Rapid Desiccation of Drywood Termites with Inert Sorptive Dusts and Other Substances

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Abstract
Previous efforts to control insects by means of desiccating dusts have been directed primarily against granary weevils and with abrasive materials. Drywood termites were found to be more susceptible to sorptive than to abrasive dusts. By means of a staining technique it was shown that sorptive dusts can remove the lipoid protective layer covering the epicuticle, causing the termites to lose water rapidly. The insects needed only to crawl about on a thin film of the dust. They died after losing about 30% of their body weight in water. Certain silica aerogels were particularly effective. Other insects, including cockroaches, fleas, bedbugs, bees, ants, vinegar flies, mosquitoes, house flies, thrips, ticks and mites, likewise succumbed rapidly to desiccation initiated by the disruption or removal of the lipoid protective layer by sorptive dusts. Although some conventional insecticides might cause more rapid knockdown, they never resulted in death of the insects tested as rapidly as the more effective desiccating dusts. Certain water-soluble fluorides have been incorporated into the silica areogels in the process of manufacture. These fluorides greatly increase the effectiveness of the impregnated aerogels, even at low relative humidities, but the advantage obtained from the impregnation increases with increasing relative humidities and consequently increases the versatility of the silicas. The presence of fluorides as monomolecular layers in the porous silica aerogel particles does not decrease the ability of these particles to adsorb wax. After the wax is adsorbed or disrupted, the water-soluble fluorides can act as contact insecticides. In addition, the strong positive charge they impart to the particles greatly increases their ability to adhere to the dusted surfaces. The addition of surface-active solutes to petroleum oil will cause increased rate of water loss, the water appearing in the form of many small droplets. Desiccation is greatly enhanced when the applied oil is later removed and the insect cuticle is thereby directly exposed to air. Death may result more rapidly than by the toxicity or suffocation that takes place when the insects are completely immersed in oil. Desiccation of drywood termites was caused by treatment with parathion, sodium fluoride, and anhydrous magnesium perchlorate. When the treated insects, as well as those shaken in a sorptive dust, were immersed in oil, water droplets appeared on the body surfaces.