Abstract
ABSTRACT Nasonia vitripeinnis is parasitic on the pupae of various muscoid flies. It has a haplo-diploid system of sex determination (Berland, 1951; Whiting, 1954), fertilized eggs producing females and unfertilized eggs males. Provided that host puparia are available continuously to the parents, the diploid females outnumber the haploid males in the ratio of 3:1. A possible mechanism for determination of this ratio has already been suggested (King, 1961). Previous work has demonstrated that the environment has a profound effect upon the sex ratio of the Hymenoptera. Clausen (1939) stated that the sex ratio varied with the sex ratio of the host, with successive generations upon the same or a different host or with different species of host, or according to whether the host population was increasing or decreasing. Chewyrew (1913), Holdaway & Smith (1932), Seyrig (1935), Taylor (1937) and Ullyet (1936) said that the proportion of males in a population depended upon the size of the host; in a small host the proportion of males was higher. Flanders (1937) working on Metaphycus stated that if the hosts were less than 1 mm. long only males were produced; the proportion of males decreased with an increase in size of the host. Whiting & Anderson (1932) working on Habrobracon, Flanders (1938) working on Tetrastichus and Wilson & Woolcock (1960) showed that the temperature affected the sex ratio.
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