BOTTLE BIOASSAYS OF FIELD COLLECTED MOSQUITOES FOR LEVEL OF ETOFENPROX RESISTANCE IN CENTRAL MASSACHUSETTS 2019 UPDATE

FRANK H. CORNINE III Central Mass. Mosquito Control Project 111 Otis Street Northborough, MA 01532 (508) 393-3055 • www.cmmcp.org • [email protected]

ABSTRACT

Using protocols and supplies distributed from the Centers for Disease Control and Prevention, CMMCP conducted bottle bioassays on locally collected adult mosquitoes against the active ingredient etofenprox. The overwhelming majority of these specimens were of the species Coquillettidia perturbans. Resistance to etofenprox was examined because the primary adulticide product of CMMCP is Zenivex® E4, of which etofenprox is the sole active ingredient. Results from these ongoing bottle bioassays are given to the CDC in an effort to help expand the understanding of pesticide resistance in mosquitoes of the United States.

BACKGROUND Although examples of pesticide resistance have been well documented, Pesticide resistance in this age of vector- the scope of the issue and its real world borne disease can hamper the ability of impact on public health control activities public health officials to successfully is not known. This is partially due to control threats. Potential resistance may varying levels of resistance surveillance also lead to the reemergence of several programs that currently exist. This factor diseases that would have been otherwise is shown in Massachusetts where some contained through control measures organized mosquito control agencies (Brogdon 1998). Current resistance in conduct zero resistance surveillance, select mosquito populations may be the while others have limited to well- result of historical insecticide use in the developed programs collecting data on agricultural and pest control industries pesticide resistance in mosquitoes. In (Rodriguez 2005). The bygone use of addition to the variety of resistance DDT for example, could have contributed surveillance programs, resistance also to current resistance to synthetic appears to be quite localized which pyrethroids, due to the mechanism for further clouds the impact. One noted resistance being similar for both example involved two separate mosquito (Brogdon 1998; McAbee 2003). Another populations that not only differed in associated and contributing factor may resistance levels, but also resistance be the contracting classes and options mechanism, all despite being only a few for public health insecticides as well as miles apart (Brogdon 1998). These growing regulatory restrictions (Brogdon continuing uncertainties surrounding 1998). insecticide resistance have supported CMMCP efforts to monitor for detection of early resistance. In the case of observed resistance, adulticide protocols Field collected mosquitoes were could be modified to ensure continued obtained by using CDC light traps (John efficacy. W. Hock Co., Gainesville, FL) deployed in areas with a history of CMMCP The primary adulticide product used by adulticide applications. The CDC light CMMCP during the 2018 season was traps used compressed carbon dioxide Zenivex® E4 (Wellmark International, gas as an attractant at a release rate of Schaumburg, IL) (EPA Reg No. 2724- 500cc/min. Once the labeled bottles 807), a synthetic pyrethroid that utilizes were coated and sufficiently dried, the active ingredient etofenprox. Prior to approximately 10-15 adult mosquitoes this season CMMCP had used another were aspirated into each bottle synthetic pyrethroid, ANVIL® 10+10 mechanically. ABC standard collection (Clarke Mosquito Control Products, Inc., nets (Clarke Mosquito Control Products, Roselle, IL) (EPA Reg. No. 1021-1688- Inc., Roselle, IL) were used in 8329). Unlike Zenivex® E4, ANVIL® conjunction with the CDC light traps and 10+10 uses the active ingredient held the mosquitoes until introduction Sumithrin along with the synergist into the bioassay bottles. Piperonyl butoxide (PBO). The absence of PBO in Zenivex® E4 is one of its With these local exposed mosquitoes advantages over ANVIL® 10+10. aspirated into the bottles, specimen knockdown percentage was recorded at MATERIALS & METHODS various intervals, up to 100% knockdown or ending at 120 minutes elapsed time. The procedure used for these bottle For the untreated control bottles lined bioassays comes from the Centers for with only acetone (zero etofenprox), Disease Control and Prevention (CDC knockdown percentage was observed at 2010). Using the CDC diagnostic similar intervals. Potential differences concentration established from naïve between the plotted knockdown curves of specimens against mosquito populations the treatment mosquito populations and from the CMMCP service area, potential the established baseline group could be resistance can be observed. In these used to determine if resistance was bottle bioassays, clean 250ml Wheaton forming in local mosquitoes. If test bottles (Wheaton Science Products, specimens survived longer than those of Millville, NJ) were lined with the baseline the baseline group, it could be an etofenprox concentration of 12.5µg/ml. indication of resistance developing. The solutions used in this project were created using pesticide grade acetone DISCUSSION (Thermo Fisher Scientific, Inc., Fair Lawn, NJ) and technical grade CMMCP used an etofenprox etofenprox supplied by the CDC. In concentration of 12.5µg/ml for bottle addition to the bottles coated with bioassays, a level predetermined by the etofenprox, untreated bottles were CDC, to help the public health community created using only the pesticide grade monitor pesticide resistance in local acetone to establish a control for the mosquito populations. Although the CDC bioassays. suggests using lab reared mosquitoes for these bottle bioassays, CMMCP currently uses field collected mosquitoes, Brogdon WG, McAllister JC. 1998. which can introduce additional variables. Insecticide Resistance and Vector Adult mosquitoes collected from the field Control. Emerg Infect Dis 4:605- may be at various ages and metabolic 613. stages, processing exposures to synthetic pyrethroids at different rates. If CDC. 2010. Guideline for evaluating resources allow, future bottle bioassays insecticide resistance in arthropod may attempt to use adult mosquitoes vectors using the CDC bottle reared from locally collected egg rafts bioassays. Atlanta, GA: Center for instead of adult mosquitoes directly Disease Control and Prevention obtained from the field. There are [accessed January 10, 2019]. several advantages to conducting the Available from: bottle bioassays in this manner. If using http://www.cdc.gov/malaria/resourc adults reared from eggs rafts, the es/pdf/fsp/ specimens will all be Culex, which helps ir_manual/ir_cdc_bioassay_en.pdf data comparisons. This method would also allow for the specimens to be McAbee RD, Kang KD, Stanich MA, manipulated to have consistent age, and Christiansen JA, Wheelock CE, metabolic stage. CMMCP will continue Inman AD, Hammock BD, Cornel to examine the local levels of mosquito AJ. 2003. Pyrethroid tolerance in resistance to etofenprox, as Zenivex® E4 Culex pipiens pipiens var molestus is slated to remain the adulticide product from Marin County, California. Pest for the 2020 season. If CMMCP changes Manag Sci 60:359-368. adulticide products to one that uses a different active ingredient, the Rodriguez MM, Bisset JA, DeArmas Y, subsequent bottle bioassays will begin Ramos F. 2005. Pyrethroid utilizing that particular chemical, and the Insecticide-Resistant Strain of corresponding CDC diagnostic Aedes Aegypti From Cuba Induced concentration. by Deltamethrin Selection. J Am Mosq Control Assoc 21(4):437-445. REFERENCES