Why are bees declining?
We are asking our pollinators to perform services in an increasingly inhospitable landscape
What are the pressures causing a decline in Ireland’s bees?
Habitat loss, fragmentation and degradation – Homelessness
Loss of natural and semi-natural habitats has been a key driver in pollinator declines. The availability of food plants and nesting sites has been drastically reduced through conversion of low-intensity farmland and semi-natural land to intensive farmland, forestry and urban/industrial use. Declines have occurred across all habitats from grasslands to woodlands, sand dunes, peat lands, and mature hedgerows. Those areas of habitat that remain have also declined in quality. This change has had most impact on wild pollinators because they are totally reliant on resources available in the landscape. It has been shown that the number of visits to crop fields by wild pollinators tends to drop with distance from semi-natural areas (Ricketts et. al. 2008). Effective pollination by wild pollinators requires crop land to be interspersed with more natural areas requiring a landscape scale/farm-wide approach.
General declines in wildflowers within the landscape – Hunger
It is important that pollinators have a balanced diet from a range of plant species. They require food (nectar and pollen) throughout their active foraging season which lasts from early spring until late autumn. Declines in wildflowers are largely due to changing farming practice, particularly the movement from hay to silage production (Fitzpatrick et al., 2007). Increases in the amount of fertiliser applied to arable fields has resulted in increased crop yields, but has led to a strong decline in species diversity and flower richness within managed fields (Kleijn et al., 2009) and in semi-natural habitats adjacent to fertilised fields (Berendse et al., 1992, Bakker and Berendse, 1999). Our tendency to tidy up the landscape rather than allowing wildflowers to grow along roadsides, field margins, and in parks and gardens is also playing a role in fewer of these resources being available. Maintaining pollination service requires providing a sufficient abundance and diversity of food plants across the landscape for our pollinators from early spring to late autumn.
Pests and disease – Sickness
When managed pollinators are imported into Ireland they can inadvertently bring with them new pests and diseases. Pests and diseases are the main threat to honeybees, particularly an introduced parasitic mite (Varroa destructor), other invertebrates, bacteria, fungi and viruses. In 2006, nearly three quarters of 135 apiaries surveyed across the Republic of Ireland were infected with Varroa destructor (Coffey et al. 2013). Wild bees may be affected by disease transfer from imported bumblebees that have been released in glasshouses and polytunnels (Murray et al., 2013; Graystock et al. 2013), and by pests and diseases traditionally considered confined to honeybees (Furst et al. 2014). Emerging pests and diseases are considered one of the key risks to wild pollinators, particularly bee populations. Vigilance and swift action from those working with managed pollinators and assessing potential future threats is essential.
Agrochemicals – Poisoning
To meet global population growth and resultant food demand, the pressure on pesticides (insecticides, herbicides, fungicides) to deliver higher standards for crop protection has increased; with agriculture currently using the highest volume of pesticides than at any other point in history (Tilman et al, 2001). These insecticides, herbicides and fungicides are applied to crops, but reach the pollinators through pollen, nectar, and through the air, water or soil. Although herbicides and fungicides may not have direct toxic effects on pollinators, herbicides reduce the amount of food available, and fungicides may interact with other pesticides and have negative impacts on bees (Iwasa et al. 2004). Insecticides can get into the nectar and pollen either as a result of foliar spraying or via systemic treatments whereby the pesticide is taken up by the plant and expressed in all plant tissues. Although the relative role of pesticides in global pollinator declines remains poorly understood, it is now more evident than ever that some insecticides show clear negative effects on the health of pollinators, both individually and at the colony level (Mullin et al, 2010; Henry et al, 2012; Whitehorn et al, 2012; Easton and Goulson, 2013; EASAC, 2015). Whilst all pesticides pose a risk to pollinators if inappropriately applied, recent concerns have focused on the risks associated with the widespread use of a class of systemic insecticides, the neonicotinoids (Goulson 2013). Although the type and intensity of pesticide use varies across Ireland (Zhao et al. 2012), there has been no field-level research on their impacts on pollinators in Ireland. The only Irish research related to pesticides and pollinators looked at organic dairy farms and found that they had higher numbers of both flowers and insects (Power and Stout, 2011). Continued research into Irish agricultural systems, chemical controls and the effect on pollinators is essential to future management of our pollinator resource.
Climate change – Changing environment
Recent studies have shown that wild pollinators are highly vulnerable to climate change (Frund et al. 2013; Rasmont et al., 2015). The impact of climate change on pollination service can be difficult to predict (Memmott et al. 2007, Hegland et al. 2009), but with likely changes in the timing of flowering, the occurrence of important life cycle events of pollinators (e.g. emergence from hibernation, production of offspring etc.), and the geographic ranges of plants and pollinator species, there is the potential for mismatches between plants and their pollinators (Thomson 2010), as well as risks associated with more frequent severe weather events (e.g. storms, floods, late frosts etc.). This means that crops or wild plants may flower before their pollinators emerge from hibernation; or the pollinators themselves may emerge first and find it difficult to survive due to a lack of food sources if the crops or wild plants are not yet flowering. Within habitat restoration work in which wild flowers are deliberately planted within the landscape, it is preferable to use locally collected seed as it is more likely to be in sync with the local climactic conditions. It is important to increase the connectivity and quality of pollinator friendly habitats so that pollinators can move in response to climate change and we retain as much resilience within our ecosystems as possible.
See All-Ireland Pollinator Plan 2015-2020 for a full list of references referred to in this text.
Why is the honeybee declining in Ireland?
Many honeybees have been imported by beekeepers from outside Ireland and are not native, although populations of the native Irish honeybee (the dark European honeybee, Apis mellifera mellifera) do still exist here. Along with bumblebees, the honeybee is extremely important for maintaining Irish pollination services.
Ireland has an estimated 24,000 bee hives and has not been exempt from global honeybee declines. In Ireland declines have been primarily caused by the varroa mite, which causes varroasis. The Varroa mite was accidentally imported here in the late 1990s. It was first identified in Co Sligo, where beekeepers were paid to destroy their stocks by the Department of Agriculture.
“Colony collapse disorder” is a phenomenon in which worker bees from hive abruptly disappear. It has been having a devastating effect on global honeybee populations, particularly in the US. The causes of colony collapse disorder are not fully understood but are proposed to include mites and diseases, malnutrition, pesticides and migratory bee keeping. There have been no reports to date of colony collapse disorder in Ireland.