I have been busy with other writing projects which has kept me from adding material to this blog for a couple of months. Hopefully this post will make up for the recent lack of content.
You could be forgiven for thinking that pollination would be a simple affair for plants with self-pollinating flowers i.e. where male and female components are contained in the same flower. Some of these so-called self-pollinators actually need quite a bit of help. For example, the pollen of tomato flowers is encapsulated inside the anthers rather than being located on the outside. The pollen must be shaken out of the anthers to hopefully land on a sticky stigma. When tomatoes are grown outdoors this may be achieved by wind or, ideally by pollinating insects known as “buzz-pollinators”. These insects vibrate the flowers at the frequency which encourages maximum pollen release.
I am lucky to live on a property where native “buzz-pollinating” blue-banded bees (Amegilla spp.) occur. I frequently see them in action on my tomato plants and other native and exotic flowering plants. Other buzz-pollinating bees create these vibrations with their thoracic flight muscles, but blue-banded bees are quite different in that they do it with their heads. Yep, they are headbangers! The bee starts by vibrating its flight muscles, but then transfers the vibration to its head. This enables the bee to bang its head on the flower’s anthers at an astounding 350 times per second. Check out this slow-mo video – Metallica fans take note!
This amazing behaviour only came to light relatively recently with the use of high-speed video by a team from RMIT and the University of Adelaide. The results were written up in the paper “Shakers and head bangers: differences in sonication behavior between Australian Amegilla murrayensis (blue-banded bees) and North American Bombus impatiens (bumblebees).” The main conclusion of the paper is that blue-banded bees may be able to extract pollen more quickly than bumblebees. Further studies are needed to compare the overall pollination effectiveness of these species.
Now let’s talk about another important group of pollinators – the flower wasps of the family Tiphiidae. Depending on the species these wasps may pollinate a range of plants or they may be the specific pollinator of certain native terrestrial orchids. The male wasps are the orchid pollinators – they are drawn to odours emitted by the orchids, which mimic the sex pheromones of receptive female wasps. That’s deception! I wrote about these wasps in a previous post Simply Irresistible in 2017.
One wasp that I didn’t talk about back then was Lissopimpla excelsa of the parasitic wasp family Ichneumonidae. Its common name is ‘orchid dupe wasp’ and is best known for the male of the species being fooled or ‘duped’ into pollinating the Cryptostylis species of native ground orchids. The orchid flowers mimic the pheromones and appearance of female wasps to attract males to ‘mate’. These duped male wasps collect pollen in the process, which is transferred to the next flower that tempts him. It must be noted at this point that this wasp is the sole pollinator of Cryptostylis orchids.
The ‘orchid dupe’ story doesn’t end there though. Female orchid dupe wasps (see above) are parasites of large caterpillars, including some very destructive agricultural and horticultural pest species. A female wasp inserts an egg inside a caterpillar using her large sting or ovipositor. The developing wasp larva feeds inside its host, which does not die until after it has pupated underground. Once the host is dead the wasp larva pupates and eventually emerges as an adult wasp.
So let’s join the dots here. The female Lissopimpla excelsa wasp is a parasite of caterpillars (some of which are pests), while the male wasp is duped by the smell and appearance of orchid flowers to be the sole pollinator of all five species of Cryptostylis orchids. If there were no pesky caterpillars for Lissopimpla wasps to breed in, there would be no Lissopimpla wasps, and therefore no Cryptostylis orchids!
And now for the ‘brawlers’. Some male insects fight each other for the right to mate with females, for example many beetles do it. The most brutal exchanges are those of Dawson’s burrowing bee (Amegilla dawsoni), an insect unique to Western Australia. These are gregarious ‘solitary’ bees which build individual burrows in colonies of up to 10,000. The fighting happens from about July onwards, when a new generation of bees hatch from underground burrows to mate. Males emerge first, stake out their territory and wait for the females to emerge. Then all hell breaks loose.
When a female emerges she may be set upon by as many as 20 males and is enveloped in a furry ball of tumbling, fighting, biting males. The biggest and strongest male usually wins, leaving behind several dead rivals, but unfortunately the female might also die in the frenzy. Undeterred the surviving males then turn their attention to the next burrow that may yield a virgin female. Eventually a male will claim a female and they head for the nearest bushes to mate in relative safety and privacy. Because of the incessant battling, by the time the last females emerge from their burrows, all the males are dead. This leaves the mated females to provision their nests with honey for their young in peace, and then they too die, leaving the young to develop in their burrows.
Below is a great little video produced by BBC Life and narrated by Sir David Attenborough about these unique bees. (Ignore the slight error about male bees ‘stinging’ each other – they can’t as they don’t have stings.)