Did Two Florida Populations of Conehead Termites Arise From a Single Colonization Event?
By John P. Roche, Ph.D.
The conehead termite (Nasutitermes corniger) is an aggressive pest of crops, wooden structures, and forests in 13 countries in Central and South America and on many Caribbean Islands. Only two populations have ever been found in the United States, both on the east coast of southern Florida: one in Dania Beach and one in nearby Pompano Beach. A group of researchers has conducted a genetic analysis of these two populations to test whether or not these populations in the U.S. arose from one colonization event or if the populations arose independently.
The study, led by Barbara Thorne, Ph.D., of the University of Maryland with colleagues Edward Vargo, Ph.D., and Laura Johnson at Texas A&M University and Eldridge Adams, Ph.D., at the University of Connecticut, was published in late August in the Journal of Economic Entomology.
Nasutitermes corniger is abundant in tropical forests, savannahs, and in areas of secondary plant growth. Whereas many pest termites are subterranean, foraging and nesting in soil, conehead termites live primarily above ground. They generally nest in trees, bushes, logs or stumps, structures, or on the ground. Their nests and foraging tunnels are easy to spot, which helps with their control.
Conehead termites provide the ecosystem-function role of recycling nutrients. As pests, though,these termites are aggressive, causing extensive damage to crops such as sugar cane and fruit trees, and to buildings and forests. Their ecological characteristics contribute to their ability to cause damage. They have a varied diet and can nest in a variety of substrates, so they can survive in a range of habitats. And their populations grow rapidly and disperse easily.
Conehead termites disperse in swarms, often after the first heavy rain of the spring. In one season, over 20,000 winged conehead termites can disperse from a single large colony. After dispersing, a new queen and king—or multiple queens and kings—start a new colony. Conehead termite colonies sampled in regions where they are native show a mixture of some nests with one queen and one king and some with multiple queens or multiple kings. However, in samples of the invasive conehead termite colonies in Florida by Thorne and colleagues since 2012, all colonies with reproductive individuals had multiple queens, and the number of queens per nest was as high as 52! The presence of multiple queens and kings in conehead termites helps create very high reproductive rates in this species.
In May 2001, conehead termites were spotted in Dania Beach Florida. Termiticide treatments were begun on populations there in April 2003. In 2016, conehead termites were spotted in Pompano Beach as well. Were these two populations the result of separate colonization events, or did a single colonization lead to both populations? Answering this question was the goal of Thorne’s study.
Thorne and colleagues sampled conehead termites from eight nests in Dania Beach in 2015 and 2017 and collected individuals from eight nests in Pompano Beach in 2016. They focused their genetic analysis on microsatellite markers within the termites’ DNA. Microsatellite markers are sections of DNA that repeat the same short sequence of from one to 10 nucleotides over and over again. Microsatellite markers are useful for genetic analyses because they mutate at a rate orders of magnitude higher than simple point mutations do. Being highly variable, they provide investigators with an increased ability to discern the degree of evolutionary relationship among biological samples.
The researchers determined the genotype of sample termites at seven out of eight of the microsatellite loci that had been previously identified as being very variable. They discovered that, for all the samples they analyzed, there were four or fewer alleles at each microsatellite locus. In contrast, in a sample of 140 colonies in Panama in another study, genetic analysis found from nine to 32 alleles at the same microsatellite loci. Because so little variation was found in the microsatellite DNA, the data from the two Florida populations supported the hypothesis that all termites in both colonies were so closely related that they arose from one colonization event. They probably arose from a single queen and king, or from offspring from a single queen and king. In their paper, Thorne and her colleagues concluded that the two populations “almost certainly descended from the same founder population.”
Thorne and colleagues explain that it would be interesting to determine the source of the two populations in Florida but that not enough genetic data are yet available to make this determination. It would also be interesting to know if the first colonization location was in Dania Beach or Pompano Beach, but the researchers report that the colonization site is not yet known definitively. However, they detail a lot of information that suggests that Dania Beach was the initial colonization site. Observations that support this hypothesis include the following:
- the termites were first seen in Dania Beach;
- they were found near docks in a marina, a likely point of arrival by a boat from the sea;
- the termites could then have dispersed to Pompano Beach in trucks that bring wood and plant debris from Dania Beach to a waste disposal facility in Pompano Beach;
- waste is transported from Dania to Pompano, but not from Pompano to Dania
- a much greater area is infested in Dania Beach, consistent with the hypothesis that the termites have been there longer.
These results have important practical implications. “Our results show that human transport of infested materials is a significant risk for spreading populations of invasive conehead termites,” Thorne says. “The operational application of this result is that, beginning immediately upon discovery of invasive coneheads (or any species in the genus Nasutitermes), alerts and precautions must be implemented to prevent movement of potentially infested materials to a new location.”
Since 2012, Thorne has served as science advisor to Florida’s Department of Agriculture and Consumer Services invasive N. corniger mitigation program. “Our focus is on complete eradication of conehead termites from south Florida and thus the United States,” Thorne says. “Due to our ‘when we find conehead termites, we attempt to control them immediately’ priority in this eradication effort, scientific research requiring weeks or months of field observations, including untreated controls, are off the table. Such studies should be conducted where the species is permanently established rather than in Florida where it is a target for eradication.”
As for the eradication program, it has been highly successful. “Currently, we do not know of any live Nasutitermes corniger in previously infested areas,” Thorne says. “But, because young colonies can remain hidden within wood for years, inspections and reinspections must continue to ensure that we catch and quickly control any resurgence.”
The Florida Department of Agriculture and Consumer Services team is going to write a field guide explaining first actions to take upon discovery of an invasive population of conehead termites or any of their relatives in the genus Nasutitermes. Thorne says, “The guide will detail integrated pest management actions, tools, protocols, and logic toward effective containment, treatment, and outreach drawing upon the lessons learned from our experiences in south Florida.”
When asked about facets of this species’ ecology that are most important to tease apart in order to better prevent dispersal and eradicate colonies, Thorne says, “Based on current knowledge, Nasutitermes corniger winged dispersing termites fly from a structure built by the colony—either foraging tunnels or, more commonly, a nest. However, because the life history of this species is so flexible, adaptable, and opportunistic, we worry that colonies still hidden within wood might produce termites that disperse without visible evidence of a colony. Determining this possible capability of conehead termites will require opportune detection by sharp eyes during the flight season. We welcome reports of such observations from anywhere in the broad range of this species!”
This study provided valuable insight into the origin of conehead termites in Florida and the likely ecological progression of their colonization there. Ongoing discoveries adding to our understanding of the ecology and behavior of this species will be essential to further improving control strategies.
Journal of Economic Entomology
John P. Roche, Ph.D., is an author, biologist, and educator dedicated to making rigorous science clear and accessible. Director of Science View Productions and Adjunct Professor at the College of the Holy Cross, Dr. Roche has published over 200 articles and has written and taught extensively about science. For more information, visit https://authorjohnproche.com.
Update, October 1, 2019: This article was updated to correct the description of the geographic location of Dania Beach and Pompano Beach.