Addressing the Emerald Ash Borer Problem
By Dan Sparks
Bloomington Ecological Services Field Office
In late 2012, Dan Sparks, environmental contaminants biologist in the Bloomington Ecological Service Field Office, provided information to the City of Bloomington, Ind., responding to a news story that suggested the use of some pesticides on lawns and trees -- on private and city property -- to control emerald ash borers. Here are excerpts from Dan’s response:
When one treats a tree (or a lawn for that matter) with the insecticide neonicotinoid (Imidacloprid or Dinotefuran), it is transported throughout the plant (roots, twigs, stems and leaves) and any insect sucking, chewing or eating portions of that plant could likely get a lethal dose of insecticide. This is great if you want effective treatment coverage, but it also has great potential for non-target species impacts. In this type of treatment, trees are treated at 10 times the level typically found in turf or garden formulations (40g vs. 4g/L). Soil soaking treatments will be taken up by more than just the tree and will be in unintended plants that beneficial insects visit.
Recent laboratory experiments have strengthened the connections between imidacloprid and adverse impacts to honeybees. We concede that imidacloprid has not yet been implicated in woodpecker deaths; however, we would encourage people to consider whether or not lethality is the only outcome that might be worth considering in this regard. The odds of finding sick or poisoned birds at known wildlife mortality incident sites are always very low for a variety of reasons, not the least of which is that a sick animal will typically hide if it can. And unfortunately, all species of insectivorous birds, from chickadees to blue jays, could be at risk from insecticide-treated trees because they are treated to be "protected" throughout the tree.
Residues of the insecticides emamectin benzoate and imidacloprid remain in leaves and stems long after leaf fall and many more species of insects are using ash trees besides the emerald ash borer. This could be especially problematic for all the species of aquatic invertebrates that turn leaves into a valuable source of energy for aquatic life in streams.
However, our biggest concern with neonicotinoid insecticides is for insectivorous bats. Research on lethal and sublethal impacts to bats from insecticides is lacking because most bat lifestyles are not easily maintained in captivity. Mice and rat toxicological studies do not adequately address the amazing physiology of the typical bat. For instance, metabolism of a small bat (average weight 7 grams) runs at maximum in the summer months while rearing young and nearly shuts completely off during several months of hibernation. These small bats can have lifespans well in excess of 20 years. The slightest metabolic alteration in these animals could alter hibernation ability and significantly alter hibernation behavior. As with the white-nose syndrome (caused by a recently introduced exotic fungus), anything that alters a bat's ability to hibernate properly can turm a sublethal irritation into widespread lethality.
The endangered Indiana bat (Myotis sodalis), is a very common species here in Monroe County, Indiana, and given the unknown potential for sublethal effects, we would not want to encourage such high dose uses of insecticides. Many of the insects that Indiana bats feed on would be reduced or would carry residues that could accumulate in bat tissues. So, despite inferences in the article, it should be made very clear that a treated ash tree can no longer be considered good for wildlife habitat. An untreated dead ash tree does however provide excellent wildlife habitat for a few years and we would advocate letting dead trees stand where they are not a safety hazard.
The long term likelihood of success against well-established exotic species is questionable. Unfortunately, ash trees are not the first North American trees under attack from foreign invaders: American elm trees (Dutch elm disease, a fungus) and American chestnut (chestnut blight, also a fungus) are other examples. The battle to control the Asian long-homed beetle (which can harm maple, birch, elm, poplar and willow trees) still goes on with some success. The loss of magnificent trees in our neighborhoods and forests is a shame, however, poisons are not an appropriate option for success against the emerald ash borer.