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<i>Halyomorpha halys</i> (Stål) (Hemiptera: Pentatomidae) is an invasive alien species and a key agricultural pest. Its native parasitoids (<i>Trissolcus japonicus</i> Ashmead and <i>Tr. mitsukurii</i> Ashmead) have been registered in several countries where <i>H. halys</i> brought dramatic economic losses and where biological control is considered to be the most effective long-term solution. By searching for stink bug egg masses and exposing sentinel egg masses, we monitored the distribution of native and exotic egg parasitoids in Trentino-Alto Adige (Italy), an area where both the host and parasitoids are in expansion. We recorded ten pentatomids, seven parasitoid species, with the first report of <i>Tr. japonicus</i> in this area and a hyperparasitoid. In the assemblage, <i>Anastatus bifasciatus</i> (Geoffroy) and <i>Tr. mitsukurii</i> were the dominant parasitoids, with a different distribution in terms of context and host plants. Sycamore was the host plant where the highest number of naturally laid parasitized egg masses (26%) were recorded. <i>Trissolcus mitsukurii</i> showed the highest parasitism rate, and was often found in apple orchards. The emergence of exotic parasitoids showed a temporal delay compared to native ones. Sequence analysis of 823 bp of the <i>CO1</i> mitochondrial gene revealed that the recovered <i>Tr. japonicus</i> and <i>Tr. mitsukurii</i> harbored one single haplotype each. These haplotypes were previously found in 2018 in Northern Italy. While sentinel egg masses proved to be very effective in tracking the arrival of exotic <i>Trissolcus</i> species, the collection of stink bug egg masses provided fundamental data on the plant host species. The results lend strong support to the adaptation of exotic <i>Trissolcus</i> species to the environmental conditions of the range of introduction, providing new information on plant host-associations, fundamental for the development of biological control programs.