Wild pollinator insects, especially bees, like diversity in their life. It’s not that they’re fussy, they just like to have different resources for nesting and foraging to choose from – just like us. This diversity in resources is important because wild pollinator communities aren’t just made up of bees, they include multiple species. We’ve (almost) figured out what honeybees like, and it’s easy to accommodate one species when you know the ins and outs of their biology. But ‘wild pollinators’ could mean solitary bees, bumblebees, huge hairy flies, delicate wasps, tiny midges, thrips, beetles, bugs, weevils, moths or butterflies. Some of these insects, particularly wasps and flies, may also control outbreaks of herbivorous insects, so they can provide multiple ecosystem services.
Suffice to say, we want them to hang around. So it’s important that management of agroecosystems considers the diverse requirements of this multitude of insects. It’s already established that wild pollinators can be found around farms when unmanaged native vegetation is nearby, and they also like farms that maintain flowering weedy patches around the margins or in headlands. However, most of the research that is available on wild pollinators has been done in Europe, North America or tropical regions. And coffee and canola seem to be the most popular study systems.
There is less knowledge of wild pollinators of tree nut crops in countries like Australia, where the trees are exotic species. This means that they have not co-evolved in a relationship with the native pollinator insects, like they have in their regions of origin. Many tree crops are pollinator-dependent, which means flowers need to be cross-pollinated with pollen from a flower on another tree, before they can set fruit. This is why the orchard industry is so reliant on managed honeybees, which is increasingly causing all sorts of stress to the bees.
I’ve just had a paper published online in the Journal of Insect Conservation with two of my PhD supervisors (Gary Luck & Margaret Mayfield), where we looked at potential wild pollinators in almond orchards in Australia. Australia is the second-biggest almond producer in the world, and we now produce more almonds than we do our native macadamia nut. The industry has grown so quickly, and much of the historical research on almond growing in Australia has been biological or economic in focus – cultivars, pollenizers, more nuts, more yields etc.
In this study, we sampled during the almond flowering season, and looked at whether ground cover in orchards is associated with more wild pollinators. Most conventional almond plantations are broadscale monocultures, covering huge tracts of land, with completely bare ground maintained throughout the orchard. We compared these plantations with smaller orchards (biodynamic and low-intensity conventional) that maintained living ground cover throughout the orchard, as well as the semi-arid mallee woodlands that are native to the region.
Although native mallee vegetation had higher species richness of pollinators, pollinators were more abundant in orchards with ground cover than in either mallee or the bare monoculture plantations. We looked at relationships between each different pollinator group (native bees, flies, wasps) and the percentage cover or richness of living ground cover, and found a few interesting things, including that bee species richness was associated much more strongly with plant richness than simply percent cover of the living ground cover. This agrees with lots of other studies that have found that non-Apis bees, like a lot of other animals, prefer heterogeneity over homogeneity.
Our study was a small-scale ‘snapshot-in-time’ study, and more detailed sampling will deliver more certainty on how growers could benefit from these insects. But it’s still given us important clues about what’s going in this system, and highlighted how simple little changes in management can produce huge benefits for the ecology, function, and therefore production, of a farm.
Ground cover doesn’t only look pretty, it can also improve soil quality and biological activity, and support more biological control agents. If it brings the pollinators too, what more could growers want!
© Manu Saunders 2013