Rapid evolution of bunyaviruses may occur by RNA segment reassortment between closely related viruses. Reassortment between viruses occurs in dually infected mosquitoes when two different viruses are simultaneously ingested or when the second virus is ingested within 2 days of the first virus. By 3 days after oral infection, interference to superinfection occurs, thus limiting the potential for evolution. Aedes triseriatus mosquitoes can also be transovarially infected (TIM) with LaCrosse (LAC) virus. In these studies, the potential for oral superinfection of TIM mosquitoes was assessed. Approximately 20 % of mosquitoes TIM with either a temperature-sensitive LAC virus or wild-type (wt) LAC virus became superinfected by ingesting blood meals containing wt LAC or snowshoe hare (SSH) viruses. LAC virus TIM mosquitoes superinfected with SSH virus were detected by blot hybridization or RT-PCR. Viruses from these mosquitoes were plaque purified and genotyped using RT-PCR. Reassortant genomes were detected in 2n3 % of the viruses genotyped, and 4n0 % of the genomes tested were diploid for one genome segment.

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At an enzootic focus of Dirofilaria immitis in coastal North Carolina, mosquito populations were sampled June-September 1985 and on several occasions during August-October 1986 and June-August 1987, to identify local vectors and to determine relative abundance and D. immitis infection rates. Predominant species collected were Anopheles bradleyi King (66.6%), Culex salinarius Coquillett (15.9%), Aedes taeniorhynchus (Wiedemann) (8.2%), and Aedes sollicitans (Walker) (4.9%). Population abundance varied within and among seasons. D. immitis infection was found in An. bradleyi (1.2%), Ae. taeniorhynchus (0.9%), and Ae. sollicitans (0.9%). Of infected An. bradleyi, 88% were collected June-2 July, whereas the highest number of infected Ae. taeniorhynchus and Ae. sollicitans were found during mid-July 1985. Ae. sollicitans and Ae. taeniorhynchus were the only infected species found during 1986 and 1987. However, based on overall relative abundance and infective rate, An. bradleyi appeared to be the primary vector of D. immitis in the study area.

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Numbers and the distribution of third-stage larvae (L3) were investigated in Aedes sollicitans (Walker) and Aedes taeniorhynchus (Wiedemann) female mosquitoes fed Dirofilaria immitis (Leidy) infectious-blood with densities of microfilariae (mf) ranging from approximately 7,100-43,400 mf/ml. At each microfilarial density, a maximum of 63-66 infective larvae were recovered from an Ae. sollicitans alive on day 15 after infection. In comparison with Ae. taeniorhynchus, Ae. sollicitans averaged greater numbers of L3 and from 1.4 to 2.4 times more L3 in the head and labium per infected female. The trend was for greater numbers of L3 to be found in the labium than in the head of Ae. sollicitans, but there were no significant differences between numbers of L3 recovered from these sites in differentially infected females. However, numbers of L3 recovered from the head versus the labium of differentially infected Ae. taeniorhynchus varied significantly with the infectious blood microfilarial density. At the two lowest and highest microfilarial densities, greater numbers of L3 were recovered from the head and labium, respectively. Variations among species in the female body size, blood meal size, and retention of L3 may be factors responsible for differences observed between the total numbers and percentage distribution of D. immitis L3 recovered from the simultaneous blood-fed Ae. sollicitans and Ae. taeniorhynchus.