Biological Control

Emerald Ash Borer: Research and Technology Development Meeting

From: V. Mastro and R. Reardon (compilers), Emerald Ash Borer Research and Technology Development Meeting, Romulus, Michigan, Oct 5-6, 2004. USDA Forest Service publication FHTET-2004-15.

Exploration for Natural Enemies of Emerald Ash Borer in South Korea during 2004

David Williams, USDA, APHIS, PPQ, Pest Survey, Detection and Exclusion Laboratory, Building 1398, W. Truck Road, Otis ANGB, MA 02542

Hai-Poong Lee, and Yeong-Seok Jo, Dongguk University, Department of Biology, 26, 3-Ga, Pil-dong, Chung-gu, Seoul 100-715, Republic of Korea

We searched for emerald ash borer populations and associated natural enemies from June through August 2004 in the northern part of South Korea. Previous to our investigations, emerald ash borer was recorded in a single citation in a Korean forestry publication under the synonym Agrilus marcopoli Obenberger. Our approach to exploring for natural enemies is threefold: to locate areas with plentiful host trees of A. marcopoli (which we assumed to be Fraxinus spp.), to locate beetle populations in the host stands, and to rear insects from beetle-infested wood and identify potential natural enemies. The Korean ash, Fraxinus rhynchophylla Hance, is very abundant, particularly in riparian habitats along rocky mountain streams, and thus, we chose it as the focus of our investigations.

Our primary strategy for locating A. marcopoli populations was trapping using girdled host trees and purple plastic traps. We established nine trapping sites across the northern end of South Korea in riparian habitats. In all, 84 ash trees were partially girdled. Plastic food wrap was stapled above and below the girdle and coated with Pestick. A total of 20 purple plastic traps (also coated with Pestick) were placed near girdled trees. The traps were checked for A. marcopoli and other Agrilus species 2-3 times from mid June through mid August. In addition to trapping, we searched for adult beetles by sweeping and visual inspection of foliage and examined trees for signs of larval damage. Despite considerable effort, we did not find any adult beetles or evidence of larval damage on F. rhynchophylla.

We also sought out Agrilus specimens in museum collections and talked with beetle collectors. In doing so, we saw specimens of A. marcopoli collected from 1983-2003 from nine locations scattered throughout the country. Clearly, A. marcopoli is indigenous to South Korea, but it is apparently at very low population levels. Future research will address the causes of this apparent rarity, as well as the identity of hosts of A. marcopoli, which may include ash species other than F. rhynchophylla.

Foreign Exploration for Emerald Ash Borer and its Natural Enemies

Paul W. Schaefer, USDA-ARS, Beneficial Insects Introduction Research 501 S. Chapel St., Newark, Delaware 19713

Two transpacific trips permitted further foreign exploration for the emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), in Korea (June 21–July 3), Japan (July 4-11), and Mongolia (Aug. 5-27) in 2004. In no case, could I reconfirm the presence of EAB. In both Japan and Korea, the situation is much the same in that the most common species of Fraxinus (mongolica and chinensis, respectively). Oleaceae can be found quite readily, but careful examination of foliage for adult beetles and bark for both exit holes (D-shaped holes) or cracking, peeling bark, and sweepnetting failed to yield EAB. Fraxinus trees were usually found in riparian habitats, near streams, lakes, or other low, wet areas. I can now only postulate that perhaps EAB is more specific in its host range and may be more closely associated with some of the lesser known Fraxinus spp. (e.g., apertisquamifera, spaethiana, and lanuginosa in Japan or sieboldiana and chiisanensis in Korea) or even other tree taxa. One recent reported find was the presence of larvae and non-emerged adults of EAB under the bark of felled logs of Pterocarya rhoifolia (Juglandaceae) in Japan. Local entomological collections do contain enough material of EAB from these countries to suggest that EAB is widespread throughout Japan (found on all major islands) and Korea but populations remains at a low density. To illustrate how low: in Fukui Prefecture, Honshu, Japan, EAB is reported as “Red Listed” or endangered with only two collection locations recorded in that prefecture.

In Mongolia, the situation is somewhat different. Rather extensive travels (more than 4,000 km) via hired jeep and driver has failed to detect the presence of any Fraxinus spp. In a published listing of the vascular plants of Mongolia, no species under the Genus Fraxinus are listed (though a number of synonyms have yet to be checked). Furthermore, no EAB can be located in the National University collection, Ulaanbaatar, and neither A. planipennis nor its synonym, A. marcopoli, are given in a comprehensive listing of the known Agrilus spp. of Mongolia. In conclusion, the listing of EAB for Mongolia appears doubtful and just may be an error brought on by associating Mongolia with Inner Mongolia (a part of People’s Republic of China), where EAB is reportedly present.

Elsewhere in Russia, our investigations have likewise failed to reconfirm recent EAB in that country. A listings of 36 Agrilus spp. represented in the collections at the Siberian Zoo-logical Museum, Novosibirsk, does not list A. planipennis (=marcopoli). I am aware of only one known published Russian record: that of Alexeev (1979), who lists EAB from one location near the Russian-Korean border. This leaves China as the only other major area known to be part of the native range of EAB, and reports from China (found elsewhere in this compilation) indicate that populations are available there.

The Upside of the Emerald Ash Borer Catastrophe: A Feast for Woodpeckers

David Cappaert, Deborah McCullough, Department of Entomology, Michigan State University, 243 Natural Science Building, East Lansing, MI 48824 and Therese Poland, USDA Forest Service, NCRS, 1407 S. Harrison Rd., Rm. 220, East Lansing, MI 48823

Under the most favorable conditions, woodpeckers reduce larval EAB density as effectively as the best pesticides. Woodpeckers work over the entire core region for free and are always more popular than spray trucks.

In the course of trapping and pesticide trials, we have dissected multiple sections of several to several dozen trees at 24 sites in southeast Michigan. For each of these datasets, we recorded the density of successful emergence holes (exits) and of woodpecker attacks where those resulted in EAB mortality. The calculated woodpecker predation rate ranges from 9-95 percent (mean=44 percent). Preliminary analyses of these data considered two variables that might explain this variation. There was no correlation between site EAB density (R2=0.00; P=0.98) or any clear pattern of a density/predation relationship for trees within sites. Categorization of sites by habitat type (street tree, open park, forest) also revealed no relationship between habitat and predation rate (ANOVA, P=0.27), although the four sites with >65 percent predation were all in a forest setting.

Our datasets varied in many ways that we have not quantified (tree size, species, stand density, non-Fraxinus tree composition, etc.), so inferences at this stage are problematic. However, the magnitude of the predation rate at some sites suggests that woodpeckers may play an important role in EAB population dynamics. Furthermore, two features of avian predators make it likely that predation may be of increasing importance over time. First, vertebrates often exhibit a functional response as prey density increases. Thus, predation intensity may increase as EAB population increases. Second, any numerical response by woodpeckers responding to increased high-quality prey may require several years to manifest; and again, woodpecker predation may increase over time.

Because woodpeckers are at present the only EAB natural enemy documented to impose more than single-digit mortality and because woodpeckers are already-established native species, we encourage researchers to examine those features of habitat and woodpecker biology that interact to identify the role and effectiveness of woodpeckers as biocontrols.

Update on Emerald Ash Borer Natural Enemy Surveys in Michigan and China

Leah S. Bauer1, 2, Houping Liu2, Robert A. Haack1, 2, Ruitong Gao3, Tonghai Zhao3, Deborah L. Miller1, and Toby R. Petrice1

1 USDA Forest Service, North Central Research Station, 1407 S. Harrison Rd., East Lansing, MI 48823
2 Department of Entomology, Michigan State University, 243 Natural Science Building, East Lansing, MI 48824
3 Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Beijing 100091, China

We began research on natural enemies of emerald ash borer (EAB), Agrilus planipennis soon after its discovery in Michigan and Ontario in 2002. Regulatory agencies in the United States and Canada adopted a strategy of eradication for EAB in an effort to protect New World ash. Should eradication fail, however, conventional biological control will be needed to suppress populations of this invasive buprestid. To this end, we are studying the natural enemies of EAB in Michigan and in China.

In 2003, we reported results from our 2002-2003 study of EAB natural enemies in a woodlot in Livonia, Michigan. Briefly, the most prevalent natural enemies of immature EAB were five species of insect pathogenic fungi, causing mortality in approximately 2 percent of EAB.. Potential larval-pupal parasitoids of immature EAB causing mortality in approximately 0.05 percent of EAB were three braconids (Atanycolus sp., Heterospilus sp., and Spathius simillimus), one chalcid (Phasgonophora sulcata), and an exotic eupelmid (Balcha sp.). A eulophid wasp, Pediobius sp., parasitized approximately 0.3 percent of EAB eggs.

This year we expanded our study of EAB insect parasitoids by sampling infested trees throughout southeastern Michigan’s EAB infestation. In early spring, we cut 2-3 trees into logs from each of 14 study sites, stored the logs in a coldroom, and placed logs in cardboard emergence tubes; all insects emerging from the logs were counted each day. During July, we collected approximately 6,000 EAB eggs on small bark flakes from infested ash trees in each study site; the eggs were returned to the laboratory, placed in petri dishes sealed with parafilm, and held until hatch and parasitoid emergence was complete. Many of the hymenopterans are tentatively identified to family, although we have not yet sent out specimens for identification. Besides the same potential larval-pupal parasitoids found last year, we found an additional four unknown ichnuemonids, three unknown braconids, one unknown pteromalid, and two other unknown species. Pediobius sp. was the most prevalent egg parasitoid. Other hymenopterans emerging from egg/bark flakes include one encyrtid, two mymarids (Ooctonus and an unknown specie), two scelionids, two trichogrammids, and one unknown specie; their status as EAB egg parasitoids is unknown.

We surveyed ash for EAB infestation at sites in Heilongjiang, Jilin, Liaoning, Hebei, Tianjin, and Shandong Provinces in October-November 2003 to locate study sites for EAB natural enemy research. Plantings of Korean ash (F. rhynchophylla), Chinese ash (F. chinensis), Manchurian ash (F. mandchurican), green ash (F. pennsylvanica), and velvet ash (F. velutina) were dissected for EAB in urban and rural areas along roadsides and fields and in parks and woodlots. We also looked for EAB attacking Korean and Manchurian ash in natural forests in Heilongjiang, Jilin, and Lioaning Provinces. EAB was present in each Province except Shandong, where velvet ash, a neoarctic species, is extensively planted due to its tolerance of saline soils. We learned the neoarctic ash species planted in China require pest management for EAB due to high susceptibility, and early efforts to maintain white ash (F. americana) in China failed due to EAB (Liu 1966). In general, native ash species in China sustain greater EAB infestation when transplanted than when grown in a natural forest.

During our initial survey, we found Spathius sp. (Braconidae) parasitizing 1 to 50 percent of the EAB larvae at sites in Changchun (Jilin Province) and Guangang (Tianjin Province). We also discovered an unknown gregarious endoparasitoid of EAB larvae at sites in Benxi (Liaoning Province) and Changchun (Jilin Province) and with a parasitism rate of 2.7 to 50 percent. Mature larvae, pupae, and adults were collected and later identified as Tetrastichus sp. (Eulophidae).

Based on these results, we established our 2004 study sites in Jilin and Liaoning Provinces in cooperation with local foresters to determine the species composition and seasonal abundance of EAB natural enemies. Larval parasitoids were similar to those species found at these sites in 2003. In addition, egg parasitoids reared from EAB eggs were identified as the encyrtid Avetianella sp.

Liu, Yiguo. 1966. A Study on the Ash Buprestid Beetle, Agrilus sp., in Shenyang. Annual Report. Shenyang Municipal Institute of Gardening-Forestry Science, Shenyang, Liaoning Province, China

Initial Studies on the Laboratory Rearing of Emerald Ash Borer and Foreign Exploration for Natural Enemies

Juli Gould, John Tanner, Deborah Winograd, and Susan Lane, USDA-APHIS-PPQ, Otis Pest Survey, Detection, and Eradication Laboratory, Building 1398, W. Truck Road, Otis ANGB, MA 02542-5008

Rearing: We tested the possibility of rearing more than one pair of emerald ash borers (EAB) per cage to reduce the space required for rearing. We found, however, that EAB adults laid significantly fewer eggs per female when three or five pairs were reared together. We tested the effect of humidity on egg hatch by rearing eggs in sealed plastic boxes over saturated salt solutions. Percent hatch was highest in boxes with 75 percent humidity (compared with 25 percent and 50 percent), which was created with a solution of sodium chloride. We tested the development and survival of EAB larvae on five artificial diets:

  1. Commercial boll weevil diet with 50 percent water,
  2. Hylobius diet with ground ash bark instead of purple loosestrife,
  3. Melanie Keena’s asian longhorned beetle diet,
  4. Ogura longhorned beetle diet, and
  5. Cottonwood borer diet.

For each diet, we tested survival on diet packed into Petri dishes and crumbled into the dishes. We collected larvae from logs in Michigan at the end of July and the beginning of August. The larvae varied in size and were randomly placed on the 10 types of diet. Survival after one month was highest on the Hylobius diet (50 percent), followed by boll weevil (19 percent), Ogura (10 percent), MK2 (6 percent), and cottonwood borer (0 percent). On the Hylobius diet, 67 percent of the larvae were still alive after one month on the packed diet; only 35 percent were still alive on the crumbled diet. We also tested neonate larvae hatched in the laboratory. We have only tested eight individuals per diet type so far. We found, however, that after four weeks, 75 percent of the neonates reared on the packed Hylobius diet had molted to the second instar and 63 percent were still alive. No neonates survived on the crumbled Hylobius diet of on any of the other artificial diets.

Creating populations of EAB by moving tree wrap: The EAB is typically difficult to find in China because it has a low population density. This complicates exploration for effective natural enemies. We decided to explore the possibility of using trap plants infested with EAB to move into areas with low density EAB populations to attract natural enemies. We erected nine screen cages, placed oviposition substrates in them, and released adult EAB into the cages. We tested potted boles, logs, and potted trees (from a nursery). All three treatments proved to be heavy and cumbersome, so we decided to see whether the EAB would lay eggs on tree wrap wrapped around the trunks of the trees. The EAB readily laid eggs on the tree wrap on nursery trees but laid very few eggs on the potted boles and the potted logs. Eggs were laid on tree wrap wrapped around park and street trees in areas where there were many EAB adults flying. Prior to egg hatch, we moved the tree wrap to a site within the quarantine area but which did not yet have populations of EAB. Twenty-seven percent of the eggs on the tree wrap hatched, and 13 percent of the larvae produced galleries in the tree trunks. While the percentages on our first try were low, we feel that this validates the concept of creating populations of EAB larvae by moving tree wrap infested with EAB eggs.

Exploration for EAB Natural Enemies in China: In September 2004, Juli visited Dr. Yang Zhong-qi of the Chinese Academy of Forestry, who has been studying EAB and its natural enemies for several years. The first site visit was to Tianjin City, where there are plantings of Fraxinus velutina that are heavily attacked by EAB. There they found the braconid parasitoid Spathius parasitizing EAB larvae. This ecto-parasitoid has four generations per year and is well synchronized seasonally with the availability of its hosts, third and fourth instar EAB. The next field site was in Changchun, Jilin Province. Here they found a moderately heavy infestation of EAB on Fraxinus mandshurica. The most prevalent parasitoid at this site was a Eulophid in the genus Tetrastichus, but braconid pupae were also found. considerable time was spent looking for EAB in the Changbaishan Mountains near the Korean border. Most of the ash trees were very healthy and showed no signs of EAB attack. However, they did find four ash trees that had been girdled.

All four trees were heavily attacked by EAB, showing that this beetle is present in the area and will attack girdled trees. Dr. Yang has initiated host specificity testing. To date, he has tested eight species (mostly Lepidoptera) and has found no evidence of attack by Spathius. He plans to test Agrilus mali and Agrilus citri soon. Dr. Yang will ship Spathius to the U.S., where we will see if it attacks Agrilus anxius, Agrilus bilineatus, or other borers.

Taxonomic Status of Two Recently Discovered Natural Enemies of the Emerald Ash Borer in China

John S. Strazanac, Plant & Soil Sciences/Entomology, West Virginia University Morgantown, WV

Soon after the magnitude of the emerald ash borer (EAB) threat to North American ash was determined, a Sino-American program was developed to study the potential for biocontrol. During the natural enemies investigation in China, a species of Spathius Nees was discovered attacking EAB larvae by Yang Zhong-Qi of the Chinese Academy of Forestry in Beijing. With 300 species described world-wide and many undescribed species known to exist, a team of systematists led by Dr. Yang was formed to determine if this was a new species and facilitate publishing a description. Individuals involved include Paul M. Marsh (USA), Sergey A. Belokobylskij (Russia), C. van Achterberg (Netherlands), and John S. Strazanac (USA). Type material was examined in London, Washington, D.C., and Beijing. It was determined to be a new species, and a manuscript with its description and biological observations has been prepared for publication.

A second species was later found attacking EAB larvae by Dr. Yang’s team. It is a Tetrastichus species (Eulophidae), and it also appears to be new to science. A manuscript by Dr. Yang with its description has been reviewed by chalcidoid systematists at AgCanada in Ottawa (John T. Huber and Gary A. P. Gibson) and USDA-ARS Systematics Laboratory (Michael W. Gates and Michael E. Schauff) in Washington, D.C.