Epizootiology of eastern equine encephalomyelitis virus in upstate New York, USA. II. Population dynamics and vector potential of adult Culiseta melanura (Diptera: Culicidae) in relation to distance from breeding site.

Abstract

The behavior of Culiseta melanura was studied at sites in, near and away from an inland endemic focus of eastern equine encephalomyelitis virus (EEEV) between 1976 and 1979 using light-CO2 traps and resting shelters. During 3 seasons, nonblooded females, blooded/gravid females and males increased and decreased synchronously at the swamp center, the swamp perimeter and at a village 2 km away from the swamp. Both sexes were more abundant at the swamp center during May and June but more abundant at the perimeter thereafter. Males were much fewer at the village and, although there were more females in and near the swamp, a significantly greater proportion of females at the village was parous and/or blooded/gravid. Light-CO2 traps caught fewer nonblooded females in the swamp than did shelters, but more than shelters at the village. Only shelters were effective in collecting blooded/gravid females and males. Population density, parity and dispersion patterns were correlated to rainfall patterns during July-to-September periods. Parity data indicated that Cs. melanura remains in the swamp when populations are low or during adverse weather conditions but, during periods of high populations or warm, wet weather, older females, and presumably older males, spread at least as far as the village. Of 2009 blooded females tested, 99.7% had fed on birds, 83% of the total on passerines. Nonavian feedings occurred simultaneously with high Cs. melanura populations and irrespective of distance from the breeding swamp. During the EEEV transmission seasons Cs. melanura populations at the perimeter had the greatest vector potential (as herein defined), but as late-season populations increased, vector potential was relatively greater more distant from the swamp. The vector potential for this inland area of New York strengthens the hypothesis advanced for coastal foci that Cs. melanura , though an unlikely epidemic vector, serves as the enzootic vector of EEEV and is responsible for carrying the virus from the swamp to domestic and peridomestic birds.