This week, from the 12th to the 19th of November, is Australian Pollinator Week. It was created to raise awareness of the importance of pollinators and of the recent declines in insect abundance. Say g'day to an insect, plant a flowering shrub, don't use pesticides, and the indispensable insects may just survive.
Why are pollinators important?
There's been a fair bit of coverage in mainstream media over the last few years about the decline of honey bees worldwide. But why is this so important?
Because plants are immobile, they need some external way of transferring pollen from the flower of one plant, to the flower of another plant, which may be a long way away. This process, known as cross-pollination, promotes genetic diversity by mixing the genes of plants together, which in turn promotes 'health' of that population. It's the plant equivalent of having sex with someone.
Some plants, for example pine trees, use wind to disperse the pollen grains. By chance, some of the pollen may land on a female pine cone. However, relying on the wind to transport the pollen directly to another receptive cone is not particularly efficient. Much better to use a direct mode of transport.
Enter the pollinators. By using pollinators to transport pollen, flowering plants can achieve much higher pollen transfer efficiency. And the key to attracting pollinators, is the flower. The evolution of the first flowers, roughly 135 million years ago, was the most significant step in the history of plant evolution, allowing a radiation of flowering plants currently numbering >300,000 species.
The vast majority of pollinators are insects, although some other groups, including many birds, also pollinate.
Plants use flowers to attract pollinators, using both visual and chemical signals.
When this Western Wattlebird sticks its bill in the Banksia coccinea flowers, it receives a little dab of pollen on its face. The orange on this birds face is all from pollen. When it visits the next flower, and the next, the pollen is transferred to the stigma (the female bit of the flower), allowing fertilisation to occur.
Insect declines
Like I said above, there's been a fair bit of coverage in mainstream media over the last few years about the decline of honey bees worldwide. But honey bees are just the tip of the iceberg when it comes to pollination, and also when it comes to insect declines. Only last month, a study was published which documented a 75% decrease in flying insects (as measured by weight) in German reserves since standardised measurements were introduced in 1989. In other words, there are only a quarter of the amount of flying insects now, compared to 25 years ago. Of course, this was a German study, but the findings can be extrapolated to the rest of the world. One of the main problems with understanding insect abundance, is that so much about insect biology, populations, species, and ecosystem roles are still completely unknown. Scientists have been warning for years about the ongoing decline in insect abundance, and more and more data are beginning to show this.
Butterflies are an important group of pollinators.
But why the dramatic collapse in insect abundance? It's not proven, but its likely that habitat clearing and widespread pesticide use are to blame. And the changing climate due to excess greenhouse gases may well compound the problem in the future.
Various types of fungus gnats, a kind of fly, are crucial to the success of the orchids I study for my PhD. Yet, little is known about the fungus gnat diversity and biology in Australia. Here, a male Mycomya gnat attempts to mate with a Pterostylis longifolia flower.
This is all bad news for plants, too, as over 75% of the world's flowering plants rely on insect pollinators to reproduce. Lower pollination means fewer seeds, which means fewer seedlings replacing the adult plants, which means loss of plant populations and species. Insect decline is also bad news for other animals, as a huge amount of animals feed on insects of various sorts.
So, what can you do? Encourage insects to visit your garden by planting native, flowering shrubs and trees. And don't use pesticides! And perhaps most importantly, just be aware of the importance of insects, and what a crucial service they provide by pollinating our plants...