Mosquito Management in the Age of Extreme Weather

As climate change drives weather patterns like intense hurricane seasons, even areas as far north as New England are seeing shifts in mosquito populations, as a Massachusetts mosquito control entomologist shares. . Here, a trap collecting cup is overflowing with adult mosquitoes.

By Kaitlyn O’Donnell

Kaitlyn O'Donnell

Kaitlyn O’Donnell

We are now well aware of the many ways climate change is reshaping the world we live in, but how do we experience these changes regionally, first-hand? As an entomologist working for a local government mosquito control organization in the Northeastern United States, we have the unique ability to closely observe mosquito populations in a specific area over an extended period of time and detect trends and changes.

There is a lot of interesting current research shedding light on the relationship between climate change and mosquitoes. Studies have linked Drought and rising temperatures increased incidence of arthropod-borne diseases and a longer mosquito season. At the other end of the weather spectrum, a lot of work has been done on mosquitoes population dynamic after hurricane flooding.

A deluge of mosquitoes

With each passing hurricane season, we are reminded of how increased frequency and severity of extreme weather events are becoming the new normal. According to the National Oceanic and Atmospheric Administration, the past six years have had above-average hurricane seasons, with 2020 marking the most active season and 2021 the third most active season in recorded history. While New England may not come to mind when thinking of hurricane fallout in the United States, the explosion of mosquito populations in 2021 after three consecutive storms may change your mind. .

After repeated flooding in the height of summer, the 2021 mosquito season has shattered all trap abundance records my district of Massachusetts has had before. I had never seen so many mosquitoes crowding into a single trap – so voracious for the carbon dioxide bait that they compressed themselves, over 23,000 of them, into a 40 cubic inch space ( about the size of a sandwich container).

The majority of these collections were made up of floodplain mosquito species, which lay eggs in a dry floodplain and wait for rain to flood the surrounding wetland with enough water for the eggs to hatch. Some common species multiply after these rainy events, but the collections are mainly made up of two in particular: Aedes vexans and Psorophore ferox.

floodplain habitat

Floodplain mosquito species lay their eggs in a dry floodplain and wait for rain to flood the surrounding wetland (like the one pictured here) with enough water for the eggs to hatch. A few common species spike after these rainy events, but recent collections in Norfolk County’s Mosquito Control District (Massachusetts) have mostly consisted of two in particular: Aedes vexans and Psorophore ferox.

In the 2021 season, these two species experienced three peaks in abundance closely following three major rainfall events throughout the summer, starting with the remnants of Hurricane Elsa, which hit the northeast. beginning of July. Mosquitoes Ps.ferox and Ah. the vexans are aggressive human biters and are capable vectors of disease; their presence does not go unnoticed. These relative abundance spikes are supported by an increase in calls from residents reporting intolerable mosquito conditions around their homes and region-wide requests for adulticide. And with the repeated rains and repeated emergences of mosquitoes, there was never any relief.

As mosquito control professionals, using this historical and current mosquito population data along with weather data is an important part of our integrated pest management toolkit. We can predict how many floods will cause an outbreak of mosquito species in floodplains and be proactive in managing populations rather than reactive. We can treat these floodplains for larvae depending on time, resources and weather conditions, which will hopefully reduce the need for area-wide adulticide.

Different species settle

Historical floodplain abundance data has also highlighted the clear shift in dominant floodplain species during an outbreak. In the past, epidemics in the floodplains were dominated by Ah. the vexans, as Ps.ferox had not yet extended its range so far north. However, in recent years, Ps.ferox populations have exploded, particularly in response to flooding, and they appear to be replacing Ah. the vexans like the dominating mosquito of the floodplains. Our historical data shows very low collections of Ps.ferox on the whole, gradually increasing each year until it is almost equal to the Ah. the vexans population in 2013, which was our last major floodplain outbreak before a dry spell in 2015 to 2016.

Since then, the traps are dominated by Ps.ferox in floodplain areas, with 2021 being by far the most productive season. Another mosquito excitement stems from the collection of a very mean and fearsome mosquito in 2020 and 2021: Psorophora ciliata. Sometimes known as the gallinipper, Ps.ciliata is a very large mosquito and gives a painful bite. Its described range covers most of the eastern United States, including the northeast, excluding Maine. The species is more common further south, but some districts in the northeast have collected individuals in recent years. My district took in our first adult Ps.ciliata in 2020, rising to three people in 2021. News organizations reported a large outbreak of this mosquito after a hurricane inundated parts of North Carolina, describing a dire situation where residents could not stay outside. outside for a while without being barred from the air by those big aggressive human biters. While we hope this doesn’t happen in New England, we expect to see more of this mosquito in the future.

I am often asked to predict the next mosquito season by news outlets, friends and acquaintances, and residents of our district. It’s never easy to do, because mosquitoes are so weather-dependent in very nuanced ways. Moving forward, after two consecutive years of heavy rainfall and growth Ps.ferox populations, it will be interesting to see what the 2022 mosquito season brings.

Kaitlyn O’Donnell, is an entomologist at the Norfolk County Mosquito Control District in Walpole, Massachusetts. Email: [email protected]

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