The two immediately apparent economic services that managed European honey bees (Apis mellifera) provide for humanity are crop pollination and the production of honey. The value of the former far exceeds the latter in developed countries and the present article will focus only on the importance of the pollination side of the activities of these amazingly industrious animals.
Of the 115 most traded crop species used for human food worldwide (grains, tubers, fruit, vegetables, nuts and seeds), roughly three quarters are dependent on animal pollination to improve yield, marketability, flavour, storage properties and gene diversity. This proportion reduces to about one third when compared by global production tonnage given just a few of the broad acre cereal and grain foods provide most of the calories in the human diet and are independent of animal pollination. However these staples are generally poor sources of most micronutrients, and whatever they have can suffer severe losses in processing and preservation. It is the pollination-dependent third, mainly fruit, that are much richer sources of vitamins (eg 90% of all vitamin C), minerals and phytochemicals, and currently many of these nutrients are in deficit ('Hidden Hunger') in over 2 billion people worldwide, particularly in developing countries, negatively impacting their health. The plants that don't rely on animal pollination may be self-or cross-pollinated abiotically (wind, gravity or rainfall) while others may not require effective pollination/fertilisation through parthenocarpic or apomictic processes, and others may reproduce exclusively by vegetative means. Some of these 115 species show unimportant (7) or only slight (21) improvement in crop features and production with pollination, and in others it can be moderate (27), highly dependent (30) or essential (13). There is a broad range of animal pollinators, from hive-managed social honey bees to stingless and solitary native bees, bumblebees and wasps, moths, butterflies, beetles and other insects to bats and birds, but the honey bee is the main one relied on in large scale intensified commercial orchards. Orchardists growing crops such as almonds, apples and melons commonly hire in many hives from bee keepers during the appropriate pollination period every year to maximise quantity and quality of their crops. The business model of many of these bee keepers can be concentrated heavily on pollination services with honey production as a secondary goal; two thirds of the 2.5-3 million colonies in the US are transported all over the country for this purpose. Both parties benefit, with the orchardist producing more and better crops and the beekeeper obtaining the rental fee and a variety of different flavoured honeys. This movement of hives around different sites also helps maintain colony health as different plant species have different levels of energy-supplying nectar and varying quality pollens (variation in protein levels, vitamins and other micronutrients).
Provided flowers of a given species are sufficiently attractive to honey bees and there are enough of them in the vicinity, they are so industrious in the number of flowers they can usually pollinate that it dwarfs the effort required when orchardists have to resort to hand pollination. Reliance on lower numbers or less effective native animal pollinators is much less controlled and usually results in decreased yield and quality from what is possible for a given species and prevailing resources. An important factor in the effectiveness of the honey bee being able to transfer pollen to stigmas concerns the extent to which bee and flower morphology match. There is evidence where the benefit to both animal and floral species is significant that key characteristics have evolved in concert over millennia eg bee proboscis length and length and position of flower anthers and stigma. Another important factor influencing pollination effectiveness may be flowering time in less favourable climatic conditions when worker bees may not forage as extensively.
Unfortunately in modern times there's been a general decline in native and managed bee populations worldwide, eg domestic honey bee stocks in Europe unintentionally decreased by 25% from 1985 to 2005. But in the last decade the problem, mainly with honey bees but also others, has accelerated alarmingly with on average 30% of entire colonies (up to 90% for some apiarists) dying each year in a matter of weeks. It was originally reported in the US, then Europe and subsequently elsewhere, and has been called 'colony collapse disorder' (CCD). This more acute phenomenon has placed the whole global food production model at grave risk if the balance between increasing demands (future population growth and the nutritional transition as undeveloped nations improve economically and are better able to afford higher value pollination-dependent crops) and pollinator servicing is compromised because of major colony declines. In addition to effects on cultivated crops, there are wider implications for threatened ecosystems and global species biodiversity. Intense efforts to understand the driving factors of CCD have been underway for several years, and while no clear consensus has emerged so far, current evidence suggests an interaction of many factors, namely infection with different species of the ectoparasitic mite Varroa and the microsporidian Nosema, sub-lethal doses of pesticides, loss and fragmentation of foraging habitat, pollen quality and poly-floral variety, and a number of viruses. Other possibilities include the effects of different stressors on social colony behaviour as a consequence of negative effects on individual bees, and also the transition from many small scale beekeepers to smaller numbers of much larger scale enterprises, similar to other sectors in many agri-industries, when opportunities for disease transmission are magnified. We're lucky in WA with our relative geographic isolation and strict quarantine regulations that so far CCD is not yet a problem, but according to Professor Boris Baer, Director of the UWA Centre for Integrative Bee Research, it's only a matter of time before we'll have to cope with it.
In the meantime at our level of operations within the club, we can all do our bit by observing the quarantine regs, ensuring our local bees can source pollen and nectar from a range of species, and use of pesticides is minimised as much as possible. Integrated pest management is advocated where possible. Use of techniques such as maintaining good orchard hygiene, netting, trapping, bait sprays, use of less toxic materials (eg pest oils) as sprays when required rather than more toxic synthetics, and separation of any sprays from flower bloom periods when bees may be visiting, can all help. These management strategies assist in reducing pest loads and allow lower levels and frequencies of cover sprays when required. Synthetic pesticides should be treated as a line of last resort, but if needed, it's easier to separate contact poison spray timing from flowering as they're only effective for short periods, but systemic insecticides represent a bigger problem because these chemicals are taken up into plant tissues and can be absorbed by bees over a much more prolonged period following spraying. Unless exposure loads of these are so high that the lethal dose to 50% of animals (LD50) becomes the issue, killing forager bees even before they return to the hive, it's the effect of lower non-lethal exposures when these chemicals in the nectar and pollen are shared with the whole colony that can threaten their collective immunity, behaviour and resistance to pests and viruses. Timing systemic sprays outside the withholding period will help reduce problems, and the maximum number of sprays in a season should be kept to the minimum to prevent excessive plant tissue build-up. As mentioned, a further consideration in CCD is that different plant species produce different quality pollens with important nutritional variations, so maintaining a variety of cropping plants that flower concurrently is also beneficial. Large scale monoculture farming has become increasingly common nowadays with increasing pressures to economise in today's highly competitive global markets, and this has contributed to negative nutritional effects. In addition, the presence of non-cropping weeds that flower at the same time as neighbouring cultivated crops should be seen as a balance between attracting bees to the garden/orchard but avoiding undue competition in order to maximise effective crop pollination. This is a separate consideration from the possibility of them competing for water and nutrient resources and being endemic sources of pests and diseases. Also, maintaining an open, airy canopy reduces disease load and this will assist in minimising the need and level of systemic fungal sprays that are suspected to contribute to CCD.
The following summary of a recent study in the international literature (Proceedings of the Royal.Society (London) B (2014) 281, 20132440) describes how honey bee pollination is important for a fruit crop of interest to us – strawberries.
Pollination improves the yield of most crop species and contributes to one-third of global crop production, but comprehensive benefits including crop quality are still unknown. Hence, pollination is underestimated by international policies, which is particularly alarming in times of agricultural intensification and diminishing pollination services. In this study, exclusion experiments with strawberries showed that bee pollination improved fruit quality, quantity and market value compared with wind and self-pollination. Bee-pollinated fruits were heavier, had less malformations and reached higher commercial grades. They had increased redness and reduced sugar–acid–ratios and were firmer, thus improving the commercially important shelf life. Longer shelf life reduced fruit loss by at least 11%; this property accounted for US$ 0.32 billion of the US$ 1.44 billion due to bee pollination in the total value of US$ 2.90 billion made from strawberry sales in the European Union in 2009. The fruit quality and yield effects are driven by the pollination-mediated production of hormonal growth regulators, which occur in several pollination-dependent crops. Thus, our comprehensive findings should be transferable to a wide range of crops and demonstrate bee pollination to be a hitherto under-estimated but vital and economically important determinant of fruit quality.
This work was conducted by a German and Swiss research group and so had a European perspective. They included 9 common varieties in the EU to assess the relative importance of this variable, used field conditions as they're more relevant to industry practice than glasshouse studies, provided honey bee hives and wild bee trap nests for effective pollination, and the commercial value of fruit was assessed according to fruit weight and EU grading guidelines which have three levels – commercial grade 1 (G1), commercial grade 2 (G2) and non-marketable (NM). All three study treatments (bee, wind and self-pollination) produced fruit but there were major differences in grade quality between the 3 treatments, with far more G1 fruit with bee pollination (approximately 48%) than with wind (28%) and self-pollination (24%), whereas the proportions of NM fruit were basically the other way round (28%, 34% and 38% for bee, wind and self-pollination resp); the G2 grades were intermediate. Malformations were one of the key reasons for fruit being categorised in the two lower categories. Pollination treatment effects were greater than those due to variety differences, and bee-pollinated fruits were on average 11% heavier than wind pollinated fruit and 30% heavier than those that were self-pollinated. So although strawberries will set fruit abiotically, you get a much improved quality and yield if bees are around to pollinate. The other important parameters they considered (firmness, shelf life, red skin colour, sugar-acid ratio and number of fertilised achenes) all improved markedly with bee pollination compared to the other two processes.
Strawberries are just one example amongst the various fruits benefitting from pollination that we grow in the club, suggesting you should look after the bees who visit your garden. Provide friendly and attractive conditions and they'll work tirelessly for you. And let's hope CCD doesn't arrive here soon.