Insect flower visitors in native plantings within the arable landscape of the Canterbury Plains : A dissertation submitted in partial fulfilment of the requirements for the Degree of Masters at Lincoln University

Abstract

This thesis investigates the value of native plantings for pollination services within the arable landscape of Mid-Canterbury, New Zealand. The vegetation of the Canterbury Plains is among the most heavily modified landscapes in New Zealand with almost all original native vegetation replaced by intensive dairy and arable farming. Arable farmers often grow a variety of vegetable or herbage seed crops that depend on insect pollination. These include carrot, radish, onion, brassicas, and white and red clover. Intensive crop farming on the Canterbury Plains can therefore be highly dependent on a good provision of insect pollinators to maintain economically viable yields. This study provides new insights into the abundance and diversity of insect flower visitors in native plantings established on arable farms. These plantings contain long-lived perennial plant species indigenous to the Canterbury Plains. There is currently strong interest in diversifying the pollinator communities in cropping farmland to reduce the risks associated with dependency on honeybees and bumblebees. Pollinator diversity and abundance may possibly be increased by providing habitats of native tree plants along crop margins that provide pollen and nectar resources, shelter, nesting or sites suitable for immatures to develop. The aim of this thesis was to assess insect flower visitation in native plantings and the movement of these visitors into the arable fields at three sites five years post-establishment. Weekly standardised surveys of flower visitors were conducted between September 2017 and February 2018. Of all observed flower visitors within the native plantings (n=3088 insects from 37 taxa), the most common were the honey bee, Apis mellifera (19.2 %) followed very closely by the native bee, Lasioglossum sp. (17.2%) and the native large hoverfly, Melangyna novaezealandiae (14.8%). Other common dipteran species were the brown blowfly Calliphora stygia and the March fly Dilophus nigrostigma (both 7.1%) followed by the blue blowfly Calliphora vicina (7%), while native bees Leioproctus spp. (5.6%) were also well represented. A slight majority of all flower visitors were natives (52%). All of these abundant insect flower visitors (at the taxa level assessed) were flower generalists, visiting five or more of the eight study plant species and the top eight are all recognised crop pollinators in New Zealand. While generalists, each species had different plant species preferences, different patterns of seasonal activity, and different responses to weather conditions. Results assessing the dispersal of insects from the native plantings into the crop field found that some (e.g. Melangyna novaezealandiae, Lasioglossum sordidum) were capable of moving distances of at least 250 m into neighbouring fields. In combination, my results suggest that native plantings are capable of supporting a diverse and abundant community of insect flower visitors, including many crop pollinators, some of which travel at least hundreds of metres from these plantings. These plantings therefore have the potential to complement and reinforce pollination services from commercial beehives. Further research is encouraged to better understand interactions between native plantings and the services they can provide to support insect crop pollination. Particularly important will be studies on pollinator food requirements, nesting resources, the capability of insect movement and quantification of influence on crop yield including pollination effectiveness and efficiency.