Parasitoid size as a function of host sex: potential for different sex allocation strategies

Parasitoid females are known to preferentially allocate female eggs to host s with the higher resource value, usually leading to oviposition of female eggs in larger hosts and male eggs in smaller hosts. For koinobiont parasit oids, if male and female hosts are of equal size at time of oviposition, bu t differ in size in later developmental stages, the sex of the host could b e used to indicate future resource value. Using parasitoids of the braconid genus Asobara, which are larval parasitoids of Drosophila, it is shown tha t parasitoids emerging from female hosts are larger than those from male ho sts. Given this difference in resource value, ovipositing females should pr eferentially allocate female eggs to female hosts. An alternative strategy would be to decrease the difference in resource value between male and fema le hosts by castrating male hosts. The primary sex ratio of A. tabida in th eir two main host species does not differ between male and female hosts. In contrast to A. tabida, A. citri is known to partially castrate male hosts, but this does not decrease the size difference between male and female hos ts. As in A. tabida, there is no difference in sex allocation to male and f emale hosts in A. citri. Despite the clear difference between the resource value of male and female hosts, these parasitoid species do not seem to mak e optimal use of this difference. They may not be able to discriminate betw een host sexes or, alternatively, there is a presently unknown fitness disa dvantage to ovipositing in female hosts.