myself. As a result, from one shelf in 2013, a whole room is now needed in 2018 to hold several hundred colonies from 1 to 5 years old, which requires a full-time technician to maintain. The goal is simple: Keep the termite colonies happy, fed, healthy, and contained. You don’t want to accidentally lose a 5-year-old colony after spending so much time and energy to keep it growing. Ironically, while it is extremely hard to kill termite colonies in the field, it is remarkably challenging to keep them alive and growing in the laboratory.
By 2017, I was in possession of several dozen uniformly grown 4-year-old colonies of approximately 60,000 termites each, and available space was becoming a problem, so I had to make a difficult decision: I had to let go of some of them. Fortunately, these colonies were reared from scratch with a purpose, other than being expensive exotic lab pets. Among many other burning questions I had in mind, I finally had an opportunity to revisit the study by Su, but this time using whole colonies. In addition, around this time, with the locally increasing density of the invasive C. gestroi, several pest-control professionals came to share their observations of “inexplicable” cases of retreatment when using liquid termiticides. The game was on. I finally could test the Su hypothesis, this time using full, relatively large colonies, with the queen and king, the brood, and all individuals. In addition, I could test what would happen if the colony could find their way around the treatment.
I had given all of my affection attention to these colonies, but then it was the time to kill them. The protocol took almost two months to setup. I needed 54 planar arenas, almost 200 meters of tubing, 12 colonies with equivalent populations, and 20 square meters of lab space for three consecutive months. Did I mention that space was at a premium? In addition, to look at the effect of the control methods at the colony level, I needed to open each colony at the end of the experiment and count and measure everything. For just a single colony, it took seven “volunteered” graduate students and staff, for eight consecutive hours of processing. In total, we processed more than three-quarters of a million termites over a two-week period: 780,000 termites in a single study, another order of magnitude higher than the previous scale of Su’s study.
The results of this colony-wide experiment, presented this month in the Journal of Economic Entomology, were unequivocal: Within 90 days, all colonies that fed on chitin-synthesis inhibitor baits were eliminated. In contrast, in colonies treated with liquid termiticides, only the termites in close proximity to the soil treatment died (less than 3 meters away from treatment), resulting in secondary repellency and avoidance by the rest of the colony. In addition, if these liquid termiticide-treaded colonies were able to find their way around the treatment, they could still cause damage to the “structure.” In fact, liquid termiticides only killed a few hundred termites (directly exposed), which did not put a dent on the remaining population, and, more critically, the queen, king, and brood were intact. This means that even if field colonies treated with liquid termiticides are temporarily excluded from a structure, these colonies overall remain virtually unaffected, and their potential for damage down the road stays intact. Ultimately, they would eventually be able to swarm, complete their life cycle, and create more colonies within the area.
Inevitably, critics will probably find something to complain about in this new study. Remarkably, 13 years after Su’s 2005 study, we have yet to see any evidence contradicting its findings, including the results of this latest study. While criticism is easy, coming up with the data to support or contradict the findings requires years of efforts. Such a large-scale experiment requires long-term planning, perseverance, a bit of luck, resources, and manpower. However, they are necessary to move our knowledge forward and challenge the status quo.
In the end, I feel lucky to work on my favorite social insect (when I don’t have to kill them). Science is not always fun or easy, but it is extremely rewarding when you get to tackle difficult questions. Especially when the scale of it requires five years of preparation and a range of expertise from diverse people. Although the setup and execution of this large-scale experiment was challenging, getting to rear large termite colonies in the first place to perform the experiment was the most difficult part.
My advice is therefore simple: If you want to know how to kill termites, you first need to know how to keep them alive.
On a more personal note, here I am with colonies growing up in the lab and I was told several times that I am essentially managing a small nursery. This is actually true in many aspects, as I cannot help but to have an anthropomorphic and paternalistic view of them. A few years ago, I actually became a father in the midst of the termite swarming season. As I was able to collect alates from the day my daughter was born (with the help of a student, since I was a bit busy at the time), I was able to establish colonies that are now literally as old as my daughter. This implies two things. First, in addition to ants, bees, and wasps, my daughter will actually be able to observe termites as a kid, and, second, I will be able to compare the growth rate of termites versus human (n=1) reared in identical conditions: a lot of love.
“Comparative Impact of Chitin Synthesis Inhibitor Baits and Non-repellent Liquid Termiticides on Subterranean Termite Colonies Over Foraging Distances: Colony Elimination Versus Localized Termite Exclusion”
Journal of Economic Entomology
Thomas Chouvenc, Ph.D., is an assistant professor at University of Florida’s Fort Lauderdale Research and Education Center, part of the UF Institute of Food and Agricultural Sciences (UF/IFAS). His research focuses on termite biology, symbiosis, evolution, and (sometimes) control. Twitter: @ChouvencL. Email: firstname.lastname@example.org
Photos courtesy of Thomas Chouvenc, Ph.D.