Diatomaceous earth (DE) can kill adult mosquitoes, but only under specific, dry conditions. This naturally occurring substance is a fine powder made from the fossilized remains of tiny, aquatic organisms called diatoms. These ancient organisms left behind hard shells composed primarily of silica, which is mined and processed into the white dust used for pest control. DE works through a mechanical action, meaning insects cannot develop resistance to it.
The Mechanism: How Diatomaceous Earth Kills Insects
Diatomaceous earth functions as an insecticide due to the physical structure of its microscopic particles. The fossilized shells of diatoms are extremely porous, giving the resulting powder strong absorptive capabilities. When insects like adult mosquitoes crawl across the fine dust, the particles adhere to their outer covering, or exoskeleton.
The tiny silica fragments have sharp, abrasive edges that physically damage the insect’s protective waxy cuticle layer. This waxy layer is vital because it prevents the insect’s body moisture from escaping. Once this barrier is compromised, the DE powder acts as a desiccant, absorbing the lipids and moisture from the insect’s body.
This dual action of physical abrasion and moisture absorption leads to rapid dehydration, or desiccation. The mechanical mode of action is effective against any insect that comes into direct contact with the dry powder.
Applying Diatomaceous Earth for Adult Mosquito Control
Controlling adult mosquitoes with diatomaceous earth depends on ensuring the insect walks directly through the dry powder. Since adult mosquitoes are flying insects, direct application is generally focused on areas where they rest, hide, or land. Effective use involves applying a light, barely visible dusting of the material to surfaces where mosquitoes may be active.
Application should target dry, sheltered locations like under decks, around dense shrubbery, or along patios and walkways. Indoors, a thin layer can be puffed into window sills, door thresholds, and cracks and crevices. A bulb duster or shaker container is the most effective tool for creating this fine, even layer.
The powder must remain completely dry to maintain its mechanical efficacy. If the DE becomes wet, it will clump and its abrasive and absorptive qualities will be neutralized. Reapplication is necessary after any rain or heavy dew to restore the effectiveness of the treatment.
Why Diatomaceous Earth is Ineffective Against Larvae in Water
Mosquitoes begin their life cycle as larvae living in standing water, but diatomaceous earth is largely ineffective in this aquatic environment. The physical mode of action requires the DE particles to be dry to maintain their sharp, abrasive structure. When the powder is introduced to water, its particles become saturated, which neutralizes their desiccating capability.
The water causes the fine powder to clump together, which prevents the individual particles from adhering effectively to the larval cuticle. For the DE to work, the larvae would need to come into contact with the dry dust, which is impossible in a liquid medium. Once the DE is wet, the powder’s ability to cause lethal dehydration is lost until the material completely dries out.
Safety and Handling Different Types of Diatomaceous Earth
It is necessary to distinguish between the two main types of diatomaceous earth before use. For pest control around the home, only Food Grade DE should be used, which is composed of amorphous silica and contains less than 1% crystalline silica. This grade is considered safe for use in food storage and around people and pets.
Filter Grade DE, often labeled for use in swimming pools, is heat-treated in a process called calcination, which converts its silica content into a high percentage of harmful crystalline silica. This crystalline form is toxic and poses a serious health hazard, specifically the risk of silicosis if inhaled. When applying Food Grade DE, wear a dust mask to prevent inhalation of the fine powder, which can cause respiratory irritation.