On March 27, Pestec’s Mosquito Abatement Courier (MAC) crew completed our first round of the mosquito control season (February through October), covering all of the City in just under 6 weeks. (For those who are new to our website, a round is the inspection of all of San Francisco’s 25,000 + public catch basins – also known as sewer drains. Catch basins holding water are treated with Vectomax, a reduced risk larvicide that kills mosquito larvae. A round should be completed within 6 weeks, the length of time that Vectomax is effective.)

This year marks the 10th season for the Pestec MAC crew and the 2015 team consists of 7 bike riders, 3 of whom are starting their first year. Despite the relative inexperience of the team, we were able to fulfill the bold prediction of one rider who said on Monday the 23rd that we would “finish by Friday,” the 27th. And we did so despite the fact that that same rider missed several basins in his assigned area (full disclosure: it was me). Fortunately, one of our “rookies” spotted the error on the morning of the 27th and we were able to complete the round that day.

After finishing the round we had enough time to get back to the Bayview for the customary pizza party we enjoy at the end of each round.

One reason we were able to finish the round ahead of time is because our rookies have proven to be fast learners who appreciate and are acquiring the strong work ethic of the 4 veteran riders. A less fortunate reason is that California’s long drought, now in its 4th year, did not cause any rain delays. But that is one of the very few benefits of this ongoing drought that continues to weaken our state. Hopes that the the drought would end with the heavy rains we had last December have disappeared with the almost complete dry spell that has started with the new year and will probably last until autumn, if not longer.

Contrary to expectations, droughts do not necessarily decrease mosquito populations. In fact, sometimes a drought canincrease the number of mosquitoes. Droughts decrease the flow of running water in creeks and rivers, leaving pools of stagnant water. So instead of more running water which flushes away mosquito eggs and larvae, more pools of standing wearer remain to provide the ideal habitat for mosquito reproduction and growth (1). The lack of water in California’s mountains, forests and deserts also forces birds to migrate to cities and suburbs. Because West Nile Virus (WNV) incubates in birds and is then transmitted by mosquitoes to humans, the increased bird population in urban and suburban areas has facilitated an increase in WNV cases in humans. Since the drought began in 2011, human WNV cases in California have increased from 158 in that year to 798 in 2014. Last year saw California tie its unenviable annual record of 29 WNV deaths. (2).  Fortunately for San Francisco we again had a year without any reported cases of WNV.

The higher temperatures caused by climate change and associated with droughts cause mosquito larvae to grow to adulthood quicker. Higher temperatures allow mosquitoes to grow from egg to adult in as little as 4 to 6 days instead of the normal 2 weeks (3). Warm weather also increases the life span of the female mosquito allowing her to reproduce more often. This may be a factor in the spread of the Asian tiger mosquito, a deadly and aggressive species that established itself in the eastern half of the USA in the 1980s and 90s and in Southern California in this century (4).

There is another way the drought can help increase mosquito populations. A significant rainfall will force the MAC team to take a rain day off but that same rain will flow into the catch basins and flush away any mosquito eggs and larvae. In a manner of speaking, the rain does our job for us for that day. (And the rain doesn’t even get paid for it!) So the lack of rainfall means that water in catch basins will remain stagnant – and mosquito friendly – throughout spring and summer and until the arrival of rains in autumn.

And without the cleansing effects of rainfall, the air in San Francisco continues to retain the volume of toxins (a nice way of saying “poisons”), allergens and other pollutants. Because of the drought, our eyes and throats are often irritated after riding all day.

So far this season, we have not had any rain days off. But because we are working every day, we will use each of those days to control San Francisco’s mosquito population.


(1) Sacramento Bee, February 23, 2015. www.sacbee.com/news/state/california/water-and-drought/article11054219.html

(2) Ibid.

(3) www.southernnevadahealthdistrict.org/mosquito-control/mosquito-life-cycle.php,



(4) wikipedia.org/wiki/Aedes_albopictus

Los Angeles Times, October 20, 2013. articles.latimes.com/2013/oct/20/local/la-me-mosquitoes-20131019