Abstract
Understanding the mechanisms of insecticide resistance to vector mosquitoes is critical for the implementation of effective control measures. A nulliparous susceptible Culex pipiens pallens (KSCP) laboratory colony and two field strains from Paju (PAJ) and Jeonju (JEO) Korea were evaluated for susceptibility to five pesticides by microapplication techniques. Unfed PAJ and JEO females demonstrated increased resistance compared to unfed KSCP females, respectively. While blood-fed KSCP females demonstrated <10-fold decreased susceptibility to pesticides compared to unfed KSCP females, blood-fed PAJ and JEO females demonstrated 25.0–50.0- and 16.0–38.6-fold increased resistance compared to unfed PAJ and JEO females, respectively. Unfed and blood-fed groups were assayed for α- and β-esterase, glutathione S-transferases, and cytochrome P-450 (P450) enzyme activity assays. P450 activity was 58.8- and 72.8-fold higher for unfed PAJ and JEO females, respectively, than unfed KSCP females. P450 enzyme activity of KSCP females assayed 1 and 7 days after a blood meal increased by 14.5- and 11.8-fold, respectively, compared to unfed KSCP females, while PAJ and JEO females demonstrated 164.9- and 148.5- and 170.7- and 160.4-fold increased activity, respectively, compared to unfed females of each population. However, other three resistance-related metabolic enzymes showed low activation at <10-fold after a blood meal. The data demonstrate that P450 acts on elevated insecticide resistance after blood meals in resistant field populations. Our findings might reveal that suppressing of the P450 protein by artificial gene mutation increases insecticidal susceptibility of Cx. pipiens and will promise effective vector mosquito control.
Highlights
The common house mosquito, Culex pipiens pallens Coquillett, is a nuisance biting mosquito in the Republic of Korea (ROK) (Kim et al 2007a, b; Shin et al 2012)
Unfed 7 day-old (U7) females demonstrated lower LC50 values than blood-fed females assayed on days 1 (E1) and 7 (E7) post-blood feeding for all insecticides tested (Table 1; Figs. 2, 3, 4)
Increased insecticide resistance might result from various resistance mechanisms, e.g., mutations of target sites and activation of metabolic detoxification enzymes, this paper focuses on the relationship between insecticide resistance and the activation of detoxification enzymes among both unfed and blood-fed groups for a susceptible colony and two field-collected test strains
Summary
The common house mosquito, Culex pipiens pallens Coquillett, is a nuisance biting mosquito in the Republic of Korea (ROK) (Kim et al 2007a, b; Shin et al 2012). Of immediate concern is the introduction of WNV to the ROK based on the potential transport of virus-infected mosquitoes via daily airline arrivals from the US and other endemic countries (Tsuda 2005) To address these concerns, in 2010, the Korea Centers for Disease Control and Prevention (KCDC) and the Japan National Institute of Infectious Disease (JNIID) specified WN encephalitis and dengue fever as potential national epidemics due to the high risks associated with the introduction of infected mosquitoes into the ROK and Japan (KCDC 2014; JNIID 2015). An insecticide-susceptible Anopheles funestus strain of unfed females did not demonstrate significant differences in susceptibility to pyrethroid insecticides, while blood-fed females demonstrated decreased susceptibility (Spilling et al 2008) These data suggest that insecticide detoxification mechanisms involved in insecticide resistance are stimulated following a blood meal, leading to enhanced expression of the resistance phenotype. We report the relative decreased susceptibility/resistance levels of a Cx. p. pallens susceptible laboratory colony and two field-collected strains from Paju (PAJ) and Jeonju (JEO) in the Republic of Korea to selected pesticides, and observed changes in the quantity of four metabolic detoxification enzymes before and after blood feeding
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