Next Article in Journal
A Review of Effects of Environment on Brain Size in Insects
Previous Article in Journal
Characterization of Cold Tolerance of Immature Stages of Small Hive Beetle (SHB) Aethina tumida Murray (Coleoptera: Nitidulidae)
Previous Article in Special Issue
The Taxonomic History of Ochlerotatus Lynch Arribálzaga, 1891 (Diptera: Culicidae)
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Brief Report

Susceptibility of South Texas Aedes aegypti to Pyriproxyfen

1
Department of Entomology, Texas A&M University, College Station, TX 77843, USA
2
BanfieldBio Inc., Woodinville, WA 98072, USA
*
Authors to whom correspondence should be addressed.
Submission received: 31 March 2021 / Revised: 10 May 2021 / Accepted: 15 May 2021 / Published: 17 May 2021

Abstract

:

Simple Summary

We evaluated the susceptibility of an Ae. aegypti strain from the Lower Rio Grande Valley (LRGV) of South Texas to the insect growth regulator pyriproxyfen. We observed a difference in the inhibition of emergence to the lowest doses of pyriproxyfen tested between our field strain and a susceptible strain. However, the doses used are 10 times lower from the recommended application of <50 ppb for vector control programs. Our results suggest that pyriproxyfen should be an effective active ingredient in the LRGV to help reduce Ae. aegypti populations in the LRGV.

Abstract

An integral part to integrated mosquito management is to ensure chemical products used for area-wide control are effective against a susceptible population of mosquitoes. Prior to conducting an intervention trial using an insect growth regulator, pyriproxyfen, in South Texas to control Aedes aegypti, we conducted a larval bioassay to evaluate baseline levels of susceptibility. We used seven serially-diluted doses ranging from 2.5 ppb to 6.3 × 10−4 ppb. We observed 100% inhibition emergence (IE) at even the lowest dose of 6.3 × 10−4 ppb in our susceptible reference colony of Ae. aegypti Liverpool. In our field strain of Ae. aegypti (F5 colonized from South Texas) we observed 79.8% IE at 6.3 × 10−4 ppb, 17.7% IE at 1.25 × 10−3 ppb, 98.7% IE at 1.25 × 10−2 ppb, and 100% emergence inhibition for the remainder of the doses. Given that commercial pyriproxyfen products are labeled for doses ranging to 50 ppb, we conclude that the field population sampled by this study are susceptible to this insect growth regulator.

1. Introduction

Aedes aegypti (L.) (Diptera: Culicidae) is an anthropophilic mosquito that is closely associated with urbanized areas across the tropical and subtropical regions of the world. This species has been a major public health concern due to its capacity to transmit arboviruses, such as dengue, chikungunya, yellow fever, and Zika [1]. In the contiguous United States, Ae. aegypti has been reported in Florida and all states that border Mexico [2]. Recently, McGregor and Connelly [3] reviewed chemical control and insecticide resistance studies of Ae. aegypti in the continental U.S. They found a paucity of data on the efficacy and susceptibility of Ae. aegypti to larvicides and emphasized this as a high priority research area.
In the Lower Rio Grande Valley (LRGV) of South Texas, we completed several studies on Ae. aegypti to better understand ecological and social aspects of this mosquito vector [4,5] and to evaluate control tools under local settings [6]. Our research team will conduct an intervention study of Ae. aegypti using pyriproxyfen from autodissemination stations in South Texas. Pyriproxyfen is an insect growth regulator that has been shown to be an effective tool to reduce the emergence of adult Aedes spp. mosquitoes in other geographic areas [7,8,9]. However, before field implementation of pyriproxyfen control tools, the susceptibility status of local Ae. aegypti needs to be assessed. This report presents a laboratory larval bioassay of pyriproxyfen on a recently-colonized population of Ae. aegypti from the LRGV to assess its potential as a control tool for the region.

2. Materials and Methods

Ae. aegypti mosquitoes were sampled from a cemetery (26°06’10.91’’ N, 98°15’16.25’’ W) in the city of Mercedes, Texas. Ovitraps (500 mL black cups, with water and hay) were placed in at least five points within the cemetery (100 m apart from each other) from March through July of 2018. Egg papers were retrieved weekly and transported to our insectary facilities in Weslaco, Texas. These samples were reared under laboratory conditions until the fifth filial generation, the colony stablished was referenced as MCF5.
For comparison we used the Ae. aegypti Liverpool strain, as a susceptible reference. We used an oil-based pre-formulation of 20% technical grade pyriproxyfen (Control Solutions Inc. Pasadena, CA, USA), 12% Tween 20 (Sigma-Aldrich, St. Louis, MO, USA), and 68% methylated seed oil (Southern Ag, Rubonia, FL, USA) to prepare a pyriproxyfen stock solution from which seven pyriproxyfen doses (6.3 × 104 ppb, 1.25 × 103 ppb, 1.25 × 102 ppb, 2.5 × 102 ppb, 6.25 × 102 ppb, 1.25 × 101 ppb, 2.5 ppb) were prepared 24 h prior their use. The carrier methylated seed oil and Tween 20 were used in prior studies of autodissemination of pyriproxyfen [8,9,10]. These doses of pyriproxyfen have been previously observed to generate a mortality range of 10–95% [11,12,13] in susceptible strains. For the bioassays, we used 20 third instar larvae at a density of one larva per 10 mL of water. Four replicates per dose were tested (see Supplementary Dataset 1). Briefly, four sets of 200 mL of each dose solution or water were placed in plastic cups; subsequently, 20 L3 larvae were added into each cup. Larvae were monitored every 24 h until all the adults in the absolute control (water) emerged. These methods follow WHO guidelines for larvicide testing [14]. Given the long duration of the test, approximately two drops of liver powder solution (10% w/v) were added every other day until pupae were found in the cups. In addition, to assure the oil-based formulation used did not cause mortality, we set up another set of bioassays using the carrier oil alone as the technical control (15% Tween 20 and 85% methylated seed oil). For statistical comparison, we used the results observed 12 days post emergence for dead pupae and adults. The data was analyzed using a generalized linear model (GLM) approach with a binomial distribution. We model the interaction effect of dose by strain using the stat and emmeans packages in R. 4.0.4 (R Core Team, Vienna, Austria) (see Supplementary Rcode) [15,16].

3. Results

From the seven doses evaluated we were unable to detect a concentration that yielded between 10 and 95% inhibition of emergence (IE) to determine the IE50 and IE90 values in the susceptible strain (Figure 1). Instead, we observed 100% IE at even the lowest dose of 6.3 × 10−4 ppb in the susceptible strain. We did not observe any statistical difference for larval or pupal development when comparing the absolute control (water) and the technical control (carrier oil), confirming that the IE observed in the susceptible strain was due to the presence of pyriproxyfen. Our field strain (MCF5) did not show 100% IE in all doses. We observed 79.8% IE (SE = 14.5%) at 6.3 × 10−4 ppb, 17.7% IE (SE = 15.1%) at 1.25 × 10−3 ppb, and 98.7% IE (SE = 2.6%) at 1.25 × 10−2 ppb (Figure 1). The GLM analysis showed that if all other variables were held constant, a statistically significant interaction between dose (1.25 × 10−3 ppb) and strain (MCF5) (estimate = −4.321, SE = 1.17, p-value ≤ 0.001) was observed. Interestingly, for the MCF5 at a dose of 1.25 × 10−3 ppb we consistently observed a lower IE than that found at the lowest dose of 6.3 × 10−4 ppb (estimate = 2.84, SE = 0.41, p ≤ 0.001). Adult emergence in all control groups was >90%.

4. Discussion

Our results show that the South Texas mosquito population MCF5 had resistance at a very low dose of pyriproxyfen that warrants more careful monitoring. We observed a difference in IE for the second lowest doses of the MCF5. Interestingly, we consistently observed a higher IE in the lowest dose tested (6.3 × 10−4 ppb; 79.8% IE) when compared to the second lowest dose (1.25 × 10−3 ppb; 17.7% IE). A pattern that was also observed in the control strain but just marginally. We believe that this might be related to the fine scale regulation that controls ecdysone biosynthesis and how juvenile hormone inhibits it [17,18]; the quantity of receptors occupied at this concentration could be ideal, and further doses closer to this range should be explored to elucidate the LD50. However, none of these concentrations used in this study approach the lowest suggested rates of current commercial pyriproxyfen products such as Admiral 10EC (10% active ingredient (AI)), Admiral Advance (10% AI), and NyGuard (10% AI), which are tenfold higher or more. Traditionally, mosquito control programs apply pyriproxyfen at a dose of <50 ppb [19]. These assays show a proof of principle that vector control tools that use pyriproxyfen as an active ingredient could serve as useful tools for controlling Ae. aegypti in the LRGV. Pyriproxyfen is an insect growth regulator that targets immature stages of mosquitoes; it acts at very low doses and it persists for several months in larval habitats [20,21]. Therefore, autodissemination stations that rely on pyriproxyfen might have a meaningful impact as a control tool in areas were source reduction campaigns are unfeasible or cost prohibitive [22]. In addition, integrating additional active ingredients targeting different insect life stages will help to mitigate the development of insecticide resistance. This study did not assess this formulation of pyriproxyfen in the field to estimate the duration of effectiveness. Moreover, this study did not evaluate sublethal doses of pyriproxyfen, which have been documented to increase resistance to pyrethroids in other mosquito species [23]. We point out that the sublethal doses observed in the MCF5 population demonstrate the importance of insecticide resistance surveillance given the potential for the establishment of a resistant wild population. This is particularly relevant to an autodissemination study since exposure to pyriproxyfen in the field is likely to vary among individuals given inconsistent doses to the container habitat. This emphasizes the importance of vector control activities to deliver an adequate dose of insecticide and that failure to do so could enhance the observed resistance. Surveillance for the development of resistance for pyriproxyfen is important as there have been reports of resistance elsewhere in the world [24,25].

Supplementary Materials

The following are available online at https://0-www-mdpi-com.brum.beds.ac.uk/article/10.3390/insects12050460/s1, Dataset 1 and Rcode.

Author Contributions

Conceptualization, S.M.G.-L., A.B., M.G.B., and G.L.H.; methodology, S.M.G.-L., A.B., and G.L.H.; validation, S.M.G.-L., J.G.J., A.B., M.G.B., and G.L.H.; formal analysis, J.G.J., S.M.G.-L., and G.L.H.; investigation, S.M.G.-L., J.G.J., A.B., M.G.B., and G.L.H.; resources, M.G.B. and G.L.H.; data curation, J.G.J., S.M.G.-L., C.M.R., and G.L.H.; writing—original draft preparation, J.G.J., S.M.G.-L., and G.L.H.; writing—review and editing, J.G.J., S.M.G.-L., C.M.R., A.B., M.G.B., and G.L.H.; visualization, J.G.J., S.M.G.-L., and C.M.R.; supervision, S.M.G.-L. and G.L.H.; project administration, S.M.G.-L. and G.L.H.; funding acquisition, M.G.B. and G.L.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Centers for Disease Control and Prevention, contract 200-2017-93141. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention or the Department of Health and Human Services.

Institutional Review Board Statement

No IRB required.

Data Availability Statement

The datasets are available in the Dataset 1 in Supplementary Material.

Acknowledgments

We would like to thank Ismael Badillo-Vargas for facilitating insectary space at the Texas A&M AgriLife Research Station in Weslaco, Texas. We thank Edwin Valdez for insectary work during the course of this study.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. WHO. Global Vector Control Response 2017–2030; World Health Organization: Geneva, Switzerland, 2017. [Google Scholar]
  2. Hahn, M.B.; Eisen, L.; McAllister, J.; Savage, H.M.; Mutebi, J.P.; Eisen, R.J. Updated reported distribution of Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus (Diptera: Culicidae) in the United States, 1995-2016. J. Med. Entomol. 2017, 54, 1420–1424. [Google Scholar] [CrossRef]
  3. McGregor, B.L.; Connelly, C.R. A Review of the Control of Aedes aegypti (Diptera: Culicidae) in the Continental United States. J. Med. Entomol. 2020. [Google Scholar] [CrossRef]
  4. Olson, M.F.; Garcia-Luna, S.; Juarez, J.G.; Martin, E.; Harrington, L.C.; Eubanks, M.D.; Badillo-Vargas, I.E.; Hamer, G.L. Sugar Feeding Patterns for Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae) Mosquitoes in South Texas. J. Med. Entomol. 2020, 1–9. [Google Scholar] [CrossRef] [PubMed]
  5. Juarez, J.G.; Garcia-Luna, S.; Chaves, L.F.; Carbajal, E.; Valdez, E.; Avila, C.; Tang, W.; Martin, E.; Barrera, R.; Hemme, R.R.; et al. Dispersal of female and male Aedes aegypti from discarded container habitats using a stable isotope mark-capture study design in South Texas. Sci. Rep. 2020, 10, 6803. [Google Scholar] [CrossRef]
  6. Garcia-Luna, S.M.; Chaves, L.F.; Juarez, J.G.; Bolling, B.G.; Rodriguez, A.; Presas, Y.E.; Mutebi, J.P.; Weaver, S.C.; Badillo-Vargas, I.E.; Hamer, G.L.; et al. From Surveillance To Control: Evaluation of A Larvicide Intervention Against Aedes aegypti In Brownsville, Texas. J. Am. Mosq. Control Assoc. 2019, 35, 233–237. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  7. Maoz, D.; Ward, T.; Samuel, M.; Müller, P.; Runge-Ranzinger, S.; Toledo, J.; Boyce, R.; Velayudhan, R.; Horstick, O. Community effectiveness of pyriproxyfen as a dengue vector control method: A systematic review. PLoS Negl. Trop. Dis. 2017, 11, e0005651. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  8. Chandel, K.; Suman, D.S.; Wang, Y.; Unlu, I.; Williges, E.; Williams, G.M.; Gaugler, R. Targeting a Hidden Enemy: Pyriproxyfen Autodissemination Strategy for the Control of the Container Mosquito Aedes albopictus in Cryptic Habitats. PLoS Negl. Trop. Dis. 2016, 10, e0005235. [Google Scholar] [CrossRef]
  9. Unlu, I.; Suman, D.S.; Wang, Y.; Klingler, K.; Faraji, A.; Gaugler, R. Effectiveness of autodissemination stations containing pyriproxyfen in reducing immature Aedes albopictus populations. Parasites Vectors 2017, 10, 139. [Google Scholar] [CrossRef] [Green Version]
  10. Unlu, I.; Rochlin, I.; Suman, D.S.; Wang, Y.; Chandel, K.; Gaugler, R. Large-scale operational pyriproxyfen autodissemination deployment to suppress the immature asian tiger mosquito (Diptera: Culicidae) Populations. J. Med. Entomol. 2020, 57, 1120–1130. [Google Scholar] [CrossRef]
  11. Sihuincha, M.; Zamora-Perea, E.; Orellana-Rios, W.; Stancil, J.D.; López-Sifuentes, V.; Vidal-Oré, C.; Devine, G.J. Potential use of pyriproxyfen for control of Aedes aegypti (Diptera: Culicidae) in Iquitos, Perú. J. Med. Entomol. 2005, 42, 620–630. [Google Scholar] [CrossRef] [Green Version]
  12. Su, T.; Thieme, J.; Lura, T.; Cheng, M.L.; Brown, M.Q. Susceptibility Profile of Aedes aegypti L. (Diptera: Culicidae) from Montclair, California, to Commonly Used Pesticides, with Note on Resistance to Pyriproxyfen. J. Med. Entomol. 2019, 56, 1047–1054. [Google Scholar] [CrossRef] [PubMed]
  13. Darriet, F.; Corbel, V. Laboratory evaluation of pyriproxyfen and spinosad, alone and in combination, against Aedes aegypti larvae. J. Med. Entomol. 2006, 43, 1190–1194. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  14. WHO. Guidelines for Laboratory and Field Testing of Mosquito Larvicides; World Health Organization: Geneva, Switzerland, 2005. [Google Scholar]
  15. Lenth, R.; Singmann, H.; Love, J.; Buerkner, P.; Herve, M. Package “emmeans.”. CRAN 2019, 1–75. [Google Scholar]
  16. Faraway, J.J. Extending the Linear Model with R: Generalized Linear, Mixed Effects and Nonparametric Regression Models, 2nd ed.; CRC Press: Boca Raton, FL, USA, 2016; ISBN 978-1498720960. [Google Scholar]
  17. Liu, S.; Li, K.; Gao, Y.; Liu, X.; Chen, W.; Ge, W.; Feng, Q.; Palli, S.R.; Li, S. Antagonistic actions of juvenile hormone and 20-hydroxyecdysone within the ring gland determine developmental transitions in Drosophila. Proc. Natl. Acad. Sci. USA 2018, 115, 139–144. [Google Scholar] [CrossRef] [Green Version]
  18. Bensebaa, F.; Kilani-Morakchi, S.; Aribi, N.; Soltani, N. Evaluation of pyriproxyfen, a juvenile hormone analog, on Drosophila melanogaster (Diptera: Drosophilidae): Insecticidal activity, ecdysteroid contents and cuticle formation. Eur. J. Entomol. 2015, 112, 625–631. [Google Scholar] [CrossRef] [Green Version]
  19. WHO. Report of the Fourth WHOPES Working Group Meeting; World Health Organization: Geneva, Switzerland, 2001. [Google Scholar]
  20. Hustedt, J.C.; Boyce, R.; Bradley, J.; Hii, J.; Alexander, N. Use of pyriproxyfen in control of Aedes mosquitoes: A systematic review. PLoS Negl. Trop. Dis. 2020, 14, 1–18. [Google Scholar] [CrossRef]
  21. Suman, D.S.; Wang, Y.; Faraji, A.; Williams, G.M.; Williges, E.; Gaugler, R. Seasonal field efficacy of pyriproxyfen autodissemination stations against container-inhabiting mosquito Aedes albopictus under different habitat conditions. Pest Manag. Sci. 2018, 74, 885–895. [Google Scholar] [CrossRef] [PubMed]
  22. Yadav, K.; Dhiman, S.; Acharya, B.; Ghorpade, R.R.; Sukumaran, D. Pyriproxyfen treated surface exposure exhibits reproductive disruption in dengue vector Aedes aegypti. PLoS Negl. Trop. Dis. 2019, 13, e0007842. [Google Scholar] [CrossRef] [Green Version]
  23. Opiyo, M.A.; Ngowo, H.S.; Mapua, S.A.; Mpingwa, M.; Matowo, N.S.; Majambere, S.; Okumu, F.O. Sub-lethal aquatic doses of pyriproxyfen may increase pyrethroid resistance in malaria mosquitoes. PLoS ONE 2021, 16. [Google Scholar] [CrossRef]
  24. Carvalho, B.L.; Germano, R.N.L.; Braga, K.M.L.; de Araújo, E.R.F.; Rocha, D.d.A.; Obara, M.T. Susceptibility of Aedes aegypti populations to pyriproxyfen in the federal district of Brazil. Rev. Soc. Bras. Med. Trop. 2020, 53. [Google Scholar] [CrossRef] [Green Version]
  25. Campos, K.B.; Martins, A.J.; de Melo Rodovalho, C.; Bellinato, D.F.; dos Santos Dias, L.; da Graça Macoris, M.D.L.; Andrighetti, M.T.M.; Lima, J.B.P.; Obara, M.T. Assessment of the susceptibility status of Aedes aegypti (Diptera: Culicidae) populations to pyriproxyfen and malathion in a nation-wide monitoring of insecticide resistance performed in Brazil from 2017 to 2018. Parasites Vectors 2020, 13, 531. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Mortalities induced by pyriproxyfen on the pupae of Ae. aegypti to the Liverpool susceptible strain and the field collected strain (MCF5) from South Texas. *** Shows statistical significance at p ≤ 0.001.
Figure 1. Mortalities induced by pyriproxyfen on the pupae of Ae. aegypti to the Liverpool susceptible strain and the field collected strain (MCF5) from South Texas. *** Shows statistical significance at p ≤ 0.001.
Insects 12 00460 g001
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Juarez, J.G.; Garcia-Luna, S.M.; Roundy, C.M.; Branca, A.; Banfield, M.G.; Hamer, G.L. Susceptibility of South Texas Aedes aegypti to Pyriproxyfen. Insects 2021, 12, 460. https://0-doi-org.brum.beds.ac.uk/10.3390/insects12050460

AMA Style

Juarez JG, Garcia-Luna SM, Roundy CM, Branca A, Banfield MG, Hamer GL. Susceptibility of South Texas Aedes aegypti to Pyriproxyfen. Insects. 2021; 12(5):460. https://0-doi-org.brum.beds.ac.uk/10.3390/insects12050460

Chicago/Turabian Style

Juarez, Jose G., Selene M. Garcia-Luna, Christopher M. Roundy, Alyssa Branca, Michael G. Banfield, and Gabriel L. Hamer. 2021. "Susceptibility of South Texas Aedes aegypti to Pyriproxyfen" Insects 12, no. 5: 460. https://0-doi-org.brum.beds.ac.uk/10.3390/insects12050460

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop