Regulatory Treatment

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.

Emerald Ash Borer Survival in Firewood

Robert A. Haack and Toby R. Petrice USDA Forest Service, North Central Research Station, 1407 S. Harrison Road, East Lansing, MI 48823

The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is native to Asia and was first discovered in Michigan and Ontario in 2002. As of October 2004, EAB was only found to breed in ash (Fraxinus) trees in North America. EAB is spreading naturally through adult flight as well as artificially through movement of infested ash nursery stock, logs, and firewood. EAB larvae feed and develop in the cambial region of host trees during summer and fall, and then overwinter in the outer sapwood or outer bark. Because EAB adults are present throughout the summer, larval development is not highly synchronized, and therefore, EAB life stages can be found beneath the bark of infested trees throughout the year. As is typical for Agrilus, early larval stages require living hosts. Therefore, if infested trees are cut early during larval development, the host tissues should dry and thus reduce Agrilus survival.

In 2002, we felled and stacked EAB-infested firewood in Michigan at various intervals from July to October. The firewood was either placed in direct sunlight or in shade. Exit holes were counted on the firewood during summer 2003. EAB were able to survive and emerge from all treatment combinations. However, survival was significantly lower on logs that had been cut during July and August vs. September and October. Similarly, EAB survival was greater on logs that had been stored in shade vs. direct sunlight. Therefore, cutting infested trees early during larval development and placing the logs in full sunlight will dramatically lower EAB survival, but apparently not kill all larvae.

A larger study was initiated in 2003, which tracked the following treatment parameters: month of felling, sun vs. shade storage, split vs. whole bolts, and tarped vs. not tarped. Exit holes were counted in late summer 2004. Again, EAB were able to survive and emerge from all treatment combinations. However, survival was significantly lower on logs cut early during larval development (July and August) and lower on split wood, especially for wood cut and split in July. Direct sunlight reduced EAB survival, especially for the earliest cut logs. Tarping either had no apparent effect on EAB survival or enhanced it. Perhaps the tarps that we used reflected a great deal of sunlight and thus temperatures beneath the tarps did not reach lethal levels.

Results from these studies indicate that even converting infested trees to firewood in July is not early enough to stop all EAB larvae from completing development and emerging as adults in the following year. We will monitor some of the firewood cut in 2003 to determine if any EAB adults emerge in 2005 (the second summer post-felling). If no adults emerge in 2005, this would indicate that firewood cut during summer of year 1 needs to be kept until at least the fall of year 2 before it could be safely moved.

Survival of Emerald Ash Borer in Chips

Deborah G. McCullough1,2, Therese M. Poland3, and David L. Cappaert1

1Dept. of Entomology and 2Dept. of Forestry, 243 Natural Science Building, Michigan State University, East Lansing, MI 48824
3USDA Forest Service, North Central Research Station, 220 Nisbet Building, East Lansing, MI 48824

The ability of emerald ash borer (EAB), Agrilus planipennis Fairmaire, to survive following chipping or grinding of infested ash trees remains a critical question for regulatory officials. In October 2002, we felled eight infested ash trees and sampled sections of the trunk and large branches from each tree to estimate EAB density. We estimated that at least 9,400 to 10,000 EAB, primarily in the prepupal stage, were present in the eight trees. Each tree was loaded into a grinder at a marshalling yard in southeast Michigan and processed; half of the wood of each tree passed through a screen with 1-inch diameter holes and the rest of the wood passed through a screen with 4-inch diameter holes. We intensively inspected samples of 1” and 4” chips for evidence of EAB survival. We also checked the relatively large chips in each pile to determine if they contained an EAB life stage. Material that passed through the 1” screen was ground to a fine, “chaff-like” consistency and we found no evidence that any EAB had survived the grinding process. In the pile of 4” chips, however, we found at least eight pieces of wood with intact prepupae.

We next investigated survival of EAB in chip piles over the winter. We prepared 45 sentinel chips by chiseling small sections of wood (approx. 6 x 3 x 1 cm) containing live overwintering prepupal or L4 larvae from infested ash logs and attaching a long section of nylon twine to each chip. In late October, we buried 22 sentinel chips 15 to 35 cm deep within the 1” chip pile (roughly 3.8 m3 volume) and 23 sentinel chips in the 4” chip pile (2.9 m3 volume). Temperature-recording dataloggers were used to monitor temperatures on and within each chip pile. Six infested ash logs (6 to 25 cm diam.), also cut in late October, were set next to the chip piles.

Sentinel chips were retrieved from the chip piles and examined on 29 April 2003. Live EAB were held to monitor survival to the adult stage. On 4 May 2003, the chip piles were moved into screen tents and ten sticky cards were suspended in each tent to capture any adult beetles that emerged from the piles. Logs that had been placed near the chip piles were dissected in early May to estimate overwintering survival.

Six of the EAB prepupae in the 45 sentinel chips (13.3 percent) survived the winter. In comparison, 32 of the 35 prepupae (91 percent) in the logs stacked adjacent to the chip piles survived the winter. Temperatures within the chip piles ranged from -18 to 39C (-2 to 102F) between October 2002 and May 2003. Temperatures in the chip piles tracked ambient temperatures closely, indicating that little heat was generated from decomposition in our relatively small chip piles. No EAB adults were captured in the screen tents.

To further evaluate the effects of temperature on EAB survival, we chiseled 56 bark sentinel chips and 56 wood sentinel chips from infested logs on 1-7 April 2004. Each chip contained a live EAB prepupae. We filled 28 plastic boxes, each 30 x 22 x 12 cm, with ash chips collected at a marshalling yard. We placed four bark sentinel chips or four wood sentinel chips in each box of ash chips and held all boxes in growth chambers at 25°C for 3 days to allow the EAB prepupae to acclimate.

On 10 April, two boxes with bark sentinel chips and two boxes with wood sentinel chips were assigned to a temperature and time treatment which included exposure to 40°C for 8, 24 or 48 hours or exposure to 60°C for 8, 24, or 48 hours. Four additional boxes (two with bark sentinel chips and two with wood sentinel chips) were left at a constant 25°C. After exposure to the designated temperature and time treatments, boxes were returned to 25°C and held until 15 June. Sentinel chips were checked daily from 1 May to 15 June and adult emergence or observations of dead EAB were recorded. All sentinel chips were dissected on June 15.

Five of the eight EAB prepupae in the bark sentinel chips and seven of the eight EAB in wood sentinel chips that were exposed to constant 25°C survived. When bark sentinel chips were held at 40°C, a total of four, three, and three of the original eight EAB survived exposure for 8, 24, and 48 hours, respectively. A total of seven, eight, and six EAB survived in the wood chips exposed to 40°C for 8, 24, and 48 hours, respectively. No EAB survived exposure to 60°C in any of the bark or wood chips, regardless of the duration of exposure. Further assessments of EAB survival at temperatures between 40 and 55°C are planned.