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Insecticide Resistance Bottle Bioassay Evaluation of Culex tarsalis Mosquitoes From Coachella Valley, 2021

Insecticide Resistance Bottle Bioassay Evaluation of Culex tarsalis Mosquitoes From Coachella... Culex tarsalis (Coquillett) permethrin, prallethrin, pyrethrin, resmethrin The objective of this study was to determine whether locally collected mosquitoes were resistant to adulticide products using the CDC bottle bioassay. The Coachella Valley Mosquito and Vector Control District evaluates adulticide resistance of field-collected mosquitoes to a susceptible colony strain on an annual basis. The results of these evaluations determine whether the products can efficiently reduce adult mosquito abundance and disrupt virus transmission. Wild Culex tarsalis mosquitoes were collected by placing carbon dioxide traps overnight and collecting the live adults the next morning. Mosquitoes were collected from the Northshore of the Salton Sea (35.5327, −116.0353). The live mixed-age females were used in the assays. The susceptible colony mosquitoes (originally from Bakersfield, CA, kept in colony since the 1950s) were raised by placing 3 egg rafts per larval rearing tray. Larvae were fed daily a mixture of liver powder, ground fish flakes, brewer’s yeast, and ground alfalfa pellets and were kept in rearing chambers at 50% RH, 28°C, and 16:8 (L:D) h cycle. During the pupal stage, preliminary pupae were removed to increase the female:male ratio, and subsequent pupae were placed in a cage for emergence. Adults were 3–5 d old with mixed sex (70F:30M ratio) and fed 10% sugar water daily. Two hundred fifty (250) ml glass Wheaton bottles were coated with 1 ml of the pesticide product diluted in acetone. Formulations of these products were calculated using the concentration of the active ingredient (a.i.) as indicated in Table 1. For the control, 1 ml of acetone solvent was added to the bottles. The inside of the bottles was fully coated before rolling in a fume hood to allow the solvent to evaporate. Once the solvent evaporated, the bottles were capped, and the assays were conducted within 24 h. Table 1. Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Open in new tab Table 1. Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Open in new tab For the assays, an average of 36 mosquitoes ranging from 23 to 63 mosquitoes was aspirated into each bottle. Four replicate bottles were used for each local sample population and the susceptible colony mosquitoes. Mosquito mortality was assessed at 15 min after initial exposure and every 15 min thereafter until all mosquitoes in a bottle were dead or the 2 h count was completed. Mosquitoes were observed as knocked down or moribund if they could no longer have controlled flight or stand. At the end of the study, the mosquitoes in each bottle were frozen, counted, and identified to species. For the collections from Northshore, the mosquitoes were comprised of 99.7% Cx. tarsalis and 0.3% other species. Results of mosquito mortality were analyzed using WHO guidelines for mosquito mortality for bottle bioassays. We observed the mosquito mortality of the wild strain when the colony strain reached 100% mortality. Resistance was evident when fewer than 80% of the mosquitoes died at this diagnostic time. The percent mortality at diagnostic dose is underlined in Table 1. This study documented evidence of resistance of local wild mosquitoes to adulticide products. The wild mosquitoes showed susceptibility against Scourge 18 + 54. There is developing resistance of the wild mosquitoes for Aqua-Reslin and Duet. Resistance is evident for Merus 3.0, perhaps due to the lack of a synergist such as PBO.1 Footnotes 1 This research was supported by the Coachella Valley Mosquito and Vector Control District as part of the routine resistance management work. No special research funds were allocated for this work. © The Author(s) 2022. Published by Oxford University Press on behalf of Entomological Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Arthropod Management Tests Oxford University Press

Insecticide Resistance Bottle Bioassay Evaluation of Culex tarsalis Mosquitoes From Coachella Valley, 2021

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Publisher
Oxford University Press
Copyright
Copyright © 2023 Entomological Society of America
eISSN
2155-9856
DOI
10.1093/amt/tsac056
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Abstract

Culex tarsalis (Coquillett) permethrin, prallethrin, pyrethrin, resmethrin The objective of this study was to determine whether locally collected mosquitoes were resistant to adulticide products using the CDC bottle bioassay. The Coachella Valley Mosquito and Vector Control District evaluates adulticide resistance of field-collected mosquitoes to a susceptible colony strain on an annual basis. The results of these evaluations determine whether the products can efficiently reduce adult mosquito abundance and disrupt virus transmission. Wild Culex tarsalis mosquitoes were collected by placing carbon dioxide traps overnight and collecting the live adults the next morning. Mosquitoes were collected from the Northshore of the Salton Sea (35.5327, −116.0353). The live mixed-age females were used in the assays. The susceptible colony mosquitoes (originally from Bakersfield, CA, kept in colony since the 1950s) were raised by placing 3 egg rafts per larval rearing tray. Larvae were fed daily a mixture of liver powder, ground fish flakes, brewer’s yeast, and ground alfalfa pellets and were kept in rearing chambers at 50% RH, 28°C, and 16:8 (L:D) h cycle. During the pupal stage, preliminary pupae were removed to increase the female:male ratio, and subsequent pupae were placed in a cage for emergence. Adults were 3–5 d old with mixed sex (70F:30M ratio) and fed 10% sugar water daily. Two hundred fifty (250) ml glass Wheaton bottles were coated with 1 ml of the pesticide product diluted in acetone. Formulations of these products were calculated using the concentration of the active ingredient (a.i.) as indicated in Table 1. For the control, 1 ml of acetone solvent was added to the bottles. The inside of the bottles was fully coated before rolling in a fume hood to allow the solvent to evaporate. Once the solvent evaporated, the bottles were capped, and the assays were conducted within 24 h. Table 1. Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Open in new tab Table 1. Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Product (a.i.) (a.i. dose µg/ml) . Strain . Mean % mortality at time (min) after exposure . . . . . . . . . . 15 . 30 . 45 . 60 . 75 . 90 . 105 . 120 . Aqua-Reslin (Permethrin) (22) Colony 99.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 53.3 81.5 83.6 72.4 91.9 95.0 96.3 96.2 Duet (Prallethrin) (11) Colony 77.9 97.1 99.0 100.0 100.0 100.0 100.0 100.0 Northshore 70.1 76.9 80.9 83.4 87.3 85.5 96.0 93.5 Merus 3.0 (Pyrethrins) (10) Colony 98.5 96.9 100.0 100.0 100.0 100.0 100.0 100.0 Northshore 31.1 57.6 72.8 71.4 86.6 87.0 89.8 89.0 Scourge 18 + 54 (Resmethrin) (11) Colony 50.2 78.8 87.5 96.3 98.1 98.8 99.4 100.0 Northshore 66.8 91.8 96.0 99.5 98.4 99.5 100.0 100.0 Open in new tab For the assays, an average of 36 mosquitoes ranging from 23 to 63 mosquitoes was aspirated into each bottle. Four replicate bottles were used for each local sample population and the susceptible colony mosquitoes. Mosquito mortality was assessed at 15 min after initial exposure and every 15 min thereafter until all mosquitoes in a bottle were dead or the 2 h count was completed. Mosquitoes were observed as knocked down or moribund if they could no longer have controlled flight or stand. At the end of the study, the mosquitoes in each bottle were frozen, counted, and identified to species. For the collections from Northshore, the mosquitoes were comprised of 99.7% Cx. tarsalis and 0.3% other species. Results of mosquito mortality were analyzed using WHO guidelines for mosquito mortality for bottle bioassays. We observed the mosquito mortality of the wild strain when the colony strain reached 100% mortality. Resistance was evident when fewer than 80% of the mosquitoes died at this diagnostic time. The percent mortality at diagnostic dose is underlined in Table 1. This study documented evidence of resistance of local wild mosquitoes to adulticide products. The wild mosquitoes showed susceptibility against Scourge 18 + 54. There is developing resistance of the wild mosquitoes for Aqua-Reslin and Duet. Resistance is evident for Merus 3.0, perhaps due to the lack of a synergist such as PBO.1 Footnotes 1 This research was supported by the Coachella Valley Mosquito and Vector Control District as part of the routine resistance management work. No special research funds were allocated for this work. © The Author(s) 2022. Published by Oxford University Press on behalf of Entomological Society of America. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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Arthropod Management Tests – Oxford University Press

Published: Jan 1, 2022

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