Biomédica 2018;38:95-105 Bti-CECIF larvicidal tablets for Aedes aegypti doi: https://doi.org/10.7705/biomedica.v38i0.3940 ORIGINAL ARTICLE Novel larvicide tablets of Bacillus thuringiensis var. israelensis: Assessment of larvicidal effect on Aedes aegypti (Diptera: Culicidae) in Colombia Wilber Gómez-Vargas¹, Kelly Valencia-Jiménez², Guillermo Correa-Londoño³, Faiber Jaramillo-Yepes² 1 Instituto Colombiano de Medicina Tropical-Universidad CES, Sabaneta, Colombia 2 Centro de la Ciencia y la Investigación Farmacéutica, Sabaneta, Colombia 3 Facultad de Ciencias Agrarias, Universidad Nacional de Colombia, Medellín, Colombia Introduction: Aedes (Stegomyia) aegypti is the vector for dengue, chikungunya, and Zika arboviruses. Bti-CECIF is a bioinsecticide designed and developed in the form of a solid tablet for the control of this vector. It contains Bacillus thuringiensis var. israelensis (Bti) serotype H-14. Objective: To evaluate under semi-field and field conditions the efficacy and residual activity of Bti- CECIF tablets on Aedes aegypti larvae in two Colombian municipalities. Materials and methods: We tested under semi-field conditions in plastic tanks (Rotoplast™) four different Bti doses (0.13, 0.40, 0.66 and 0.93 mg/L) in the municipality of Apartadó, department of Antioquia, to assess Bti-CECIF efficacy (percentage of reduction of larval density) and the residual activity in water tanks containing A. aegypti third-instar larvae. The efficacy and residuality of the most lethal dose were subsequently evaluated under field conditions in cement tanks in the municipality of San Carlos, department of Córdoba. Results: Under semi-field conditions, the highest tested dose exhibited the greatest residual activity (15 days) after which larval mortality was 80%. Under field conditions, the highest tested Bti-CECIF doses showed 100% mortality and exhibited a residual activity of seven days in 90% of the tanks. Conclusion: Bti-CECIF tablets effectively controlled A. aegypti larvae under field conditions for up to seven days post-treatment. Key words: Aedes; Bacillus thuringiensis; disease vectors; dengue; chikungunya virus; Zika virus; Colombia. doi: https://doi.org/10.7705/biomedica.v38i0.3940 Nuevas tabletas larvicidas de Bacillus thuringiensis var. israelensis: evaluación del efecto larvicida sobre Aedes aegypti (Diptera: Culicidae) en Colombia Introducción. Aedes (Stegomyia) aegypti es el vector de los arbovirus del dengue, el chikungunya y el Zika. Para el control de este vector, se diseñó y desarrolló un bioinsecticida en presentación de tableta sólida, el Bti-CECIF, que contiene Bacillus thuringiensis var. israelensis (Bti) de serotipo H-14. Objetivo. Evaluar en condiciones de ‘semicampo’ y de campo, la eficacia y la actividad residual de las tabletas de Bti-CECIF en larvas de A. aegypti en dos municipios colombianos. Materiales y métodos. En el municipio de Apartadó, departamento de Antioquia, se probaron bajo condiciones de ‘semicampo’ en tanques de plástico de 250 l (Rotoplast™) cuatro dosis diferentes de Bti (0,13, 0,40, 0,66 y 0,93 mg/l) para evaluar la eficacia del Bti-CECIF (porcentaje de reducción de la densidad larvaria) y la actividad residual en tanques de agua que contenían larvas de tercer estadio de A. aegypti. La eficacia y el efecto residual de la dosis más letal fueron posteriormente evaluadas en tanques de cemento bajo condiciones de campo en el municipio de San Carlos, departamento de Córdoba. Resultados. Bajo condiciones de ‘semicampo’, la mayor dosis probada exhibió la mayor actividad residual (15 días), después de lo cual la mortalidad de las larvas fue de 80 %. Bajo condiciones de campo, la máxima dosis probada de Bti-CECIF mostró una mortalidad de 100 % y exhibió una actividad residual de siete días en el 90 % de los tanques. Conclusión. Las tabletas Bti-CECIF controlaron eficazmente A. aegypti en condiciones de campo durante siete días a partir de su aplicación. Palabras clave: Aedes, Bacillus thuringiensis; vectores de enfermedades; dengue; virus chikungunya; virus Zika; Colombia. doi: https://doi.org/10.7705/biomedica.v38i0.3940 Author’s contributions: Wilber Gómez-Vargas: Study design, fieldwork, and manuscript writing Kelly Valencia-Jiménez: Development of Bti-CECIF tablets and review of the manuscript Guillermo Correa-Londoño: Statistical analysis and manuscript writing Faiber Jaramillo-Yepes: Development of Bti-CECIF tablets; drafting and review of the manuscript 95 Gómez-Vargas W, Valencia-Jiménez K, Correa-Londoño G, et al. Biomédica 2018;38:95-105 Vector-borne diseases account for over 17% of Health Organization (WHO) has proposed the use all infectious diseases and are a significant con- of biolarvicides such as Bacillus thuringiensis var. tributing cause of human deaths worldwide (1). israelensis (Bti) for the prevention and control of Dengue, chikungunya, and Zika arboviruses arboviral diseases (document CD55/16) depending are transmitted by the vector Aedes (Stegomyia) on the particular conditions of each country (14). aegypti and they represent a permanent global Since 1950, one of the most successful strategies health threat with social and economic impacts (2). for controlling this vector has been the use of Bacillus Currently, dengue is the most frequent arboviral thuringiensis var. israelensis (Bti) bacteria, whose disease diagnosed in tropical and sub-tropical coun- biolarvicidal effect is specific for controlling species tries. Recently, it has been estimated that there are of the Culicidae family, including A. aegypti (15-18). 390 million dengue infections per year, of which 96 In Colombia, Bti is available and commercialized million manifests with clinically apparent disease as “VectoBac 200G™”, and contains Bti serotype (3). In the Americas, a total of 580,395 cases of H-14 as the bioactive ingredient. Once ingested by dengue were reported in 2017, of which 1,940 cases larvae, peptide toxins known as delta-endotoxins were of severe dengue and 306 cases were deaths are activated. Delta-endotoxins are pore-forming (4). In Colombia, the estimated average of dengue toxins that bind to the gut epithelium and lyse infections per year between 2013 and 2017 was cellular membranes, and ultimately lead to the 91,454 cases, of which 1,728 were severe dengue, death of A. aegypti larvae (15-18). and 111 were deaths (Sivigila, Instituto Nacional However, this commercially available product de Salud) (5-9). In 2016, the reported incidence of presents several drawbacks, including the fact dengue was 101,016 cases (99.1%) and 899 cases that it is not locally produced and must, therefore, of severe dengue (0.9%) (8). Additionally, 26,279 be imported, increasing its cost significantly. cases of dengue were reported in 2017 (9). Furthermore, application volumes of this granular Furthermore, the recent introduction of Zika formulation vary and to properly dose it, a special and chikungunya arboviruses in the Colombian equipment must be used to weigh the amount Caribbean region expanded throughout the entire of required product. Additionally, the product is country. In 2014 and 2015 a total of 106,763 susceptible to physicochemical instability after and 360,570 chikungunya cases were reported, package opening and given that VectoBac 200G™ respectively (10), while up to the epidemiological is commercialized by a single company, its acces- week 52 of 2016, 19,435 cases of chikungunya virus sibility may be occasionally restricted. were reported (11). Additionally, 106,660 cases of In order to overcome these issues, at the Centro de Zika virus were reported from the epidemiological la Ciencia y la Investigación Farmacéutica, CECIF, week 32 of 2015 to the epidemiological week 52 we designed and developed a bioinsecticide in a of 2016 (12). solid tablet presentation that contains Bti serotype Dengue, chikungunya, and Zika arboviruses are H-14, the same bioactive ingredient of VectoBac a public health concern as they may lead to epi- 200G™, which will be referred to as Bti-CECIF in demics in large cities and metropolitan areas the present article. (13). For this reason, the main course of action In this study, we assessed the efficacy and residual to reduce transmission of these diseases is activity of Bti-CECIF tablets on A. aegypti larvae based on the control of the vector A. aegypti with under semi-field conditions in the municipality of insecticide aspersion, as well as larvicide control Apartadó (department of Antioquia), as well as and management means to reduce breeding sites. under field conditions in two neighborhoods of the The main vector-control strategy focuses today municipality of San Carlos (department of Córdoba). on insecticide aspersion, which can be expensive and difficult to maintain. For that reason, the World Materials and methods Tablets Corresponding author: Wilber Adolfo Gómez-Vargas, Carrera 43A N° 52 sur-99, Throughout the product design and development Sabaneta, Antioquia, Colombia process, efficacy trials were run at laboratory scale Telephone: (574) 305 3500, extension 2522 reporting the mortality percentage according to Bti [email protected] serotype H-14 concentration. Additionally, differ- Received: 23/06/17; accepted: 26/04/18 ent production processes were tested in order to 96 Biomédica 2018;38:95-105 Bti-CECIF larvicidal tablets for Aedes aegypti identify the appropriate method to compress this Experimental protocol for semi-field bioassay. We type of raw material, which were then validated evaluated Bti-CECIF tablets efficacy and residual by physicochemical and microbiological