Flower visitors of lettuce under field and enclosure conditions

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.

Hybridization rates between lettuce (Lactuca sativa) and its wild relative (L. serriola) under field conditions

“…The importance of pollinators for the effective pollination of Lactuca flowers has already been demonstrated (Goubara et al, 2003;. Jones (1927), showed that bagged flowers of L. sativa had significantly less or no pollen grains on their inner stigmatic surfaces, compared to open-pollinated flowers.…”

“…Moreover, they have an influence on seed set (Mejias, 1994). Not surprisingly, distance and pollinator availability have been found to be the most relevant factors for pollen migration between different L. sativa varieties (Goubara and Takasaki, 2003;Thompson et al, 1958). While wild × crop hybridization cannot be inferred directly from the results presented above, we can assume that the main factors influencing the pollination of prickly lettuce by the crop are the same, since the species are very closely related.…”

Pollination effects of the sweat bee Lasioglossum villosulum trichopse (Hymenoptera: Halictidae) on genic male-sterile lettuce

“…This ground-nesting bee is a species native to our field where various kinds of flowering plants (lettuce cultivars and their allied species belonging to the tribe Lactuceae) are cultivated in 24.0 or 24.5 cm plastic pots as foraging resources for the insects (Goubara and Takasaki, 2003). Setting 'bee-beds', wooden boxes filled with clay soil and sand, on the ground for the nesting substrate, we commenced the rearing of sweat bees in 1995 in an arched, vinyl-roofed cage (7.0ϫ7.0ϫ3.5 m in height of top) and continued in 1998 in the field.…”

“…'V', 'Summer Red' and 'Tima Santyu' were contained in 16, 11 and 19 pots, respectively, in the field, and 10 pots of each were set in the cage. Eight species of bees, including L. villosulum trichopse, in about 270 nests were reared in the cage (Goubara and Takasaki, 2003). On the other hand, seven species of bees, not including L. villosulum trichopse, were reared in the field.…”

“…To find potential pollinators for hybrid lettuce seed production, we surveyed visitors to lettuce flowers and selected a candidate pollinator, the sweat bee Lasioglossum (calina-less Evylaeus) villosulum trichopse (Strand), based on the frequency of visitation and foraging behavior (Goubara and Takasaki, 2003). The pollinator showing the most potential, L. villosulum trichopse, had daily flight activities which corresponded with the morning blooming time of the lettuce, showed the highest visitation frequency and showed continual nectar foraging.…”