Michael Moorhouse
While the exact mechanisms of El Niño aren’t fully understood — not surprising, given it involves a complicated back-and-forth between ocean waters and the atmosphere — there is one thing for sure: Its impacts are felt around the globe.
From snow-starved Japanese ski resorts to meager West African cocoa harvests, the 2015-16 El Niño was among the strongest on record. And, though on the surface there may not seem to be a direct correlation between El Niño and mosquito populations, some researchers suggest the climate phase’s heightened temperatures in Southeast Asia are enhancing mosquito-borne illnesses there. So, what does that mean for the mosquito season here on the Western Hemisphere?
What We Know About El Niño
To start this analysis, let’s first dissect what El Niño actually is. Simply put , El Niño occurs when the eastern side of the tropical Pacific Ocean heats up in connection with slackening west-blowing trade winds; the usually warmer western tropical Pacific, meanwhile, cools down. This flip-flop of ocean temperatures has worldwide reverberations.
Among them is the southern migration of the subtropical jet stream that usually channels storm systems into the Pacific Northwest and across the northern United States. Closer to the equator, the El Niño-affected jet stream often brings this storminess into the southern U.S. and northern Mexico instead. Southern California’s January deluges were a good example of this. While it’s not always so cut-and-dry, the southern U.S is typically cooler and wetter than usual during an El Niño winter, while the north experiences a warmer and drier climate. As we’ve seen in 2016, that’s exactly what happened.
What We Know About Mosquitoes
So, how is this connected to the migratory and reproductive patterns of mosquitoes? Well, with nearly 200 species of mosquitoes active in the U.S., there’s a lot of variety when it comes to environmental requirements (some are more tolerant to cold than others, for instance.) In general, however, mosquito season in a given area tends to kick in when temperatures start consistently hitting 50 degrees or higher. In a normal year, mosquitoes may be hatching out by the beginning of February in southern Texas, Louisiana and Florida; by April, the bloodsuckers are starting to swarm across much of the central part of the country.
Because mosquitoes lay their eggs and mature in standing water, plentiful rain may foster quite a population explosion as well. In that sense, the above-average precipitation for the southern U.S. associated with El Niño could mean ramped-up mosquito numbers come spring. That theory is further supported by the fact that parts of the southern U.S. saw an atypical second wave of mosquitoes in the fall of 2015, likely due to El Niño-spurred October downpours.
But, it’s not only precipitation we need to consider: There’s also the factor of temperature. A study examining the impacts of the 1997-1998 El Niño on mosquito numbers in western Los Angeles County showed that cool-weather mosquitoes prospered well into summer that year courtesy of lower-than-usual temperatures.
How It’s All Connected
Of course, the presence of mosquitoes is a generally unappealing thing for most people, but this potential increase in populations is especially concerning when it comes to mosquito-borne diseases. Viruses like West Nile and the new threat of Zika are often most apparent in late summer or early autumn when populations of infected hosts (in West Nile’s case, birds) and mosquitoes have had enough time to build up significant levels of the virus in turn creating more opportunities for the virus in question to be passed along to humans. Some experts are now worried that a prolonged mosquito season in parts of the U.S. due to El Niño could increase the likelihood of West Nile, Zika, chikungunya and other mosquito-borne ailments.
While climatologists believe the current El Niño peaked and diminished during the first half of 2016, it’s still expected to have impacts, however small, on the timing and nature of springtime mosquito emergence — with the strongest impacts expected in the western and southern parts of the country. Temperatures a few degrees cooler may marginally delay mosquito breeding, but the pooled and puddled water derived from continued El Niño rainstorms could provide more extensive habitat for eggs, larvae and pupae.
In other words, we still aren’t completely sure what the impacts will be, but there’s no question that El Niño will influence the mosquito patterns of the coming months — making now the best time to prepare for it.
Michael Moorhouse is vice president of Mosquito Shield, a mosquito and tick control franchise company with more than 15 years in the industry. With more than six years with Mosquito Shield, Michael has established a proven track record in marketing and business development, and extensive experience in the fast-paced environment of sales.
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