Diatomite is of value as an insecticide, because of its abrasive and physico-sorptive properties.[17] The fine powder adsorbs lipids from the waxy outer layer of the exoskeletons of many species of insects; this layer acts as a barrier that resists the loss of water vapour from the insect's body. Damaging the layer increases the evaporation of water from their bodies, so that they dehydrate, often fatally.
Arthropods die as a result of the water pressure deficiency, based on
Fick's law of diffusion. This also works against
gastropods and is commonly employed in gardening to defeat
slugs.
However, since slugs inhabit humid environments, efficacy is very low. Diatomaceous earth is sometimes mixed with an attractant or other additives to increase its effectiveness.
The shape of the diatoms contained in a deposit has not been proven to affect their functionality when it comes to the adsorption of lipids; however, certain applications, such as that for slugs and snails, do work best when a particular shaped diatom is used, suggesting that lipid adsorption is not the whole story. For example, in the case of slugs and snails large, spiny diatoms work best to lacerate the epithelium of the mollusk. Diatom shells will work to some degree on the vast majority of animals that undergo
ecdysis in shedding
cuticle, such as
arthropods or
nematodes. It also may have other effects on
lophotrochozoans, such as
mollusks or
annelids.
Medical-grade diatomite has been studied for its efficacy as a
deworming agent in cattle; in both studies cited the groups being treated with diatomaceous earth did not fare any better than control groups.
[18][19] It is commonly used in lieu of
boric acid, and can be used to help control and possibly eliminate
bed bug,
house dust mite,
cockroach,
ant and
flea infestations.
[20]
Diatomaceous earth is widely applied for insect control in grain storage.
[21]
In order to be effective as an insecticide, diatomaceous earth must be uncalcinated (i.e., it must not be heat-treated prior to application)
[22] and have a mean particle size below about 12 μm (i.e., food grade –
see below).
