Double Trouble May Loom Ahead for Deer Tick
By Jan Suszkiw
July 22, 1997
Natures own fungi and
microscopic worms could help stop black-legged ticks in parks and backyards
before they try to latch onto a human host.
The ticks can transmit Lyme disease. But scientists at USDAs
Agricultural Research Service have found
that certain fungi and wormlike nematodes have potential to thin populations of
the ticks, Ixodes scapularis. White-tailed deer often carry the ticks
into residential areas.
The new approach could offer a natural alternative to outdoor spraying of
tick-killing chemicals called acaricides. One nematode recruit,
Steinernema, wriggles into natural body cavities of engorged female
ticks. Another, Heterohabditis, uses a single sharp tooth to gnaw
through the ticks cuticle, or outer covering. The nematodes kill by
unleashing bacteria that liquefy the ticks tissues. But they dont
harm people or animals--only ticks and specific insects.
The fungi secrete enzymes that eat away the soft cuticles of immature tick
larvae and nymphs. Then the fungi kill the ticks by growing inside them.
Ixodes nymphs are the most likely tick stage to be the culprit when
people contract Lyme disease. Thats because the nymphs small size
allows them to feed undetected long enough to transmit the bacterium that
The ARS scientists discovered one of the tick-infecting fungi. Theyve
tentatively identified it as a new species of Gliocladium. In lab tests,
it killed 60 percent of tick nymphs in two weeks. Another fungus,
Metarrhizium anisopliae, killed 100 percent in one week.
But the nematodes are the quickest, killing engorged adult female ticks
within 24 hours. The researchers plan to follow up their lab findings with
small-scale field studies. These will also help show where, when and how best
to apply the nematodes and fungi to tick infested areas--and which
concentrations work best. Toxicity studies, such as tests to make sure the
fungis enzymes are safe for humans and deer, would be needed before this
approach to tick control could be approved for use.
Scientific contact: Dolores Hill and
Parasite Biology and
Epidimiology Laboratory, Beltsville, Md., phone (301) 504-8770 (Hill),
(301) 504-8772 (Allen), email@example.com andPALLen@ggpl.arsusda.gov.