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. 2013 Oct 3:3:2779.
doi: 10.1038/srep02779.

Diesel exhaust rapidly degrades floral odours used by honeybees

Robbie D Girling  1 , Inka Lusebrink, Emily Farthing, Tracey A Newman, Guy M Poppy
Affiliations

Diesel exhaust rapidly degrades floral odours used by honeybees

Robbie D Girling et al. Sci Rep. .

Abstract

Honeybees utilise floral odours when foraging for flowers; we investigated whether diesel exhaust pollution could interrupt these floral odour stimuli. A synthetic blend of eight floral chemicals, identified from oilseed rape, was exposed to diesel exhaust pollution. Within one minute of exposure the abundances of four of the chemicals were significantly lowered, with two components rendered undetectable. Honeybees were trained to recognise the full synthetic odour mix; altering the blend, by removing the two chemicals rendered undetectable, significantly reduced the ability of the trained honeybees to recognize the altered odour. Furthermore, we found that at environmentally relevant levels the mono-nitrogen oxide (NOx) fraction of the exhaust gases was a key facilitator of this odour degradation. Such changes in recognition may impact upon a honeybee's foraging efficiency and therefore the pollination services that they provide.

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Figures

Figure 1
Figure 1. The effects of diesel exhaust pollution upon the abundance of a synthetic oilseed rape floral odour blend.
(a), An oilseed rape flower (photographed by RDG). (b), Percentages of each component of the synthetic floral blend, replicating the ratio at which they are naturally emitted from oilseed rape flowers. The colours and letters that represent each chemical are consistent throughout the figure. (c–j), Mean volatile abundances (±s.e.m) of the eight synthetic floral chemicals in ambient ‘clean’ air (darker lines) compared to their abundances in diesel exhaust polluted air (lighter lines) at four different times points after exposure (n = 5). (k), The changes in mean floral chemical abundance in diesel exhaust polluted air relative to ambient air; which were either statistically significant (▾; P ≤ 0.05), or in the case of both α-terpinene and α-farnesene where the chemical was no longer detectable in diesel exhaust polluted air (▾). Directions of arrowheads indicate either increases or reductions in relative abundance.
Figure 2
Figure 2. The effects of varying concentrations and ratios of NO and NO2 upon the abundance of of a synthetic oilseed rape floral odour blend.
Circles indicate the percent change in mean abundances of the synthetic floral chemicals in ambient ‘clean’ air (dashed circle) compared to their abundances in either diesel exhaust polluted air, or air contaminated with NO and NO2 (filled circles) at a ratio of 10:1 or 1:1, with NO at concentrations of 10, 1 or 0.1 ppm for both ratios (n = 4). Abundances were measured after 30 minutes. Statistically significant changes in abundance are denoted by an arrowhead that indicates a significant increase or decrease (* P < 0.05, ** P < 0.01, *** P < 0.001). An (X) indicates that the chemical was no longer detectable in those treatments.
Figure 3
Figure 3. Tests of honeybee recognition of synthetic odour blends.
(a), A honeybee worker foraging on an oilseed rape flower (photographs by R Girling, C Reitmayer). (b–c), A honeybee worker (photographs by R Girling, C Reitmayer) restrained for a proboscis extension reflex (PER) assay with proboscis retracted (b) and extended (c). (d), The percentage of forager honeybees which, after learning the full synthetic floral blend, extended their proboscis (indicating recognition) when presented with the synthetic blend minus either α-farnesene (-αf), α-terpinene (-αt) or both chemicals (-both). The data are expressed as the per cent PER recognition of each blend relative to the PER recognition of the full synthetic blend (n ≥ 25), where on average 93% of forager honeybees learnt the full blend. Asterisks indicate a significant reduction in PER recognition of that blend in comparison to the full synthetic blend (P < 0.05).
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