Background

The use of mosquito coils is a common method of protection against mosquito bites and mosquito borne diseases. These coils are widely marketed and used by households in Malaysia to prevent mosquito associated problems.

Objective

To determine the bioefficacy of commercial d-allethrin and d-trans allethrin spatial repellents against the dengue vector Aedes aegypti.

Method

We evaluated the knockdown and mortality effects of spatial repellents containing d-allethrin (0.3% w/w) and d-trans allethrin (0.1% and 0.15% w/w) on Ae. aegypti in a Peet Grady Chamber, relative to a reference product (0.2% w/w d-allethrin).

Results

The spatial repellent containing 0.3% d-allethrin had the shortest knockdown times (KT₅₀ and KT₉₀) and these were significantly different from the other products including the reference coil except the 0.15% d-trans allethrin coil. The spatial repellent containing 0.3% d-allethrin elicited a mortality response of 96%, which was significantly different from the mortality response to the other coils, except for the 0.15% d-trans allethrin formulation.

Conclusions

Spatial repellents containing 0.3% d-allethrin or 0.15% d-trans allethrin had higher efficacies against Ae. aegypti than repellents containing 0.2% w/w d-allethrin or 0.1% d-trans allethrin and their use by households could offer better relief from Ae. aegypti

Mosquito coils are insecticides commonly used for protection against mosquitoes due to their toxic effects on mosquito populations. These effects on mosquitoes could induce the expression of metabolic enzymes in exposed populations as a counteractive measure. Cytochrome P450 family 4 (CYP4) are metabolic enzymes associated with a wide range of biological activities including insecticide resistance. In this study, the efficacies of three commercial mosquito coils with different pyrethroid active ingredients were assessed and their potential to induce the expression of CYP4 genes in Aedes albopictus analyzed by real-time quantitative PCR. Coils containing 0.3 % d-allethrin and 0.005 % metofluthrin exacted profound toxic effects on Ae. albopictus, inducing high mortalities (≥90 %) compared to the 0.2 % d-allethrin reference coil. CYP4H42 and CYP4H43 expressions were significantly higher in 0.3 % d-allethrin treated mosquitoes compared to the other treated populations. Short-term (KT50) exposure to mosquito coils induced significantly higher expression of both genes in 0.005 % metofluthrin exposed mosquitoes. These results suggest the evaluated products provided better protection than the reference coil; however, they also induced the expression of metabolic genes which could impact negatively on personal protection against mosquito.

Cytochrome P450 is a group of heme-containing enzymes. They have been detected in virtually all organisms examined from bacteria to mammals. In insects, P450s are involved in the oxidative metabolism of a large number of exogenous compounds (xenobiotics) from natural or anthropogenic origins (plant allelochemicals and insecticides) and endogenous compounds such as steroid hormones ecdysteroid hormones and pheromones. Thus the P450s have an important role in controlling insect growth, development, and evolutionary adaptation to environments containing potentially toxic compounds. A novel cDNA clone encoding a cytochrome P450 gene has been isolated from the mosquito, Ae. aegypti strain VCRU. The cDNA is 1731 bp in length and has an open reading frame from 277 bp to 1647 bp encoding a protein of 529 aa. The classic heme-binding characteristic motifs of P450s (FXXGXRXCXG, RxxR and EVLR) are present and conserved in this gene. The EVDTFMFEGHDTT motif characteristic of CYP4 family is also found in this new gene. The full length cDNA clone for CYP4H28v2 is 98% identical to CYP4H28 of The Liverpool strain Ae. aegypti. So, we propose that  this is an allele of that gene.

Cytochrome P450 monooxygenases are versatile biocatalysts that incorporate oxygen into an enormous range of molecules. The cytochrome P450 proteins are involved in the catalysis of different reactions and these properties have been used for drug improvement. The protein family also includes compounds producing properties such as resistance to insecticides, and the synthesis of valuable chemicals. In this review, we will discuss various aspects of the structure and function of the cytochrome P450s