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Putative epidemic/epizootic eastern equine encephalomyelitis virus (EEE) vector populations were compared at 15 recent (1982-90) human and horse case sites in Bristol and Plymouth counties in southeastern Massachusetts. Carbon dioxide-baited American Biophysics Corporation light traps were used for trapping adult mosquitoes to estimate biting risk in these foci of known transmission. Population data suggest that Coquillettidia perturbans, Aedes canadensis, and Culex salinarius are more likely vectors of EEE in Massachusetts than Aedes vexans, Anopheles punctipennis, and Anopheles quadrimaculatus.

To determine which of 11 trapping methods best sampled populations of 6 potential epidemic vectors of eastern equine encephalomyelitis (EEE) virus, we compared New Jersey (NJ) light trap, CDC light trap, CDC with octenol, CDC with CO2, CDC with CO2 plus octenol, American Biophysics light trap with flickering light (AB flicker), AB steady light, AB flicker with octenol, AB flicker with CO2, AB flicker with CO2 plus octenol, and 3 resting boxes. There was no significant difference between CDC and AB light traps (P > 0.05). The addition of octenol increased trap catch with both CDC and AB light traps; however, this increase was not statistically significant (P > 0.05). Both brands supplemented with CO2 collected more Aedes canadensis, Coquillettidia perturbans, Culex salinarius, and Anopheles spp. than did unbaited light traps (P < 0.05). The addition of octenol to CO2 increased collections of Anopheles spp. and decreased collections of Aedes spp. and Cq. perturbans at some sites, but these changes were not statistically significant (P > 0.05). Resting boxes were best for sampling bloodfed or parous Anopheles spp. The NJ, AB flicker, and AB steady light traps were not effective for sampling potential vectors of EEE virus.

To estimate human exposure to potential vectors of eastern equine encephalomyelitis (EEE) virus, we compared collections of putative EEE virus vectors from human biting collections with collections from CDC, AB (American Biophysics), and New Jersey light traps and resting boxes in enzootic/epidemic foci of EEE virus in southeastern Massachusetts. Human biting collections caught significantly more host-seeking females than resting boxes or unbaited light traps (P < 0.05). Regression analysis of human biting collections to AB traps supplemented with CO2 could predict 60-70% of the actual human biting risk by Aedes and Coquillettidia perturbans. The AB traps supplemented with CO2 and octenol could predict 65% of Anopheles biting risk. No single sampling method was accurate for predicting human biting risk by Culex salinarius, and no method could predict human biting risk by all potential vectors surveyed.

We tested susceptibility to per os infection and potential salivary transmission for eastern equine encephalomyelitis (EEE) virus in Aedes canadensis (Theobald), Aedes vexans (Meigen), Anopheles quadrimaculatus (Say), Anopheles punctipennis (Say), Coquillettidia perturbans (Walker), and Culex salinarius (Coquillett). Culiseta melanura (Coquillett), the documented enzootic vector of EEE virus, was our control. Based on these estimates of laboratory vector competence and other behavioral and ecological components of vectorial capacity, we ranked these 6 species from the most to least probable epidemic vectors: Cx. salinarius, An. quadrimaculatus, Ae. canadensis, Cq. perturbans, Ae. vexans, and An. punctipennis.

The numbers of blacklegged tick, Ixodes scapularis Say, per hectare that engorged as larvae and nymphs on white-footed mice, Peromyscus leucopus (Rafinesque), were estimated at 3 sites in coastal Massachusetts. Estimates of numbers of engorged ticks dropping per day from trapped mice were multiplied by mark-recapture estimates of the density (numbers per hectare) of white-footed mice to estimate numbers of ticks engorging on mice per hectare. In 1991, estimates of seasonal totals per hectare of I. scapularis nymphs completing blood meals on P.leucopus ranged from 825 +/- 68 at Nonamesset to 6,654 +/- 770 at Menemsha. This absolute sampling method (the drop-off method) was compared with drag sampling for nymphal ticks. Per hectare estimation of engorgement rates overcomes a shortcoming associated with drag sampling because site-to-site comparisons can be made even where vegetation structure differs markedly among sites. The drop-off method may be used to quantify the contribution of any host to the engorged tick population, provided sufficient such hosts can be collected on a weekly basis.

Three isolates of Jamestown Canyon virus and one isolate of snowshoe hare virus (California serogroup) were obtained from adult Aedes females collected in western Massachusetts in 1982. Jamestown Canyon virus was isolated from Aedes abserratus/punctor once, and from Aedes intrudens twice. Snowshoe hare virus was isolated from Aedes stimulans group mosquitoes. La Crosse encephalitis (LAC) virus was not isolated from 1,552 adult Aedes triseriatus, nor from 22,557 Aedes triseriatus larvae. However, sera from 1/178 eastern chipmunks, 5/31 gray squirrels, and 8/144 white-tailed deer had neutralizing antibody to LAC virus. No sentinel rabbits placed at sites yielding virus isolates seroconverted to CAL viruses in either year.

The insect growth regulator, fenoxycarb, when applied at 0.06 kg AI/ha (0.05 lb AI/acre) as 1% sand granules was highly effective (97.5% corrected mortality) against Aedes communis, Ae. stimulans and Ae. canadensis in snowmelt pools in Massachusetts, and 100% effective against Ae. abserratus in an insectary study. No larval mortality owing to fenoxycarb treatment was observed, and most mortality occurred in the pupal stage as opposed to aborted adult emergence.