Impact of climate change on crop pollinator in New Zealand

Insect pollinated seed crops contribute at least NZ$60Million annually in export earnings. These crops are pollinated by a range of insects including honey bees, bumble bees, native bees and flies, and maintaining pollinator diversity can be important for maximising crop yields. However, different pollinators are active at different times of the day and under varying climatic conditions (activity windows). Climate change may impact pollinator activity windows by altering foraging periods and also their behavior (e.g. time spent on flowers and distances moved within and between plants). The aim of this programme was to test the hypothesis that pollinator activity windows differ with changing climate (specifically a 4oC increase in temperature, but also humidity, light intensity and wind). This leads to altered: 1) pollinator abundance and diversity 2) pollinator behaviour and movement To assess whether changing climate influences pollinator activity windows, thereby altering pollinator abundance and diversity we used an existing dataset comprising some 85,000 individual observations collected across a number of important annual seed crops, especially the brassica pak choi (open pollinated) and F1 hybrid onions, across both North and South Islands, combined retrospectively with weather data for each site. To assess whether changing climate influences pollinator activity windows, thereby altering pollinator behaviour and movement we collected further data on behavior of insect pollinators on the crops to supplement and extend an earlier dataset. Previous New Zealand studies indicated that a relatively small assembly of insects is dominant in abundance and a smaller subset of these provide the majority of pollination services to these crops. Six key pollinator species (honey bees, bumble bees and four species of fly) were monitored as individual insects for foraging behavior on flowers as well as frequency and distance of travel between flowers. Weather data were collected on site for the new dataset. Honey bees were found to be the most abundant pollinators within the crops examined. This was not surprising since beehives are generally introduced to the crops, while other insects are present as part of the landscape insect abundance. The requirement of hybrid seed crops for cross-pollination requires the movement of pollinators between male fertile and sterile plants which are normally grown as separate rows. This restricts the relative value of some of these pollinator species since some species express strong floral constancy to a hybrid type (ie will forage on just one hybrid line). Apart from a few species-specific anomalies, changes in climate variables (particularly temperature) were found to affect pollinator activity windows leading to a change in pollinator diversity and abundance. These data confirmed a relationship between temperature and insect pollinator activity on crops, with time of day superimposed for honeybee activity. Other climate variables (e.g. relative humidity and light intensity) also showed relationships with some taxa; however, there were strong correlations between climatic variables themselves. Therefore, it was not possible to determine the level of direct influence each climatic variable contributed to each insect taxa. A key feature of the insect activity is the increased relative abundance of flies and bumble bees at the lower temperatures (RH80%). Time of day, independently of other variables, influenced insect abundance on these crops. Overall abundance was strongly dominated by honey bee presence in the middle of the day, but two fly taxa (Seedcorn and Ephydrid flies) showed a strong preference for activity in the 6–8a.m. and 4–9p.m. periods of the day. Changes in climate variables (specifically temperature) were also found to affect pollinator activity windows leading to a change in behavior. This was demonstrated by a general increase in the rate of stigma contacts at higher temperatures by all six pollinating species assessed. However, changing climate did not correspond with changes in movement between inflorescences. Overall, these finding verify the hypothesis with exception that changing climate leads to changes in pollinator movement. Climate change predictions for regional New Zealand over the remainder of the century suggest a marked increase in number of days which exceed 25oC and reduced rainfall in some regions could see lower relative humidity. These conditions should affect the activity windows of honey bees leading to increased abundances and an extension of foraging time. However, climate change forecasts also predict an increase in extreme weather events such as droughts and floods in New Zealand. Such events could significantly impact honey bee pollination. To reduce the potential impact of increased climate variability on crop pollination, management strategies should focus on building pollinator diversity by encouraging pollinators that are active across highly variable and changeable climatic conditions. Although some preliminary research has been conducted on native bee nesting preferences and providing conditions suitable for them, very little research has been conducted on the more important fly species biology or means of ensuring abundance on crops. This is potentially important for these annual seed crops as their siting in the cropping landscape varies annually to fit crop rotation and isolation distance requirements. Assuming climatic conditions remain suitable for growing the crops in their current regions this programme suggests that we take cognizance of the likely increased reliance on the currently vulnerable honeybee for pollination purposes. Taking steps now to better understand what drives abundance of currently unmanaged species, especially flies and native bees, aiming to find a practical solution to ensuring their presence in suitable numbers for pollination requirements, is a definite step that industry can take. This will provide benefits now as well as into the future, particularly for securing pollination services to the more valuable, but insect pollinator challenging, F1 hybrid crops.MPI Technical paper 2013/30 www.mpi.govt.nz/dmsdocument/4101-impact-of-climate-change-on-crop-pollinator-in-new-zealan