14 Jul, 2015 04:00 AM
A blue blowfly, one of the most effective pollinators among fruit trees.
Some crops seem to be more attractive to flies than others
THE old practice of placing roadkill carcasses under fruit trees to increase pollination now has scientific backing. What’s more, native flies, not bees, have been found to be the dependable workers.
University of New England researcher Romina Rader monitored Mareeba mango orchards for pollination rates of native insects. The lecturer in environmental management found native flies were one of the top mango pollinators.
Dr. Rader investigated the efficiency of different pollinators that visited mango flowers on 10 farms in the Mareeba region.
“We found that native flies visited 20 percent more frequently than bees and they were among the top transporters of pollen,” she said.
The study found 44 different insects visited the flowers during the survey.
The 12 most frequent included two bee species, nine flies and one beetle.
“Of all the flies, the small black-tip fly (Rhiniidae) visited with the highest frequency, and beetles accounted for less than 4pc of all visits,” Dr. Rader said.
The research also looked at how much pollen each insect transferred in a single flower visit.
The highly revered honeybee was not in top spot.
“In terms of the amount of pollen transferred to a single mango flower, the native bee and several flies performed better than the honeybee."
“The native bee transferred on average about seven pollen grains per visit, the honeybee 2.7 pollen grains and the blue blowfly about 6.8 pollen grains.”
Mareeba’s density of mango orchards and accessibility were key reasons the area was selected. Being located in the tropics with abundant remnant habitat, the diversity of pollinators was also high.
Keen eyes and patience were vital tools in monitoring. Researchers measured three different aspects to ascertain pollination rates.
The first was how frequently the insects visited flowers.
“We do this by mapping out 10 mango trees in a row and walking along the row and counting how many of each insect we see in a 20-minute period."
“Second, we measure how much pollen is deposited by each insect when they visit a flower, and lastly we watch their behavior and record how much they move between flowers and between trees.”
While the study was done in a tropical environment, Dr. Rader is looking into the effectiveness of native flies in other crops. She said it appears flies visit a range of crops (not just tropical tree fruits), but it depends on the crop and the surrounding habitat.
“Some crops seem to be more attractive to flies than others, and some crops which you would think were attractive do not have the food and nesting sites around to cater for wild insects.”
Growers who want to attract and keep these pollinators need to give them the resources needed to see out their life cycle, Dr. Rader says.
“This may include planting native plants close to your orchard that produce lots of nectar and pollen at times when the mango tree isn’t in flower,” she said.
While there is no clear list of exactly what plants attract native flies, most plants with freely available nectar and pollen appeared to do the trick.
Dr Rader now hopes to expand her work to include pollen viability and how yield differs when pollen is transferred by different insects.
She intends to work out whether these patterns hold for other mango growing areas such as northern NSW, Western Australia, the Northern Territory and other parts of Queensland, and the extent to which native insects increase fruit set or not.
“We are also working on other crops such as macadamia, avocado and melons to try and ask the same questions.”
As for carcasses under trees, Dr. Rader said several farmers told her about the practice.
“Some fly larvae need decaying carcasses to complete their larval life stage, but as adults they drink nectar and eat pollen."
“So it depends on life stage and also depends on species of fly. Activity of some flies (eg blowflies) is definitely promoted by roadkill, which are good pollinators of mango.”