Isolation and identification of α-proteobacteria from Culex pipiens (Diptera Culicidae) larvae

A survey of drainage ditches in suburban areas of La Plata, Buenos Aires province, Argentina for pathogens of Culex pipiens larvae was conducted from 2003 to 2006. C. pipiens larvae of opaque, white color were found in several of those field collections. When the white larvae were dissected and observed by phase-contrast microscopy in wet-mount preparations, the presence of bacteria, located in the hemocoel, was recorded. Laboratory experiments were performed to elucidate the pathway for transmission of this pathogen. Although approaches involving traditional culturing had failed to reveal the identity of the new microorganism present, molecular techniques to identify the pathogen in the studies reported here were successful. The partial sequence of the 16S-rRNA gene constitutes a powerful tool for the detection of new isolates from the hemocoele of C. pipiens larvae. These bacteria were characterized as belonging to the genus Novispirillum. In spite of the genus's wide distribution in different aquatic environments, information related to the parasitic relationship of Novispirillum spp. to aquatic insects is scarce, and this association has not been described in other mosquito species. This report constitutes the first documentation of Novispirillum spp. as a pathogen for mosquito larvae.

Highlights► Bacteria in the hemocoel of Culex pipiens larvae (opaque white color) was recorded. ► This bacteria was characterized as belonging to Novispirillum genus by 16S-rRNA gene sequence. ► The infection of larvae occurs when the bacteria enter through cuticle injuries. ► This is the first record of Novispirillum spp. as a pathogen for mosquito larvae.