The Tomato Magazine
August 2007
By Sharon Durham
A bacterium discovered by Agricultural Research Service (ARS) scientists
that is toxic to Colorado potato beetle also has been found to be toxic
in varying degrees to gypsy moth, small hive beetle
and tobacco hornworm. Microbiologist Phyllis Martin, molecular biologist
Dawn Gundersen-Rindal, and entomologist Michael Blackburn at the ARS Insect
Biocontrol Laboratory, Beltsville, Md., and chemist Jeffrey Buyer at the
Sustainable Agricultural Systems Laboratory in Beltsville found and described
the new bacterial species, Chromobacterium suttsuga, now called Chromobacterium
subtsugae sp. nov.
The group then found that the bacterium displayed toxicity to Colorado
potato beetle. The findings are published in the May issue of the International
Journal of Systematic and Evolutionary Microbiology. Soil rich in decomposed
hemlock leaves, collected from the Catoctin Mountain region in central
Maryland, was the source of the new species. The team isolated the microbe
by suspending samples of forest soil in water and then plating it directly
on growth medium that doesn’t contain glucose. Bacteria in the samples
initially formed small and cream-colored colonies,
which gradually turned to light-to-dark violet from the center of the
colony outward.
Fifty percent of small hive beetles died within fi ve days when fed a
pollenbased diet containing the bacteria, and the survivors weighed only
10 percent as much as small hive beetles that weren’t exposed to
the bacteria. Tobacco hornworm and gypsy moth weren’t killed by the
bacteria, but their weights were drastically reduced due to feeding inhibition.
Weights of tobacco hornworms that were fed
the bacteria-laced diet were drastically reduced—24 milligrams for
bacteria-treated insects compared to 119 milligrams for insects that didn’t
eat the bacteria. Gypsy moths eating the bacteria weighed 40 percent less
than gypsy moths that weren’t fed the bacteria.
Martin and her colleagues will work to isolate the toxin from the bacteria. Insects usually develop resistance to toxic substances, so it is important to identify new toxins. In previous studies conducted by Martin, Chromobacterium subtsugae sp. nov. was also found to be toxic, in varying degrees, to western corn rootworm, southern corn rootworm and diamondback moth.
© 2007 Columbia Publishing
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