Implementing mass rearing of Trissolcus japonicus (Hymenoptera: Scelionidae) on cold-stored host eggs

Authors: BITTAU, BARBARA - University Of Bologna, Italy; DINDO, MARIA LUISA - University Of Bologna, Italy; GIOVANNI, BURGIO - University Of Bologna, Italy; SABBATINI-PEVERIERI, GIUSEPPINO - Crea; Hoelmer, Kim; ROVERSI, PIO FEDERICO - Crea; MASETTI, ANTONIO - University Of Bologna, Italy

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2021
Publication Date: 9/18/2021
Citation: Bittau, B., Dindo, M., Giovanni, B., Sabbatini-Peverieri, G., Hoelmer, K.A., Roversi, P., Masetti, A. 2021. Implementing mass rearing of Trissolcus japonicus (Hymenoptera: Scelionidae) on cold-stored host eggs. Insects. 12(9) 840. https://doi.org/10.3390/insects12090840.
DOI: https://doi.org/10.3390/insects12090840

Interpretive Summary: Brown marmorated stink bug, a pest of Asian origin, causes severe damage to Italian fruit and vegetable crops. Because of the limited efficacy of currently available pesticides, classical biological control by releasing the samurai wasp, an exotic natural enemy of the pest in Asia that attacks stink bug eggs, is a favored solution for managing the stink bug. In 2020 Italy authorized field releases of this natural enemy, and an effective mass rearing program was needed to produce large numbers of parasitoids. We studied parameters that influence the rearing of the samurai wasp in insectaries, such as the effect of storage temperature and storage time of stink bug egg masses, length of exposure to parasitoids, parasitization by single females vs groups, and repeated parasitization bouts by the same parental wasps. Our results showed that host eggs could be stored successfully at various temperatures before and after parasitism by wasps, providing flexibility in handling and scheduling field releases and ensuring efficient production of large numbers of wasps for field release or for long-term colony maintenance.

Technical Abstract: Halyomorpha halys, a pest of Asian origin, causes severe damage to Italian agriculture. Because of the limited efficacy of currently available management strategies (primarily chemicals), the application of classical biological control by releasing Trissolcus japonicus, an exotic egg parasitoid co-evolved with the pest in Asia, appears to be the most suitable solution for pest control. In Italy, T. japonicus releases in the field were authorized in 2020, and the development of an effective mass rearing was needed to produce the numbers of parasitoids required for the release program. We studied parameters that could influence the rearing of T. japonicus in insectaries. We studied the effect of storage temperature and storage time of H. halys egg masses, exposure time of host eggs to parasitoids, parasitization by isolated females vs parasitization by a group of 10 females, and successive parasitization bouts by the same parental female. The impact of storage at 16 °C on the survival and fertility of adult parasitoids was also investigated. A significantly higher emergence rate was found from host eggs stored at 6 °C (86.45 %) compared to -24 °C (48.81%) for up to two months prior to exposure for parasitism. There were no significant differences in the emergence rates of progeny from single females exposed in a vial with only one egg mass (83.19%) or six females inside a cage with 10 egg masses (83.91%). The exposure to parasitoids of refrigerated (+ 6°C) egg masses of H. halys for 72 h led to a significantly higher emergence rate (62.10%) compared to shorter exposures for 48 (44.03%) or 24 h (37.14%). A decline in parasitization rate by the same female was detected between the first (62.10%) and the second parasitization (41.25%). Adult parasitoids stored at 16 °C up to 90 days showed 87.10% survival rate, but a significant decrease in fertility was detected. These parameters could be adjusted to different rearing regimes of T. japonicus aimed at production of individuals for field release or colony maintenance.