Arjun Khadka, Steven Richardson and Qian “Karen” Sun
The Formosan subterranean termite, Coptotermes formosanus, is a highly destructive pest and an invasive species to the United States. In Louisiana, this termite was first reported in Lake Charles and New Orleans in the 1960s. Since then, it has spread to 42 parishes (Figure 1). Because the Formosan subterranean termite has a larger colony size than the native subterranean termites, more damages are incurred in less time by this species. Each year, $1 billion nationally is funneled into control of this pest and repair of damaged structures. Foraging behavior, such as searching for food, is essential for the survival of termite colonies, and this behavior plays a critical role in structural damage and economic loss. The comprehensive understanding of foraging behavior is an integrative component of termite management.
Subterranean termites nest underground and construct extensive tunnels in soil to search for cellulose-based food sources, including decaying logs, wooden structures and trees. Termites are social insects that live in highly organized colonies. Workers constitute the bulk of the colony, and they are responsible for tunneling, food collection and feeding other colony members, including the reproductives (the queens and kings), brood and soldiers. The foraging range of a Formosan subterranean colony may extend to 300 feet. Foraging is a collective effort and a complex process, and this behavior is influenced by a variety of social conditions and environmental factors. A larger colony constructs exploratory tunnels more efficiently. Once food is encountered, workers lay a scent trail, known as the trail pheromone, to recruit more colony members for food collection. Subterranean termites are attracted to moisture in soil, but they are deterred by predators, which are mainly ants.
LSU AgCenter researchers are investigating how environmental factors, such as humidity, moisture and food availability, affect the survival and foraging behavior of the Formosan subterranean termites. Desiccation is an important environmental stressor, and substrate moisture either from soil or food is required for the survival and foraging activity of these termites. Research findings showed that, without substrate moisture, workers and soldiers died of desiccation under 15% relative humidity within a day and did not survive for more than two weeks under 98% relative humidity. AgCenter scientists further examined the effects of different soil moisture contents on termite survival, tunneling and feeding activity. An experiment was performed using a planar arena filled with sand (Figure 2), where termites were kept for 28 days under six moisture regimes, 0%, 1%, 5%, 15%, 25% and 30%. The results showed that no tunneling or feeding activity was performed when the sand was completely dry (0% moisture). Termites were able to initiate tunneling activity at 1% moisture, but a minimum of 5% moisture was required for their survival and food consumption. Foraging activities in sand were optimal at 15% and 25% moisture. The findings highlighted the importance of soil moisture for subterranean termite activity. Homeowners are advised to eliminate moisture problems around their structures, such as fixing dripping faucets outdoors and repairing leaks in the roof or pipes, to prevent subterranean termite infestation.
In addition, food deprivation is a stimulating factor for foraging in the Formosan subterranean termite. When termites were starved for one day, they tunneled more extensively and consumed more food, while starvation for a longer time (seven days) did not promote foraging activity. Using termites collected from Baton Rouge and New Orleans (Figure 3), more research is being conducted to determine the molecular mechanisms of foraging behavior. Based on previous studies in fruit flies and honeybees, AgCenter scientists have identified a foraging gene in the Formosan subterranean termite. This gene is highly conserved in animals and is a known regulator of foraging behavior in many insects. Future studies on foraging and other genes involved in foraging behavior will reveal new molecular targets that may aid in developing novel termite management tactics.
Arjun Khadka and Steven Richardson are graduate students, and Qian “Karen” Sun is an assistant professor in the Department of Entomology.
(This article appears in the winter 2022 issue of Louisiana Agriculture.)
Figure 1. Known distribution (purple) of Formosan subterranean termite in 42 parishes of Louisiana as of 2021.
Figure 2. A planar arena showing tunneling and feeding activity of termites. Inner dimension of the arena is 10 by 10 by 0.2 cm. The arena is filled with moist sand, and 50 termites are introduced. Filter paper is placed at the lower left corner as a food source for termites. Photo by Arjun Khadka
Figure 3. Arjun Khadka, current doctoral student in the Department of Entomology, collects termites using cardboard traps at the Bluebonnet Swamp Nature Center, Baton Rouge. Photo by Justice Rougeau