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Insensitivity to the spatial repellent action of transfluthrin in Aedes aegypti: a heritable trait associated with decreased insecticide susceptibility.

Wagman JM, Achee NL, Grieco JP - PLoS Negl Trop Dis (2015)

Bottom Line: Reported here are findings from a series of in vitro studies that investigated the plasticity and heritability of spatial repellent (SR) behaviors in Aedes aegypti exposed to airborne transfluthrin, including results that indicate a possible link between repellent insensitivity and insecticide resistance.Selective breeding of SR responders for nine generations did not change the proportion of mosquitoes repelled in any generation.Results also highlight the critical need to develop new repellent active ingredients with novel mechanisms of action.

View Article: PubMed Central - PubMed

Affiliation: Department of Preventive Medicine and Biometrics, Division of Tropical Public Health, Uniformed Services University of the Health Sciences, Bethesda, Maryland, United States of America.

ABSTRACT

Background: New vector control paradigms expanding the use of spatial repellents are promising, but there are many gaps in our knowledge about how repellents work and how their long-term use might affect vector populations over time. Reported here are findings from a series of in vitro studies that investigated the plasticity and heritability of spatial repellent (SR) behaviors in Aedes aegypti exposed to airborne transfluthrin, including results that indicate a possible link between repellent insensitivity and insecticide resistance.

Methodology/principal findings: A dual-choice chamber system was used to observe directional flight behaviors in Aedes aegypti mosquitoes exposed to passively emanating transfluthrin vapors (1.35 mg/m3). Individual SR responder and SR non-responder mosquitoes were identified, collected and maintained separately according to their observed phenotype. Subsequent testing included re-evaluation of behavioral responses in some mosquito cohorts as well as testing the progeny of selectively bred responder and non-responder mosquito strains through nine generations. At baseline (F0 generation), transfluthrin actively repelled mosquitoes in the assay system. F0 mosquitoes repelled upon initial exposure to transfluthrin vapors were no more likely to be repelled again by subsequent exposure 24 h later, but repelled mosquitoes allowed to rest for 48 h were subsequently repelled at a higher proportion than was observed at baseline. Selective breeding of SR responders for nine generations did not change the proportion of mosquitoes repelled in any generation. However, selective breeding of SR non-responders did produce, after four generations, a strain of mosquitoes that was insensitive to the SR activity of transfluthrin. Compared to the SR responder strain, the SR insensitive strain also demonstrated decreased susceptibility to transfluthrin toxicity in CDC bottle bioassays and a higher frequency of the V1016Ikdr mutation.

Conclusions/significance: SR responses to volatile transfluthrin are complex behaviors with multiple determinants in Ae. aegypti. Results indicate a role for neurotoxic irritation of mosquitoes by sub-lethal doses of airborne chemical as a mechanism by which transfluthrin can produce SR behaviors in mosquitoes. Accordingly, how prolonged exposure to sub-lethal doses of volatile pyrethroids might impact insecticide resistance in natural vector populations, and how already resistant populations might respond to a given repellent in the field, are important considerations that warrant further monitoring and study. Results also highlight the critical need to develop new repellent active ingredients with novel mechanisms of action.

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Related in: MedlinePlus

The high throughput screening system (HITSS) spatial repellency assay (SRA).The treatment chamber (right hand metal cylinder) is covered internally by nylon organdy netting treated with transfluthrin dissolved in 100% acetone. The control chamber (left hand metal cylinder) contains netting treated with acetone only. Cohorts of 20 mosquitoes are introduced into the central (clear) chamber and directional flight behaviors are observed (See text, Adapted from Grieco, et al. 2007. J Am Mosq Control Assoc 2005, 21:404–411).
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pntd.0003726.g001: The high throughput screening system (HITSS) spatial repellency assay (SRA).The treatment chamber (right hand metal cylinder) is covered internally by nylon organdy netting treated with transfluthrin dissolved in 100% acetone. The control chamber (left hand metal cylinder) contains netting treated with acetone only. Cohorts of 20 mosquitoes are introduced into the central (clear) chamber and directional flight behaviors are observed (See text, Adapted from Grieco, et al. 2007. J Am Mosq Control Assoc 2005, 21:404–411).

Mentions: SR behavior was evaluated using a high throughput screening system (HITSS-SRA configuration) (Fig 1), previously described by Grieco et al. (2007) [41] and recently adopted by the WHO as a standard procedure for in vitro efficacy testing of spatial repellents [9]. The dual-choice chamber system, which allows the observation of directional mosquito movement in response to a single chemical stimulus outside the context of host cues, consists of a clear Plexiglas central unit connected at opposite ends to one treatment chamber housing repellent-treated netting and one control chamber housing a net treated with acetone only (Fig 1). Tests were conducted to evaluate Ae. aegypti SR responses to passively emanating transfluthrin (2,3,5,6-tetrafluorobenzyl (1R)-trans-3-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropanecarboxylate) (S.C. Johnson and Son, Inc., Racine WI), a volatile synthetic pyrethroid with widely demonstrated SR efficacy against mosquitoes [7, 36, 37, 12]. Briefly, reagent grade (unformulated) transfluthrin was dissolved in 100% acetone (Hofius Ltd./Ace Hardware, Belize City and Fisher Scientific, Waltham MA). This solution was then applied evenly by micropipette across the surface of 11cm x 25cm pieces of nylon organdy netting (No. I10N, G-Street Fabrics, Bethesda MD) and allowed to air dry a minimum of 15 minutes before use. Industry guidelines (M.C. Meier, personal communication, 16 August 2011) and concurrent experimental hut studies using transfluthrin in Belize [42] indicate a standard field application rate (FAR) of 1.35mg active ingredient per cubic meter of airspace to produce indoor SR activity against mosquitoes via passive emanation. Accordingly, HITSS treatment nets delivering 1x the FAR into the assay system were treated with 0.9mL of a 2.2x10-6 M (8.4x10-4 mg/mL) solution. Concentrations tested ranged from 0.5xFAR to 1000xFAR. Control nets were treated with 100% acetone only.


Insensitivity to the spatial repellent action of transfluthrin in Aedes aegypti: a heritable trait associated with decreased insecticide susceptibility.

Wagman JM, Achee NL, Grieco JP - PLoS Negl Trop Dis (2015)

The high throughput screening system (HITSS) spatial repellency assay (SRA).The treatment chamber (right hand metal cylinder) is covered internally by nylon organdy netting treated with transfluthrin dissolved in 100% acetone. The control chamber (left hand metal cylinder) contains netting treated with acetone only. Cohorts of 20 mosquitoes are introduced into the central (clear) chamber and directional flight behaviors are observed (See text, Adapted from Grieco, et al. 2007. J Am Mosq Control Assoc 2005, 21:404–411).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4400042&req=5

pntd.0003726.g001: The high throughput screening system (HITSS) spatial repellency assay (SRA).The treatment chamber (right hand metal cylinder) is covered internally by nylon organdy netting treated with transfluthrin dissolved in 100% acetone. The control chamber (left hand metal cylinder) contains netting treated with acetone only. Cohorts of 20 mosquitoes are introduced into the central (clear) chamber and directional flight behaviors are observed (See text, Adapted from Grieco, et al. 2007. J Am Mosq Control Assoc 2005, 21:404–411).
Mentions: SR behavior was evaluated using a high throughput screening system (HITSS-SRA configuration) (Fig 1), previously described by Grieco et al. (2007) [41] and recently adopted by the WHO as a standard procedure for in vitro efficacy testing of spatial repellents [9]. The dual-choice chamber system, which allows the observation of directional mosquito movement in response to a single chemical stimulus outside the context of host cues, consists of a clear Plexiglas central unit connected at opposite ends to one treatment chamber housing repellent-treated netting and one control chamber housing a net treated with acetone only (Fig 1). Tests were conducted to evaluate Ae. aegypti SR responses to passively emanating transfluthrin (2,3,5,6-tetrafluorobenzyl (1R)-trans-3-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropanecarboxylate) (S.C. Johnson and Son, Inc., Racine WI), a volatile synthetic pyrethroid with widely demonstrated SR efficacy against mosquitoes [7, 36, 37, 12]. Briefly, reagent grade (unformulated) transfluthrin was dissolved in 100% acetone (Hofius Ltd./Ace Hardware, Belize City and Fisher Scientific, Waltham MA). This solution was then applied evenly by micropipette across the surface of 11cm x 25cm pieces of nylon organdy netting (No. I10N, G-Street Fabrics, Bethesda MD) and allowed to air dry a minimum of 15 minutes before use. Industry guidelines (M.C. Meier, personal communication, 16 August 2011) and concurrent experimental hut studies using transfluthrin in Belize [42] indicate a standard field application rate (FAR) of 1.35mg active ingredient per cubic meter of airspace to produce indoor SR activity against mosquitoes via passive emanation. Accordingly, HITSS treatment nets delivering 1x the FAR into the assay system were treated with 0.9mL of a 2.2x10-6 M (8.4x10-4 mg/mL) solution. Concentrations tested ranged from 0.5xFAR to 1000xFAR. Control nets were treated with 100% acetone only.

Bottom Line: Reported here are findings from a series of in vitro studies that investigated the plasticity and heritability of spatial repellent (SR) behaviors in Aedes aegypti exposed to airborne transfluthrin, including results that indicate a possible link between repellent insensitivity and insecticide resistance.Selective breeding of SR responders for nine generations did not change the proportion of mosquitoes repelled in any generation.Results also highlight the critical need to develop new repellent active ingredients with novel mechanisms of action.

View Article: PubMed Central - PubMed

Affiliation: Department of Preventive Medicine and Biometrics, Division of Tropical Public Health, Uniformed Services University of the Health Sciences, Bethesda, Maryland, United States of America.

ABSTRACT

Background: New vector control paradigms expanding the use of spatial repellents are promising, but there are many gaps in our knowledge about how repellents work and how their long-term use might affect vector populations over time. Reported here are findings from a series of in vitro studies that investigated the plasticity and heritability of spatial repellent (SR) behaviors in Aedes aegypti exposed to airborne transfluthrin, including results that indicate a possible link between repellent insensitivity and insecticide resistance.

Methodology/principal findings: A dual-choice chamber system was used to observe directional flight behaviors in Aedes aegypti mosquitoes exposed to passively emanating transfluthrin vapors (1.35 mg/m3). Individual SR responder and SR non-responder mosquitoes were identified, collected and maintained separately according to their observed phenotype. Subsequent testing included re-evaluation of behavioral responses in some mosquito cohorts as well as testing the progeny of selectively bred responder and non-responder mosquito strains through nine generations. At baseline (F0 generation), transfluthrin actively repelled mosquitoes in the assay system. F0 mosquitoes repelled upon initial exposure to transfluthrin vapors were no more likely to be repelled again by subsequent exposure 24 h later, but repelled mosquitoes allowed to rest for 48 h were subsequently repelled at a higher proportion than was observed at baseline. Selective breeding of SR responders for nine generations did not change the proportion of mosquitoes repelled in any generation. However, selective breeding of SR non-responders did produce, after four generations, a strain of mosquitoes that was insensitive to the SR activity of transfluthrin. Compared to the SR responder strain, the SR insensitive strain also demonstrated decreased susceptibility to transfluthrin toxicity in CDC bottle bioassays and a higher frequency of the V1016Ikdr mutation.

Conclusions/significance: SR responses to volatile transfluthrin are complex behaviors with multiple determinants in Ae. aegypti. Results indicate a role for neurotoxic irritation of mosquitoes by sub-lethal doses of airborne chemical as a mechanism by which transfluthrin can produce SR behaviors in mosquitoes. Accordingly, how prolonged exposure to sub-lethal doses of volatile pyrethroids might impact insecticide resistance in natural vector populations, and how already resistant populations might respond to a given repellent in the field, are important considerations that warrant further monitoring and study. Results also highlight the critical need to develop new repellent active ingredients with novel mechanisms of action.

Show MeSH
Related in: MedlinePlus