Gregg Henderson and Bal Gautam

The population of East Baton Rouge Parish has jumped from 412,852 in 2000 to 445,227 in 2013, and downtown is booming with new construction and more entertainment events. But as the city grows, so do some problems; a hidden one is the growing population of the invasive subterranean termite, the Formosan subterranean termite, or Coptotermes formosanus. Of the six species of subterranean termites considered economically important in the U.S., Formosan termites are the most destructive, especially in Louisiana. In New Orleans alone this termite causes more than $300 million in losses every year by feeding on houses, other wooden structures, electric and telephone poles and underground cables, railroad ties, and live trees. In addition, the termites are suspected of compromising the floodwalls and levees in New Orleans with devastating results after Hurricane Katrina in 2005.

With the help of Baton Rouge residents, LSU AgCenter researchers have been monitoring the annual flight numbers of this species using light traps (Figure 1). Starting in 2009, about 15 light traps (Figure 2) were placed on government property, research stations and residential homes around Baton Rouge, and daily catches of alates (winged termites) were recorded through May and June.

The average number of alates caught per trap indicates that the Formosan subterranean termite populations are increasing at an alarming rate in the Baton Rouge area (Figure 3). In 2009, there were only 32 alates caught per trap in the whole season, whereas in 2014, the number of alates caught per trap increased to 596, an almost 20-fold increase. More Formosan subterranean termites were caught in residential areas than at research stations, possibly because of more structures and human-related activities, such as movement of infested materials like mulch, landscaping timbers, large planters and other wood-based materials. Peak flight dates were noticed as early as May 3, 2012, to as late as May 22, 2014 (Figure 4).

The AgCenter researchers wanted to develop a diagnostic tool to better determine when the first peak flight of the year would occur. Investigating what triggers C. formosanus swarming in Louisiana may help to predict the potential flight date with reasonable accuracy, which in turn can caution homeowners and the termite control industry to take necessary steps before major swarming.

There is a general belief that subterranean termite swarming is triggered when a certain accumulative temperature has been reached at the initiation of the flight season. This temperature is measured in terms of heat units. For example, one heat unit is 1 degree Celsius above a specified “base” temperature, a temperature at which foraging of subterranean termites slows to a crawl. For C. formosanus, this base temperature is considered to be 13 degrees C (55 degrees Fahrenheit). At this temperature most termites will stay in the ground, unless they already have invaded your cozy warm home. The heat unit accumulation was calculated with a start date of July 1, the date when the current season’s two-month flight ends, to the date when the first peak flight was recorded for each of the six years of data collection. When Formosan termites decide to exit en masse, almost every light post in the city will have some termites flying around it. The swarming pattern shows multiple major flights during its swarming season and many more smaller localized (single colony) flights. Since termites fly in the early evening and are attracted to lights, it is recommended that homeowners turn off unnecessary outside lighting during this time. Figure 1.

Based on six years’ survey data, a minimum of 2,203 heat units are required before the first peak flight of the season in Baton Rouge (Table 1). The first peak flight always occurred in May, but the dates varied. The second peak flights occurred nine days, on average, after the first peak flights (range six to 12 days). All of them happened in May, except in 2013, when one occurred on June 2. On average, there were 110 extra heat units that accumulated after the first peak flights and before the second peak flight. By comparison, the first swarm of the native subterranean termites in Texas occurs after only 602 heat units accumulate. Native subterranean termites are a more temperate region insect, whereas Formosan termites are more subtropical in nature.

Statistical analysis of six years’ survey data showed a significant correlation between the average number of alates and the year. Possibly even more important is the fact that the number of alates is increasing every year in Baton Rouge, an indication that the C. formosanus population is growing and expanding its destructive nature. It is important to note that a light to moderate rainfall event occurred one to seven days before the peak swarm dates in all years studied. In conclusion, we suggest minimum heat units of 2,203 in association with precipitation at the beginning of the swarm season will provide the estimates of C. formosanus peak swarming events.

Gregg Henderson is a researcher and professor, and Bal Gautam is a research associate, both in the Department of Entomology.
 
(This article was published in the winter 2015 issue of Louisiana Agriculture.)