I received the 1995 McColgan Grant-in-Aid to study a fungus infecting larval Aedes canadensis in a vernal pool in Bristol, Rhode Island. Dr. Alan Gettman, Rhode Island Office of Mosquito Abatement, identified the fungus as Erynia (=Entomophthora) aquatica and this identification was confirmed by Dr. Theodore Andreadis of the Connecticut Agricultural Experiment Station.

On May 8th, 1995 numerous dead mosquito pupae covered with fungal hyphae were found in a vernal pool approximately 100 ft2 and six inches deep in a several-acre wood lot in Bristol, Rhode Island. On April 4, 1996 I returned to the pool and collected Aedes canadensis larvae (mostly third instars) but found no evidence of infection. Larvae were collected and held at approximately 65o for several weeks but pupated without sign of infection. Additional larvae were collected on April 28th but no infected larvae or pupae were found.

On May 19th, infected larvae and pupae were found, as well as some pupal skins indicating some mosquitoes had successfully emerged as adults. Additional samples were collected May 22nd and delivered to Dr. Gettman for identification. The site required treatment at that time to prevent further adult emergence. Unlike the previous year, when close to 100% of the pupae observed were infected, the infection rate this year was about 50%.

Erynia aquatica is an Entomophthorales fungus, and is the only species of the genus known to infect the immature aquatic stages of mosquitoes. It was first discovered infecting Aedes canadensis and Culiseta moristans larvae in woodland pools in Hartford County, Connecticut from late May to early June (Anderson & Ringo 1969). It has since been recovered in early May from Aedes stimulans in woodland pools near the village of Cambridge, New York (Molloy & Wraight 1982) and from Aedes cantator on May 21, 1981 in a shallow salt meadow pool in Milford, Connecticut (Andreadis & Magnarelli 1983).

Donald Steinkraus and John Kramer (1989) collected Aedes fitchii larvae infected with E. aquatica from a semi-permanent woodland pool in Tompkins County, New York. They used infected pupae to successfully transmit the disease to emerging adult Aedes aegypti, on which resting spores of the fungus developed.

Erynia aquatica has characteristics which make it attractive as a microbial agent: it is capable of causing epizootics, has been found in both freshwater and brackish water mosquitoes and has a resting spore stage that may survive well in storage. Operating against it is the fact that it has only been found in cooler, springtime waters. One thought is that infected pupae may be removed from the original infestation site and placed in other, nearby pools. A fungus that kills in the pupal stage works against its own spread. This fungus deserves additional study.

Thanks to Alan Gettman and Theodore Andreadis for their identification work, references and to Sean Healy for his slides of the fungus.

REFERENCES CITED

Anderson, John F. and Sandra L. Ringo. 1969. Entomophthora aquatica sp. n. infecting larvae and pupae of floodwater mosquitoes. J. Invert. Pathol. 13:: 386-393.

Andreadis, Theodore G., and Louis A. Magnarelli. 1983. Erynia aquatica in a salt-marsh mosquito, Aedes cantator. J. Invert. Pathol. 42:277-279.

Molloy, Daniel and Stephen P. Wraight. 1982. rediscovery of Erynia aquatica (Entomophthoraceae) in snowpool mosquitoes. J. Invert. Pathol. 40:142-145.

Steinkraus, Donald C. and John P. Kramer. 1989. Development of resting spores of Erynia aquatica (Zygomycetes: Entomophthoraceae) in Aedes aegypti (Diptera: Culicidae). Environ. Entomol. 18(6): 1147-1152.

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