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The activity of the pyrrole insecticide chlorfenapyr in mosquito bioassay: towards a more rational testing and screening of non-neurotoxic insecticides for malaria vector control.

Oxborough RM, N'Guessan R, Jones R, Kitau J, Ngufor C, Malone D, Mosha FW, Rowland MW - Malar. J. (2015)

Bottom Line: The efficacy of WHO recommended cone, cylinder and tunnel tests was compared for pyrethroids and chlorfenapyr.The endogenous circadian activity rhythm of anophelines results in inactivity by day and raised metabolism and flight activity by night.A model which explains improved toxicity of chlorfenapyr ITN when tested at night, and during the day at higher ambient temperature, is that activation of chlorfenapyr and disruption of respiratory pathways is enhanced when the insect is more metabolically and behaviourally active.

View Article: PubMed Central - PubMed

Affiliation: Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK. oxandbull@hotmail.com.

ABSTRACT

Background: The rapid selection of pyrethroid resistance throughout sub-Saharan Africa is a serious threat to malaria vector control. Chlorfenapyr is a pyrrole insecticide which shows no cross resistance to insecticide classes normally used for vector control and is effective on mosquito nets under experimental hut conditions. Unlike neurotoxic insecticides, chlorfenapyr owes its toxicity to disruption of metabolic pathways in mitochondria that enable cellular respiration. A series of experiments explored whether standard World Health Organization (WHO) guidelines for evaluation of long-lasting insecticidal nets, developed through testing of pyrethroid insecticides, are suitable for evaluation of non-neurotoxic insecticides.

Methods: The efficacy of WHO recommended cone, cylinder and tunnel tests was compared for pyrethroids and chlorfenapyr. To establish bioassay exposure times predictive of insecticide-treated net (ITN) efficacy in experimental hut trials, standard three-minute bioassays of pyrethroid and chlorfenapyr ITNs were compared with longer exposures. Mosquito behaviour and response to chlorfenapyr ITN in bioassays conducted at night were compared to day and across a range of temperatures representative of highland and lowland transmission.

Results: Standard three-minute bioassay of chlorfenapyr produced extremely low levels of mortality compared to pyrethroids. Thirty-minute day-time bioassay produced mortality closer to hut efficacy of chlorfenapyr ITN but still fell short of the WHO threshold. Overnight tunnel test with chlorfenapyr produced 100% mortality and exceeded the WHO threshold of 80%. The endogenous circadian activity rhythm of anophelines results in inactivity by day and raised metabolism and flight activity by night. A model which explains improved toxicity of chlorfenapyr ITN when tested at night, and during the day at higher ambient temperature, is that activation of chlorfenapyr and disruption of respiratory pathways is enhanced when the insect is more metabolically and behaviourally active.

Conclusions: Testing according to current WHO guidelines is not suitable for certain types of non-neurotoxic insecticide which, although highly effective in field trials, would be overlooked at the screening stage of evaluation through bioassay. Testing methods must be tailored to the characteristics and mode of action of each insecticide class. The WHO tunnel test on night-active anophelines is the most reliable bioassay for identifying the toxicity of novel insecticides.

No MeSH data available.


Related in: MedlinePlus

Comparison of bioassay response inAnopheles gambiaeKisumu to chlorfenapyr and alphacypermethrin-treated nets using standard WHO bioassay techniques: day-time cone and cylinder bioassays and night-time tunnel tests.
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Fig2: Comparison of bioassay response inAnopheles gambiaeKisumu to chlorfenapyr and alphacypermethrin-treated nets using standard WHO bioassay techniques: day-time cone and cylinder bioassays and night-time tunnel tests.

Mentions: Under laboratory conditions a standard three-minute cone bioassay on chlorfenapyr ITN 200 mg/sq m produced <5% mortality, while three-minute exposure to the same chlorfenapyr netting in cylinder tests killed 30%. More prolonged, 30-minute exposure in cylinder tests produced 37% mortality. When tested in overnight tunnel tests, mortality was far greater reaching 100% (Figure 2). Adopting the WHO success threshold of 80% mortality in cone or cylinder bioassay, chlorfenapyr failed to meet this criterion with the standard three-minute exposure. Not even 30 minutes exposure was sufficient to reach 80% mortality. But chlorfenapyr did reach the 80% threshold using the tunnel test. By contrast, the 25 mg/sq m alphacypermethrin netting produced 100% mortality of susceptible An. gambiae Kisumu in cone and cylinder tests with three-minute exposure. Alphacypermethrin therefore met the WHO success threshold of 80% within the standard three-minute exposure and therefore did not need to undergo tunnel testing to achieve this criterion.Figure 2


The activity of the pyrrole insecticide chlorfenapyr in mosquito bioassay: towards a more rational testing and screening of non-neurotoxic insecticides for malaria vector control.

Oxborough RM, N'Guessan R, Jones R, Kitau J, Ngufor C, Malone D, Mosha FW, Rowland MW - Malar. J. (2015)

Comparison of bioassay response inAnopheles gambiaeKisumu to chlorfenapyr and alphacypermethrin-treated nets using standard WHO bioassay techniques: day-time cone and cylinder bioassays and night-time tunnel tests.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4390098&req=5

Fig2: Comparison of bioassay response inAnopheles gambiaeKisumu to chlorfenapyr and alphacypermethrin-treated nets using standard WHO bioassay techniques: day-time cone and cylinder bioassays and night-time tunnel tests.
Mentions: Under laboratory conditions a standard three-minute cone bioassay on chlorfenapyr ITN 200 mg/sq m produced <5% mortality, while three-minute exposure to the same chlorfenapyr netting in cylinder tests killed 30%. More prolonged, 30-minute exposure in cylinder tests produced 37% mortality. When tested in overnight tunnel tests, mortality was far greater reaching 100% (Figure 2). Adopting the WHO success threshold of 80% mortality in cone or cylinder bioassay, chlorfenapyr failed to meet this criterion with the standard three-minute exposure. Not even 30 minutes exposure was sufficient to reach 80% mortality. But chlorfenapyr did reach the 80% threshold using the tunnel test. By contrast, the 25 mg/sq m alphacypermethrin netting produced 100% mortality of susceptible An. gambiae Kisumu in cone and cylinder tests with three-minute exposure. Alphacypermethrin therefore met the WHO success threshold of 80% within the standard three-minute exposure and therefore did not need to undergo tunnel testing to achieve this criterion.Figure 2

Bottom Line: The efficacy of WHO recommended cone, cylinder and tunnel tests was compared for pyrethroids and chlorfenapyr.The endogenous circadian activity rhythm of anophelines results in inactivity by day and raised metabolism and flight activity by night.A model which explains improved toxicity of chlorfenapyr ITN when tested at night, and during the day at higher ambient temperature, is that activation of chlorfenapyr and disruption of respiratory pathways is enhanced when the insect is more metabolically and behaviourally active.

View Article: PubMed Central - PubMed

Affiliation: Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK. oxandbull@hotmail.com.

ABSTRACT

Background: The rapid selection of pyrethroid resistance throughout sub-Saharan Africa is a serious threat to malaria vector control. Chlorfenapyr is a pyrrole insecticide which shows no cross resistance to insecticide classes normally used for vector control and is effective on mosquito nets under experimental hut conditions. Unlike neurotoxic insecticides, chlorfenapyr owes its toxicity to disruption of metabolic pathways in mitochondria that enable cellular respiration. A series of experiments explored whether standard World Health Organization (WHO) guidelines for evaluation of long-lasting insecticidal nets, developed through testing of pyrethroid insecticides, are suitable for evaluation of non-neurotoxic insecticides.

Methods: The efficacy of WHO recommended cone, cylinder and tunnel tests was compared for pyrethroids and chlorfenapyr. To establish bioassay exposure times predictive of insecticide-treated net (ITN) efficacy in experimental hut trials, standard three-minute bioassays of pyrethroid and chlorfenapyr ITNs were compared with longer exposures. Mosquito behaviour and response to chlorfenapyr ITN in bioassays conducted at night were compared to day and across a range of temperatures representative of highland and lowland transmission.

Results: Standard three-minute bioassay of chlorfenapyr produced extremely low levels of mortality compared to pyrethroids. Thirty-minute day-time bioassay produced mortality closer to hut efficacy of chlorfenapyr ITN but still fell short of the WHO threshold. Overnight tunnel test with chlorfenapyr produced 100% mortality and exceeded the WHO threshold of 80%. The endogenous circadian activity rhythm of anophelines results in inactivity by day and raised metabolism and flight activity by night. A model which explains improved toxicity of chlorfenapyr ITN when tested at night, and during the day at higher ambient temperature, is that activation of chlorfenapyr and disruption of respiratory pathways is enhanced when the insect is more metabolically and behaviourally active.

Conclusions: Testing according to current WHO guidelines is not suitable for certain types of non-neurotoxic insecticide which, although highly effective in field trials, would be overlooked at the screening stage of evaluation through bioassay. Testing methods must be tailored to the characteristics and mode of action of each insecticide class. The WHO tunnel test on night-active anophelines is the most reliable bioassay for identifying the toxicity of novel insecticides.

No MeSH data available.


Related in: MedlinePlus