Impact of environmental temperatures on resistance to organophosphate insecticides in Aedes aegypti from Trinidad / Repercusión de las temperaturas ambientales sobre la resistencia de Aedes aegypti a los insecticidas organofosforados en Trinidad

OBJECTIVE: To examine the effects of increasing larval rearing temperatures on the resistance status of Trinidadian populations of Aedes aegypti to organophosphate (OP) insecticides. METHODS: In 2007-2008, bioassays and biochemical assays were conducted on A. aegypti larvae collected in 2006 from eight geographically distinct areas in Trinidad (Trinidad and Tobago). Larval populations were reared at four temperatures (28 ± 2ºC, 32ºC, 34ºC, and 36ºC) prior to bioassays with OP insecticides (fenthion, malathion, and temephos) and biochemical assays for esterase enzymes. RESULTS: Most larval populations reared at 28 ± 2ºC were susceptible to fenthion (>98% mortality) but resistant to malathion and temephos (< 80% mortality). A positive association was found between resistance to OP insecticides and increased activities of α- and β-esterases in larval populations reared at 28 ± 2ºC. Although larval populations reared at higher temperatures showed variations in resistance to OPs, there was a general increase in susceptibility. However, increases or decreases in activity levels of enzymes did not always correspond with an increase or decrease in the proportion of resistant individuals reared at higher temperatures. CONCLUSIONS: Although global warming may cause an increase in dengue transmission, based on the current results, the use of insecticides for dengue prevention and control may yet be effective if temperatures increase as projected.

OBJETIVO: Examinar los efectos del aumento de las temperaturas de desarrollo larvario sobre el estado de resistencia a los insecticidas organofosforados de las poblaciones de Aedes aegypti en Trinidad. MÉTODOS: En 2007 y 2008 se llevaron a cabo ensayos biológicos y bioquímicos en larvas de A. aegypti recogidas en el 2006 de ocho áreas geográficamente separadas en Trinidad (Trinidad y Tabago). Las poblaciones larvarias se desarrollaron en cuatro temperaturas (28 ± 2 ºC, 32 ºC, 34 ºC y 36 ºC) antes de los ensayos biológicos con insecticidas organofosforados (fentión, malatión y temefós) y los análisis bioquímicos para las enzimas de esterasa. RESULTADOS: La mayoría de las poblaciones larvarias que se desarrollaron a 28 ± 2 ºC fueron susceptibles al fentión (mortalidad > 98%) pero resistentes al malatión y al temefós (mortalidad < 80%). Se encontró una asociación positiva entre la resistencia a los insecticidas organofosforados y la mayor actividad de αy β-esterasas en las poblaciones larvarias que se desarrollaron a 28 ± 2 ºC. Aunque las poblaciones larvarias que se desarrollaron a temperaturas mayores mostraron variaciones en la resistencia a los organofosforados, hubo un aumento general de la sensibilidad. Sin embargo, los aumentos o las disminuciones en los niveles de actividad de las enzimas no siempre se correspondieron con un aumento o disminución en la proporción de individuos resistentes desarrollados a las temperaturas más altas. CONCLUSIONES: Aunque el recalentamiento del planeta puede causar un aumento de la transmisión del dengue, según los resultados de este estudio el uso de insecticidas para la prevención y el control del dengue todavía puede ser eficaz si las temperaturas aumentan según lo proyectado.

Laboratory bio-assay of temephos and fenthion against some vector species of public health importance.

Laboratory studies carried out using Temephos and Fenthion, two commonly used larvicides under Urban Malaria Scheme (NMEP) and NFCP for the control of mosquito larvae. The results revealed that the LC50 and LC90 values for temephos against Aedes aegypti 0.0177 and 0.0559, Anopheles stephensi 0.0148 and 0.0472, Culex quinquefasciatus 0.0157 & 0.0480 and for Culex vishnui group of mosquitoes 0.043 & 0.0118 ppm respectively. The results obtained revealed that there is a 62.8 & 94.12 times increase in the LC50 & LC90 of Cx. Quinquefasciatus which indicates that the species has developed resistance to temephos. There were 6.32 & 8.34 fold increase in Ae. aegypti and 2.27 & 2.34 fold increase in LC50 & LC90 values of An. stephensi are indicative of development of tolerance against temephos. Similarly LC50 and LC90 values estimated for fenthion against Ae. aegypti 0.0173 & 0.0392, An. stephensi 0.0274 & 0.0992 and Cx. quinquefasciatus 0.03 & 0.0469 respectively. The slope values were found to be higher in fenthion as compared to temephos. It was recorded to be 2.72 times higher in Cx. quinquefasciatus and 1.54 times against An. stephensi. However, much difference was not observed in the slope values of temephos and fenthion in Ae. aegypti.

Ultrastructural changes in testis of gobiid fish Glossogobius giuris (Ham) induced by fenthion.

Pesticides are known to affect the testis in fishes and cause cytomorphological changes or gross physiological alterations due to changes in its histology, retard gonadotrophic secretions thereby causing regression of the gonads. Light and ultrastructural studies were made on control and fenthion treated testis, interstitial gland and sperms of G. giuris during spawning phase after exposing them to different sub-lethal concentrations (0.05, 0.25 and 0.5 ppm) fenthion for a short-term period (24, 48, 72 and 96 hr). The results indicated extensive cytotoxic damages in the testis including atrophy of testis, reduction in lipoidal material in the interstitial cell and degeneration of sperms. The alteration in histology of testis, interstitial cell and sperms progressively increased with the increase in the sub-lethal concentration of pesticides.