Effects of an optical brightener and an abrasive on iridescent virus infection and development of Aedes aegypti

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The insecticidal properties of certain entomopathogenic viruses can be greatly improved in mixtures with substances that affect the integrity of the insect peritrophic membrane, particularly optical brighteners. We aimed to determine the effect of an optical brightener, Blankophor BBH, and an abrasive compound, silicon carbide, alone and in mixtures, on the prevalence of patent and covert infection of Aedes aegypti (L.) (Diptera: Culicidae) by Invertebrate iridescent virus 6 (IIV-6) (Iridoviridae). The prevalence of patent infection by IIV-6 was <1.5% in all treatments involving virus. Contrary to predictions, there were significantly fewer patent infections in virus treatments involving Blankophor with or without silicon carbide compared with controls. Covert infection of adults detected by insect bioassay was between 6.7 and 12.2%, although no significant differences were observed between treatments. Exposure to IIV-6 alone or silicon carbide alone did not significantly increase larval mortality compared to the controls, whereas exposure to Blankophor alone, or in any combination with IIV-6 or silicon carbide, clearly increased larval mortality. These effects did not carry-over to the pupal stage. Adult females emerged =1.5 days later than males. Compared to control insects, female development rate was extended by 11.4 and 12.6% in the treatments involving IIV-6 alone and silicon carbide alone, respectively. The sex ratio at adult emergence did not differ significantly between control insects and those of other treatments. These results support the hypothesis that the gut is unlikely to represent the principal point of infection of mosquito larvae by iridescent viruses. eng