Harold Bernhardt of Dunedin asks :-

Why are flowers fragrent? Can bees smell?

Brad Howlett, a pollination entomologist with Crop and Food Research, responded.

The key reason to why many flowers are fragrant is to attract insects such as bees, flies, beetles, butterflies and moths to pollinate them. Many insects, particularly bees, can smell these fragrances through special structures located on their antennae. These are called chemoreceptors. Different insects have different abilities to smell fragrances (just like dogs can smell odours that we cannot). Honey bees are particularly good at detecting fragrances because each bee has 170 odorant receptors.

Different insects respond to different scents. Many blow flies respond to flowers that smell like decaying animals. Blow flies are attracted to decaying animals because that is where their offspring (maggots) develop. Thus flowers mimic this smell to attract flies that will pollinate them. Plants will also release odours at different times of the day. Many plants release their odour during the day to attract day flying insects. However, some flowers release their fragrance at night to attract night flying insects such as moths. The reason as to why different flowers release such different smelling fragrances and at different times of the day is to avoid competition with other flowers, increasing their probability of pollination.

A key benefit of flower fragrances is to attract insects from a distance where the insect cannot see the flower. Insects usually use the flower fragrances as a guide to bring it close enough to the flower so that it can also use sight for accurate location of the flower. Interestingly, flowers that rely on birds for pollination are often showy but are not particularly fragrant. This is because birds have a poor sense of smell but have very good eye-sight.