Does development mode organize life-history traits in the parasitoid Hymenoptera?

1. Several authors have proposed that inter-specific variation in parasitoi d life histories can be classified according to a dichotomy of development modes: ectoparasitoids and idiobionts with one suite of traits, and endopar asitoids and koinobionts with an opposing set of traits. 2. The factual evidence for such a dichotomy is presently scant. Here, 10 p redictions of the dichotomous hypothesis are assessed using life history da ta from 474 species of parasitoid Hymenoptera. 3. A degree of support for the dichotomy is found. As predicted, koinobiosi s is associated with endoparasitism, and idiobiosis with ectoparasitism. En doparasitism and/or koinobiosis are also associated with a shorter adult li fespan, a shorter window for parasitism, smaller eggs, a longer pre-adult l ifespan and, in larval parasitoids, a greater oviposition rate and fecundit y than ectoparasitism/idiobiosis. 4. However, several predictions are not upheld by the data. No significant relationship is found between development mode and either body size, the de gree of host concealment or the stage of host attacked. Some trends are onl y found amongst larval parasitoids, and others do not hold for both endopar asitism and koinobiosis. 5. We conclude that there is at least some merit to the dichotomous hypothe sis, though the most extensive depictions go beyond the present data. As a step towards formulating the dichotomy in a more rigid theoretical base, we discuss the selective pressures and constraints that are likely to account for the observed trends.