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Hi Kirsten,
probably Xanthogramma pedissequum. Genus Xanthogramma is very confusing and needs revision.
In Serbia are few species - X. pedissequum, X. dives, X. stackelbergi, X. laetum and X. citrofasciatum (probably complex with 2 species).
The most similar to X. pedissequum is X. dives, which has yellow lateral margine of sternites 3 and 4, clear first basal cell and few large yellow signs on pleurae.
X. pedissequum has black lateral margine of sternites 3 and 4, black mark in first basal cell and one yellow sign on pleurae (on posterior anepisternum usually).
X. stackelbergi is the most similar to X. dives because it has yellow lateral margine of sternites, but doesn't have black mark on wings.
Do you have photo of pleurae (lateral view)?
Greetings, Mihailo.