In Vitro Development of Trichogramma spp. (Hymenoptera: Trichogrammatidae) in Long-term Stored, Freeze-dried Artificial Media

Abstract

Freeze-dried media were successfully used to facilitate the rearing of oophagous parasitoids of the Trichogramma genus under artificial conditions. These media can be prepared when biological material, such as insect haemolymph, is available, and then stored for later use for several months. The development of two Trichogramma dendrolimi strains from China (TdC) and Italy (TdI) and Trichogramma brassicae (Tb) in rehydrated freeze-dried media was tested with artificial host egg cards. About 5560 artificial host eggs were used in the experiments. The percentages of parasitism, pupation and emergence were similar in rehydrated freeze-dried media stored for 8 months and in fresh media. For TdI, the freeze-dried media centrifuged after rehydration induced a higher percentage parasitism, and media that were not centrifuged induced a higher percentage pupation. This could be due to minor modifications in the balance between free and total amino acids. The development parameters observed varied slightly according to the species or strain of Trichogramma tested (TdC, TdI or Tb). Polyvinyl alcohol smeared on the artificial eggs strongly improved egg laying and reduced the variability of the development parameters. Freeze-drying, which does not alter the performance of the media, is a process suited for the long-term storage of artificial media for parasitoids.