Pollination needs and foraging behaviour of bees in grapefruit plantations (Citrus paradisi Macf)

CHACOFF, NATACHA P; PATRICIA FERNANDEZ

Berlin, Alemania

Simposio; 12th Symposium Insect-Plant Relationship; 2004

Citrus flowers produces nectar copiously, have sticky pollen, a pleasant fragrance and have a whitish contrasting color of the flowers with the dark green background of the leaves, all this characteristics makes them very attractive to insects, specially bees. However, Citrus has been considered as a crop of no need for insect pollination, but the increased knowledge is changing this, suggesting a wide range of pollination needs. In grapefruit, apparently cross-pollination is not required, but this does not mean necessarily that no benefit is derived from insect transfer of pollen within the cultivar and some of them set more fruits in cross pollinations experiments than self-pollinated. In the zone, we recorded 52 species of insects visiting grapefruit flowers. We studied pollinators needs to set fruits and foraging behavior of honeybees and stingless bees in grapefruit plantations of the northwest of Argentina. We found that at least in this varieties an insect vector is needed to set fruits, because fruit set in natural open flowers set 6 times more fruits than closed bagged flowers where pollinators were excluded. Apis mellifera was the main flower visitor to grapefruit flowers performing 97% of the visits, followed by some stingless bees. Honeybees were more actives between 9:30-12.30 and between 15:30-18:00 and visited mass blooming trees and, T. argentina were more active foragers between 13:00-15.30, suggesting a kind non overlap foraging behavior. Nectar availiabily was maximun in the early morning. Apis mellifera persisted in the same tree in 89% of the 1932 observations, while Trigona  argentina continued in 75% of the 20 cases observed, Tetragonisca angustula and Plebeia sp persisted in 90% and 78%. This results suggest different strategies of foraging of T. argentina and A. mellifera and that although the first is not very common, it may be more effective in crossing pollen between trees than A mellifera that is a very frequent pollinator and mainly performs geitonogamy pollinations.