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

1. Several authors have proposed that inter-specific variation in parasitoid life histories can be classified according to a dichotomy of development modes: ectoparasitoids and idiobionts with one suite of traits, and endoparasitoids and koinobionts with an opposing set of traits. 2. The factual evidence for such a dichotomy is presently scant. Here, 10 predictions of the dichotomous hypothesis are assessed using life history data from 474 species of parasitoid Hymenoptera. 3. A degree of support for the dichotomy is found. As predicted, koinobiosis is associated with endoparasitism, and idiobiosis with ectoparasitism. Endoparasitism and/or koinobiosis are also associated with a shorter adult lifespan, a shorter window for parasitism, smaller eggs, a longer pre-adult lifespan and, in larval parasitoids, a greater oviposition rate and fecundity 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 degree of host concealment or the stage of host attacked. Some trends are only found amongst larval parasitoids, and others do not hold for both endoparasitism and koinobiosis. 5. We conclude that there is at least some merit to the dichotomous hypothesis, 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.