[Annual Termite Control Issue] Insights Into the Growth of Young Termite Colonies

The life cycle of subterranean termites is complex, but critical to understanding the establishment and spread of species. The termite life cycle begins with the dispersal of winged male and female swarmers (alates, winged adult termites) from their natal (parent) colony. These swarmers are potential reproductives that are attempting to establish new colonies at new sites.

What happens to alates that don’t fly from their natal colony? Well…their nestmates cannibalize them. It’s either fly or die! And, even then, flight doesn’t offer a significant likelihood for survival as only a small number of swarmers live long enough to establish a new colony. The majority of swarmers die from desiccation or predation.

Once termite swarmers fly from their natal colony and land, each swarmer typically quickly sheds its four long wings (each wing breaks off along a suture line, leaving behind a small wing scale attached to the body). Wing shedding is a critical step because a swarmer’s wings can easily become trapped in a water droplet or moisture condensation and this will doom the rather fragile, soft-bodied termite.

Once the wings have been shed, the termite is called a de-alate. Male and female de-alates are attracted to each other by emitted pheromones, and many pairs can be found in tandem with the male closely following behind the female. Sometimes numerous de-alates can be seen closely following each other in a long, twisting train of rapidly moving individuals. Eventually, a male and female pair locate a suitable nest site, which they enclose, if necessary, and enlarge their “nuptial chamber,” where mating then takes place. The male and female now are the new colony’s king and queen, respectively (designated K and Q herein).

In this study, we followed the first year of colony growth in the eastern subterranean termite, Reticulitermes flavipes, which is the most widespread and economically important native species in the United States. Because subterranean termites have cryptic nesting habits and are very difficult to study in the field, lab-reared colonies were observed. We started by collecting a large number of swarming alates (see photos above) from a barn near Columbus, Ohio. The sex of each individual was determined by microscopic examination (see diagrams below), and a male and female pair was placed into a small plastic container provisioned with moist mulch and filter paper (see photos below).

A grand total of 180 R. flavipes colonies was censused in a one-year period, with 15 different incipient colonies examined each month. The census procedure involved careful removal of all termites and eggs from each container. Immature termites were examined using a dissecting microscope and categorized as larvae (first and second instars [stages]), workers or soldiers, and their numbers were recorded (see Thorne [1996] for information on terminology used for termite stages/castes). The weight of each group of termites (biomass) was obtained using an analytical balance. Each reproductive (K or Q) was individually weighed.
 

Results.

Throughout the first year of colony development, the number of individuals varied dramatically from month to month (see Figure 1 below). There was an initial peak in total colony members that decreased dramatically from an average of 22.3 termites and eggs at two months to 13.9 at five months. However, the number of colony members eventually rebounded, with an increase from the fifth month onward. One-year-old colonies ranged in size from 20 to 40 individuals (all stages), with an average of 28.9 individuals (Fig. 1).

The sharp decline in termite numbers in our newly established colonies (less than five months old) indicates that not every egg hatched and not all offspring survived. Snyder and Popenoe (1932) observed cannibalism of eggs, larvae and workers in incipient colonies, with healthy young being eaten despite adequate food, and this may have been a contributing factor.

Egg production was intermittent, and there were times when few eggs were present. There were three cohorts of eggs — the first occurred during the first and second month, the second occurred in the sixth and seventh month, and the third spanned months nine through twelve. In the incipient colonies, larvae were observed at one month, and workers were first observed at two months (Fig. 1). Workers constituted the majority of colony members from the second month onward, and 1-year-old colonies had an average of 18 workers (range 13-27). A soldier was observed in some colonies beginning in the sixth month; this is consistent with Snyder and Popenoe’s (1932) observations of soldiers being first found in 7-month-old colonies. No nymphs (termites with wing buds) were observed during the first year, which is consistent with Grube and Forschler’s (2004) observation that nymphs were first found in 24-month-old R. flavipes colonies.
 

We observed that the weight of the K and Q greatly decreased during the first few months, most likely because the reproductives were using their internal fat stores to raise their first offspring. However, the reproductives’ weight remained relatively constant thereafter through the one-year census. Grube and Forschler (2004) noted that R. flavipes queens experience significant weight gain during the second year of colony development. Eventually, as the colony grows, brood care tasks and nest construction will be taken over by workers, then egg production may become continuous.

In the young colonies in our study, the biomass of the reproductives (K & Q) and their offspring was equal at the second month. However, the number and size of young termites rapidly increased and their overall biomass quickly surpassed that of their parents. Offspring biomass was double that of the reproductives at the third month, triple at the tenth month and more than quadruple at the twelfth month (see Figure 2 above). This indicates that termite colony growth is fast in the first year, and the K and Q quickly establish their new colony.

Overall, our study provides insights into growth dynamics of termite colonies in their first year of development. However, regional diversity among termite colonies is expected to be an important factor influencing colony growth rates, and Grube and Forschler (2004) observed a much faster growth rate of R. flavipes incipient colonies that had been established with inbred and outbred alates collected from Georgia, USA. We expect that the genetic diversity of our inbred colonies, all headed by reproductives from a single location in Ohio, would be somewhat limited. For example, at the 12 month-census, there was some variation among our 15 sampled colonies, which ranged from 13-27 workers, but nothing as extreme as observed by Grube and Forschler (2004) whose smallest R. flavipes colony had 15 workers and largest colony had 259 workers (averages not provided).

Fei and Henderson (2003) specifically studied the effect of mate relatedness in a total of 338 sibling and nonsibling incipient colonies of the Formosan subterranean termite, Coptotermes formosanus, and they found that outbred colonies had significantly increased fecundity compared to inbred colonies. Hence, inbreeding may be an important factor in the slower growth rate of some R. flavipes colonies.

Editor’s note: This article was adapted from Janowiecki, M.A., S.C. Jones and J.L. Bryant. 2013. Population growth characteristics of incipient colonies of the eastern subterranean termite, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae). Socio-biology 60(4): 441-445.

All of the work for this paper was done in the Department of Entomology at The Ohio State University where Jones is a professor and Bryant is a research associate. Janowiecki currently is a master’s student at the University of Arkansas. This research was Janowiecki’s senior honors thesis at Ohio State. Email Jones at sjones@giemedia.com.