Larvicide

Many people believe that “Mosquito Control” is only the loud flashing truck you hear at night, spraying mist out the back of it.  However, it is quite the contrary.  In a fully integrated pest management (IPM) operation, there is much more involved behind the scenes.  Larvaciding plays the biggest role in terms of the Alamosa Mosquito Control District’s (AMCD) IPM. Approximately 65% - 70% of our District’s mosquito control efforts are geared toward larvicide control.  The goal is to eradicate and control mosquito larvae populations while they are still in condensed areas and in their growth (non-biting) stages.  Within the boundaries we service, there are large amounts of standing water which provide mosquitoes with their ideal breeding habitat.  Our larvicide crews seek out water that are providing habitat for growing mosquito larvae.  Our crew members often walk great distances or use our ATVs and land/water amphibian machines to check the water for larvae by using a dipper cup (a cup attached to a 4’ stick).  Once larvae are found, there are several factors we consider before treating the water with larvicide.

 

How We Control Mosquito Larvae

   About 95% of the larvicide used at the AMCD is a naturally occurring soil bacterium (Bacillus thuringiensis israelensis - Bti) which specifically targets specific flies (mosquitoes included) during their larval stage.  Once applied, the larvae will ingest the bacteria & die.  Since mosquito larvae only feed during the first four stages of growth and Bti is ineffective on the pupae, other larvicides may be applied afterwards.  These other larvicides include a monomolecular surface film (MMF) which produces a film over the surface of the water, causing the larvae to drown.  Depending on the habitat, we may also use a growth-regulating larvicide which will prevent the mosquito larvae from reaching the pupal stage.  This larvicide is slow-releasing, providing control for a minimum of 30 days and can re-activate if a site dries and then wets again. 

Factors
 
  • Thresholds: the size of the body of water vs. the number of mosquito larvae found per dip

  • Type of habitat: clear water vs. abundant growth (grass, weeds, algae, cattails, etc.)

  • Larval growth stage

  • Water's last treatment date

  • Average daily temperature

  • How soon the site will dry up

How We Monitor Mosquito Larvae 

 

  • Overflow Ponds

  • Flood irrigated fields

  • Pockets of standing water

  • Cattle hoof prints

  • Storm drains

  • Discarded tires, drink containers and steel cans

  • Rain gutters

  • Bird baths

  • Kid's swimming pools, etc.