ABSTRACT:
Eastern equine encephalitis virus (EEEV) is an arbovirus that is maintained in a natural cycle between its enzootic vector Culiseta melanura (Coquillett) and birds. Epidemics of this RNA virus are uncommon, but they can produce devastating pathologies in humans and equines. In addition, outbreaks of EEEV often lead to widespread public concern with serious economic ramifications (Morris 1988).
I studied an area of EEEV natural history that may lead to increased knowledge for the prevention and control of outbreaks. I determined seasonal patterns in age distribution of Cs. melanura larvae by observing the annual population dynamics in an area of persistent enzootic cycling.
The study site was part of Belleplain State Forest in Dennisville, Cape May Co., New Jersey, and is a collection site for the EEEV surveillance program in New Jersey. I sampled 20 crypts that were randomly selected from a larger pool of marked crypts. Once a month between January 1996 and June 1997 a 2L sample was taken from each crypt using a modified bilge pump. Water temperature and level was recorded for each sample. The head capsules of Cs. melanura were measured to determine instar for each larva.
The water temperature ranged from an
average of 0.1 oC (± 0.1 oC SE) in February 1996 to 23.9oC (± 0.2 oC SE) in July 1996. I collected 2,190 Cs. melanura larvae. Flooded crypts were found to produce significantly less Cs. melanura larvae (P<0.05) than non-flooded crypts. Age structure of the larvae varied seasonally. In the winter 76.5% (±4.3 SE) of the larvae were fourth instar and in the spring 40.3% (± 9.0 SE) of the larvae were first instar larvae. During the fall, the percentage of first and second instar larvae decreased and the percentage of third and fourth instar larvae increased.
Fall and spring are important for Cs. melanura populations.
The adult population in September must produce enough larvae to
ensure survival through the winter. In spring after emergence,
adults dominate the population. A low Cs. melanura population
in the summer may result if these adults fail to reproduce. This
in turn may result in fewer adults to transmit EEEV.
Morris C. D. 1988. Eastern equine encephalomyelitis. p 1-19. In
T. P. Monath ed. Arboviruses epidemiology and ecology Vol. III.
CRC Press, Inc., Boca Raton, FL. 256 pp.
ACKNOWLEDGMENTS
I would like to thank everyone who helped me, especially Don Caccamise, Wayne Crans, Farida Mahmood and Jim McNelly. I would also like to thank the Cape May County Mosquito Extermination Commission and the Rutgers Research and Development Center. The funding for my research has been provided by the New Jersey Water Resources Research Institute and scholarships from the Northeast Mosquito Control Association, the New Jersey Mosquito Control Association, Inc. and the New Jersey Agricultural Experiment Station.