EFFECT OF TEMPERATURE ON THE DEVELOPMENT OF CULISETA-MELANURA (DIPTERA, CULICIDAE) AND ITS IMPACT ON THE AMPLIFICATION OF EASTERN EQUINE ENCEPHALOMYELITIS VIRUS IN BIRDS

Eastern equine encephalomyelitis virus (EEE) is perpetuated in a maint enance cycle that involves Culiseta melanura (Coquillett) as the enzoo tic vector and passerine birds as the amplifying hosts. Amplification of virus in any given year requires an influx of nulliparous Cs. melan ura in the presence of susceptible avian hosts. We conducted laborator y experiments at constant temperatures from 10 to 34 degrees C to deve lop thermal heat summation models to predict emergence in nature. Embr yonic development progresses slowly at 10 degrees C, and the time to e closion decreased significantly as temperatures increased to 28 degree s C. High temperatures were lethal and eggs failed to hatch at 32 degr ees C. The thermal minimum (t(0)) for embryonic development was 9.38 d egrees C, and 38.46 degrees-days (DD) were required for egg hatch. The time for larval development decreased with increasing temperatures. C s. melanure larvae develop in subterranean habitats (crypts) where wat er temperatures remain below 20 degrees C throughout the summer. Under controlled conditions, egg hatch to emergence took 8 mo at 10 degrees C, 3 mo at 16 degrees C, and 1 mo at 22 degrees C. The thermal minimu m for larval development (t(0)) was 8.5 degrees C, and 467.29 DD were required from eclosion to adult emergence. Our findings indicate that Cs. melanura is well suited to develop in cold water crypts where the larvae are collected most frequently. The mosquito appears to be bivol tine in the northeast with an overwintering generation of larvae that emerges as a spring brood of adults and a summer generation of larvae that emerges in fall. Higher than normal water temperatures hasten dev elopment of the summer generation and increase the probability for amp lification of EEE by bringing large numbers of nulliparous mosquitoes into contact with recrudescing virus for subsequent transfer to the gr owing population of susceptible juveniles. Water temperatures in the c rypts also may regulate the northern limit for virus amplification eac h year.