ID & SURVEILLANCE

Surveillance in Hernando County consists of trapping adult mosquitoes and the subsequent identification of the mosquitoes trapped.  Surveillance can also include collecting larvae or pupae samples,  investigating resident complaints and conducting landing counts in problem areas.

Our department has 16 permanent mosquito traps that run year-round throughout the county.  The traps are collected several times a week during mosquito season, and they are checked routinely off season.  We also have temporary traps that may be placed at a location having a persistent problem. Apart from giving us a "heads up" for increased mosquito activity, the traps are the method by which we monitor mosquito populations throughout the season.

In addition to giving us a handle on mosquito activity in a specific area, the surveillance technician identifies the mosquitoes trapped to a species.  This is an important part of surveillance, because by knowing which species are present, the field technicians in turn have an idea where to look for potential breeding sites in the area (breeding habitats vary between species).  Species information also lets us know if potential disease-carrying mosquitoes are present.  While in the field, technicians regularly "dip" areas with standing water to see if larvae or pupae are present.  They will sometimes bring the specimens back to the lab where they let them hatch off so they can be identified.

Our department uses our own department-designed Hybrid Mosquito Trap (shown below) which consists of a small computer fan, a low voltage light, a timing device and mosquito collection bottle.  The trap is powered by a 12V rechargeable battery.   We can program the trap to run at specific time periods to take advantage of peak mosquito hours. 

The light at the top of the trap attracts mosquitoes, which are then pulled down and into the collection bottle by the computer fan at the bottom of the trap.  The mosquitoes remain in the collection bottle until collected and brought back to the lab for identification to species. 

Our step-by-step manual to assemble this trap is available in PDF format: 

NOTE:  The hybrid trap was designed and is used for surveillance purposes only.  The trap is not meant to be used, nor does our department use it, as a means to control mosquito populations.  

SOURCE REDUCTION

Source reduction is exactly what it says, removing or eliminating sources that are currently breeding mosquitoes or have the potential to breed mosquitoes.

The task of source reduction can be something as simple as turning over containers that are holding water, or time consuming labor which can consist of  mowing lakebeds/perimeters, digging ditches to divert standing water, or herbiciding lakes and roadside ditch lines.

Property owners can do their own source reduction by checking their property for potential breeding sites and keeping grass and weeds mowed (see Mosquito Habitats).

An aggressive biter, and one that stays "close to home," is the Asian Tiger mosquito (Ae. albopictus), which commonly breeds in discarded tires.    Our field technicians routinely collect tires which have been illegally dumped along road sides or on vacant property.  Tires are one of the county's biggest mosquito breeding sources, and as a result, much time and effort goes into the collection and proper disposal of them by the mosquito field technicians.

Tires on private property should be covered or kept in sheltered areas so they will not hold water. Residents are encouraged to take their discarded tires to the landfill for proper disposal.  These simple tasks will greatly help to eliminate a potential breeding infestation of these nasty daytime biters.

Herbiciding is an important aspect of source reduction.  In many instances there may be natural water bodies (lakes, creeks) that have an abundance of natural predators present, but they are unable to keep the mosquito population at bay due to vegetation growing in or around the water body.  In addition, certain species of mosquito larvae either attach themselves directly to plant roots or hide in between the dense vegetation making them inaccessible to predators or larvicides.  In these cases, it's necessary to use herbicides to eliminate the vegetation present.   Some examples of aquatic vegetation that harbors or enables mosquitoes to grow are cattails, water hyacinth, duckweed, and water lettuce.

"Pre" and "Post" treatment of water hyacinth infested water body

Herbicide is also used to eliminate excessive vegetation that may be growing along roadside ditch lines, prime targets for breeding sites after heavy rains and flooding.  Manicured ditch lines provide little shelter for mosquitoes and give larvicides or biological control agents full access to any larvae or pupae that may be present.  

LARVICIDING

Larviciding is the method by which chemicals are used to treat and destroy mosquito larvae.  This process prevents the larvae from completing their life cycle and becoming breeding adults. 

Larviciding is by far the most logical method by which to deal with mosquitoes.  While in the larval stage mosquitoes are confined to a treatable area, there is no guesswork or hit-or-miss treatment as occurs with adulticiding (mosquito spray truck).  Knowing that one female mosquito has the potential to produce thousands of offspring before she dies, it makes sense to eliminate them before becoming adults.  

Each field tech is assigned to a specific territory within the county, and as a matter of course, they patrol and monitor their area year round for potential breeding problems.  Routine inspections and "dipping" (above right) keep them up-to-date on what's going on in their zone.  It is common practice for the field techs to pre-treat their known flooding areas in an attempt to nip problems in the bud.  This is commonly done about a month prior to mosquito season in the form of 5-month briquets (Altosid) placed in areas that are either holding water or are dry, but are known to flood.  They may also place Gambusia (see Biological Control below) in areas holding water. 

Examples of Larvicides Used by our Department

BIOLOGICAL CONTROL

Chemicals are a legitimate environmental concern.  With this in mind, one of the best ways to tackle the mosquito is by using biological control… nature battling nature.

Mosquitoes have natural predators laying in wait to feast on them from larval stage through adulthood.  These predators alone, however, are neither prevalent enough or physically able to do the job necessary to control the populations we see, for they are not preying exclusively on mosquitoes.

A common misconception is that no rain is a good thing as far as mosquitoes go.  In some ways this is true, but with regard to ongoing biological control it's not.  When we go through a period of drought, the mosquito predator populations dwindle or cease to exist.  A lack of rain may mean a lack of adult mosquitoes, but the mosquito eggs are still present awaiting rain (see mosquito biology section).  When these rains finally do arrive, natural predator populations that would normally be present must now first repopulate in order to start eliminating mosquito larvae & pupae.   This repopulation of predators can take time, giving mosquitoes plenty of time to reproduce several times over.

Some insects that prey on mosquito larvae are:  water scorpion, damselfly naiad, dragonfly naiad, mayfly naiad, giant water bug, water beetle, beetle larva, crayfish, freshwater shrimp, tadpole.        

Our department has had very good luck over the years placing Gambusia (mosquito fish) throughout the county in DRA’s, ponds, ditches and any bodies of water that will be standing for fairly long periods of time.  In addition to considering mosquito larvae a delicacy (so we think), Gambusia reproduce very rapidly once placed in their new environment, so they provide on-going maintenance.  Using mosquito fish eliminates the need to use chemicals, which is a big plus for both the environment and our budget.

Adult mosquitoes have predators as well.   Frogs, dragonflies, birds and bats are known to eat mosquitoes.  Research shows, however, that although mosquitoes do make up part of these creatures' diet, given the opportunity, they would rather feast on a nice juicy moth as opposed to a scrawny little mosquito.  The number or mosquitoes they eat over the course of a night are not significant enough to make a dent in mosquito populations.  On the other hand, any help the we can get from these critters puts us that much ahead of the game!

ADULTICIDING

Adulticiding consists of spraying tiny droplets of chemical into the air that, upon coming in contact with flying mosquitoes, knocks them down and eventually kills them.

Adulticiding is the last component of Integrated Pest Management. It's the icing on the cake, if you will, to knocking down mosquito populations. Although every effort is taken to eliminate mosquitoes before they "take to wing" (become adults), it's just not humanly possible to find and treat every breeding source throughout the county. Therefore, we have these adults to deal with, in addition to any neighboring county's mosquitoes that may come visiting in search of a meal or a mate.

HOW DO WE DECIDE TO SPRAY ?

Our decision to start spraying for mosquitoes is governed by state guidelines. Justification to spray is based on surveillance/trapping results, daily inspections by field technicians, landing counts and resident complaints.

EXCEPTIONS TO THE RULE

1. NO SPRAY ZONES - Areas where people have phoned in requesting no spraying due to health concerns or other possible reasons.

2. Sensitive lands - By law, adulticiding is not allowed in or near certain sensitive lands (i.e., SWFWMD, state forest) due to potential environmental contamination. However, exceptions may be made if a medical emergency is issued in the area.

 

SPRAY HOURS OF OPERATION

Depending upon time of year and degree of infestation, spray trucks are scheduled to operate between the hours of 8 p.m. (dusk) and 6 a.m. (dawn). Typical mosquito season spray hours are between 8 p.m. and midnight. In past years, however, heavy rains and storms have given us cause to request a 2nd adulticiding shift which sprays during the hours of 2 a.m. – 6 a.m. This additional shift gives us a second chance to knock down mosquitoes before the sun comes up and they look for someplace to hide.

WHAT CHEMICALS DO WE USE ?

We are currently using two products, Kontrol 4-4 and Duet.  Both these chemicals are a great improvement over Malathion, the chemical that had been used since the inception of mosquito control in Hernando County. 

The active ingredient in Kontrol is permethrin, a second-generation synthetic pyrethroid.  Label MSDS

Using Kontrol gives us an opportunity to spray during the day in areas that may be experiencing an abundance of daytime biters. These mosquitoes generally hide at night, so the night spray trucks do not have an affect on these species.

A new product we are using is Duet.  Duet is effective in helping us target the mosquitoes known to carry and transmit West Nile diseases.  Duet is comprised of two chemicals, one that agitates and gets resting mosquitoes up into the air, and the other chemical to kill them once they are in flight.  Label  MSDS