The exotic, invasive emerald ash borer (Agrilus planipennis) is an extremely challenging insect to manage. Its larvae burrow under the bark of ash trees (Fraxinus sp.) which slowly cut off the source of water and food that the tree needs to survive and is almost always fatal to North American ash species. The EAB larvae are well-protected under the bark of the tree, so it is not feasible to simply spray an insecticide to protect ash trees. The most effective treatment for EAB is to inject an insecticide into the tree which penetrates into the area where the larvae are feeding. Urban foresters have treated approximately 100 trees throughout Fairfax County with this method. Although the treatment is effective, it is also labor intensive and expensive and not feasible for all trees in the urban forest.
Soon after EAB was found in the United States, researchers began to look for biological control or biocontrol agents. These are predators, parasites, or other organisms that evolved together with a particular pest or host. In that case, their life histories and survival are intricately linked and can be exploited to control exotic species introduced to new areas. EAB is native to Eastern Asia and China.
Many years of testing found four EAB-specific parasitoid wasp species to use for biocontrol. These wasps lay their eggs inside the larva or eggs of EAB which kills the developing host and controls its population.
In mid-June Rachel Griesmer-Zakhar, Charles Layton, Troy Shaw and Tim Stalzer, all of whom are with the Forest Pest Management Branch, Urban Forest Management Division (UFMD), received and released 2400 Oobius agrili (EAB egg parasitoid), 821 Spathius agrili (larval parasitoid) and 1821 Tetrastichus planipennisi (larval parasitoid) at four sites including Flatlick Stream Valley Park, Cub Run Stream Valley Park (two sites) and the Confederate Fortifications Historic Site. The egg parasitoid, O. agrili, were in orange plastic vials called "Oobinators" as pupae. The larval parasitoid, S. agrili, were released as adults from clear plastic drink cups. The larval parasitoid, T. planipennisi were contained within ash bolts, or small logs, as pupae. In the next few weeks, these pupae and adults will emerge and disperse to find and feed on EAB.
These wasps are available to agencies who have the personnel to release and monitor the insects over time. In 2015, UFMD began the process to request these parasitoid insects from the U.S. Department of Agriculture, Animal and Plant Inspection Service. The parasitoids were produced and supplied by Animal and Plant Health Inspection Service (APHIS), Plant Protection and Quarantine (PPQ) EAB Parasitoid Rearing Facility in Brighton, MI.
In addition to the injections with insecticide, Urban Foresters hope that the parasitoids will help protect the next generation of ash trees from EAB. The parasitoids, once they establish, will find and attack the larvae and eggs of EAB. After a few years, the parasitoids' populations will synchronize with the EAB population and be able to attack enough of their larvae and eggs to reduce the pest pressure and stress on both existing and future ash trees. It is hoped that these wasps will spread to other areas of the county where releases were not made to reduce the population of EAB in those areas as well.
The parasitoids were produced and supplied by the U. S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS), Plant Protection and Quarantine (PPQ) EAB Parasitoid Rearing Facility in Brighton, MI. For parasitoid information call 866-322-4512.