Orchids, Insects and Fire

Recently, 10th February 2016, Anita Marquart, PhD student, Adelaide University spoke at the Field Naturalists Society of South Australia. She is a recipient of the Society’s Lirabenda Endowment Fund Research Grant.   At the meeting she gave a summary of her research – Orchids, Insects and Fire: Investigating the impacts of prescribe burning on orchid pollinators in Southern Australia. Though she has not finished collating the data she has kindly supplied a summary of her talk with her preliminary findings.

It is always encouraging to see research on our native orchids. They are the Barometer of the Bush, so the more we can discover about them, hopefully the more we will better understand how to manage our native bushland.

 

Orchids, Insects and Fire: Investigating the impacts of prescribed burning on orchid pollinators in Southern Australia

Anita Marquart, Renate Faast, José M. Facelli, Andrew Austin

School of Earth and Environmental Sciences,

The University of Adelaide, Adelaide 5005 Australia

PhD Project

Summary

Fire is an important ecological factor in Australian ecosystems. Orchids that depend on specific pollinators may be more susceptible to disturbance than more generalist species. Therefore, declines or changes in pollinator communities due to prescribed burns and wild fires could lead to reduced pollination success and consequently declines in orchid populations. The project combines traditional plant and insect ecology with advanced molecular techniques to identify orchid pollinators and assess their response to prescribed burns and wild fires. Insect relevant habitat characteristics (such as floral abundance, vegetation height, presence of logs, litter and standing litter) were assessed and trapping surveys of potential orchid pollinators were conducted in spring, before and after prescribed burns. The effect of both spring burns and autumn burns is being investigated.

Study sites are located in the Adelaide hills with always one burn and one adjacent control site respectively in Kersbrook Native Forest, Millbrook Reservoir, Para Wirra Recreation Park and South Para Reservoir. Some parts of the study sites in Kersbrook and Millbrook were affected by the Sampson Flat Bushfire. Affected sites are used to compare the effects on orchid pollinators after prescribed burns in contrast to wild fires.

Potential orchid pollinators are being identified using DNA barcoding with the mitochondrial cytochrome oxidase I (COI) gene. Sequencing results will be compared with existing databanks and confirmed using morphological identification. As the data accumulates it will build up a reference library of COI barcodes for the species found in the surveys.

The outcome of this research project might help to advise the optimal management of orchid species under fire-managed regimes in the Mount Lofty region of South Australia, as well as more generally in south eastern Australia.

160219 Anita Marquart Melangyna collatus on Caladenia rigida

A hoverfly, Melangyna collatus on Arachnorchis rigida syn Caldenia rigida (Rigid White Spider Orchid)

 

Orchids and their pollinators

Native bees, thyninne wasps and Syrphid flies are known orchid pollinators of South Australian orchid species. Orchids of main interest for this study were Caladenia rigida, Caladenia behrii, Caladenia tentaculata and Glossodia major. Caladenia tentaculata and C. behrii are sexually deceptive orchids and are known to be pollinated by thynnine wasps (Bates 2011). In contrast, C. rigida is food advertising and uses a broad range of bee and fly species, such as native bees and hoverflies (Faast et al. 2009). Glossodia major is a generalist in its pollination strategy and is using small native bees of several genera (Bates 2011, personal observations).

Preliminary findings

Syrphid flies were successfully separated into different species using DNA barcoding methods. Results show that we have two dominating species on our field sites in the Adelaide hills. Both species, Melangyna collatus and Symosyrphus grandicornis are common native Australian species. Both species were caught with orchid pollinia attached and were observed on Caladenia rigida flowers.

First findings suggest that hoverflies don’t seem to be much affected by prescribed burns or bushfires. Syrphid fly numbers vary greatly between the years of sampling, but we did not find a significant impact of prescribed burning or the Samson Flat bushfire.

Statistical analyses for the data on syrphids, native bees and thynnine wasps are currently underway.

Preliminary findings suggest that a range of pollinators are still present on field sites after prescribed burns and even after bushfires. Nevertheless, some specific species might be more sensitive to fires and might have disappeared from the study sites. For example, orchids relying on one species of wasp could be more affected by changes in the abundance of their pollinator after fire, than orchids that are pollinated by a number of different insects.

We will have to analyse our results in more detail to look into the specific species composition for the insect families, especially for native bees and thynnines, rather than looking at overall abundance.

160219 Anita Marquart Melangyna collatus with pollinia

Hoverfly, Melangyna collatus with orchid pollinia attached

References:

Faast R, Farrington L, Facelli JM, Austin AD (2009). Bees and white spiders: unravelling the pollination syndrome of Caladenia rigida (Orchidaceae). Australian Journal of Botany 57, 315–325.

Bates, R. J. (2011). South Australia’s Native Orchids. Native Orchid Society of South Australia.

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