Biological Control of Emerald Ash Borer
|Biological Control of Emerald Ash Borer (1)|
Jian J. Duan, Research Entomologist (Lead Scientist)
Roger W. Fuester, Collaborator
Philip B. Taylor, Entomologist
Jonathan Schmude, Biological Science Technician
Kristi Larson, Biological Lab Assistant
In 2003, we began research on natural enemies of emerald ash borer (EAB), Agrilus planipennis, in response to the impact of the then newly-discovered pest in Michigan. If efforts by federal and state regulatory agencies to eradicate EAB in the Great Lakes Region are not successful, biological control will be needed for suppression of this pest. There have been very few biological control projects directed at wood boring insects, and we know of none for buprestid beetles, so there are no precedents as to the prospects for success in biological control of this pest. In 2005, work on biological control of emerald ash borer at the ARS Beneficial Insects Introduction Research Unit was expanded to include studies on natural enemies of the pest in both the Far East and North America. In addition, we have been cooperating with Michael Smith of this laboratory in studies on parasitoids of Asian longhorned beetle, Anoplophora glabripennis.
Our current program has two major objectives: (1) Exploration for and discovery of natural enemies of the emerald ash borer - this includes foreign exploration in the Far East and also a search for native natural enemies of indigenous buprestid beetles. Subobjectives include finding suitable investigation areas, constructing and inventory of natural enemies, investigations into the structure of the enemy complex, and field studies of their impact on the target pest. (2) Bioecological studies on promising natural enemies discovered - these include studies on life history and behavior, host specificity (Asiatic species), synchronization with the pest, physiological tolerance to different climatic factors, and establishment of priorities in utilization of promising species based upon their biological characteristics.
Research in Progress
In 2003-2004, Paul W. Schaefer, (Research Entomologist, retired) conducted explorations for natural enemies of EAB in Japan, South Korea, and Mongolia, but no suitable populations were found. Therefore, we intend to work in China this year and next. The most promising area to look for specialized parasitoids of both emerald ash borer and Asian longhorned beetle in natural settings would be the region north of Korea straddling the 130th meridian. This region has deciduous and pine-deciduous forests containing substantial components of ash (Fraxinus spp.) and maple (Acer spp.), preferred host plants of EAB and ALB, respectively. Of course, EAB is not confined to a single region of China, but occurs in a number of provinces. Because man plants trees wherever he wants to, pests often take advantage of new host sources, ranging far outside their ancestral home to invade the new plantings. Usually, these secondary distribution areas are of limited interest to biocontrol workers, because natural enemies tend to lag behind, resulting in an impoverished parasitoid complex. Such a situation exists in Shandong Province, which has substantial plantings of velvet ash, a North American species. Thus, we will not dismiss such areas out of hand, because they might prove to be sources for parasitoids that would attack EAB on Nearctic species of ash.
In 2008, JJD conducted another a foreign exploration in three northern Provinces of China (Jilin, Heilongjiang, and Hebei), and collected two species of EAB parasitoids (Tetrastichus planipennisi and Sclerodermus sp.) in Heilongjiang and Hebei Provinces, respectively, which were subsequently imported to the BIIR quarantine laboratory in October, 2008. Through collaboration with USDA APHIS, an additional strain or species of Tetrastichus sp. was collected from the Primorski Kraj region of Russia, and subsequently imported to BIIR quarantine laboratory in May, 2009. Since then, one of the most promising candidates (T. planipennisi) have been successfully reared in quarantine, and released several forest plots against EAB in MI and MD in the summer of 2009. In addition, two other previously introduced parasitoids (Spathius agrili and Oobius agrilli reared by USDA-APHIS and FS) were also released in MI, where their potential impact on EAB populations was being evaluated by placing EAB eggs in bark slits on ash tree trunks, using sentinel logs or sticks infested with EAB eggs, and caging egg-laying adult EAB. As of August of 2009, two species of the introduced parasitoids, T. planipennisi and O. agrili) were successfully recovered from larval and/or egg cohorts of EAB established in two of the three study sites in MI.
Because some North American parasitoids might adapt to EAB (or ALB), we have begun studies on parasitoids attacking buprestid and cerambycid beetles in Pennsylvania and Delaware. Two approaches are used: (1) girdling preferred host plants (white, green and black ash for EAB and maples, poplars, willows and others for ALB), then felling them at intervals thereafter, and (2) taking infested material from sites with recent logging debris. In the latter sites, we can capture foraging females of parasitic wasps with an insect net for laboratory study. Usually, bolts are taken from the field to an unheated insectary. Bolt ends are waxed to inhibit desiccation, and the bolts are then stored in ventilated trash cans or cardboard tubes for emergence of borers and their parasitoids. Containers are checked three times a day for emergence, and parasitoids are placed in mating cages if both genders are recovered. This line of research only started in July, so we have a limited view of what is out there. So far, we have recovered buprestids in the genera Dicerca and Chrysobothris from ash. With respect to parasitoids, we have recovered at least four species of parasitic wasps: a braconid in the genus Atanycolus, two ichneumonids, one chalcidoid and one tachinid. Field-collected or mated females are exposed to the target pest (EAB or ALB) in quarantine. The Atanycolus, has been observed probing a number of other tree species in the field, including hickory, red maple, and red oak, so we suspect that it is a generalist. We have made over 100 exposures of this species to EAB or ALB but have yet to observe any successful parasitism. However, our recent field studies in PA, MD, and MI have resulted in discovery of five species of parasitic Hymenoptera, including Balcha indica, Eupelmus pini, and Dolichomitus vitticrus, Spathius laflammei and Atanycolus nigropyga, which successfully attack various stages of EAB larvae and/or pupae. These extant or indigenous parasitoids may play a potential role in suppressing populations of EAB in North America. In addition, this study was noteworthy because two species (S. laflammei, A. nigropyga) had not been found in the Great Lakes Region in previous studies.
Host specificity is a major consideration in the classical approach to biological control of insect pests, because it determines whether unwanted shifts of biocontrol agents to attack non-target species are likely to occur after introduction. Differences in parasitoid biology profoundly influence host suitability. Koinobionts (endoparasitoids that develop in living hosts) have venoms, teratocytes, and symbionts that suppress the host's immune system, and host range is usually determined by host phylogeny; whereas idiobionts (ectoparasitoids or endoparasitoids that attack eggs or any stage lacking an immune system) do not need to suppress the host's immune system, and habitat or host plant is more likely to determine host range than host phylogeny. Host specificity in parasitoids of woodborers and other insects living in concealed places is often determined ecologically rather than by host phylogeny. Because the emerald ash borer attacks Fraxinus spp. nearly exclusively, host plant species might be an important determinant of the host range of its natural enemies. Different approaches might need to be developed to test nontarget species selected for testing promising candidates found overseas. We are adopting a modified approach in which host phylogeny, host plants, and habitat similarities will be used to select non-target species for host specificity testing. Both choice and no-choice tests will be used in evaluating host range. The overall goal is to use methods that prevent the release of any organism likely to have an unacceptable level of economic or environmental impact, but minimize the likelihood that safe and potentially useful biological control agents will be rejected.
Learn More About Emerald Ash Borer and its Control (Click here)
(Shockwave multimedia by Kathy Duan, Northwestern University)