Interspecific competition between the principal larval parasitoids of the pine sawfly, Neodiprion sertifer (Geoff.) (Hym.: Diprionidae).

Interspecific competition between the 3 principal larval parasitoids of the pine sawfly, Neodiprion sertifer, is of common occurrence when total larval parasitism, and hence multiple attack rates, are high. At the intrinsic level, the ectoparasitoid Exenterus abruptorius is superior to the 2 endoparasitoids, Lophyroplectus luteator and Lamachus eques, respectively, whereas L. luteator is superior to L. eques only. During mass outbreaks of the host competition between Exenterus and Lophyroplectus is most intense, whilst Lamachus fails to build up in the presence of its 2 competitors (Fig. 1). However, due to its superior host finding ability, Lamachus dominates in areas of low host densities where the 2 other species are less efficient (Table 1). L. luteator frequently sustains heavy losses in direct competition with E. abruptorius, but these can be largely compensated in the next generation because its fertility is about 5-times higher than that of Exenterus.