Pesticide Resistance Monitoring Program

Pesticide resistance is an emerging global issue for many mosquitoes and some ticks, including those that transmit vector-borne diseases to humans and animals. Unfortunately, pesticide resistance monitoring in the United States is limited. As the burden of vector-borne disease spreads, it is crucial to monitor for pesticide resistance to ensure our tools for vector control remain effective in emergency situations.

The  Northeast Regional Center for Excellence in Vector-Borne Diseases  (NEVBD) is working to assist the Centers for Disease Control and Prevention (CDC) and collaborators throughout the northeastern U.S. to address the resistance monitoring gap through our  Pesticide Resistance Monitoring Program .

How Does Pesticide Resistance Happen?

1. A pesticide is used to kill a target pest, like mosquitoes. But, sometimes not all of the mosquitoes die when the pesticide is applied. Some individuals are able to survive contact with the pesticide.
2. The surviving mosquitoes will pass their ability to survive contact with this pesticide to their offspring. The number of these resistant individuals increases in the mosquito population.
3. The next time that pesticide is used, there are more resistant mosquitoes in the group who can survive. They also pass this ability to their offspring, again increasing the number of resistant individuals in the population.
4. After a few generations, a large portion of the mosquito population is resistant to the pesticide, making that product less effective at controlling mosquito populations. This can be a major issue when disease outbreak emergencies occur.

What are We Doing to Address the Pesticide Resistance Monitoring Gap?

Our Pesticide Resistance Monitoring Program is taking the following steps to address this pressing need:

• Pesticide Use and Resistance Survey: a yearly survey designed to reveal the extent of current resistance monitoring operations in our region, understand barriers, and determine priorities for our program
• Educational Resources: webinars, protocols, and hands-on technical assistance provide to vector control professionals across the region in pesticide resistance monitoring fundamentals and techniques
• Specimen Submission System: vector control professionals in the region can submit Culex pipiens and Aedes albopictus mosquitoes to our facilities at Cornell University to be tested for resistance to a variety of routinely-used pesticides. Results are reported back to submitting agencies.
• Adult & Larval Mosquito Testing: NEVBD tests adult and larval mosquitoes using the CDC Bottle Bioassay and NEVBD larvicidal resistance assay

Explore results from our submission & testing system by season in the interactive maps below!

You can also learn more about how to access our services by visiting our primary website at  https://neregionalvectorcenter.com/resistance .

Since our program initiated operations in 2019, we have processed 125,638 mosquito specimens for resistance testing at our Cornell University facilities, submitted from 41 public health and vector control agencies across the northeast region. Sixty-three percent (78,579) of these specimens have been tested for resistance to adulticides, with the remaining 37% (47,059) tested for resistance to larvicides.

Our program has tested for resistance to seven pyrethroid and two organophosphate adulticides; as well as larval resistance to two mosquitocidal bacteria and one insect growth regulator. The majority of our adulticide assays to-date have tested for resistance to sumithrin, permethrin, and etofenprox. The majority of our larvicide assays to-date have tested for resistance to the insect growth regulator methoprene.

We have received mosquito samples from 259 sites across 11 states in the Northeast region. Close to half of the specimens from these sites (47%) were susceptible to the pesticides we tested against. However, the number of sites with samples testing as low, moderate, and high resistance have increased across the years of our testing program.

Our program received 40,561 mosquito specimens from 19 agencies across 7 states in our region. Specimens were collected between 24 June and 13 September 2024. Of these submissions, 28,230 mosquitoes were tested for resistance to seven adulticide products and 12,331 mosquitoes were tested for resistance to three larvicide products.

Within the samples tested, a subset of 548 Culex spp. mosquitoes from one location in the mid-Atlantic region were tested for resistance to four adulticide products with the use of inhibitors. An additional subset of 190 Culex spp. mosquitoes from one location in the New England region were tested for resistance to one adulticide product with the use of inhibitors.

We continued to observe widespread low- to moderate-level resistance to methoprene in Culex pipens/restuans populations across the northeast region, with high-level resistance observed in Massachusetts. The number of locations with moderate to high-level resistance to pyrethroids increased between 2023 and 2024, with high resistance continuing to be detected in Culex spp. populations in Virginia, New Jersey, New York and Massachusetts, as well as new locations in Maine. No resistance to adulticides was detected in the Ae. albopictus samples tested.

Inhibitors were used in conjunction with the CDC bottle bioassay to identify potential mechanisms the mosquito might be using to detoxify the pesticide through a metabolic process. An increase in mortality when an inhibitor is used indicates a group of enzymes that may play a role in resistance. A subset of mosquitoes from Suffolk, Virginia, were tested using two inhibitors:

• PBO: piperonyl butoxide - inhibits oxidase activity
• DEF: S.S.S-tributlyphosphorotrithioate - inhibits esterase activity

A subset of mosquitoes from Barnstable County, Massachusetts, were also tested using the inhibitors PBO and DEF.

Our program received 30,373 mosquito specimens from 23 agencies across 7 states in our region. Specimens were collected between 5 June and 7 September 2023. Of these submissions, 18,648 mosquitoes were tested for resistance to nine adulticide products and 11,725 mosquitoes were tested for resistance to three larvicide products.

Within the samples tested, a subset of 725 Culex spp. mosquitoes from one location in the mid-Atlantic region were tested for resistance to three adulticide products with the use of inhibitors. An additional subset of 163 Culex spp. mosquitoes from one location in the New England region were tested for resistance to two adulticide products with the use of inhibitors.

We continued to observe widespread low- to moderate-level resistance to methoprene in Culex pipens/restuans populations across the northeast region. The number of locations with moderate to high-level resistance to pyrethroids increased between 2022 and 2023, with high resistance continuing to be detected in Culex spp. populations in Virginia, New Jersey, and Massachusetts, as well as new locations in New York. No resistance to adulticides was detected in the Ae. albopictus samples tested.

Inhibitors were used in conjunction with the CDC bottle bioassay to identify potential mechanisms the mosquito might be using to detoxify the pesticide through a metabolic process. An increase in mortality when an inhibitor is used indicates a group of enzymes that may play a role in resistance. A subset of mosquitoes from Suffolk, Virginia, were tested using three inhibitors:

• PBO: piperonyl butoxide - inhibits oxidase activity
• DEF: S.S.S-tributlyphosphorotrithioate - inhibits esterase activity
• DM: Diethyl maleate - inhibits glutathione transferase activity

A subset of mosquitoes from Plymouth County, Massachusetts, were also tested using the inhibitor PBO.

Our program received 24,527 mosquito specimens from 22 agencies across 6 states in our region. Specimens were collected between 13 June and 19 September 2022. Of these submissions, 20,133 mosquitoes were tested for resistance to seven adulticide products and 4,394 mosquitoes were tested for resistance to three larvicide products.

Within the samples tested, a subset of 1,390 Culex spp. mosquitoes from the mid-Atlantic region were tested for resistance to three adulticide products with the use of inhibitors.

We continued to observe widespread low-level resistance to methoprene in Culex pipens/restuans populations across the northeast region and some Ae. albopictus populations. The number of locations with moderate to high-level resistance to pyrethroids increased between 2021 and 2022, with high resistance continuing to be detected in Culex spp. populations in Virginia and New Jersey, as well as new locations in Massachusetts. No resistance to adulticides was detected in the Ae. albopictus samples tested.

Inhibitors were used in conjunction with the CDC bottle bioassay to identify potential mechanisms the mosquito might be using to detoxify the pesticide through a metabolic process. An increase in mortality when an inhibitor is used indicates a group of enzymes that may play a role in resistance. A subset of mosquitoes from Suffolk, Virginia, were tested using three inhibitors:

• PBO: piperonyl butoxide - inhibits oxidase activity
• DEF: S.S.S-tributlyphosphorotrithioate - inhibits esterase activity
• DM: Diethyl maleate - inhibits glutathione transferase activity

Our program received 11,226 mosquito specimens from 19 agencies across 8 states in our region. Specimens were collected between 6 June and 23 September 2021. Of these submissions, 7,622 mosquitoes were tested for resistance to seven adulticide products and 3,604 mosquitoes were tested for resistance to three larvicide products.

Within the samples tested, a subset of 955 Culex spp. mosquitoes from the mid-Atlantic region were tested for resistance to three adulticide products with the use of synergists.

We continued to observe widespread low-level resistance to methoprene in Culex pipens/restuans populations across the northeast region. The number of locations with moderate to high-level resistance to pyrethroids increased between 2020 and 2021, with high resistance detected in Culex spp. populations in Virginia and New Jersey. No resistance was detected in any Ae. albopictus samples tested.

Inhibitors were used in conjunction with the CDC bottle bioassay to identify potential mechanisms the mosquito might be using to detoxify the pesticide through a metabolic process. An increase in mortality when an inhibitor is used indicates a group of enzymes that may play a role in resistance. A subset of mosquitoes from Suffolk, Virginia, were tested using two inhibitors:

• PBO: piperonyl butoxide - inhibits oxidase activity
• DM: Diethyl maleate - inhibits glutathione transferase activity

Our program received 8,047 mosquito specimens from 10 agencies across 7 states in our region. Specimens were collected between 16 June and 14 August 2020. Of these submissions, 2,072 mosquitoes were tested for resistance to four adulticide products and 5,975 mosquitoes were tested for resistance to three larvicide products.

Submissions to our program were lower than expected in the 2020 season, largely due to constraints imposed on vector control programs by the SARS-CoV-2 pandemic. We continued to observe widespread low-level resistance to methoprene in Culex pipiens populations across the northeast region. Moderate to high-level resistance to pyrethroids, and emerging resistance to organophosphates, was detected in mosquito populations in the mid-Atlantic region.

Our program received 18,942 mosquito specimens from 13 agencies across 6 states in our region. Specimens were collected between 22 July and 31 September 2019. Of these submissions, 4,210 mosquitoes were tested for resistance to seven adulticide products and 14,732 mosquitoes were tested for resistance to three larvicide products.

The majority of the resistance assays conducted in 2019 focused on larvicide resistance. Widespread low-level resistance to methoprene was detected among Culex pipiens tested from across the region; no resistance to methoprene was detected in Ae. albopictus. No resistance to Bti or L. sphaericus were detected through our larvicidal assays.

Few adulticide assay requests were submitted in 2019. Resistance to pyrethroids was detected in several Culex pipiens populations; the resistance level detected varied by location. Pyrethroid resistance was also detected in some Ae. albopictus populations, mostly from New Jersey.