The importance of larviciding … including out of sight

In the 4-part mosquito life cycle*, the most vulnerable stage is the larva. Eggs are designed to survive, pupae don’t eat and their chief enemy would be rough water preventing them from breathing, and adults as we all observe are elusive fliers.

But larvae depend on feeding on organic matter in unclean standing water. If they get too hot or cold, don’t find enough food, or can’t breathe regularly at the surface, they will develop into adults either slowly or not at all.

Underground breeding: Out of sight not out of mind!

It is often said that mosquitoes become more numerous in wet weather, because they find more attractive (to them) surface-level breeding water (as long as there isn’t so much rain that the eggs, larvae, or pupae are washed away or drowned).

But in built-up areas, we often notice more mosquitoes in dry weather. That is a pretty sure sign that they are readily reproducing in water that does not dry up in dry weather.

Since residents are being more and more attentive about preventing breeding at surface level on their property, maybe the mosquitoes are finding other standing water, out of sight, below ground level.**

One place we may not think of looking is in drains on our property, which may catch water from driveways, natural surface draining paths, or downspouts off roofs.

Here we see a largish drain in an individual yard, into which water can flow either from higher ground or from storm drains on streets higher up a sloping terrain.

If you have such a drain, please look down it with a flashlight 4 or 5 days after a rain. If there is water sitting there, you are about to breed mosquitoes and should apply the bacteria-based larvicide. Any significant rain would wash out the future mosquitoes… and also any larvicide; so we need to remain alert to conditions.

Bti is widely used to stop larvae from growing by preventing their digestive tract from functioning. See more on Bti here.

Municipal storm drains and pipes

Mosquitoes also like to breed in municipal storm drains. Storm drains are the drains at street level where rain water pours down into what is known as a sump or catch basin. Any water that stands in the sump provides an ideal mosquito incubator: stagnant, organic-rich, and undisturbed (at least, until the next rain).

Theoretically water should drain out entirely after the rainfall ceases. It’s hard to see if a sump really does drain but sometimes you can look down with a flashlight.

According to the PA West Nile website (from the download Stormwater Management and West Nile Virus:

Are stormwater catch basins significant production areas for WNV carrying mosquitoes?

Catch basins can be important production areas for mosquitoes in the genus Culex (the primary vector of WNV in Pennsylvania). Many storm drain systems are designed to quickly direct water from impervious surfaces to nearby streams. Sometimes these systems can become clogged with debris, which can lead to standing water and mosquito production. Malfunctioning systems should be reported to local authorities for repair. Older catch basins were designed to trap debris and hold a small portion of the storm water after a rainfall event. These catch basins are a significant source of mosquito production and need to be treated for mosquito larvae on a regular basis. Some counties actively treat catch basins with mosquito larvicides to prevent mosquito production.

Here we see a storm drain, also fortunately dry even the day after a rain, at the corner of two streets.

Many cities routinely larvicide their storm drains, such as San Francisco, which larvicides 23,000 storm drains and has no mosquito problem. Alexandria, VA, an old town like West Chester, determined that storm drains were their main location of mosquito breeding and applies larvicide to fight the problem. Shaker Heights, the community on which we modeled our proposed West Nile Task Force Plan, larvicides all of its 850 drains.

Whether or not storm drains hold water right under the edge of the street, it is very hard to construct a large underground pipeline that has no dips or other irregularities that could hold stagnant water.

In case of doubt, let’s larvicide!

How far along an underground pipe (from either the drain end or the outflow end) will a mosquito fly to lay eggs in stagnant water? How long might water stand in an underground pipe before is leaks out or evaporates? Would any larvicide in the sump be carried into depressions in the pipe by a light rain but be carried out the end of the pipe by a strong rain? What is the water temperature in storm drains and downline pipes and what temperature range suits mosquito larvae?

We just haven’t seen good answers to those questions. We did measure the surface temperature of water standing in a storm drain on an August afternoon. The air temperature was about 78 degrees and the water 70 degrees, definitely in the mosquito comfort zone.

In research we have found, mosquitoes favor 80+ degrees and their larvae develop more slowly as the water gets cooler, but they definitely mature down to at least 50 degrees, maybe less. Local science experiment, anyone?

If some observant citizen noticed a swarm of mosquitoes flying out of a dry street drain, that would be valuable evidence, as it would suggest that they grew to maturity farther down the pipe underground. Or, if we could put a mosquito netting over a storm drain 5+ days after a rain, we might see what comes out.

Until we know more, DSM feels it is important, at least in hot dry weather and when mosquito numbers are rising, to get larvicide into any water standing in a drain or farther down the pipe, especially in flatter areas.

This could involve mixing some Bti in a quantity of water and pouring it down suspect street or residential drains. Anyone who has thoughts or experience in this, please let us know!

*For a quick outline (and appreciation of how varied and adaptable mosquitoes are), see “Life cycle” at American Mosquito Control Association. Or, for more detail, West Valley Mosquito and Vector Control District.

**Or out of sight above our heads! We also need to be sure the gutters than drain off water from the edge of roofs are unclogged and do not hold rain water.

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Citizen measures for mosquito control become more urgent!

As often happens in mid-summer, mosquito traps set by the County are starting to show some West Nile virus positives. This means that at certain trap sites, over a 24-hour period, one or more mosquitoes out of the scores or hundreds trapped were carrying the virus.

No humans are known to have been affected so far in Chester County, but this means we citizens should redouble our efforts to curb the mosquito population and fend off spraying, whose harmful effects are known and whose benefits, if any, are unproven beyond the initial destruction of adult insects of all species.

Two West Nile Virus positives this month have occurred at Greenfield Park at S. Franklin St.,and Greenview Alley, West Chester, just south of E. Nields St., in West Chester, ward 4, in the southeast part of the Borough

Also, there have been positives in a couple of other sites around the County.

To do your part, please refer to “What can I do to reduce the mosquito population?” and the concrete advice on the Borough site’s Mosquito Awareness page about suppressing standing water.

In West Chester, Block Captains should by now have distributed both 1) a letter from Mayor Jordan Norley and 2) a doorhanger from the Borough.

If you live outside West Chester Borough, please contact us and we will put you in touch with others in your community.

The sump pump danger

Please examine closely:

Potential mosquito breeding ground, right? Nice dirty stagnant water, gathering at the bottom of a bulkhead to be pumped out.

Can mosquitoes fly in? Certainly; no bulkhead is constructed tight enough to keep out a small insect.

Has the homeowner taken the right precautions?

Yes! Note the Bti larvicide tablet floating on the left side. Very good!

The mosquitoes are coming… to East Bradford!

Thanks to the East Bradford municipal administration for giving their residents useful guidelines for protection against breeding and being bitten by mosquitoes. The article below is from page 6 of the East Bradford summer 2017 newsletter.

In addition, East Bradford’s Environmental Advisory Council (EAC) has prepared further information which you can download at the EAC site, including a very thorough In-Depth Report and a Summary.

DSM wishes East Bradford residents as mosquito-free summer as possible!

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Tire piles: mosquitoes’ favorite breeding ground

If you spot a pile of tires exposed to precipitation, please let us know. Tires, whether old or new, are mosquitoes’ best breeding territory, because they warm up in the sun and hold water long-term invisible to human eyes. N.b. in West Chester, tires should be stored inside, not  outside.

Excerpt from “What Tire Pile Owners Should Know About West Nile Virus” download at PA DEP:

Could a tire pile be a mosquito-breeding site?

Tire piles could provide suitable areas for mosquitoes to live, including those known to carry WNV. When discarded tires are allowed to accumulate even a small amount of water, they become attractive sites for mosquitoes to lay their eggs. For example, during the course of one season, thousands of mosquitoes can emerge from just one tire. If tires infested with mosquito eggs, larvae or pupae are transported, the potential to spread mosquito populations increases. This is one of the theories on how WNV was introduced into the United States.

How can a property owner prevent mosquito breeding?

It is the responsibility of the tire pile owners to make sure that the pile does not create a nuisance or health hazard. There are a number of ways to eliminate mosquito production in tire piles.

Standing water in the tires should be eliminated. This can be accomplished by properly storing tires under a tarp or other cover, removing the side wall, or drilling holes in the back of the tire.

In situations where eliminating mosquito production areas is not a practical alternative, larviciding is the most effective control technique….

read the full download here: Tire piles 3800-FS-DEP2535

The Zika virus and Chester County

by Nathaniel Smith, The Times of Chester County, 9/1/16

Getting rid of standing water is more effective than spraying

News has come around lately that “Pennsylvania Is Now One Of The Top States With Zika Virus ” (Phoenixville Patch, 8/23/16). Currently PA ranks 5th in the number of diagnosed Zika cases. Of course, no one knows how many undiagnosed cases there are anywhere.

Quick quiz: how is Zika spread? If you answered “by mosquitoes,” you’re only half right. It’s our fault too.

It’s important to focus on this note in the article: “All of the cases were travel-related, according to the Centers for Disease Control and Prevention.”

That means no human has acquired Zika from a mosquito in PA. Although the prime mosquito host for Zika, aedes aegypti, does exist in Pennsylvania, it doesn’t do well this far north (yet).

The fact is that Zika is spread not only by mosquitoes but also by people, whether through sexual contact (CDC offers explicit advice on this aspect) or from carrying the virus (usually without symptoms) and being bitten by a mosquito that in turn bites someone else, who thus acquires the disease. The aedes albopictus mosquito, often called “Asian tiger,” has become very numerous in PA but fortunately does not seem to transmit Zika very well (yet).

Spraying pesticides is a limited, short-term fix that leaves many adult mosquitoes alive and does not affect eggs and larvae but harms many forms of life and can lead to acquired immunity. Mosquitoes breed over 500 times faster than people, so they will become immune to whatever we do against them much faster than we can evolve to resist them. Mosquitoes in Puerto Rico and Florida are already becoming resistant to permethrin, the standard anti-mosquito pesticide.

This is all not good news, except that in PA we do have some time to get ready for present and future mosquito-borne diseases….

read more at The Times of Chester County

Mosquito traps made from old tires are 7 times more effective than standard traps

by Melissa Breyer, treehugger, April 8, 2016

A new study found this cheap, easy system significantly reduced virus-carrying Aedes mosquitoes in Guatemala.

Called an ovillanta, a simple mosquito trap fashioned from old tires spells doom for mosquito eggs. So effective is the cheap eco-friendly system that during a 10-month study in Guatemala, the team collected and destroyed over 18,100 Aedes mosquito eggs per month, almost seven times the eggs collected compared to standard traps. Anecdotally, the researchers note that there were no new reports of dengue during the time in the area, normally during that timeframe the community would have reported up to three dozen cases.

The Aedes genus of mosquitoes is primarily responsible for transmitting a host of vexing viruses, including Zika, dengue, chikungunya, and yellow fever. Aedes is notoriously tough to control, according to the World Health Organization. Pesticide-resistance, lack of resources, and a boost in mosquito-friendly environments have hindered traditional methods of controlling the pest’s quick spread.

Created in collaboration by researchers from Canada and Mexico, the ovillanta is made of two 20-inch sections of old car tire secured together in the form of a mouth, with a fluid release valve at the bottom. A milky mosquito-luring non-toxic solution is poured in the bottom – the solution includes a mosquito pheromone that tells female mosquitoes that it’s a safe place to lay eggs. The mosquitoes enter, lay eggs on a paper or wooden strip that is floating in the “pond” … twice a week the little egg raft is removed, the eggs destroyed, and the solution drained and filtered before being reused in the trap again….

ovillanta old tire mosquito trap

read more at treehugger

Larviciding with Bti

A larvicide (or larvacide) kills larvae.

In a rare too-good-to-be-true moment, the biological agent Bti prevents mosquito larvae from maturing. It’s made from bacteria called Bacillus thuringiensis israelensis, which affects no other forms of life except two other nuisance insects (black flies and midges). It is organic and totally non-toxic.

You can use mosquito dunks in any standing water that you can’t dump out regularly: a small pond or stagnant stretch of stream in your yard, or a built-in plant soaking area that no longer drains, etc.

For a small surface area, just break up the dunks in pieces. In any case, reapply every month or so to be sure the Bti is still active.

Dunks usually come in packs of 6 dunks. If you buy more than one at a time at ACE hardware store in East Bradford (720 W Strasburg Rd., just west of West Chester borough, after Daily Local News), ask for a discount.

Just to remind you, we oppose the use of pesticide sprays and SPRAYS HAVE NO EFFECT ON LARVAE (or on eggs, or on pupae, the cocoon-like form that larvae go through before emerging as adults).

For detailed information on Bti, see “Best Natural Mosquito Control: Bti” at mosquitoreviews.

Mosquito dunks

The Shaker Heights plan

Shaker Heights, Ohio, initiated a successful mosquito control program in 2002. They outlined a plan with 6 levels of response, with the highest being the type of health crisis that suggests that pesticide spraying is necessary. Their Health Director, Sandi Hurley, reported to Don’tsprayme in June of 2016 that, during the 14 years that these guidelines have been in place, Shaker Heights has had no serious cases of West Nile virus and no health emergency that required spraying.

That community, which is about 6 square miles with a population of 28,000 people, works together cooperatively to keep Shaker Heights safe by reducing standing water and mosquitoes and by not spraying pesticides. One of their chief lines of defense is larviciding all storm drains. West Chester, working with the County, has been larviciding storm drains on a selective basis in 2016.

To download their 6-step plan, of which we are preparing a modified version to recommend for West Chester, click here: Shaker Heights WNV Response Plan

Mosquitoes, meet your maker. A DIY trap kills thousands of the biting bugs

[Please let us know if you try this non-toxic mosquito elimination method… and give thanks we don’t have the biting population New Orleans does!] By Susan Langenhennig, The Times-Picayune, May 27, 2014

If you’re waging war on mosquitoes, don’t waste your money on a bug zapper. They aren’t much of a solution. You’re more likely to catch moths than mosquitoes in the buzzing devices, and, as the New Orleans Mosquito, Termite and Rodent Control Board says, “bug zappers do more harm than good.”

If you want a DIY weapon for your fight against the bite, Dan Rojas of GreenPowerScience.com has an easy, inexpensive trap that’s both effective (it will kill thousands of mosquitoes in just 24 hours) and gratifying (you take the battle to the bugs without lifting a bottle of DEET).

In a video posted on Ebaumsworld.com, Rojas uses magnets to attach a mesh screen to the back of a standard-issue box fan, the kind you can find in any big-box home improvement store….

read more and see video at The Times-Picayune