Saturday, January 17, 2009

Giant water scavenger beetle, and Are Pesticides Affecting Monarch Butterfly as well as Amphibians in the Sierra Nevada?

Today, I was preparing a portion of the backyard for planting vegetables this spring. There are several old concrete stepping stones which I was removing for the soon-to-be-garden. Six of the stones had the usual subterranean invertebrate fauna under them - termites, earthworms, Argentine ants. But underneath one of them was an adult giant water scavenger beetle (Hydrophilus triangularis). When I picked up the stone, it began crawling around, but did not fly away. I suspect it flew into the backyard during some night time rainstorms a few weeks ago. Giant water scavenger beetles are very common in the Sacramento Valley, and it is not uncommon to find them at lights, especially mercury vapor lights, during the winter rainy season. In southern California they are rare, in twenty five years of collecting there, I found only one dead one at Point Mugu Naval Air Station.

This week I attended the California/Nevada Amphibian Population task Force's 2009 Annual Meeting at the Bodega Bay Marine Laboratory. There were several talks about the decline of amphibians in the Sierra Nevada. It appears that pesticides, especially in areas downwind of the Central Valley where the application of chemical agents on crops exceed 500,000 kilograms a year, have resulted in the reduction or loss of these animals. Some of the biologists at the meeting had found that these chemicals are toxic to tadpoles of certain Sierra Nevadan frog species at parts per billion levels (note: one part per billion is equal to about one teaspoon of water in a standard residential swimming pool!). It struck me that these pesticides also could be impacting the the monarch butterfly. In an earlier post, I speculated that ranchette and urban development in the foothills had caused the tremendous decline of this insect at their coastal California wintering colonies. The number of butterflies at sites such as the famous Washington Park in Pacific Grove, Natural Bridges State Beach in Santa Cruz, and Ellwood in Santa Barbara, are dramatically smaller than ten or twenty years ago (all anecdotal - no hard numbers). But pesticides, such as chlorpyrifos, malathion, diazinon, and their toxic breakdown products could be the culprit in the semingly steady decline of the number of monarch butterflies at the wintering colonies in the Golden State. Perhaps pesticides blown in to the Sierra Nevada and foothills from the Central Valley are killing the eggs, larvae, and pupae of Danaus plexippus, just as these chemicals are killing amphibians.
Photo courtesy of U.S. Fish an Wildlife Service


beetlesinthebush said...

Interesting thought - I would guess it has more to do with land use changes that reduce the amount of milkweed available for larval feeding. Pesticide drift tends to have mostly a localized (and to the valley itself, devastating) effect.

By the way, I notice the link to my blog in the sidebar points to the old address - the "new" Beetles In The Bush can be found here.


Paul Cherubini said...
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