The paper deals with connections between solar flare activities and light-trap collection of insects. The authors have worked out the catch data of European corn borer (Ostrinia nubilalis Hbn.) adults, as published for the period of 1976–1997 by the Hungarian national light-trap network. The results proved that both the daily and annual catches were significantly modified by the Q-indexes, expressing the different lengths and intensities of the solar flares. On days with high Q-indexes relative to the ones of the average swarming periods, the number of catches are considerably lower. In those years when the Q-index is high, the average individual number and the number of caught moths are lower by 30% as compared to the average number of total cycles (11 years) and the average population density of a given biotope. On the contrary, in years with low Q-indexes an increase as high as 45% can be experienced in the number of individuals collected. Thus, by evaluating the light-trap catches a strong modifying effect of solar flares has to be considered.