Abstract
We conducted two experiments on the oviposition strategy of the gregarious parasitoid, Apanteles glomeratus. First, we estimated the relationship between the egg number per host (N) and the reproductive sucess of the eggs in terms of dry weight of parasitoid offspring. The reproductive success gained from one egg was maximized when 10≲N≲20, while the reproductive success gained from one host attained its maximum when N⋍40.There are certain limitations in the egg supply and life span of a wasp, hence the number of hosts in which she can oviposit in her lifetime is also limited. Consequently, if natural selection favoured behaviour to maximize total reproductive success of all eggs laid by the wasp throughout her life, and if the wasp can estimate the host density by the frequency of host encounters, the number of eggs to lay in each host would be determined in the following manner. When the host density is low and there are few prospects of finding enough hosts in which to deposit all her eggs, the best strategy is to maximize the reproductive success gained from each host. On the contrary, when the density of hosts is high enough to deposit all her eggs, it is better to maximize the reproductive success gained from each egg. The result of the second experiment agreed with this prediction; when the wasps were offered the hosts at long intervals, they laid 35-40 eggs in each host, while when offered the hosts with high frequency, they reduced the egg number per host to ca. 20.
