Carl Herzog's Comments about Spraying for West Nile Virus
Carl Herzog (
State Wildlife Grants Biologist, New York Department of Environmental Conservation) responded to a query by Peter Youngbaer asking about the possible impact from spraying for West Nile Virus. Youngbaer noted that he had read the New York plan for West Nile Virus, which came about after 9 deaths from encephalitis in Manhattan. The spraying plan, a last resort strategy, is focused on Manhattan and the adjacent counties, not farther upstate.

Carl Herzog's response to Youngbaer's message is below

May 3, 2008

Pesticides could possibly be related to this problem in at least two different ways. One is accumulation of contaminants in the bats' bodies. Several folks (our own lab and several others) have looked into this, examining affected bats looking for all of the usual suspects (pesticides, pcb's, heavy metals, etc.) So far nothing significant has shown up, although work continues on this front. West Nile spraying, in particular, mainly involves chemical types (pyrethroids) that seem to have very little possibility to have negative effects on mammals. If that is a problem then it will have to be some new type of effect that hasn't been seen yet in toxicity testing that has been done.

Perhaps you are hinting at the second route, though, that being the potential for reduced insect prey availability for the bats. In some ways this is a more difficult question to answer. If it's part of the problem we won't be able to tell until this late summer / fall, because that's when the bats put on the fat they need for winter. We (and many other agencies) plan to track the condition of bats as they prepare to enter hibernation to see if they are putting on the normal amount of fat.

Sampling insect availability directly seems, at first, to be a more direct approach but it will be a lot harder than it sounds, for several reasons, among them:

1)The affected bats eat a wide variety of insects (moths, caddisflies, small beetles, etc.), so sampling would have to look at a lot of different insect types. By extension, of course, any problem caused by spraying would probably have to be spread across a wide range of insect types.

2) Methods of quantitative sampling for insects are not well developed.

3) Even if we know there are a lot of insects out there it's difficult to tell if they are actually available to the bats as food.

Currently we are thinking the insect availability question seems less likely than other possible causes for a bunch of reasons. One of the most compelling is that we have two hibernacula in the lower Hudson Valley about 1 mile apart. One has been devastated and the other is affected much less. We have good information that the bats in those sites spend the summer in the same places. If it was insect availability on their summer range then the problem should affect both sites equally. Add to that the wide spread nature of the bat problem and its sudden onset. One of our pesticide experts assures me with high degree of certainty that there has been no corresponding increase in insect spraying of any type - for West Nile or otherwise - in NY that could explain this.

All that being said, until we have an explanation we are considering all possibilities.

Thanks for your interest. The caving community has been a wonderful partner in this investigation and we would be a lot further behind in our understanding of this issue without their help. Feel free to pass that on to anyone you see fit.
Feel free to use what I wrote. We are completely in favor of sharing information with the caving community and others, although please understand that everybody working on this problem has been a bit overwhelmed. If we fail to communicate outside of our own circles it is not because we don't want to share, it's because we simply can't do it all. We have heard hints that some of the cavers would like to be kept in the loop better. The extent to which you can help address that with your efforts would be welcome by us at DEC and, I'm confident to say, by the other agencies and researchers working on the issue. I'll do what I can to assist you.

The only secret here is the one mother nature is keeping from us about what is causing this problem.

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This page last updated or verified on May 4, 2008