Aedes aegypti and Culex quinquefasciatus are mosquito vectors for several tropical diseases that represent a current public health problem. The ecological requirements for each species are different, however, both species show high biological adaptability, which promotes their coexistence in the same breeding sites. The purpose of this study was to assess the effect of larval association between Ae. aegypti and Cx. quinquefasciatus under different laboratory conditions of food supply and temperature, and under field simulated conditions like peridomestic containers. Our findings showed that under field simulated conditions there was no asymmetrical competition in mixed cultures with the different Cx. quinquefasciatus/Ae. aegypti ratios tested. However, under laboratory conditions in which different doses of food supply were evaluated, it was observed that competition between the two species takes place. Larval coexistence under food scarcity conditions (0.95 mg/larva) showed that Ae. aegypti had a greater adult emergence than Cx. quinquefasciatus and was capable of depriving Cx. quinquefasciatus of the food needed to complete metamorphosis. In an intermediate dose of food (1.9 mg/larva), the dry weight of Cx. quinquefasciatus adults decreased, and their larval development time increased when Cx. quinquefasciatus/Ae. aegypti ratio was low. Also, a temperature effect was assessed demonstrating that Cx. quinquefasciatus was more vulnerable to changes in temperature. We suggest that Ae. aegypti is more successful in exploiting microhabitats when food is scarce, due to its scrape active feeding habitats and fast larval development times. Therefore, in conditions of food paucity both species will compete, and Ae. aegypti larvae will prevail.

Lysinibacillus sphaericus (Bacillales: Planococcaceae) is a spore-forming bacillus used for the biological control of mosquitoes (Diptera: Culicidae) due to its larvicidal activity determined by various toxins and S-layer protein produced either during sporulation or by the vegetative cell. Aedes aegypti and Culex quinquefasciatus are the vectors of arboviruses that cause tropical diseases representing a current public health problem. Both species may coexist in the same larval development sites and are susceptible to the larvicidal activity of L. sphaericus. In this study, we compared the larvicidal effects of L. sphaericus 2362 (WHO Reference strain) and native strains III(3)7 and OT4b.25 against Cx. quinquefasciatus and Ae. aegypti in single-species and mixed-culture bioassays. Findings showed that L. sphaericus spores, vegetative cells and a combination thereof possessed high larvicidal activity against Cx. quinquefasciatus larvae, whereas only the formulation of L. sphaericus vegetative cells was effective against Ae. aegypti larvae. Similar results were obtained for field-collected larvae. We propose that a formulation of vegetative cells of L. sphaericus 2362 or III(3)7 could be a good alternative to chemical insecticides for the in situ control of mixed populations of Ae. aegypti and Cx. quinquefasciatus.

Over the past ten years, more than twenty fires have affected the El Noviciado estate located in Cerro Majuy, Colombia, leading to a loss of soil nutrients and infertility. Lysinibacillus sphaericus, a Gram-positive, mesophilic, and spore-forming bacterium, can be used in soil amendment in the replantation processes, given its ability to fix nitrogen, and nitrify, and solubilize phosphorus, increasing soil nutrients used for plant growth. In this study, we evaluated the soil-amendment potential of L. sphaericus by monitoring the nutrient content of a selected fragment of soil in the El Noviciado estate. For this purpose, we added a mixture of L. sphaericus OT4b.31, OT4b.49, CBAM5, III(3)7, and 2362 strains and determined the ammonium, nitrites, nitrates, phosphorus, and indole acetic acid concentrations in soil. Alnus acuminata sbsp. acuminata, a native model plant known for its restoration effect, was used for replantation. Results indicated that soils with added L. sphaericus presented significant differences in ammonium, nitrites, nitrates, phosphorus, and indole acetic acid concentrations when compared to control soils. Further, results showed no significant differences between soil that had been pre-inoculated in greenhouse and soil directly inoculated in field. We propose that L. sphaericus could be a good nutrient enhancer and plant growth promoter that can be used for the amendment of fire-impacted soils and replantation treatments.

The increased incidence of vector‐borne diseases and insecticide resistance in mosquitos constitute public health concerns in the tropics. Biological control is an effective alternative in the management of Aedes aegypti Linnaeus populations. Lysinibacillus sphaericus a bacterium proved to be harmless for non‐target organisms has shown promising entomopathogenic activity. In Colombia, the control of A. aegypti using L. sphaericus has not been contemplated as part of vector control programmes. To assess the susceptibility of three A. aegypti populations to a L. sphaericus formulation consisting of vegetative cells of 2362 and III(3)7 strains, simulated‐field bioassays were conducted in the municipalities of Ricaurte in Cundinamarca and Tauramena in Casanare, as well as in the municipal inspection of San Joaquin, Cundinamarca. Sixty larvae were deposited in a test device, which contained nine litres of chlorine‐free tap water and 100 ml of the bacterial formulation (109 CFU/ml). Six replicates were set‐up for treatment with bacteria and for the control. Larvae mortality was recorded at 24 and 48 hr. The three A. aegypti populations were susceptible to L. sphaericus formulation with a mortality rate higher than 90% at 48 hr. The formulation of L. sphaericus comprised of vegetative cells of 2362 and III(3)7 strains showed promising results that could guarantee the implementation of this formulation to control of A. aegypti populations.