POLLINATORS POLLINATION AND FOOD PRODUCTION

THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION
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2. DRIVERS OF CHANGE OF POLLINATORS,
POLLINATION NETWORKS AND POLLINATION
bees negatively in contaminated areas (Meindl and Ashman,
2013). In 2012, Moroń et al. detected a steady decrease in
the number, diversity and abundance of solitary wild bees
along heavy metal gradients in Poland and the UK. While
in 2013 Moroń et al. also found a direct negative impact
of zinc contamination on the survival of the solitary bee
Osmia bicornis along this pollution gradient. Bees had fewer
offspring with a higher mortality rate with increasing pollution
level and also the ratio of emerging males and females in
offspring was changed, due to probably higher mortality of
males, with increasing contamination. Whereas Szentgyörgyi
et al. (2011) did not find a significant correlation between
heavy metal pollution level of the environment (with
cadmium, lead and zinc) and the diversity of bumble
bee species caught on Polish and Russian heavy metal
gradients. Despite the small number of available studies, in a
questionnaire undertaken by Kosior et al. (2007), specialists
considered heavy metal pollution to be one of the more
important factors associated with bumble bee decline in
Europe (ranked 6 th of 16 stressors surveyed).
Besides heavy metal pollution, there is a growing concern
about non-metal pollutants, e.g., arsenic or selenium.
Arsenic occurs as by-product of coal and other ore
mining, including copper production. Air pollution by
arsenic was shown to destroy honey bee colonies near
an arsenic discharging electrical plant (for review see
Lillie, 1972). Selenium, on the other hand, is an essential
trace element, but as with most trace elements it is toxic
in high concentrations. Due to mining and other industrial
activities, as well as through drainage water from irrigation
of seleniferous soils, some areas are highly contaminated.
In the environment selenium bioaccumulates and therefore
bees may be at risk through the biotransfer of selenium
from plant products such as nectar and pollen (Quinn et
al., 2011). Recent studies showed that selenium increased
mortality in honey bee foragers (Hladun et al., 2012) and
negatively affected larval development (Hladun et al., 2013).
already described in ant colonies, in which individuals had
lower levels of pollutants in their bodies’ concomitant with
higher positions in the nest hierarchy (Maavara et al., 2007).
This might explain why honey bees can be used as good
indicators of environmental pollution for even relatively high
levels of pollution (Rashed et al., 2009). In solitary species
such protection of reproducing females is simply lacking and
therefore they might be more susceptible to pollution, as
shown by the contrasting result of Moroń et al., in 2012 on
bee diversity and Szentgyörgyi et al., in 2011 on bumble bee
diversity on similar gradients of heavy metal pollution.
2.3.4.2 Nitrogen deposition
Besides the aforementioned heavy metals and non-metals,
another driver that has also received relatively little attention
to date is atmospheric nitrogen deposition (Burkle and
Irwin, 2009; Burkle and Irwin, 2010; Hoover et al., 2012),
which can reduce the diversity and cover of flowering plants
that provide pollinator foods (e.g., Burkle and Irwin, 2010;
Stevens et al., 2011). The individual impact of nitrogen
deposition on pollinators, networks and pollination may be
relatively weak (Burkle and Irwin, 2009; Burkle and Irwin,
2010). Nonetheless, nitrogen in combination with climate
warming and elevated CO 2 produced subtle effects on
bumble bee nectar consumption and reduced bee longevity
(Hoover et al., 2012). Nitrogen deposition was shown to
have another, indirect effect – nitrogen deposition near
freeways in California favoured growth of grasses eliminating
butterfly hostplants of an endangered species. If grazing is
used to reduce the grass, this effect of N deposition can be
reversed (Weiss, 1999). Further work is required to elucidate
the potential of nitrogen deposition as part of a suite of
pressures affecting pollinators.
2.3.4.3 Light pollution
Bee larvae feed mainly on pollen (Michener, 2000); thus, in
polluted sites, they may consume food that is contaminated
with heavy metals or other pollutants. The main source
of pollution of pollen is probably soil dust deposited on
flowers or on the pollen during transport to and placement
in the bee’s nest (Szczęsna, 2007), and probably
hyperaccumulation of pollutants by plants in floral rewards
(Hladun et al., 2011; 2015). This suggests that both soil
type and flower type can affect the deposition of pollutants,
such as heavy metals on pollen (Szczęsna, 2007). For bee
species nesting in the ground, the impact of pollution may
be larger because besides pollen, larvae can also come into
contact with contaminated soil during their development.
Sociality may also affect susceptibility to pollution: a
hierarchy in the nest protects reproducing individuals
(queens) from pollution, therefore allowing the colony to
reproduce (Maavara et al., 2007). This phenomenon was
Light pollution, a driver clearly affecting nocturnal species
and growing in importance due to urbanization has to be
mentioned. Its effect is still scarcely studied, though artificial
night light is known to alter the perception of photoperiod
(Hölker et al., 2010, Lyytimäki, 2013) and even at low levels
can affect the organism (Gaston et al., 2013). Artificial
night light was shown to influence moth physiology and
behaviour, e.g., inhibit the release of sex pheromones by
females (Sower et al., 1970), suppress their oviposition
(Nemec, 1969), negatively affect the development of
nocturnal larvae of Lepidopteran species (van Geffen et
al., 2014), or act as ecological traps for some vulnerable
species, drawing them to suboptimal habitats like urban
areas (Bates et al., 2014). Moths are known pollinators of
some plants, especially plants whose flowers open at night
(MacGregor et al., 2015), however their role as pollinators is
still not evaluated in depth (MacGregor et al., 2015). Studies