Molecular Ecology of Pyrethroid Knockdown Resistance in Culex pipiens pallens Mosquitoes

Pyrethroid insecticides have been extensively used in China and worldwide for public health pest control. Accurate resistance monitoring is essential to guide the rational use of insecticides and resistance management. Here we examined the nucleotide diversity of the para-sodium channel gene, which confers knockdown resistance (kdr) in Culex pipiens pallens mosquitoes in China. The sequence analysis of the para-sodium channel gene identified L1014F and L1014S mutations. We developed and validated allele-specific PCR and the real-time TaqMan methods for resistance diagnosis. The real-time TaqMan method is more superior to the allele-specific PCR method as evidenced by higher amplification rate and better sensitivity and specificity. Significant positive correlation between kdr allele frequency and bioassay-based resistance phenotype demonstrates that the frequency of L1014F and L1014S mutations in the kdr gene can be used as a molecular marker for deltamethrin resistance monitoring in natural Cx. pipiens pallens populations in the East China region. The laboratory selection experiment found that L1014F mutation frequency, but not L1014S mutation, responded to deltamethrin selection, suggesting that the L1014F mutation is the key mutation conferring resistance to deltamethrin. High L1014F mutation frequency detected in six populations of Cx. pipens pallens suggests high prevalence of pyrethroid resistance in Eastern China, calling for further surveys to map the resistance in China and for investigating alternative mosquito control strategies

Effects of operating conditions on flow and heat transfer characteristics of mist cooling in a square ribbed channel

Flow and heat transfer characteristics of mist/steam cooling and mist/air cooling in a square channel with 60º rib angle are numerically investigated for a wide range of operating parameters, such as Reynolds number ranging from 10000 to 60000, reference pressure from 0.1 MPa to 0.5 MPa and inlet temperature from 120 °C to 200 °C. Also, the heat transfer characteristics of mist cooling are compared with the corresponding cases of single-phase coolant such as steam and air. The 3D steady Reynolds-averaged Navier–Stokes equations with a standard k-ω turbulent model are solved by using commercial software ANSYS CFX. The CFD model has been validated by experimental data for steam-only case with a good agreement. In addition, distribution and evolution of secondary flow in the ribbed channel are analyzed by vortex core technology and their effects on heat transfer are investigated for these four coolants. The results show that the strength of longitudinal secondary flow has a significant influence on the Nusselt number (Nu) distribution on the ribbed surface. The Nusselt number distribution is periodical in stream-wise direction for steam and air cooling, whereas Nusselt number gradually increases for mist/steam and mist/air cooling. It is found that longer travelling distance of droplets in the ribbed channel result in a higher heat transfer enhancement of mist cooling. The heat transfer characteristics of mist cooling are insensitive to pressure, but inversely correlated with coolant inlet temperature compared with steam and air cooling for the tested parameter ranges