Joint Action of Two Pesticides and an Oxidase Inhibitor on The Snail Lymnaea Acuminata

Studies were conducted on synergism between an Organophosphate, Nuvan (dichlorvos) mixed with a carbamate, Sevin (carbaryl) in a 1:46 ratio against the snail Lymnaea acuminata. It was found that Sevin enhances the activity of Nuvan and thus the LC values ( LC10, LC50, LC90 ) obtained from this mixture were low as compared to Nuvan or Sevin alone. The acetylcholinesterase (AChE) inhibition was higher in case of Nuvan + Sevin (16.17%) as compared to Nuvan or Sevin (34.7% , 69.1%) alone. When Piperonyl Butoxide (PB), a mixed function oxidase inhibitor was given with Nuvan and Sevin in a 1:46:5 ratio, the LC value decrease still further. It appears that, in the tertiary mixture, while PB reduce the oxidative detoxification of Nuvan and Sevin the carbamate may also be preventing the hydrolysis of Nuvan may tertiary mixture lethal than of its components.

Reversal of Resistance to the Larvicide Temephos in an Aedes aegypti (Diptera: Culicidae) Laboratory Strain From Cuba

The objective of this investigation was to know whether the organophosphate temephos resistance developed in larvae from a laboratory strain of Aedes aegypti (Linnaeus, 1762) from Cuba could be reversed. The resistant laboratory strain of Ae. aegypti, named SAN-F6, was left without temephos selection pressure for 12 generations. The level of temephos resistance was determined using WHO bioassays and mechanisms of metabolic resistance were determined based on enzyme activity levels detected by biochemical assays. Bioassays and biochemical assays were conducted on the SAN-F6 parental strain and every three reversal generations (SANRevF3, SANRevF6, SANRevF9, and SANRevF12) without temephos selection pressure. After 19 yr of keeping the SAN-F6 strain under selection pressure with the LC90 of temephos, the resistance ratio (RR50) was 47.5×. Biochemical assays indicated that esterase and glutathione S-transferase are still responsible for temephos resistance in this strain, but not mixed-function oxidase. Experiments on resistance reversal showed that temephos susceptibility could be recovered as α esterase activity levels decreased. The SAN-F6 strain has provided an essential basis for studies of temephos resistance in Cuba. It was demonstrated that the resistance developed to the larvicide temephos in Ae. aegypti from this Cuban lab strain is a reversible phenomenon, which suggests that similar outcomes might be expected in field populations. As such, the use of temephos alternated with other larvicides recommended by WHO such as Bti or pyriproxyfen is recommended to maintain the effectiveness of temephos and to achieve more effective control of Ae. aegypti.