The sex ratio and oogenesis 
of Pseudococcus citri. 
By Franz Schrader, Bryn Mawr College, Bryn Mawr, Pa., U.S. A. 
(Plate 2—5.) 
(Eingegangen September 11, 1922.) 
Data On The Sexes. 
Our knowledge of sex determination in coccids is extremely limited. 
In view of the fact that the life history of only a few members of this 
large family has been worked out thoroughly, and that in most cases 
observations are made only with difficulty, such a lack of information 
is of course not surprising. The present work, which was begun several 
years ago, has been confined to the common mealy bugs of the genus 
Pseudococcus. Although my primary aim was to throw some light on 
sex conditions, it often became necessary to make observations on the 
habits and behavior of the species investigated. 
My attention was drawn to these coccids by the apparent scarcity 
of males in Pseudococeus eitri. In random counts made on adults and 
individuals of the last- instars, only 16 out of 245 were classified as 
males, a percentage of less than 7°/o. I suspected that some irregula- 
rity in the sex determination, possibly a facultative parthenogenesis 
giving rise to females, exists in these insects. Both in conversation 
and correspondence with several coccidologists, this suspicion was 
strengthened, for I found that they too had observed a rarity of males 
in these species and believed parthenogenesis to be a possible cause of 
the abnormal sex ratio. In recent publications on the subject, similar 
views are often expressed. PIERANTONI (1910) remarks that males are 
more or less rare in Pseudococeus citri; EMEIS (1915) states that eggs 
of the same species probably develop parthenogenetically; and Mac 
GILLIVRAY (1921) says that “of the eggs deposited only a small number 
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