Effects of culture medium and formulation on the larvicidal activity of the mosquito pathogen Lagenidium giganteum (Oomycetes: Lagenidiales) against Aedes aegypti.

In this work, we examined the production of infective zoospores of Lagenidium giganteum in four culture media, and the larvicidal activity of the cultures was determined against Aedes aegypti larvae, as well as the effect of polymer encapsulation. Medium containing sunflower seed extract showed the greatest production of zoospores, 5.92×10(6) zoospores/ml after six days of fermentation at 25±2°C and 150rpm shaking. This culture tested against A. aegypti 1st stage larvae caused different mortality rates at 24, 48 and 72h posttreatment. The LC(50) obtained was 43.9, 41.1 and 42.9µl of total culture/ml, at 24, 48 and 72h posttreatment respectively, while the culture grown in medium with soybean meal showed 3-5 times higher LC(50) values. Finally, the total culture including mycelium, zoospores and presporangia formulated with 2.5% pectin showed significantly higher mortality rates, around 100% more than the unformulated culture, whose values were from 40 to 1% at 3, 6, 9, and 12d posttreatment in the bioassays carried out in the laboratory to determine residual activity.

Predatory capacity and prey selectivity of nymphs of the dragonfly Pantala hymenaea.

Predatory capacity and prey selectivity of nymphs of the dragonfly Pantala hymenaea (Odonata: Libellulidae) were evaluated on larvae of the mosquito Culex quinquefasciatus (Diptera: Culicidae) and larvae of the midge Chironomus plumosus (Diptera: Chironomidae) as prey. With functional response methodology, 7 larval densities were exposed to predator individuals in a glass jar under laboratory conditions. The study was performed in 2 experiments. The 1st was a test system with each prey species alone. The 2nd tested a mixture of both prey species in a 1:1 ratio. Prey selectivity and prey capacity were significantly greater on midge larvae than on mosquito larvae.

Evaluation of polymer-based granular formulations of Bacillus thuringiensis israelensis against larval Aedes aegypti in the laboratory.

A strategy to increase residual activity of Bacillus thuringiensis serovar. israelensis (Bti) extract through slow-release formulations and protection from solar radiation was studied. The median lethal concentration (LC50) and 90% lethal concentration (LC90) levels of laboratory-reared early 4th-stage larval Aedes aegypti after exposure to Bti extract were determined. Formulations with 4 polymers and 1 solar protectant were prepared, and their shelf lives were evaluated for year-long storage at 20-35 degrees C and 50-80% relative humidity. Also, the effect of ultraviolet light on unformulated (extract) and formulated Bti larvicidal activity persistence was determined. Laboratory bioassays were conducted with larval Ae. aegypti introduced into treated and control containers at 1, 2, 7, 14, 21, 28, 35, and 42 days after treatment, and larval mortalities were checked 24 h after introduction. Probit analysis of Bti extract showed LC50 and LC90 values of 0.016 and 0.051 mg/liter, respectively. The polymer-based Bti formulations showed no significant loss of insecticidal activity after 8 months of storage. Ultraviolet irradiation reduced activity of unformulated Bti extract after different exposure times, up to 40-46%, whereas Bti formulated with gelatin or acacia gum showed lower variation in larvicidal activity than formulations with sodium alginate and paraffin for protecting the activity of Bti toxin. Residual activity against 4th-stage Ae. aegypti in the laboratory for the formulation containing acacia gum at 10% (w/w) was 80% mortality at 14 days after treatment, whereas the Bti formulation containing gelatin (10%, w/w) caused 65% mortality. In addition, Bti formulations made with paraffin at 5% (w/w) sustained up to 60% mortality for 21 days. Unformulated Bti showed only 2.6% mortality, and a commercial preparation maintained 37% mortality, both at 14 days after treatment.