Relation of mortality to amounts of hydrocyanic acid recovered from fumigated resistant and nonresistant citrus scale insects

Abstract does not appear. First page follows.

Resistance to fumigation with hydrocyanic acid gas (HCN) in the red scale, Aonidiella aurantii (Mask.), was first noted in 1914; and resistance in black scale, Saissetia oleae (Bern.), in 1915 (Quayle, 1938).5 Sufficient experimental data have accumulated to establish definitely the existence of two strains or races of red scale in the citrus areas of California: one race that is susceptible and another that is tolerant to HCN fumigation. These two races have been reared in the laboratory for the past seven years, under identical conditions in separate insectproof rooms, through an average of nine generations per year, or a total of some sixty generations; and they are still maintaining the original differential in susceptibility to HCN. As (Dickson (1941)) demonstrated, this difference in susceptibility depends on a single gene or group of closely linked genes in the X chromosome and therefore is sex-linked. The black scale has been less studied, because of the difficulties involved in rearing it from generation to generation; but, according to recent work by (Lindgren and Dickson (1943)), the resistant and the nonresistant black scale differ as much in their tolerance to HCN as do the two races of red scale, or even more.

In an effort to determine the basis for the difference in the reaction of the resistant and nonresistant races of scale insects to HCN fumigation, two lines of investigation were followed in the present experiments. In the first, the fumigation experiments, an attempt was made to evaluate separately the influence of HCN concentration and of exposure on the mortality of the two races of red scale. In the second, the sorption experiments, an attempt was made to correlate the mortality of fumigated resistant and nonresistant races of both red and black scales with the amounts of HCN sorbed (as measured by the amounts recovered); the effects of varied dosages, exposures, and pre-treatments on sorption and mortality were studied.

Materials and Methods

In the experiments here reported, studies were made of resistant and nonresistant mature adult female red scale, reared under controlled laboratory conditions, in insectproof rooms. The variation in age of the insects was less than 24 hours, since the scale crawlers were transferred to grapefruits from the stock cultures several times daily.