Neonicotinoid effects on bees

Q: Are bee populations falling?
Honey beeA: Yes. In recent decades, there have been declines in the number of wild bee species and the number of wild bee colonies, and the area in which they thrive has become smaller.

Q: When did these declines start?
A: In the US, there was a 59% loss in wild bee colonies between 1947 and 2005. In Europe, there was a 25% loss between 1985 and 2003.

Q: So some declines were seen before neonics were introduced?
A: Yes. But it is still important to determine whether neonics have contributed to these ongoing trends.

Q: Why are these changes so important?
A: Loss of biodiversity is an important issue wherever it occurs. However, in addition to the desire to protect bee species themselves, bees form an important group of pollinators that is essential for the pollination of food crops and wild plants.

Q: What is pollination?
A: Pollination is the transfer of pollen between plants by insects, other animal agents or wind, which starts the process of fruit or seed formation. Without pollination, many of our crops would not yield any produce.

Q: How many crops depend on insect pollination?
A: 87 of the leading food crops globally depend on insect pollination. This accounts for over a third of the world’s food production by volume and has an estimated global value of £136 billion annually.

Q: Which insects perform pollination?
A: Many different species contribute, but bees are the main pollinators. This includes honey bees, bumblebees and other wild and solitary bees, all of which are involved in the pollination of not only crops, but also many wildflowers and hedgerow shrubs.

Q: Which bees are most important?
A: Many bee species pollinate. Although domesticated honey bees are by far the most numerous (and also provide honey), bumblebees are thought to be almost solely responsible for the pollination of certain crops, including soft fruits.

Q: Are the changes in bee populations a result of neonic use?
A: We don’t know. Neonics were not available commercially until the 1990s, and usage only became widespread towards the end of that decade, so it seems unlikely that they are exclusively responsible. But it is important to find out whether they have contributed, and if so to what extent.

Q: Aren’t insecticides tested to ensure they are safe to other species?
A: Yes, but those tests look at exposure over four days, and determine the dose at which 50% of bees die in that time. Procedures for licensing do not currently look at longer-term effects of lower doses.

Q: So how could neonics be causing bee declines?
A: It may be that long-term, low-level (sublethal) effects are causing problems for bee health or behaviour. It is important to clarify whether this is happening, either alone or in combination with other factors.

Q: What other factors?
A: The main factor identified in most studies is habitat loss – of both breeding sites and suitable flowers for feeding. As well as this, adverse weather, disease, insecticides other than neonics, and the introduction of new parasites may all have played a role.

Q: Are bees exposed to neonics when crops are treated?
A: Yes. As the chemical is present throughout the plant, the pollen and nectar also contain neonics and bees ingest this.

Q: Do they absorb it?
A: Yes. Evidence shows low levels of neonics can sometimes be measured in bees.

Q: Are these levels high?
A: No. The levels detected are well below those that are lethal to bees, but we don’t know if they cause sublethal effects.

Q: What sort of effects could they have?
A: There is evidence to show that exposed bees from various species have reduced navigational and communication abilities, reduced foraging abilities, a weaker immune system, and fewer queens may be produced. There may also be effects on developing larvae.

Q: What does this mean?
A: More bees may be lost. The individuals as well as the colonies may be more susceptible to disease or stress. Individuals may forage for food less effectively, fewer new bees may be produced, and the colony may be less healthy and less likely to thrive.

Q: Where does this evidence come from?
A: Some experiments are done in laboratories, and some are ‘semi-field’, which are done partly outside. They provide a starting point for researchers but they may not reflect what happens in commercially treated fields.

Q: How do we know if these effects are really happening?
A: At the moment we don’t know for sure, although evidence is accumulating. The only way to study this is with large-scale field studies. Some have been done recently, and more are under way, some in the UK.

Q: What do they show?
A: The picture that is gradually appearing is that honey bees seem to have a higher tolerance for neonics than other wild bees.

Q: So are honey bees not affected?
A: Several field studies published recently have not demonstrated an effect on honey bee colonies. However, other evidence does detect a link between honey bee colony losses and areas of increased neonic usage. The evidence is not yet conclusive.

Q: What effects have been detected in other bees?
A: Bumblebees and other wild bees seem to be particularly susceptible to neonics, with evidence of reduced foraging, reduced wild bee density, solitary bee nesting, and bumblebee colony growth and reproduction. However, once again some reports suggest the opposite conclusion: that bumblebees are unaffected by neonics under field conditions.

Q: Are species other than bees affected?
A: There is recent evidence that the declines in a number of common butterfly species may be more severe in areas with higher neonic use, but the significance of this remains unclear. It may be that neonics caused the declines, or it may be that neonic use is a marker for something else associated with increased farming intensity that is responsible.

Q: So the evidence is not clear?
A: The interpretation of the evidence is not straightforward. For example, differences in study procedures, or use of different dose levels or exposure times, can make it hard to compare results from different studies. There is some evidence that neonics can have a negative effect on some species, but it is not conclusive. There is also evidence that neonics are not as damaging as they are sometimes presented. This is a case for watchfulness and further study to determine the appropriate response.

Q: When will there be more research evidence?
A: A great number of studies have been carried out, with more under way. However, some scientists report that studies showing no effect are less likely to be published by scientific journals because a zero response is less interesting to report. If true, this may affect the overall debate.

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