Ecosystem Services Against Illegal Immigration: The Natural Control of the Migratory Butterfly Painted Lady ( <i>Vanessa cardui</i> ) by <i>Cotesia vestalis</i> (Hymenoptera, Braconidae) on Organic Soybean in Ukraine

ABSTRACT The Painted Lady, Vanessa cardui (Linnaeus) (Lepidoptera: Nymphalidae), a cosmopolitan migratory butterfly, was recorded as a significant pest of organic soybean ( Glycine max L.) in central Ukraine. Multiple immigration waves of V. cardui from southern regions were observed in the Poltava Region (Kremenchuk District), notably during severe and moderate outbreaks in the summers of 2019 and 2022, respectively. Despite notable early‐season defoliation in June, soybean crops demonstrated strong recovery, attributed to high levels of natural biological control. Caterpillars of V. cardui were heavily parasitized by the braconid parasitoid Cotesia vestalis (Hymenoptera: Braconidae: Microgastrinae) during July and August, with parasitism rates reaching up to 100% in several surveyed fields. Only isolated spots of V. cardui caterpillars persisted into late July–early August in both years, all of which were quickly suppressed by the parasitism of C. vestalis . In the studied region, C. vestalis also parasitized the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), on wild Brassicaceae, which is likely serving as an alternative host during periods of low V. cardui abundance. This facultative host association may enhance the resilience and early‐season availability of C. vestalis populations. The observed levels of natural suppression in organic systems contrast markedly with conventional practices, where broad‐spectrum pesticides were routinely applied during V. cardui outbreaks. These findings highlight the value of conserving functional parasitoid communities in agroecosystems. For organic growers, reliance on ecosystem services provided not only effective pest control but also economic benefits through reduced input costs.