Ohio State Researchers Conduct Key Studies on Destructive Ash Pest

October 20, 2003

WOOSTER, Ohio —- Ohio State University scientists are studying the flight behavior of the emerald ash borer (EAB) and the resistance of different species of ash to this exotic beetle, which has been found in four northwestern Ohio counties and has an appetite voracious enough to turn ash to dust in as little as one season. A native of China and other Asian countries, EAB was first confirmed in Ohio Feb. 28 in Whitehouse, Lucas County. Subsequent infestations have been detected between August and September in Hicksville (Defiance County), Paulding County, and Perrysburg (Wood County), all of which have been traced back to ash logs and nursery stock imported from Michigan in the past few years. The beetle, Agrilus planipennis, was discovered for the first time in the United States July 2002 near Detroit. It has also been found in Windsor, Ontario and most recently in Maryland. EAB infests both weakened and healthy ash threes during two to three years, causing them to gradually decline and eventually die. But heavy infestation can kill a tree in one year. “It’s kind of demoralizing to find these new infestations,” said Dan Herms, an entomologist with the Ohio Agricultural Research and Development Center (OARDC). “I fear that this is just a preview of things to come next year and the years after. Michigan authorities estimate that more than 5 million ash trees are dead or dying in the Detroit area.” A strong flier Herms said a key question that remains unanswered is just how far the beetle will fly after emergence from an infested ash tree —- which occurs in mid-May —- to lay eggs on other trees. “That determines how far out from an infested site an eradication effort will have to take place,” he explained. “Right now, it’s a completely open question. But what has become clear is that emerald ash borer is a very good, strong flier.” Fellow OARDC entomologist Robin Taylor agrees. He has teamed up with U.S. Forest Service and Canadian Forest Service researchers in East Lansing, Mich. and Sault Ste. Marie, Ontario to characterize EAB’s flight patterns and capabilities. Since July, the trio has been studying the airborne beetle with the help of flight mills —- devices used to measure the speed and other flight variables of insects in the laboratory. “Based on the preliminary data we have collected, we are fairly confident that they are capable of flying at a speed of at least 10 kilometers (approximately six miles) per hour in bursts of five to 10 minutes totaling at least one hour a day,” Taylor said. “So, if there are no ash trees to distract them, it’s very realistic to say that emerald ash borer might fly at least 10 kilometers in search of an ash tree.” Another factor that contributes to insect dispersal is how much time recently emerged adults dedicate to habitat exploration. EAB female adults can live as long as three months. During that time, they look for ash trees to prepare for mating and laying eggs, while males look for females that have found a tree. “There are indications that there is quite a large time lapse between emergence of the adult and first egg laying, at least several days and maybe as much as a couple of weeks,” Taylor explained. “So there’s a lot of time available to explore new habitats while they feed at this time. The implication here is that if these females have emerged and are flight-worthy, but their reproductive organs are not yet fully developed, then they have built into their life history strategy a period for habitat exploration. And that may include leaving this habitat and looking for another one.” Taylor said that the flight-mill studies seem to support indications that emerald ash borer is spreading more rapidly than other invasive pests, such as gypsy moth. “One would like to think that the spread is due to insects being carried by human agents,” he pointed out. “And certainly that’s the case with the infestation in Hicksville and several of the known infestations in Michigan. But the spread out from the port of Detroit and Windsor is not due entirely to human agents. This was caused by the species, by individuals flying form an ash tree to another.” Other concerns Flight behavior of emerald ash borer —- which two years ago didn’t even have a common name —- is only one of many knowledge gaps researchers are attempting to bridge. At a recent research review meeting sponsored by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) in Port Huron, Mich., Herms and fellow researchers highlighted the need to identify effective insecticides and determine the best method and proper timing to apply them. Also needed is the development of lures and traps to monitor the beetle’s distribution without having to cut down trees and remove their bark. Herms is involved in a research project aimed at answering another vital question: What species of ash, if any, are resistant to EAB? Herms will evaluate resistance and susceptibility of different species of ash to the pest, as well as the role of environmental stress on susceptibility. “This research relates more to living with infestation in the event (the beetle) becomes established,” Herms said. This information will help forestry, landscape and nursery professionals, as well and forest-health authorities, make more informed decisions when dealing with the wood-boring pest. Ash is one of the most common Ohio trees, present in every forest type of the state. According to the most recent forestry survey (1991), there are 3.8 billion ash trees in Ohio, covering 850,000 acres of the state’s 8 million acres of woodlands. Thus far, EAB has been found in all native species of ash present in the affected area —- white, green and black. Herms said that blue ash, which grows in the lime-rich soils of southwestern Ohio, is likely to be vulnerable to the beetle if it ever gets there. White ash is one of the primary commercial hardwoods in the United States, used, among other things, for flooring, cabinets and baseball bats. In Ohio, the market for ash is centered around the manufacturing of tool handles. The state has approximately 2.1 billion board feet of ash saw timber that is worth almost $1 billion at the sawmill. Ash is also an extremely popular landscape tree because of its tolerance of less-than-ideal planting conditions and its resistance to gypsy moth and other pests. Ohio nursery and landscaping industries would suffer if the emerald ash borer infestation gets out of control —- the Buckeye state is one of the top ash producers in the country, with 27,000 trees valued at $2.3 million a year. In Michigan, a major grower of ash for landscape purposes, EAB is expected to cost green industry firms within the infested area an estimated $8 million, according to a Michigan Nursery and Landscape Association survey. The pest is forcing growers to destroy all ash inventories, and landscapers have to replace trees to fulfill guarantees. OARDC is the research arm of Ohio State’s College of Food, Agricultural, and Environmental Sciences. Editor: Photographs for this article are available. Please contact Ken Chamberlain at (330) 263-3779 or chamberlain.1@osu.edu.

Author(s): 
Mauricio Espinoza
Source(s): 
Dan Herms