Introduction of Aedes albopictus into a La Crosse virus--enzootic site in Illinois.

In late summer and fall 1997, Aedes albopictus mosquitoes were found in Peoria, Illinois, a long recognized focus of La Crosse virus transmission. Larvae were found in tires and other artificial containers, biting adults were recovered, and eggs were collected in oviposition traps within a 25-ha area. One chipmunk trapped < 0.25 km from the infested area tested positive for neutralizing antibodies against La Crosse virus.

Isolation of La Crosse, Cache Valley, and Potosi viruses from Aedes mosquitoes (Diptera: Culicidae) collected at used-tire sites in Illinois during 1994-1995.

Prospective studies were conducted at used-tire sites in Illinois during 1994-1995 in an effort to isolate arboviruses from mosquitoes, particularly Aedes albopictus (Skuse) and Aedes triseriatus (Say). Three isolates of Potosi virus were obtained from Ae. albopictus collected at a waste tire site in Jasper County during 1994 and 1995. Also, a single isolate of Cache Valley virus was obtained from Ae. albopictus collected at the Jasper County site during 1995. These are the first records of arbovirus isolations from Ae. albopictus in Illinois and the first isolate of Cache Valley virus from this mosquito species. During 1994, two isolates of La Crosse virus were made from Ae. triseriatus collected at a used-tire site in Peoria County in proximity to the residence of a human La Crosse encephalitis case. This is the first evidence in Illinois that indicates increased risk to humans living near used-tire sites, which may serve as foci for production of Ae. triseriatus, the vector of La Crosse virus. Tire removal and improved environmental sanitation at such sites may greatly reduce the abundance of vector mosquitoes, and, therefore, the risk of arbovirus transmission.

Gonotrophic cycle duration, population age structure, and onset of sugar feeding and insemination of Aedes triseriatus (Diptera: Culicidae).

During two successive summers, laboratory-reared Aedes triseriatus (Say) were marked and released into two woodlots in central Ohio. Several cohorts of two groups of mosquitoes were marked and released: blood-engorged, 10-12-d-old females and unfed, 2-d-old females. The parity of marked mosquitoes captured during daily biting collections were used to estimate the duration of the gonotrophic cycle. The parity rate of unmarked mosquitoes, in conjunction with the cycle estimate, yielded data on age structure and daily survival. Information on the onset of insemination and sugar feeding also was obtained. The mean and median duration of the first gonotrophic cycle, based on females released after blood feeding and later finding the collector, was 12 d. Unfed females required a median of about 8 d to feed on sugar, mate, and locate the collector, but required 22-32 d to sugar feed, mate, find a natural host, become parous, and then find the collector. The median duration of the natural gonotrophic cycle was estimated to take 14 d during warm (22 degrees C) weather. The parity rate of the natural population remained between 29 and 51% during the last 3 mo of each summer. The high proportion parous indicated that daily survival rate of unmarked females was above 0.9. Marked females moved between woodlots for distances as far as 400 m and were more likely to emigrate from the small woodlot than the large one.