Abstract
Insects visiting lettuce flowers were investigated under field and enclosure conditions. In a 4-year field survey, visitors of 11 species belonging to 3 orders were observed. Most species visiting the flowers were sweat bees (Hymenoptera; Halictidae). The frequency (total days of visitation to lettuce flower/total days of flight by the insect) of visitations by the sweat bee Lasioglossum villosulum trichopse was obviously higher at 65.5% than those of other insects. Honeybees were not observed on the lettuce flowers. In a 5-year survey under enclosure conditions, 10 of 17 bee species reared and a hoverfly were observed to visit the lettuce flowers. The highest frequency of visitation was shown by L. villosulum trichopse (59.4%), followed by Andrena knuthi (19.2%) and Osmia cornifrons (8.6%). Most visitors were one-day foragers and classified as temporary nectar foragers and continual pollen (and nectar) gatherers. Continual nectar foraging was observed in only 3 species, L. villosulum trichopse, An. knuthi and Ceratina boninensis. Daily flight activities of L. villosulum trichopse and the Lactuceae oligolectic bee An. knuthi corresponded to the morning blooming time of lettuce. The sweat bee L. villosulum trichopse may be a pollinator for hybrid seed production of lettuce.
