Sunflower (Helianthus annuus L.) is an allogamous plant that needs insects in flowering, especially honey bees for seed production. The collection of nectar and pollen by honey bees in agricultural crops is essential for beekeeping, as well as for a better understanding of the biology of plants. The feeding behavior of Africanized Apis mellifera L. (Hymenoptera, Apidae) and its efficiency of pollination in seed yield of sunflower genotypes (open pollination and restricted pollination) was evaluated. There were peaks of A. mellifera visits for nectar collection on days 2 and 3 of flowering between 7:00 and 8:30. The average density of A. mellifera during the increase in visits varied from 2.27 to 2.94 bees per capitulum. The nectar collecting bees were more frequent (2.28 bees per capitulum) than the pollen collection (0.40 bees per capitulum). On the third day of flowering, the Helio 360 and Aguará hybrids had the highest number of bee visits per flower head (p ≤ 0.05) than the other genotypes. The seed yield was 43% higher (p ≤ 0.05) of sunflower plants that were visited by pollinating insects compared to plants restricted to pollinators.
The sunflower buds are very suitable for pollination of insects, since the agglomeration of the flowers guarantees the conspicuosity and the pollination of a maximum number of flowers for a single visit of insects. The honey, secreted at the base of the style, is protected by the corolla tube from the visits of short-tongue insects. When the flower opens, the receptive surfaces of the two stigmas are pressed together and occupy a position at the base of the tube formed by the anthers together; the latter is divided in the interior and the released pollen fills the cavity of the tube and exposes it to contact with the visiting insects. Fianll, the style protrudes through the tube of the anther and the stigmas are separated and expose their receptive surfaces previously hidden. Therefore, the history of the life of the flower is divided into two stages: the first male and the second female. This favors cross-pollination compared to self-pollination. Therefore, the flower of the sun is practically self-sterile, although self-pollination can take place at a late stage, when cross-pollination has failed.
Pollination in legumes:
Pollination: Because flowers are protandrous, cross-pollination usually occurs. In pollination of Lathyrus and Pisum. The pollination mechanism in Fabaceae is 'piston mechanism'. The type of pollination is entomophilic. Insects are attracted by the standard petal. They perch on the petals of the wing and press them down in search of the nectar collected in the resistance. Because of this, the petals of the keel are also pressed down and open exposing the stigma and stamens. The stigma that comes out first, brushes the abdomen of the insect and picks up the pollen. When the anthers come into contact with the insect, pollen is deposited on its body. As the insect leaves the flower, the essential organs return to their normal position. Since the movement of the essential organs is like that of a piston, it is called 'piston mechanism'.