Egg parasitoid complex of the pine processionary moth in NW Italy

Abstract

ABSTRACT Investigations on the egg parasitoid complex of the pine processionary moth (PPM), Thaumetopoea pityocampa, were performed in 2020-2022 in seven sites located in NW Italy to determine the parasitoid species composition, seasonal emergence, parasitoid species incidence, and parasitism rate. Furthermore, we examined whether the egg batches parameters and the parasitism rate were influenced by altitude and summer temperatures. A sample of 832 egg batches was collected, each batch consisting on average of 206 ± 5.73 eggs. In total, 35,881 egg parasitoids emerged, mainly represented by four primary species, namely Ooencyrtus pityocampae, Baryscapus servadeii, Anastatus bifasciatus and Trichogramma sp.. Parasitism ranged from 4.27% to 24.41% and the most representative species were O. pityocampae (68.38%) in 2020-2021, and Trichogramma sp. (56.50%) in 2021-2022. The altitude of the sites (808-1303 m a.s.l.) had a negative correlation with all the investigated egg batches parameters (e.g. batch length), and with the parasitism rate by A. bifasciatus and B. servadeii, while a positive correlation was found only for O. pityocampae. The number of days with temperatures above 30°C was positively correlated with parasitism rate for A. bifasciatus and O. pityocampae, and negatively for Trichogramma sp., while no correlation was found with B. servadeii. Since the performance and distribution of the natural enemies is highly dependent on climatic conditions, the regulating effect of parasitoids, reducing PPM population needs to be further investigated, to compare the complex of natural enemies across a wider geographic and climatic range.