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In Italy, Aedes albopictus Skuse is currently recognized as the most dangerous mosquito, and as currently applied conventional control methods gave unsatisfactory results, we are developing alternative strategies such as the sterile insect technique. To find the optimal sterilizing dose, male pupae were exposed to different doses of gamma rays in the range 20-80 Gy, generated by a Cesium-137 source. The effects of male pupal age at irradiation and gamma ray dose on adult male emergence, sterility level, longevity, and mating capacity were evaluated, and dose-response curves of residual fertility were calculated. Radiation tests were also performed on female pupae to observe their reproductive capacity in case of accidental release. Results confirmed that the age at which the male pupa is irradiated is an important factor that affects the longevity of the adult, whereas the effect of age on the induced sterility level is less pronounced. When male pupae older than 30 h were irradiated, the longevity of the adults was not affected by doses up to 40 Gy. The 40-Gy dose appeared sufficient to induce high level of sterility (>99%) at any male pupal age for all the strains tested. The duration of coupling and the number of mated females per male appeared to be affected by the radiation received by male pupae only at doses higher than 40 Gy. The female pupae were more sensitive to radiation than male pupae, with strong reduction in fecundity and fertility at 20 Gy and complete suppression of oviposition at higher doses.

The mosquito Aedes albopictusi is a competent vector of harmful human pathogens, including viruses causing dengue and chikungunya. Cytoplasmic incompatibility (CI) induced by endosymbiotic Wolbachia can be used to produce functionally sterile males that can be released in the field as a suppression tool against this mosquito. Because the available sexing methods are not efficient enough to avoid unintentional release of a few transinfected females, we assessed the CI pattern in crosses between wPip Wolbachia-transinfected (ARwP) females and wild-type males of Ae. albopictus in this study. Quantitative polymerase chain reaction was used to monitor the titer of the Wolbachia strains that naturally infect Ae. albopictus, that is, wAlbA and wAlbB, in age-controlled males and females. Data were coupled with incompatibility level detected when the above-mentioned males were crossed with ARwP females. Wolbachia infection titer was also monitored in samples of wild caught males. Incompatibility level was positively correlated only with wAlbA density. Crosses between wild-type males having very low wAlbA density (<0.001 wAlbA/actin copy numbers) and ARwP females were partially fertile (CIcorr = 68.06 ± 6.20). Individuals with low wAlbA titer were frequently found among sampled wild males (30%–50% depending on the site and period). ARwP males can be as considered as a very promising tool for suppressing Ae. albopictus. However, crosses between wild males having low wAlbA density and ARwP females may be partially fertile. In the case of local establishment of the transinfected mosquito line, this occurrence may favor the replacement of the wild-type mosquitoes with the ARwP line, thus reducing the long-term efficacy of incompatible insect technique. Various alternative strategies have been discussed to prevent this risk and to exploit Wolbachia as a tool to control Ae. albopictus.

Wolbachia is a maternally inherited endosymbiont inducing various effects in insects and other invertebrate hosts that facilitate the invasion of naive host populations. One of the effects is a form of sterility known as cytoplasmic incompatibility (CI) through which females are effectively sterilized when they mate with males harboring a different Wolbachia strain. The repeated mass release of cytoplasmically incompatible males can be a tool to suppress insect populations. Here, we attempt to infect an Aedes albopictus (Skuse) (Diptera: Culicidae) strain, artificially deprived of the natural Wolbachia infection, with a new Wolbachia strain from Culex pipiens (L.) (Diptera: Culicidae). Further experiments were designed to study the effects of the new infection on Ae. albopictus fitness and evaluate key parameters that affect infection dynamics, including CI level and maternal inheritance. Using embryonic microinjection, the new Wolbachia strain was successfully established in Ae. albopictus. Crosses demonstrated a pattern of bidirectional CI between naturally infected and transinfected individuals. Specifically, egg hatch was essentially absent (i.e., CI was very high) in all crosses between the transinfected males and females with a different infection status. Furthermore, naturally infected Ae. albopictus males were incompatible with the transinfected females. Maternal inheritance was close to 100%. Moreover, the new infection did not affect immature and adult survivorship, but it significantly reduced female fecundity and egg hatch rate. The results are discussed in relation to the potential use of the new Ae. albopictus-Wolbachia symbiotic association as a suitable system for the study and development of CI-based strategies for suppressing populations of this important pest and disease vector.