Inheritance of resistance to hydrocyanic acid fumigation in the California red scale

Abstract does not appear. First page follows.

Introduction

About 1914, the California red scale, Aonidiella aurantii (Mask.), was first observed to have become difficult to kill by hydrocyanic acid fumigation in a small district at Corona, California (Quayle, 1938), p. 187).4 Since that time, resistance of red scale to fumigation has increased throughout many of the citrus areas of southern California.

In 1936, the two recognized strains of red scale, “resistant” and “nonresistant,” were obtained from Corona and Glendora, California, respectively, and were grown in separate insectproof rooms in the insectary at the Citrus Experiment Station. Banana squash and, later, grapefruits were infested from these stocks at intervals of approximately six months and fumigated to determine whether these strains would maintain their difference in susceptibility to HCN. Preliminary results (Quayle, 1938) showed that the differences were maintained through several generations; later results have confirmed this (Lindgren, 1941) and show that resistance to fumigation is inherited.

The experiment described in this paper was conducted to determine how resistance to HCN fumigation is inherited in the red scale.

Review of Literature

(Hough (1928)), working with two strains of codling moth which differed in their ability to enter arsenic-sprayed apples, crossed the two strains and found the F₁ hybrids intermediate between the parental strains in this regard. Later he reported (Hough, 1929) that the F₁ hybrids from the reciprocal crosses were similar and that the F₂ resembled the F₁. By 1934 he had carried the progeny of both crosses to the F₁₀ and still found them similar and intermediate between the parental strains (Hough, 1934). F₅ moths from these crosses were backcrossed with each parental strain, and in each case the resulting progeny were found to approach, but not to be identical with, the introduced parental strain in ability to enter arsenic-sprayed fruit.