Attractants and rewards are required for

To sustain insects and other animals visits, flowers have to provide reward to the insects. Majority of insect pollinated flowers are large, colourful, fragrant and rich in nectar. Colour & fragrance are attractants while nectar & pollen grains are rewards. Pollination by insects called entomophily so attractants and rewards are required for entomophily. For hydrophily and anemophily other floral features of stamen & stigma are required while cleistogamy always shows self pollination there is no need of attractant or reward.