SUMMARY
Sunflower (Helianthus annuus) is an oilseed crop pollinated by Apis mellifera L. and other diurnal bees in different regions of the world. However, their flowers are also visited by insects active at night. During three agricultural years, the diversity of nocturnal visitors to sunflower heads was assessed in five different sites in Argentina. The foraging behavior of the main visitors as well as the stigmatic receptivity variations along the day were also studied in order to determine whether or not these visitors contribute to pollination. At least 67 species or morpho-species belonging to four nocturnal visitor orders were recorded. The richest and most abundant order was Lepidoptera (44 species or morpho-species, five families), followed by Coleoptera (18 species or morpho-species, nine families), Orthoptera (three morpho-species, one family) and Blattaria (two species, one family). Lepidopterans foraged exclusively for nectar while species in other orders consumed pollen and/or floral parts. However, stigma receptivity was greater during the day, peaking at midday (12:00 - 14:00). Unexpectedly, moth species widely outnumbered bee species as sunflower visitors. Since moths potentially transfer pollen at a time of the day when stigmas are least receptive, it is unlikely that they do effectively pollinate sunflowers