Researchers in the US have revealed that even very brief exposure to a termiticide can be enough to eliminate a termite colony.
A new study published in the Journal of Economic Entomology has shown that exposure to chitin synthesis inhibitor (CSI) baits for as little as one day may be sufficient to eliminate colonies of the Asian subterranean termite (Coptotermes gestroi).
In the US, two invasive species, the Formosan subterranean termite (Coptotermes formosanus) and the Asian subterranean termite (Coptotermes gestroi) are causing increasing economic damage.
University of Florida entomologists, Dr Thomas Chouvenc, and Dr Nan-Yao Su, wanted to answer an important question about controlling these termites with CSI baits: how long do termites have to feed on the bait to acquire a lethal dose that will eliminate a colony?
CSIs affect termites by inhibiting the synthesis of chitin, the main component of insect exoskeletons. This disrupts termite moulting, leading to death. The bait and therefore CSI is spread within colonies through trophallaxis and the eating of dead nestmates. CSIs offer the advantage of not causing something called secondary repellency, which is when termites avoid the immediate area around a bait because it is surrounded by dead termites. With CSIs, mortality is delayed, so termites leave the immediate vicinity of the bait and go back to the central nest to moult. Because CSIs disrupt the moulting process, the amount of time for individuals to be affected by the bait is determined by the time of moulting, which in turn impacts the time taken to eliminate the colony.
In their study, the researchers created more than 100 termite colonies from single mating pairs. They then selected nine colonies at random to serve as manipulated treatment colonies and chose five colonies at random to serve as controls. Of the nine treatment colonies, three were exposed to CSI insecticide baits for one day, three were exposed to baits for three days, and three were exposed to baits for ten days. The investigators added blocks of wood to each control colony instead of CSI baits. They left all the colonies alone for 80 days, and then opened each and counted the termites. They counted the termites again at 90 days.
After 80 days, one colony in the one-day group was eliminated, two colonies in the three-day group were eliminated, and all three colonies in the ten-day group were eliminated. But, by 90 days all termites in all treatment groups were eliminated. This means that the effectiveness of the CSI baits over the 90-day period was 100%. In contrast, all of the control colonies survived.
The bait affected the colony in three ways key ways: by eliminating individuals, decreasing the amount of food gathered by the colony, and preventing the production of alates.
Dr Chouvenc said, “For two reasons, this study supports the use of baits for control of subterranean termite colonies. First, the timeframe for colony elimination is much shorter that we previously thought. Just one day after starting feeding on baits, the termite colony is doomed. Second, we proved that the amount of active ingredient required to kill a colony is ridiculously small.”
Dr Chouvenc pointed out that the amount of damage the termites would be causing was reduced long before 90 days. “Within a month after feeding on the bait,” he said, “termites become sluggish and slowed down their feeding activity. Therefore, even if the termites were still alive, they would not be causing much damage at that point.”
Further research by the University of Florida is looking into ways to speed up the moulting process, resulting in even quicker collapse of the colony.
Reworked extract from: Subterranean Termites Feeding on CSI Baits for a Short Duration Still Results in Colony Elimination by John P. Roche, PhD. Entomology Today, 13 November 2017.
Journal reference: Thomas Chouvenc, Nan-Yao Su. Subterranean Termites Feeding on CSI Baits for a Short Duration Still Results in Colony Elimination. Journal of Economic Entomology, Volume 110, Issue 6, 5 December 2017. Pages 2534–2538.