Sabrina Hahn: New CSIRO research sheds light on remarkable relationship between boronias and South West moth

Many West Australians will remember the fragrant bunches of brown boronia being sold as a cut flower in the city. Boronia megastigma has to have one of the most intoxicating perfumes in the plant kingdom.

Boronias have puzzled botanists for many years regarding their pollination process. The flowers are closed, making it extremely difficult for insects to effectively pollinate them. Making it even more of a challenge for pollinators, some of the anthers (the male part) are sterile, and the stigma (the female part) can be too large for certain insects to handle.

A team of researchers from CSIRO, led by Douglas Hilton, thought a small moth might be the mysterious pollinator of boronia flowers and began their research into the tiny Heliozelidae group of moths. They discovered there were thousands of Heliozelidae species in Australia, most of them unnamed.

A group of 15 Heliozelidae moth species in the South West of Western Australia was found to have a specific relationship with a particular species of boronia. One of these moth species was found exclusively on this specific boronia species. These moths have an intricate structure at the dorsal tip of their abdomen that collects pollen as the moth moves around the flower.

During spring, the female moth lays eggs inside the boronia flower. As she moves around the flower, the pollen collects in her abdomen. She will visit many flowers and spread the pollen as she goes.

The eggs hatch into caterpillars which eat the flowers and some of the seeds; the caterpillar grows and pupates in the soil, making a cocoon, and emerging as a moth who visits the flowers — and so the life cycle goes on.

For certain species, such as the brown boronia, moths may be the only visitors to their flowers. This indicates a reciprocal relationship where both the moth and the plant rely on each other for reproduction and, ultimately, for survival. This type of symbiotic relationship is reminiscent of the connection between figs and fig wasps.

Why is this research important for gardeners? Many of us aim to eliminate caterpillars from our gardens, but studies on plant-insect relationships are still in their early stages. This scientific discovery highlights the vast amount we don’t yet understand. What we do know is that many of our native plants have intricate relationships that have evolved over hundreds of thousands of years. In some cases, a plant’s survival may depend entirely on a single species of insect, and vice versa.

With rapid deforestation due to mining and land clearing, along with climate change and inadequate environmental protection laws, biodiversity is declining at an alarming rate. We can never replace what has already been lost.

Tip of the week

When caterpillars are eating your plants, find out what they become, and let some develop into adulthood. They may be an important part of biodiversity survival in your garden.

Three jobs to do now

1. During heatwaves with temperatures above 38C, hand-water affected plants in the late afternoon.

2. Put up umbrellas around veggies like capsicums, tomatoes, hydrangeas, and plants that have sunburnt leaves. Protect the trunk of avocado and frangipani trees.

3. Some plants will experience leaf-drop during the heat. Ensure mulch is around 5cm thick, and that water penetrates through the mulch into the soil.

Do you have a question for Sabrina?

To submit a question to Green With Envy, inside Saturday’s The West Australian, write to Ask Sabrina, GPO Box D162, Perth, 6001 or email home@wanews.com.au.

Please include your full name and suburb. Due to the volume of questions, not all of them will be answered.