University of California

The stupefaction of red scale, Aonidiella aurantii, by hydrocyanic acid


D. L. Lindgren

Author Affiliations

D. L. Lindgren was Junior Entomologist in the Experiment Station.

Publication Information

Hilgardia 11(5):211-225. DOI:10.3733/hilg.v11n05p211. May 1938.

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Both the red scale, Aonidiella aurantii (Mask.), and the black scale, Saissetia oleae Bern., become more difficult to kill if they have first been exposed for a short time to a sublethal concentration of hydrocyanic acid gas. The term applied to the effect of small charges of HCN is “protective stupefaction.” It may be brought about in the field by the leakage of gas through the tents or by poor diffusion of the gas within the tent. Since most workers agree that the red scale becomes stupefied when prefumigated with a sublethal concentration of HCN, an investigation was begun to determine the length of time these insects remain stupefied.

Earlier Investigations

(Gray and Kirkpatrick (1929)) concluded that under the laboratory conditions of their experiments:

Both the resistant and nonresistant strains of black and red scales exhibit a characteristic which is termed “protective stupefaction,” that is, when a lot of scale is first exposed to a sublethal, but stupefying concentration of hydrocyanic acid in air, followed by a normally lethal concentration, more of them are able to survive than a lot upon which the reverse procedure has been followed.


Correlated field and laboratory observations and experiments, not fully described in this paper, furnish good circumstantial evidence that protective stupefaction is sometimes a factor adversely affecting the results of scale kill in commercial fumigation.

(Pratt, Swain, and Eldred (1931)) found that protective stupefaction is a fact in the case of both black and red scales when exposed to lethal concentrations of HCN after 10- or 3-minute exposures to sublethal concentrations, but that protective stupefaction does not follow exposure for only 1 minute to sublethal concentrations.

Literature Cited

Gray G. P., Kirkpatrick A. F. The protective stupefaction of certain scale insects by hydrocyanic acid vapor. Jour. Econ. Ent. 1929. 22:878-92.

Knight Hugh. Factors affecting efficiency in fumigation with hydrocyanic acid. Hilgardia. 1925. 1(3):35-53. DOI: 10.3733/hilg.v01n03p035 [CrossRef]

Mackie D. B., Carter W. B. Pest control in rural warehouses and suggested improvements. California State Dept. Agr. Mo. Bul. 1937. 26:275-93.

Moore William. Studies of the “resistant” California red scale Aonidiella aurantii Mask. in California. Jour. Econ. Ent. 1933. 26:1140-61.

Peters Gerhard. Chemie und Toxikologie der Schädlingsbekämpfung. 1936. Stuttgart: Ferdinand Enke. 120p.

Pratt F. S., Swain A. F., Eldred D. N. A study of fumigation problems: “Protective stupefaction,” its application and limitations. Jour. Econ. Ent. 1931. 24:1041-63.

Quayle H. J. The development of resistance to hydrocyanic acid in certain scale insects. Hilgardia. 1938. 11(5):183-210. DOI: 10.3733/hilg.v11n05p183 [CrossRef]

Quayle H. J., Rohrbaugh P. W. Temperature and humidity in relation to HCN fumigation for the red scale. Jour. Econ. Ent. 1934. 27:1083-95.

Snedecor George W., Irwin M. R. On the chi-square test for homogeneity. Iowa State College Jour. Sci. 1933. 8:75-81.

Lindgren D. 1938. The stupefaction of red scale, Aonidiella aurantii, by hydrocyanic acid. Hilgardia 11(5):211-225. DOI:10.3733/hilg.v11n05p211
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