Although insects are generally interested in nectar, some take pollen directly to consume it. Depending on their use of pollen and whether they are present on a single species or many species of plants, pollination is more or less efficient!
Hymenoptera, champions of pollination
The presence of hairs that attach pollen grains to the body makes Hymenoptera good pollinators. Diet and foraging behaviour are also important. Adults and larvae of bees and bumblebees have a diet that depends exclusively on resources from flowers. Many bees take pollen directly from flowers to feed themselves or their larvae. To avoid frequent trips back and forth between plants and their larvae, they have hairs on their hind legs called corbicula, or under their abdomen forming small pollen sacs.
Insects of certain species prefer to pollinate one species or type of flower during their lifetime, this is called floral constancy. This fidelity allows efficient pollination of the flower by favouring the deposition of pollen of the same species.
Nectar, pollen and infidelity
In Diptera, hoverflies and bombylids are also covered in hair and are also good pollinators but only the adults feed on nectar (and pollen for hoverflies), they do not build up reserves of pollen and nectar for the larvae, so they make fewer visits to the flowers than Hymenoptera and carry less pollen.
In Lepidoptera (butterflies), it is often the hair on the abdomen on which pollen grains cling while the insect collects nectar with its proboscis.
Some beetles consume pollen and, like other insects, have dense hair on their thorax and under their abdomen to carry this pollen. However, as they are not faithful to a particular plant species, they are often not very efficient in pollination. In addition, they generally stay on the same plant for a long time and therefore allow little exchange of pollen.