BackgroundThe insect gut harbors a variety of microorganisms that probably exceed the number of cells in insects themselves. These microorganisms can live and multiply in the insect, contributing to digestion, nutrition, and development of their host.Recent studies have shown that midgut bacteria appear to strengthen the mosquito's immune system and indirectly enhance protection from invading pathogens. Nevertheless, the physiological significance of these bacteria for mosquitoes has not been established to date. In this study, oral administration of antibiotics was employed in order to examine the contribution of gut bacteria to blood digestion and fecundity in Aedes aegypti.ResultsThe antibiotics carbenicillin, tetracycline, spectinomycin, gentamycin and kanamycin, were individually offered to female mosquitoes. Treatment of female mosquitoes with antibiotics affected the lysis of red blood cells (RBCs), retarded the digestion of blood proteins and reduced egg production. In addition, antibiotics did not affect the survival of mosquitoes. Mosquito fertility was restored in the second gonotrophic cycle after suspension of the antibiotic treatment, showing that the negative effects of antibiotics in blood digestion and egg production in the first gonotrophic cycle were reversible.ConclusionsThe reduction of bacteria affected RBC lysis, subsequently retarded protein digestion, deprived mosquito from essential nutrients and, finally, oocyte maturation was affected, resulting in the production of fewer viable eggs. These results indicate that Ae. aegypti and its midgut bacteria work in synergism to digest a blood meal.Our findings open new possibilities to investigate Ae. aegypti-associated bacteria as targets for mosquito control strategies.

In this work we show that the lumen of Aedes aegypti midgut is highly colonized by bacteria that were identified by culture-dependent and culture-independent methods. rDNA sequences obtained were compared with those from GenBank and the main bacterial genera identified were: Serratia, Klebsiella, Asaia, Bacillus, Enterococcus, Enterobacter,Kluyvera and Pantoea. All genera were identified in midgut except Enterobacter that was observed only in eggs. Asaia and Pantoea were also identified in eggs and ovary, respectively. In addition two yeast genera were observed in A. aegypti: Pichia isolated from midgut and Candida identified in midgut and ovary. The genus Serratia was dominant in all isolation assays representing 54.5% of the total of microorganisms. Thirty-nine and 24 bacterial clones were successfully obtained from midguts 24 and 48h after blood feeding (ABF), respectively. The majority of clones obtained were from Serratia sp. (48.7% and 50% for 24 and 48h ABF, respectively). Light microscopy showed that bacteria were located preferentially in the posterior midgut, around the blood meal and associated with peritrophic matrix. Scanning electron microscopy images showed a high number of bacteria in midgut during blood digestion and the peak of bacterial enumeration was reached 48h ABF, stage in which lumen was almost totally occupied by bacteria that were also interacting with epithelial microvilli. Our results show the dynamics of microbial colonization and their distribution in midgut during blood digestion.

We show for the first time that the ventral diverticulum of the mosquito gut (impermeable sugar storage organ) harbors microorganisms. The gut diverticulum from newly emerged and non-fedAedes aegypti (Diptera: Culicidae, Aedini) is the main urban vector for the human diseases yellow fever and dengue fever (Nasci & Miller 1996). The vector control, mainly by insecticide application and elimination of oviposition sites, has been used as the best solution to decrease the diseases incidence. Explore new strategies for blocking the insect transmitted diseases such as dengue fever is urgent in Tropical countries (Sperança & Capurro 2007). Microorganisms associated with the insect may have an important role for human infectious diseases epidemiology. Once a key role bacterium is discovered, it may be modified in order to affect the pathogen development and, consequently, the disease transmission (Azambuja et al. 2005, Riehle & Jacobs-Lorena 2005.The alimentary canal of the mosquito is composed by the foregut, midgut and hindgut. The foregut is involved primarily with ingestion, conduction and storage of food (Romoser 1996). In the alimentary canal of the mosquito three diverticula arise near the posterior end of the esophagus: two from the dorso-lateral and one from the ventral wall of the gut, all surrounded by a thin impermeable cuticle. The ventral diverticulum (VD), or crop, is large and may extend into the abdomen (Dapples & Lea 1974). Usually all three diverticula are filled with air bubbles and are used as food reservoirs (Thompson 1905, Consoli & Lourenço-de-Oliveira 1994. The sugar meal, such as floral nectar, is stored in the diverticula and passes slowly to the midgut, where it is digested (Thompson 1905).Microorganisms play important and often essential roles in the growth and development of many insect species. Despite the importance of these microbial associations with insects there are relatively few studies that elucidate their components and their roles in the interactions. Insects that rely on nutritionally poor diets tend to possess bacterial endosymbionts. Aphids, for example, which subsist solely on plant sap, harbor Buchnera spp., believed to provide amino acids and vitamins to their hosts (Douglas 1989). Blood is known to be severely deficient in essential B vitamins and some amino acids. Bloodsucking arthropods such as ticks, lice, bedbugs, reduviid bugs, and tsetse flies usually harbor symbiotic microorganisms (Buchner 1965). Symbiotic relationships have already been reported for blood feeding insects and some are very well established, as in the case of Rhodnius prolixus that maintains an association with the actinomycete bacteria Rhodococcus rhodnii (Dasch et al. 1984); and tsetse flies genus Glossina, which harbor three distinct symbiotic microorganisms: Wigglesworthia glossinidia, Sodalis glossinidius (commensal), and the parasitic microbe Wolbachia pipientis (Aksoy et al. 1997, Chen et al. 1999.Many key questions about bacteria within the mosquito's midgut remain largely unanswered, and ob...

In the first part of this study, four isolates of the fungus Beauveria bassiana (Bals.) Vuillemin (LPP1, LPP2, CG05 and CG24) and one isolate of Metarhizium anisopliae (Metsch.) Sorokin (CG46) were tested against adult foragers of Atta sexdens rubropilosa. Ants were allowed to walk on filter paper discs, inside Petri dishes, previously impregnated with 1 ml of a conidia suspension (2 x 10(7) conidia ml(-1)), maintained at 80% RH and 26 degrees C for 24 h and subsequently, transferred to sterile Petri dishes, maintained at 23 degrees C, 80% RH, 24 h dark. The mean values of LT(50) for LPP2, LPP1, CG46, CG24 and CG05 were 3.5, 3.7, 3.8, 4.2 and 4.4 days, respectively. Control insects for all tests in this study showed less than 10% mortality. Experiments were carried out to test the toxicity of imidacloprid (IMI) to A. sexdens rubropilosa. Mortality was evaluated 10 days following a 24 h exposure to the insecticide. Percent mortality caused by 500, 200, 100 and 10 ppm IMI was 77.8, 56.7, 45.5 and 5.5 respectively. Insects treated with 10 ppm IMI were observed to have reduced locomotor activity 24 h after exposure to the insecticide. The LC(50) of IMI was 154.3 ppm. Subsequent tests were carried out to evaluate the combination of a sub-lethal dose of IMI (10 ppm) and infection by CG24 (1 x 10(7) conidia ml(-1)). Mortality due to fungal infection alone was 43.3%. Mortality of insects treated with IMI followed by exposure to the fungus was 64.3%. These results indicate that IMI significantly increases the susceptibility of ants to infection by B. bassiana CG24.

Chemical analyses of the hemagglutinating fraction from Scorpaena plumieri venom revealed that it contains five components (Sp-CL 1-5) with similar chromatographic elution profiles (35-38% of acetonitrile), molecular masses (16,800-17,000 Da) and N-terminal sequences, suggesting that they are isoforms of the same protein. The amino acid sequence of Sp-CL4 was determined and shown to have homology with fish C-type lectins. These data demonstrate for the first time the presence of C-type isolectins in a scorpionfish venom.