Comparative emergence phenology of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae) and its parasitoids (Hymenoptera: Pteromalidae and Platygastridae) under controlled conditions

The orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), is a wheat (Triticum aestivum L.) pest that can cause significant yield losses. Several hymenopterous parasitoids are known to attack S. mosellana. For the effective biological control of this pest by its parasitoids, the host-parasitoid synchrony is particularly important. The synchronization between the emergence of S. mosellana and its parasitoids was studied under controlled conditions with soils sampled from two locations. For both sites, three parasitoid species were identified: Macroglenes penetrans (Kirby) (Hymenoptera: Pteromalidae), Euxestonotus error (Fitch) (Hymenoptera: Platygastridae) and Platygaster tuberosula (Kieffer) (Hymenoptera: Platygastridae). The hypothesis that parasitoid emergence is triggered by the same rainfall that induces host emergence was tested by simulating three rainfall events, a week apart. The parasitoid M. penetrans emerged later than S. mosellana with a mean of 57 ± 7 DD (degree-days above 7 °C) for insects collected from Juprelle and 68 ± 10 DD for those from Veurne (i.e., 4-5 days after its host). M. penetrans was therefore closely synchronized with its host through the same inductive rainfall, but this was not the case for E. error or P. tuberosula. Depending on when the rainfall that triggered the emergence of S. mosellana occurred, E. error and P. tuberosula emerged either before or after their host. M. penetrans is a more effective biocontrol agent of S. mosellana compared to P. tuberosula and E. error. Greater knowledge about parasitoid emergence could lead to the better positioning of insecticide treatments against wheat midge that protect and conserve the parasitoid populations.