Double Trouble May Loom Ahead for Deer Tick

Nature’s 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 USDA’s 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 tick’s cuticle, or outer covering. The nematodes kill by unleashing bacteria that liquefy the tick’s tissues. But they don’t 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. That’s because the nymphs’ small size allows them to feed undetected long enough to transmit the bacterium that causes Lyme.

The ARS scientists discovered one of the tick-infecting fungi. They’ve 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 fungi’s 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 Patricia Allen, USDA-ARS Parasite Biology and Epidimiology Laboratory, Beltsville, Md., phone (301) 504-8770 (Hill), (301) 504-8772 (Allen), dhill@ggpl.arsusda.gov and PALLen@ggpl.arsusda.gov.