Polymorphism in male genitalia of Aedes (Ochlerotatus) scapularis Rondani, 1848.

Morphology of male genitalia of culicids is generally species-specific and often used as a taxonomic marker. However, some characters of the male genitalia vary intraspecifically and are not taxonomically diagnostic. This might be the case of Aedes scapularis, a Neotropical culicid with vector competence for arboviruses and filarial worms. Males of this species may or not present a retrorse process (RP) in the genitalic claspette filaments, which led authors to suspect that this variance might be indicative of population divergence or incipient speciation process. This suspicion has not been investigated hitherto and it is not known if there are variable patterns of RPs. We hypothesized that the presence of the RP varies intraspecifically in Ae. scapularis and then we statistically evaluated the variability of this character in a single population. To this study the genitalia of 73 males of Ae. scapularis were prepared, and their RPs were meristically quantified and categorized according to the phenotypes observed. We noted that the presence or RPs is a polymorphic character because it varied inter and intra-individually. The presence of a single RP on each claspette filament was the predominant pattern (77%), but absent or multiple RPs in each filament were also found either in bilateral symmetry or asymmetry. Thus, we conclude that the presence of RPs owing to its high variability is not indicative of populational divergence or diagnostic of species complex within Ae. scapularis.

Immune transcript variations among Aedes aegypti populations with distinct susceptibility to dengue virus serotype 2.

The innate immune response of insects is one of the factors that may dictate their susceptibility to viral infection. Two immune signaling pathways, Toll and JAK-STAT, and the RNA interference (RNAi) pathway are involved in Aedes aegypti responses against dengue virus (DENV), however natural differences in these antiviral defenses among mosquito populations have not been studied. Here, two field Ae. aegypti populations from distinct ecological environments, one from Recife and the other from Petrolina (Brazil), and a laboratory strain were studied for their ability to replicate a primary isolate of dengue virus serotype 2 (DENV-2). Virus infectivity and replication were determined in insect tissues collected after viral exposure through reverse-transcription real time PCR (RT-PCR). The expression of a transcript representing these defense mechanisms (Toll, JAK-STAT and RNAi) in the midgut and fat body was studied with RT-PCR to evaluate variations in innate immune mechanisms possibly employed against DENV. Analyses of infection rates indicated that the field populations were more susceptible to DENV-2 infection than the lab strain. There were distinct expression patterns among mosquito populations, in both control and infected insects. Moreover, lower expression of immune molecules in DENV-2-infected insects compared to controls was observed in the two field populations. These results suggest that natural variations in vector competence against DENV may be partly due to differences in mosquito defense mechanisms, and that the down-regulation of immune transcripts after viral infection depends on the insect strain.