Interactions between the Douglas-fir seed chalcid, Megastigmus spermotrophus (Hymenoptera : Torymidae), and the western conifer seed bug, Leptoglossus occidentalis (Hemiptera : Coreidae)

In two laboratory experiments, adult western conifer seed bugs, Leptoglossu s occidentalis Heidemann, did not feed on seed infested by the Douglas-fir seed chalcid. Metastigmus spermotrophus Wachtl. When presented with seed lo ts containing 0, 20, 40, 60, 80, or 100% chalcid-infested seed, seed bugs f ed on uninfested seed only when the percent chalcid infestation was less th an or equal to 40% (Exp. 1), less than or equal to 20% (Exp. 2, females), o r less than or equal to 60% (Exp. 2, males). In a third experiment, nymphs exposed to similar seed lots did not feed on M. spermotrophus when sound se eds were present. However, when exposed to 100% chalcid-infested seed, nymp hs in two of 10 replicates fed on M. spermotrophus. Feeding by seed bugs ca used seeds to lose 51% of their weight on average, but 18% of 43 test seeds on which seed bugs had fed germinated In three Douglas-fir orchards survey ed, both species exhibited a clonal preference, but the ranking of clones p referred by each species was not the same. These results suggest that the i mpacts of L. occidentalis and M. spermotrophus are segregrated and additive .