Vectolex WG® Biological Larvicide

VectoLex Brochure

Bacillus sphaericus (Bs) Strain 2362, the active ingredient in VectoLex, is a naturally occurring, spore-forming bacterium found throughout the world in soil and aquatic environments. At the time of sporulation, Bs produces a delta-endotoxin, which is toxic to many species of mosquito larvae when ingested.


When VectoLexis applied to a larval habitat, larvae ingest the delta-endotoxins which are attached to the bacterial spores and encased in a parasporal body. The toxins are activated by enzymes and the high pH that is found in the larval midgut. The toxins then exert their effect upon cells of the midgut epithelium, causing pore enlargement and cell destruction.  Fluids from the larval haemolymph then mix with midgut fluids and the pH of the midgut is neutralised which leads to larval mortality which is usually seen within 48 hours of ingestion. Early instars are highly susceptible to the toxins, however, non-feeding, late fourth instar larvae, and pupae will remain un-affected.


Extended residual activity in the environment is an outstanding property of VectoLex WG. This persistence is thought to be the result of the stability and slow settling rate of the Bs toxin. Added to this, many of the larvae that die accumulate on the water surface. The Bs spores then germinate inside the larval cadavers, grow, and produce toxin which is then “recycled” back into the larval habitat. It is often seen that the greater the larval population upon initial treatment, the greater residual effect of Bs. It should be noted that spot treatments with VectoLex WG tend to deliver less residual activity than treatment of the whole water body and that VectoLex WG also gives good efficacy and residual effect in highly polluted habitats.



Stagnant and standing ponds, flood and irrigation water, ditches, storm water retention areas, tidal water and salt marshes, water with moderate to high organic content, sewage settling ponds.

Culex spp.
Anopheles spp.

0.5 - 1.5 kg/ha
  1. Apply in 2 to 150 L water per hectare to achieve even coverage within the capacity of chosen equipment and spray equipment.Adjust spray concentration to achieved desired rate selected from stated rate range.
  2. Use for control of 1st to early 4th instar.
  3. Use lower rates (0.5 – 1.0 kg/ha) in habitats and conditions where local experience indicates that satisfactory initial and residual control will be achieved. Typical conditions include low to moderately polluted waters, stable or declining water levels, and moderate vegetative cover.
  4. Use higher rates (>1.0 kg/ha) in habitats with high organic load such as sewage settling ponds or where there is water movement or exchange in the habitat, or dense border vegetation, or where local experience indicates that acceptable initial and residual control are not achieved with lower rates.
  5. Reapply at 14 - 21 day intervals when the appearance of late 3rd and 4th instar larvae reach locally prescribed treatment threshold, and ensure that a resistance management strategy is in place.


VectoLex WG may be applied by conventional ground or aerial, liquid application equipment. It should be diluted with sufficient water to provide uniform coverage of the target area. When venturi-type mixers are NOT used, fill the spray tank with two thirds of the desired quantity of water, start agitation to provide moderate circulation before adding the required quantity of VectoLex WG. Add the remaining water while agitating to achieve final spray volume. For extended operations, check and clean the filters of the mix tank regularly. VectoLex WG suspends readily in water and will stay suspended over normal application periods. Recirculation may be necessary if the spray mixture has sat for several hours or longer. Continuous agitation should be avoided and spray mixes should be used within 12 hours of mixing. Alkaline or dirty water should never be used for the spray mix.


VectoLex WG should be used in sites that are known habitats for susceptible mosquito species. These include habitats such as flooded grasslands, permanent water bodies and highly polluted areas. Re-treatment should occur when densities of 3rd and 4th larval instars reach their pre-treatment densities or the local treatment triggers. Post application monitoring is essential to judge the best time to retreat.


Aquatic organisms are vital components of our ecosystems and often occupy the same habitats as mosquitoes. VectoLex WG has shown to have a very specific action causing minimal effects on non-target species. Because of this specific action, this product is well suited for use in mosquito-infested waters in cities, suburbs, recreational sites and all other environmentally sensitive locations.


VectoLex WG should be stored in a cool (less then 25oC), dry place, in an intact product container. Once the container is opened, moisture can be absorbed by the product, which will lead to loss of activity over time. VectoLex WG is stable for 2 years if stored as indicated.


VectoLex WG is available in 500 gram jars.

® Registered Trademark of Valent BioSciences Corporation, Libertyville, Illinois, USA