Limits...
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 experimental hut mortality of free flying wildAnopheles arabiensismosquitoes in the presence of occupied ITNs and ball bioassay mortality after three and 30 minutes exposure to the same ITNs (see [8]).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Comparison of experimental hut mortality of free flying wildAnopheles arabiensismosquitoes in the presence of occupied ITNs and ball bioassay mortality after three and 30 minutes exposure to the same ITNs (see [8]).

Mentions: Three-minute ball bioassay with 100 mg/sq m chlorfenapyr-treated netting resulted in mortality of only 5% against F1 wild An. arabiensis, compared to 48% in experimental hut trials of chlorfenapyr-treated nets against wild, free-flying An. arabiensis (Figure 1). Clearly, three minutes exposure in bioassay failed to predict performance against host-seeking mosquitoes in huts. Prolonged exposure of 30 minutes resulted in 58% mortality, closer to the mortality of free-flying mosquitoes. Mortality of pyrethroid-resistant F1 An. arabiensis [22,23] was also low for the alphacypermethrin netting in three-minute ball bioassay (1%) but the alphacypermethrin-treated nets were effective in experimental hut trials and killed 50%. Prolonged exposure of An. arabiensis to alphacypermethrin netting in bioassay (30 minutes) killed 88%.Figure 1


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 experimental hut mortality of free flying wildAnopheles arabiensismosquitoes in the presence of occupied ITNs and ball bioassay mortality after three and 30 minutes exposure to the same ITNs (see [8]).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Comparison of experimental hut mortality of free flying wildAnopheles arabiensismosquitoes in the presence of occupied ITNs and ball bioassay mortality after three and 30 minutes exposure to the same ITNs (see [8]).
Mentions: Three-minute ball bioassay with 100 mg/sq m chlorfenapyr-treated netting resulted in mortality of only 5% against F1 wild An. arabiensis, compared to 48% in experimental hut trials of chlorfenapyr-treated nets against wild, free-flying An. arabiensis (Figure 1). Clearly, three minutes exposure in bioassay failed to predict performance against host-seeking mosquitoes in huts. Prolonged exposure of 30 minutes resulted in 58% mortality, closer to the mortality of free-flying mosquitoes. Mortality of pyrethroid-resistant F1 An. arabiensis [22,23] was also low for the alphacypermethrin netting in three-minute ball bioassay (1%) but the alphacypermethrin-treated nets were effective in experimental hut trials and killed 50%. Prolonged exposure of An. arabiensis to alphacypermethrin netting in bioassay (30 minutes) killed 88%.Figure 1

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