Biology of Agrilus subcinctus

Research Issue

As of spring 2008, emerald ash borer (eab, Agrilus planipennis) is currently established in Illinois, Indiana, Maryland, Michigan, Ohio, Pennsylvania, Ontario, and West Virginia.  eab has already killed millions of ash trees in North America, drastically changing tree composition in many forested areas.  Trap-tree surveys are being conducted in many states to monitor for eab.  This procedure often involves debarking ash trees and looking for eab life stages, especially larvae.  In eastern North America there is one native species of Agrilus that attacks ash: Agrilus subcinctus.  Little is known about this native ash-infested agrilid, except that A. subcinctus adults are brown in color, only about half as long as eab adults, and tend to lay eggs on twigs and branches.  Given that all Agrilus larvae have a similar body shape, there is concern that trees infested with young A. subcinctus larvae could be confused with eab larvae.  In addition, it is not known how the increase in eab-induced mortality of ash trees will affect population dynamics of A. subcinctus.  We developed studies to document the life cycle, habits, and natural enemies of this native agrilid. 

 Our Research

To monitor A. subcinctus adult flight, we placed yellow sticky cards on ash foliage of live trees where we knew A. subcinctus was present at field sites in Michigan.  We also collected and dissected ash twigs throughout the growing season to monitor A. subcinctus egg and larval development and any observed mortality.  We examined the larvae dissected from twigs under a microscope to determine their stage of development (instar).  As well as to identify any characters that could be used to distinguish between larvae of A. subcinctus and eab.

Expected Outcomes

Our results will aid in developing survey methods for eab that will avoid confusion with A. subcinctus.  Our work will also help in determining the best characters to use when distinguishing between larvae of these two Agrilus species.  In addition, these studies will increase our knowledge of how eab influences the population dynamics of native insects that are associated with ash trees.

Research Results

We have not yet published any papers on Agrilus subcinctus.  However, our results to date indicate that A. subcinctus adults were very attractive to yellow sticky cards when placed near foliage of ash trees.  Adult were most abundant between late May and early July in southern Michigan.  Adults fed on ash foliage and laid eggs primarily on recently dead ash twigs.  Larvae developed in the phloem of the dead twigs throughout the summer and fall and overwintered as larvae or pupae.  Because A. subcinctus develops mostly on dead ash twigs, it appears that there is little spatial overlap between these two agrilids on a given tree.  Therefore, by concentrating debarking efforts of trap trees to the main trunk and base of major branches it appears that there is little chance of confusion with A. subcinctus.

Populations of A. subcinctus increased primarily in areas with an abundance of recently dead ash trees.  Given that eab is killing millions of ash trees, it should be expected that A. subcinctus populations will peak 1 to 2 years behind peak eab populations.  Although not documented yet, we expect A. subcinctus populations to collapse after the ash trees have been dead two or more years given that the phloem tissue will no longer be suitable for A. subcinctus development.

Research Participants

Principal Investigators

• Robert Haack, US Forest Service- Northern Research Station Research Entomologist
• Toby Petrice, US Forest Service- Northern Research Station Entomologist

Principal Partners

• Jonathan Lelito, Michigan State University, Forestry Faculty
• John Strazanac, West Virginia University, Research Associate