Biological control refers to the use of predators, parasitoids, or pathogens to reduce populations of a particular pest. The degree to which predators and parasitoids naturally regulate the abundance of medically important ticks is unknown. Flocks of helmeted guineafowl have been reported to reduce populations of blacklegged ticks in penned areas. However, since most predators, including guineafowl, feed on a variety of species, it is unlikely that impact on tick populations would be significant. Further, the establishment of free-ranging flocks of guineafowl in residential communities would be undesirable, if not impractical.
Surveys of several islands off the New England coast identified a wasp, Ixodiphagus hookeri, parasitizing up to 40% of blacklegged tick nymphs. Despite this high rate of parasitism, tick populations on these islands remain high. Subsequent studies have shown the abundance of this wasp and the rate of parasitism to be relatively low in mainland environments. Therefore, the use of this parasitoid wasp in an integrated tick control program will be limited.
Certain nematodes are parasites of ticks. However, the nematodes studied to date are only effective against engorged female blacklegged ticks that have already fed on and possibly infected a host, and their inability to survive at colder temperatures makes them of limited value as a viable biological control agent against ticks.
Offering greater promise as an effective biological control agent are pathogenic fungi. Although commercially available formulations of specific fungi have been successful in controlling blacklegged ticks in limited trials, additional research is needed.
Blacklegged tick parasitized by fungus. Photo courtesy of Kirby C. Stafford III, CAES.
Engorged female blacklegged tick parasitized by nematodes. Photo courtesy of Elyes Zhioua.
Ixodiphagus hookeri. Photo courtesy of Kirby C. Stafford III, CAES.