Differential hyperparasitism reduces the likelihood of competitive displacement between two competing parasitoids

Nearly all species of primary parasitoids are attacked by hyperparasitoids (aka, secondary parasitoids), yet their role in parasitoid and herbivore community structure is greatly understudied. Here we explore whether the competition between two parasitoids of Pieris rapae, Cotesia glomerata and C. rubecula, is altered by the presence of hyperparasitoids. We compared the diversity and parasitism rates of hyperparasitoids attacking Cotesia glomerata in Colorado (where C. rubecula is absent) with the diversity and parasitism rates of hyperparasitoids attacking both C. glomerata and C. rubecula in Maryland where both Cotesia species co-occur and frequently attack the same individual caterpillar. Hyperparasitoids inflicted greater whole-brood mortality on the solitary C. rubecula than on the gregarious C. glomerata. Furthermore, C. rubecula cocoons are larger than C. glomerata possibly explaining the apparent preference of hyperparasitoids for C. rubecula. Differential hyperparasitism may enable the coexistence of C. glomerata with its congener C. rubecula, which usually outcompetes and displaces C. glomerata.