A Study of Pollen in Historical Insect collections – A view into the past to predict change, risks and opportunities, by Julia Kasper, Curator Invertebrates, Te Papa.

Plants provide food, habitats and other resources for a wide range of species including humans, and nearly 90 per cent of flowering plant species depend on the transfer of pollen by animals, mostly insects. A few species of bees are managed such as the western honey bee (Apis mellifera) and some bumble bees. However, the vast majority of pollinators are wild and include solitary bees, wasps, butterflies and moths, flies, beetles, ants, as well as vertebrates.

Wild and managed pollinators’ assemblages are not well understood, for both, wild and even cultivated plants, due to a lack of some very basic knowledge, such as taxonomy of pollinator species, their diet and behavior (e.g. competition and mating), co-evolution of mouthparts and blossom morphology as well as the mechanism of how plants attract the insects.

The abundance, diversity and health of pollinators and the provision of pollination are threatened by direct drivers that generate risks to societies and ecosystems. Threats include land-use change, intensive agricultural management and pesticide use, environmental pollution, invasive alien species, pathogens and climate change. Faced with the decline of pollinators it is important to strengthen our understanding of the whole plant-pollinator web.

The idea

What if researchers investigate how pollination and pollinator communities have changed over decades by identifying pollen from historical insect samples, sourced from museum collections?

The aims are to explore the complex pollination networks across time and space understanding which pollen sources are used by NZ insects.

Photo by Mary Knowles 2020, Te Papa

 

The Gurr Collection of bumble bees, Te Papa

  • 3,000 specimens
  • All four species
  • Collected between 1954 and 1972
  • 200 localities around the South Island, NZ
  • Donated from Massey University in 1997

 

Bees and Bumblebees in NZ

New Zealand offers the rare chance to investigate the threats and ecology of pollination networks as human impact on these networks are young compared to the rest of the world.

Originally New Zealand dis not possess social bees that have long mouthparts but solitary small bees.

So for honey production and pollination of European crop plants honey bees and bumble bees needed to be imported. In 1839 Apis mellifera was introduced to New Zealand, followed by four bumblebees species (Bombus terrestris, B. ruderatus, B. hortorum, B. subterraneus) 44 years later, in Christchurch.

The bumble bees were necessary to pollinate Lucerne (important fodder crop) and red clover (nitrogen fixer), which require heavy insects for pollination with long tongues.

(Bombus terrestris has a shorter tongue and is most effective pollinating lucerne but ‘robs’ clover by biting a hole in the corolla tube to collect nectar.)

Photos by J-C Stahl 2020, Te Papa

 

 

 

 

 

 

Pollen Screening

Mary Knowles for Te PapaPollen-screening

Researchers have carefully removed pollen from hair and pollen baskets with fine brushes and scalpels from 56 bumblebees of 3 species sampled over several years 40 years ago across the South Island. Those pollen samples have been processed (acetolysis) and mounted on slides and the team are now waiting for the food plant identification conducted by a palynologist.

Land-use change

By the time Europeans arrived to New Zealand forests had been reduced from 85 percent of land to 53 percent. Since 1840, a second wave of deforestation reduced forest cover to 23 percent.

Economic factors had an important role in driving land use change. High market prices for sheep during the Korean War wool boom in the 50s resulted in farmers converting large areas into pasture  The 70s saw an introduction of farming subsidies to protect the industry form the overseas market. The Livestock Incentive Scheme (LIS) and the Land Development Encouragement Loan (LDEL) Scheme funded low interest rate loans for land development targets with the aim to increase production.

With a pre-human forest cover of 85 percent, New Zealand’s soils predominantly evolved with low levels of nitrogen, phosphorus and sulphur and therefore need to have nutrients added for crops and pasture. Clover is an important nitrogen fixer, enriching the soil’s nitrogen levels.

The end of this studies’ time period marked an important shift in farming in New Zealand. With the change in government from Muldoon’s protectionist policies to the newly elected Labour government in 1984, farming subsidies were removed and farmers were exposed to market forces overnight. Farmers responded by increasing efficiency and diversifying. Since 1982, sheep numbers have reduced dramatically, being replaced by forestry and dairy farming practices.

New Zealand’s indigenous forests are highly valued by beekeepers for the clean nectar and pollen sources of toxin-free high-quality monofloral honeys, which has led to the mānuka honey gold-rush and additional change of land use after human settlement.

Indicator for insect decline and climate change
This is only one part of a bigger research project. Because if these results are compared with similar studies with different species sampled at different times, the differences between species can be reconstructed: their distribution over time, native/introduced plant preferences, competition with native bees, oligolecty (diet specialisation) put this data in context with climate data and the change of land use. This will enable us to better manage our conservation and farming land and even to better understand the effects of climate change on insect decline.

Various Victoria University interns worked with Te Papa Curators to produce these amazing infographic posters on their research into different insects, of which bees feature!