Native and Non-Native Egg Parasitoids Associated with Brown Marmorated Stink Bug (Halyomorpha halys [Stål, 1855]; Hemiptera: Pentatomidae) in Western Slovenia

SIMPLE SUMMARY: Halyomorpha halys, the brown marmorated stink bug (BMSB), is an invasive pest causing serious damage to agricultural production. Managing this pest species is challenging because of its wide host range and lack of effective control measures. Biological control of H. halys through natural enemies seems to be the most environmentally friendly and sustainable solution. Extensive knowledge of the native egg parasitoid fauna is needed prior to the introduction of a biological control program. The main purpose of the study, carried out in the Goriška region of Western Slovenia, was to detect egg parasitoid species associated with H. halys and to evaluate their impact on the pest population under local environmental conditions. High species richness was identified during the study, and five egg-parasitoids were recorded for the first time in Slovenia. The native species Anastatus bifasciatus dominated in urban and suburban areas, while the non-native Trissolcus mitsukurii prevailed in agricultural areas. Rapid recruitment of native parasitoids, the presence of an effective alien parasitoid species in the region and increasing overall parasitism rates are very encouraging results and valuable information for future activities regarding the biological control of H. halys in Slovenia. ABSTRACT: Halyomorpha halys (Hemiptera: Pentatomidae), native to East Asia, has become a globally invasive pest, as a serious threat to agricultural production and a notorious nuisance pest in urban areas. Considerable efforts have been made so far to develop effective pest control measures to prevent crop damage. Biological control of this invasive stink bug by egg parasitoids has proven to be the most environmentally sustainable long-term solution. Knowledge of the native egg parasitoid fauna is of key importance when implementing a biological control program. Therefore, the main objective of our study was to detect egg parasitoid species associated with H. halys in the Goriška region (Western Slovenia) and to evaluate their impact on the pest population under field conditions. In the years 2019 and 2020, around 4600 H. halys eggs were collected in the wild and more than 3400 sentinel eggs were exposed to detect parasitoids in the field. Five egg-parasitoid species emerged from H. halys eggs: Anastatus bifasciatus (Hymenoptera: Eupelmidae), Telenomus sp., Trissolcus basalis, Trissolcus mitsukurii (Hymenoptera: Scelionidae) and Ooencyrtus telenomicida (Hymenoptera: Encyrtidae), all of them are new records for Slovenia. The native species, An. bifasciatus, dominated in urban and suburban areas, while non-native Tr. mitsukurii prevailed in agricultural areas. Overall parasitism rates of naturally laid eggs by the parasitoid species complex in 2019 and 2020 was 3.0 and 14.4%, respectively. Rapid recruitment of native parasitoids, early detection of an effective alien parasitoid species and increasing overall parasitism rates are very encouraging results, which need to be followed and verified in future research.