New Insights into the Phenology and Overwintering Biology of Glyptapanteles porthetriae, a Parasitoid of Lymantria dispar

<i>Glyptapanteles porthetriae</i> (Hymenoptera: Braconidae) is a solitary larval endoparasitoid of the spongy moth, <i>Lymantria dispar</i> (Lepidoptera: Erebidae). Previous studies suggested that only the spring generation of the wasp parasitizes early instars of <i>L. dispar</i>, while subsequent generations develop in larvae of unidentified alternative hosts and overwinter exclusively as endoparasitic larvae within these hosts. In a declining outbreak population of <i>L. dispar</i> in Austria, we observed two successive generations of <i>G. porthetriae</i> developing in spongy moth larvae during spring and early summer. The high abundance of parasitoids in the third outbreak year prompted us to test alternative hypotheses proposing a univoltine, monophagous life cycle with strong specialization on <i>L. dispar</i>. We exposed various developmental stages of <i>L. dispar</i> embryonic larvae to wasp females and evaluated potential dormancy induction in <i>G. porthetriae</i> larvae or pupae by assessing developmental parameters and respiratory activity under different environmental conditions. <i>G. porthetriae</i> did not develop from <i>L. dispar</i> individuals exposed in the egg stage, and no dormancy was observed in <i>G. porthetriae</i> developing in <i>L. dispar</i> larvae. These findings disprove the univoltine, monophagous development hypotheses and highlight the reliance of <i>G. porthetriae</i> on suitable alternative hosts to complete its life cycle.