Pollination is a vital service that many insect species do us the honour of performing. Pollinators allow us to enjoy the many different flowers, fruits and vegetables that grow as a result. In New Zealand the exotic honey bee (Apis mellifera), along with the bumblebee, is the most abundant pollinator. But with honey bee populations declining across the world, the future of pollination is unclear.
Canterbury has well established crop farms, providing us with bounties of pak choi, clovers, onions, carrots and radishes. Honey bees are the main pollinators of these crops. It is important that one species of pollinator alone is not relied on for pollination, especially with honeybee populations at risk. Unfortunately, there is heavy use of pesticides on crops in Canterbury and high variation in flower and nectar availability. These environments do not easily support large numbers of different pollinators.
Without a variety of wild pollinator insects, crops are at risk of low production or even failure. Because of this, it is more important than ever to find ways of increasing the diversity of different pollinators that visit our crops.
Planting native flowering species in crops fields is thought to attract wild populations of bees. The increase in wild bees that visit crops can improve crop yield and can also make the crops more reliable. Non-bee insects, such as flies, are also important pollinators and it is possible that they are also attracted to native flowering species. Franziska Schmidlin from Lincoln University, along with Jon Sullivan, Mike Bowie and Brad Howlett set out to find if native plantings really do increase pollinator diversity and secure the future for our arable crops.
Farms that had native plantings established in 2013 were ideal sites to test. Each site had no less than 30 different plant species. Some of the native flowering plants included cabbage tree (Cordyline australis), makahikatoa (Kunzea serotina), flax (Phormium tenax) and manuka (Leptospermum scoparium). The native plantings were observed when they were in full bloom and the various different pollinator visitors were recorded.
Incredibly, the native plants brought in a whole host of pollinator species from across four different insect orders. The most common group of pollinators to visit were the flies. Bees and wasps closely followed, with beetles, butterflies and moths also being attracted to the plants. Honey bees did make a large appearance across all of the farms, but it was the humble native bee (Lasioglossum sordidum) that stole the show. The small native bee visited the most trees out of any other pollinator, making up 20% of all insect visitors .
One of the most exciting things found by this study was that many insect species were as numerous as honey bees, and that they also visited a wider range of plants. The small native bee is an example, as well as the native large hoverfly (Melangyna novaezelandiae) and the brown blowfly (Calliphora stygia). The large hoverfly made up 16% of the total insect visitors and was the only insect to visit all of the different native tree species that were planted. The native bee and the brown blowfly also visited a wide range of plants, getting to around 50-80% of the different native species.
Insect species that were equally or more abundant than the honey bee, also visited a wider range of flowering plants. This gives us hope. In the past these species have been found to be good crop pollinators and so if we can ensure that they visit the crop sites, we can help maintain crop pollination, and therefore the quality and yield. Other insect species can provide crops with pollination, just as well as the honeybees, so if honeybee populations continue to decrease, the crops will not suffer as much as we thought that they might.
Clearly, the natives really do bring all the bees (and flies) to the yard. If all crop fields had native planting nearby, the future of crop pollination would be more secure. Not only would insect pollinators increase, but the ecosystem would benefit overall. Arthropod (creepy-crawly) populations would be increased and these creepy-crawlys are likely to feast on the pest insects that we use pesticides to kill. At the very least, native plantings would increase local biodiversity with the added bonus of looking great. The benefits are endless!
Rachel Watt is a postgraduate student in the Bachelor of Science (Honours) at Lincoln University. She wrote this article as part of her assessment for ECOL 608 Research Methods in Ecology.
Schmidlin, F. G., Sullivan, J. J., Bowie, M. H. and Howlett, B. G. (2018). Insect flower visitors of planted native species within the arable landscape on the Canterbury Plains, New Zealand. New Zealand Plant Protection. 71.