Remember that roughly 80% of the quarter million or more flowering plant species rely on pollinators to move pollen from the male to female parts, thereby facilitating fertilization, fruit and seed production. That’s a lot of the food we and most animals eat, and that’s also the next generation of plant. The abundance and diversity of plants and their pollinators mystified early scientists, including Darwin who called it an ‘abominable mystery’. Plants have evolved complex strategies to attract pollinators using colors, scents and ultraviolet visual cues, with the strongest one being nectar, the ultimate sweet reward.
Pollinators adapted accordingly, some with long tongues to reach deep into tubular flowers, others with branched hairs or special sacs for carrying pollen. Flies developed a fondness for the scent of decay, pollinating stinky flowers that bees avoid. Moths took on the night shift, preferring highly aromatic, white flowers that bloom at night. Examples are nearly endless.
Many flowers are structured so that small pollinators such as birds and insects inadvertently brush the protruding pollen laden anthers en route to the nectar reservoir. They are ‘accidental’ pollinators, as are larger mammal visitors, such as human passersby or bats. Interestingly there are approximately the same number of pollinator species, from ants and birds to butterflies and humans, as there are species of angiosperm. In the tropics, birds, moths and butterflies are important pollinators; less so in the temperate zones. Most pollinators are generalists, visiting a wide range of flowering plants. Some plant-pollinator relationships are those of mutual co-dependence, called ‘obligate’, a precarious situation where a single species of plant relies entirely on a single pollinator and vice versa. The best example in this country is yucca and the yucca moth.
Despite the hundreds of thousands of pollinators, most plants rely on visits from bees. And while there are 20,000 species of bees, just two or three species do much of the work: honey bees. Why? Bees evolved from the ants, wasps and bees family of insects (hymenoptera), and unlike the other insects, they rely entirely on flowers for food. Pollen is their sole source of protein, without which they could not raise young. Bees’ total reliance on pollen means that they diligently collect pollen, rather than just bumping into it as they locate the sweet nectar. Studies show that these purposeful foragers are 10 times more effective than the ‘accidental’ ones. Equally important, most bees collect one kind of pollen per foraging trip making them exceptional pollinators (pollen from one species of plant (apple) cannot pollinate a different species (pear)).
Another important fact: social bees such as honey and bumble bees feed their young directly, in the larval stage. Solitary bees like mason bees or leaf-cutters and most sweat bees, don’t feed their young directly, but they do provision the nest, laying eggs on a large ball of food made from honey and nectar. Honey bees are even more effective because they live in large, perennial colonies with big pollen and nectar requirements.
So what’s really going on with pollinator health and populations? And what does it all mean for us concerned gardeners? Stay tuned…
Written by Extension Master Gardener Volunteer, Diane Almond.