Overwintering and establishment of Aedes albopictus (Diptera: Culicidae) in an urban La Crosse virus enzootic site in Illinois.

In 1997, Aedes albopictus (Skuse) was discovered in Peoria, IL, a known focus of La Crosse (LAC) virus transmission. This accidental introduction provided an opportunity to determine whether Ae. albopictus would reemerge in the spring or summer and, if successful overwintering occurred, to follow changes in the geographic range of Ae. albopictus, and to compare its distribution to that of the local treehole mosquito and LAC vector Aedes triseriatus (Say). In 1998, 25 oviposition traps were placed in and around the area of the initial finding of Ae. albopictus, with adult collections by aspirators and larval collections from water-holding containers used to identify areas of additional activity. Ae. albopictus successfully survived the mild 1997-1998 El Niño winter, and expanded its range during 1998. By September 1998, Ae. albopictus oviposited in all 25 traps, including traps near and in wooded sites. Intensity of oviposition activity (number of eggs per positive trap) ranged from 20-40, lower than the range for Ae. triseriatus, which was as high as 175 eggs per infested trap in mid-August. Prevalence of Ae. albopictus increased through September, where as the prevalence of Ae. triseriatus declined starting in mid-July. Although direct competition between the two mosquito species cannot be inferred based on this surveillance effort, a gradual range expansion was observed, and Ae. albopictus eggs were collected in traps where initially only Ae. triseriatus oviposition activity was detected.

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.

Binaural release from masking for a speech sound in infants, preschoolers, and adults.

Binaural masked thresholds for a speech sound [ba] were estimated under two interaural phase conditions (NoSo and NoS pi) in three age groups (infants, preschool children, and adults). A computer-based head-turn with visual reinforcement procedure was used to test the infants. Preschoolers were tested using a modified play audiometry task, and adults were tested conventionally with the same apparatus as used with the infants. Differences in masked threshold as a function of both age and interaural phase condition, and differences in the binaural masking level difference (BMLD) with age, were found when the masker intensity was the same for each group. However, testing of adults with maskers of reduced intensity to compensate for hearing threshold differences relative to the two younger groups (a possible confounding variable in the estimate of the BMLD) eliminated the difference in BMLD between adults and preschoolers. The difference between infants and adults remained statistically significant, suggesting a possible developmental change in binaural hearing early in life. The relevance of developmental change in binaural hearing with respect to both infant auditory processing and the methods we use to assess it are discussed.