The Protective Stupefaction of Certain Scale Insects by Hydrocyanic Acid Vapor

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Abstract
Apparatus and technique are described for use in observing live scale under fumigation with accurately determined concentrations of hydrocyanic acid. Selected resistant and non-resistant black scale crawlers were first exposed in a cell to a sub-lethal but stupefying concentration of hydrocyanic acid, then to a normally lethal concentration. The percentage of survivors from this procedure was compared with that resulting from the reverse order of exposure. Resistant and non-resistant red scale on lemons were fumigated in a gas-tight fumigatorium and also under regular fumigating canvas. Half of the lots were prefumigated with a stupefying dose of hydrocyanic acid and then with the regular dose only. The percentage of survivors from these two procedures were compared. It was concluded from these experiments, that, when a lot of black or red scale is first exposed to a sub-lethal but stupefying concentration of hydrocyanic acid in air, followed by a normally lethal concentration, more of them are able to survive than of a lot upon which the reverse procedure has been followed. This characteristic has been termed “protective stupefaction.” The effect of this phenomenon on commercial fumigation is discussed and suggestions offered for preventing or overcoming it.

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