University of Queensland honours student Sue McGrath doesn't mind doing the dirty work to learn more about insect diversity.
Her recent honours thesis with the Entomology Department found that insect problems associated with composting toilets could be lessened through the management of materials before disposal.
For her study, Ms McGrath donned protective gloves, coat and face-mask to sift through more than 30 samples from 11 composting toilets to increase understanding of insects' role in the systems.
The first of its kind, her study supervised by Entomology Department head Professor Gordon Gordh and senior lecturer Dr David Walter will add to moves to have composting toilets approved for use in Brisbane by the Brisbane City Council.
The Department was approached to do the study by Dean Cameron, principal of composting toilet manufacturer, Dowmus Resource Recovery.
Dowmus composting toilets recycle grey water (for example, from shower, washing machine etc), human and household waste (for example, fruit and vegetable peelings and paper) into clear water and compost for the garden. The key to the system is filtration of materials through worm beds.
Mr Cameron's company has developed the toilets, known as the Dowmus Biolytic Filters, since 1987 with 600 installed throughout Australia.
Mr Cameron obtained the study samples from systems in, under or near homes in the Crystal Waters permaculture village near Maleny. Samples were collected in peak insect times of spring, summer and autumn and sent to Ms McGrath for laboratory analysis.
The impetus for the study stemmed from customer concerns over scuttle flies breeding in the systems. Mr Cameron is seeking a natural control agent for scuttle fly larvae in the composting toilets. The use of chemicals is detrimental to all biota in the systems.
'The study identified no clear seasonal trends for the fly and revealed the extremely complex interaction between insect species inside the systems. It highlighted the need for more research before a natural control agent can be introduced,' Mr Cameron said.
Ms McGrath, who now works as a technical officer and tutor with the Entomology Department, completed a detailed statistical analysis of each composting system using variables such as what each user put into the system, whether it was flushed with water or left dry, and its location in sun or shade.
The analysis was related to her record of insect types present and used to predict which species could be added to control the fly without upsetting the ecological balance.
She found the presence of around 30 insect families in the toilets including flies, mites, earwigs, beetles and springtails.
'I found that while earth, king and tiger worms were chief composting agents, some insects also played a part once material was reduced in size by the worms,' she said.
Her study identified a predatory mite as being most suitable to control scuttle fly larvae but further research is required to confirm this finding.
Her study also found that composting toilet users could take steps themselves to reduce fly numbers.
'Seventy-three percent of those householders who added fruit and vegetable scraps to the system also had a fly problem. Scraps were generally being left open to the air before being placed in the composting toilet,' she said.
'In other words, flies had a greater opportunity to infiltrate the system before the food was even added.'
She said this finding enabled the company to warn customers of potential fly numbers from the outset and advise them on steps they could take to reduce the incidence such as keeping scraps in airtight containers and installing flyscreens on windows and doors.
For more information, contact Ms McGrath (telephone 07 3365 7085) or Mr Cameron (telephone 0754 999 828).
