Phlebotomus papatasi is one of the most medically important sand fly species in the Old World, serving as a vector of Leishmania parasites and phleboviruses. Chemical control is still considered the most effective method for rapidly reducing populations of flying insects involved in vector-borne disease transmission, but is increasingly threatened by insecticide resistance in the target insect posing significant problems for entomologists responsible for control programs. This study was conducted to determine pyrethroid resistance mechanisms and the biological, physiological, and molecular impacts of resistance in Ph. papatasi, and to compare their resistance mechanisms against those reported for mosquitoes and other intensely studied dipterans. Field-collected Ph. papatasi from Aswan, Egypt, were subjected to sublethal doses of permethrin and reared as a resistant strain under laboratory conditions through 16 generations. Biological parameter observations of resistant Ph. papatasi revealed an association of resistance with productivity cost. Physiological analysis revealed that concentrations of oxidase and esterase enzymes increased in early generations of the resistant colony, and then subsided through the F16 generation to levels similar to those in a susceptible colony. The activity levels of acetylcholinesterase were higher in field-collected Ph. papatasi than in susceptible colony flies, but decreased significantly despite subsequent exposure to permethrin. The molecular search for gene mutations in the resistant strain of Ph. papatasi failed to identify any mutations common in pyrethroid-resistant mosquitoes. Our study revealed that the mechanism of pyrethroid resistance in sand flies is different than that in mosquitoes, at least at the genetic level.
By transmitting major human diseases, mosquito species represent a serious threat worldwide in terms of public health. Most vector control programmes aiming to control life-threatening mosquitoes rely on the use of chemical insecticides. For the reason that only a few insecticides are used for public health, maintaining the efficacy of control programmes mostly relies on resistance management strategies. Development of such strategies requires understanding the factors influencing resistance together with characterizing the mechanisms involved. In this context, the present study aims to update current knowledge about the effect of temperature on the mosquito Culex pipiens population response to chemical insecticides. The results demonstrated that alteration of the temperature significantly affects Cx. pipiens populations. High temperature (25, 30°C) resulted in high survival rate (90, 95% respectively); while at temperature 20°C the survival rate was 80%. Egg hatching percentage was 95% after 24 h, at temperature 30°C and 50% after 24h, 50% after 48h at 25°C; however at 20°C egg hatching percentage was 100% after 48 h. In case of Cx. pipiens larvae that were reared under various temperatures pupated on day 5, 9 and 12 at 30°C, 25°C and 20°C, respectively. At high temperature 30°C, females emerged before males. On the other hand resistance of all Cx. pipiens populations to the selected chemical insecticides decreased with raising temperature. The obtained results also showed that there was significant change in acetylcholinesterase and glutathione-S-transferase level in both larvae and adult due to temperature changing. These results indicate that temperature is an important parameter that must be considered during the application of chemical assays or control of Cx. pipiens populations.
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Pyrethroids are the most commonly used insecticides in the vector control programs. This insecticide group is one of the common recommended groups by the World Health Organization (WHO) for mosquito control. Recently, Pyrethroid resistance had rapidly spread worldwide which had its consequences on the effectiveness of control programs and threats public health. In this study, selection of Pyrethroid resistance in field-collected population of Culex pipiens was monitored after exposed to 0.05% Lambda-cyhalothrin for multiple generations. Activities of three detoxification enzymes namely; Oxidases, Nonspecific Esterases and Glutathione-S-transferases (GST), that synchronized with the resistance development, were monitored. Enzyme activities showed proportional relationship to Pyrethroid resistance. The results presented in this study will elucidate the Pyrethroid resistance development and its relation to the metabolic mechanisms. This may explain the complexity of resistance mechanisms in vector management and help to mitigate control failure due to insecticide resistance.
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