2012 Annual Report
1a.Objectives (from AD-416):
1: Assess treatment success of the Formosan Subterranean Termites in the French Quarter at the level of alate swarms. This study is to determine alate numbers, spatial and temporal distributions and sex-ratios of alates in swarm gregations, and infer colony numbers contributing to swarm aggregations and origins of alates from genotypic profiles. 2: Microsatellite development and population genetic studies of invasive termites by developing microsatellite markers for termite species, which already are invasive or are likely to become invasive and which pose a significant threat to agriculture or urban structures if established in the United States. We will then use microsatellite genotyping to describe population genetic structure and colony breeding systems to identify factors that facilitate invasiveness and track points of origin and paths of movement of invasive termite in the United States. The knowledge gained from this study will help to guide decisions about treatment and prevention of spread of invasive termites.
1b.Approach (from AD-416):
Alates from light traps and workers from inground stations, infestations of trees and structures that are active during the respective swarm season will be collected throughout the French Quarter of New Orleans with the assistance of USDA/ARS and New Orleans Mosquito and Termite Board (N.O.M.& T.C.B). The alates will be counted, sexed and stored and each colony will be identified by its genotypic profile. This allows us to test whether the alates originate from colonies in the vicinity of their capture and establish how often the same colonies swarm during a swarm season and over the years, and how far alates from a particular colony fly. Microsatellite development: DNA will be extracted and digested with restriction enzymes from at least 20 termites per colony from at least 20 colonies per population and multiple populations per geographic region. Protocols for microsatellite genotyping will be optimized for each species. Samples will be assigned to colonies and the breeding system (simple or extended family) and degree of inbreeding will be determined for each colony. Population genetic structure will be described using F-statistics. Genetic distances among colonies and populations will be used to track origin and spread of invasive termites.
Alates from 5 traps that contained high alate numbers at 2 to 7 peaks during the swarming season of 2008 were analyzed. Diribonucleic acid (DNA) was extracted from at least 20 male and 20 female alates from each trap. Microsatellite genotyping was used to determine genetic diversity based on which the number of colonies found in each swarm aggregation can be estimated. Results were compared to previous years. The French Quarter of New Orleans, LA, has been the site of an ongoing, area-wide treatment program for the management of Formosan subterranean termites since 1998. The USDA sponsored treatment was expected to lead to a decline of foraging activity of colonies assessed with untreated inground monitoring stations and of swarming activity assessed with alate traps. ARS scientists have previously shown that proper treatment successfully eliminates termite colonies. Also, alate numbers showed a decrease at the start of the program, but leveled off thereafter. At the same time, the untreated inground monitors have remained infested and there are some residual infestations left in trees and structures. This leads to the question if colonies foraging in monitoring stations, trees and structures serve as a major source for persisting alate swarms in the vicinity. Similar to the assignment of alates sampled in 2003, to their colonies of origin, the 2007 study showed that the inground monitoring stations, infested trees and structures within the program area contribute less than 4% of alates found in swarm aggregations. Thus, the location of the majority of colonies contributing to alate swarms is not known. Alate assignments also confirmed that alates are capable of long-distance dispersal (1 km and more). Thus, alates from outside of the program area are probably contributing to the alate counts.
The most important finding of the long-term monitoring of the composition of alate swarm aggregations using genetic data is that the number of colonies contributing alates to swarm aggregations has significantly dropped since 2003. Colony numbers contributing to swarm aggregations collected in light traps have dropped from an average of 13 per trap in 2003 to 7 in 2007 and only 2 per trap in 2008. This is proof that the effective population size, i.e. the number of colonies producing alates, has been significantly reduced, in all likelihood due to the persistent treatment effort.