The pollinators
Insect
insights
Ann Fullick FSB
Think of an animal and what is the first
image in your mind? A horse, cat, or
elephant - whatever it is, it will probably
have a backbone. Most people think of
animals only as vertebrates, and the
majority stick with mammals too - yet
almost 60% of all the known animal species
are insects! They have a major impact, both
direct and indirect, on the lives of other
living organisms, including human beings.
For biologists, studying insects can give us
insights not only into the world of these
fascinating invertebrates, but also into wider
biological issues ranging from population
dynamics to genetics and behaviour.
The link between insects and human food is
a very close one. Around a third of all food
crops depend on animals to pollinate them –
and most of these pollinators are insects,
from bees and wasps to beetles and flies.
Fruits including apples, pears, citrus fruits,
figs and tomatoes are all insect pollinated.
Many more food crops – for example the
brassicas – need insects to pollinate them to
form the seeds which will produce the next
generation of crop plants.
Perhaps the best known of all pollinators are
bees and their importance in ecosystems
and in food production cannot be
underestimated. Just how much of our food
depends on the activities of bees is
becoming very clear as the population
numbers of bees decline.
Farmers around the world use bee colonies
to help pollinate their crops. Around 1.4
million colonies of bees are used to pollinate
the 550,000 acres of almond orchards in
California alone. Yet by 2006 the honey bee
population had fallen so low that bees had
to be imported from abroad to make sure
there was a successful almond harvest. In
China wild bees have always pollinated the
fruit orchards. However in recent years the
wild bee populations have fallen
dramatically, to the point that in south west
China there are no longer enough bees to
pollinate the massive apple and pear
orchards. Farmers are actually pollinating
these important crops by hand, using paint
brushes and even getting small children to
climb up and reach the highest blossoms!
Just two of the
estimated 6-10 million
speci es of insects
currently alive on the
Earth
Without bees, people have to
pollinate the apple blossom or
there will be no apple
harvest .
The decline in bee populations around the
world seems to be the result of a number of
factors – the overuse of pesticides, the loss of
habitat for wild bees, parasites and new
diseases. Varroa mites appear to be spreading
a deadly virus through bee hives worldwide, a
new and dangerous threat to the bee
population.
Bees are not only useful as pollinators.
Honeybees make honey. There is clear
evidence of the ancient Egyptians using honey
both as food and medicine. In recent years
modern science has shown that honey –
particularly made from Leptospermum species
such as manuka and tea trees – is effective in
treating many pathogens including Candida
albicans, the fungi which cause thrush, some
antibiotic-resistant bacteria such as MRSA
and possibly some viruses.
Bees versus elephants – an example of
biological pest control
Biological pest control involves using one
organism to control another species which is a
pest. In many African countries elephants are a
major pest, pushing their way through thick
protective thorn hedges to eat precious crops.
A British biologist, Dr Lucy King, observed that
elephants don’t feed on trees which contain
bee hives, and that elephants will run away
from a recording of bees buzzing. Once an
elephant has been stung by a bee, particularly
on the end of the trunk, it never forgets and is
always afraid of the insects.
Dr King discovered that if bee hives are hung
in the hedges at about 10 metre intervals,
elephants not longer attack the hedge. What is
more, farmers don’t even need a hedge. When
the hives are set up on a simple wire fence, if
an e lephant disturbs the wire the bees will
come out and attack – and the elephants run
away. In fact just the buzzing from the hives is
enough to make the elephants keep their
distance. The use of bee fences is spreading –
a clear example of an insect-based solution to
a mammalian problem.
(Look at http://www.bbc.co.uk/nature/life/
African_Bush_Elephant#p00qj34x to see this
example of biological pest control in action)
Insects behaving …
Plants have some amazing adaptations to
ensure that insect pollination takes place.
These can give us an opportunity to study
some extremely complex interactions
between living organisms – and also to see
that too much alcohol is as bad for insects as
it is for people!
In the UK wasps pollinate orchids known as
Broad-leaved Helleborines. The wasp is lured
to the orchid by a special chemical produced
by the flower. Normally the wasps feed on
cabbage white caterpillars. When cabbage
leaves are bitten by caterpillars they give off
an ‘alarm chemical’ which signals to wasps
that the cabbage is under attack. The wasps
fly up the chemical concentration gradient to
the cabbage and eat the larvae.
Broad-leaved Helleborines have evolved to
mimic the cabbage's ‘under attack’ signal.
Once the wasp reaches the orchid it doesn’t
find a caterpillar but it does find sweet nectar.
As the wasp goes into the flower to get the
nectar, clumps of pollen called pollinia are
pushed down and stick to its head or body.
However the nectar contains morphine
derivatives which make the wasp high and
dopey and ethanol (produced by symbiotic
yeast), which makes the wasp drunk. Wasps
normally clean themselves very effectively and
would remove the pollinia from their heads as
soon as they leave the flower. However as a
result of being drunk and high, the wasp
cannot remove the pollinia. When it flies into
the next flower to drink more alcoholic nectar
the wasp carries out pollination on the way.
This drunken wasp can not
control its front leg s to
remove the l arg e white
pollinia stuck to its head.
Shortly after this photo
was taken it toppled over
and fell to the grou nd, too
i nebri ated to fly to another
flower and polli nate it!
young and defend the nest, so ants and other
social insects such as bees and termites are
sometimes referred to as ‘super-organisms’.
The whole colony works together and in some
ways acts as one organism.
Studying the way an ant colony is organised
and controlled provides insights into the
interactions between nervous, hormonal and
pheromone control and animal behaviour.
A massi ve colony of woo d ants are sunning themselves
on a woodland floor .
Insects as food
Protein is an important part of the diet, but it is
impossible to support the number of meat
mammals – cows, sheep, pigs, goats etc. –
that are needed to provide animal protein for
the world population. However, as there are
40 metric tonnes of insects for each human
being, some biologists suggest eating insects
is a sensible way of providing animal protein
whilst at the same time possible reducing the
populations of some pest insects. In some
areas of the world insects are already an
important part of the diet.
Crickets and meal worms are both possible
protein sources but UK temperatures are not
high enough to support the large numbers of
insects needed to supply food. Successfully
using insects as food in the UK would involve
farming them, which in turn needs an input of
energy for heating, or importing them. The
biggest barrier to this at the moment is the
public perception of insects and a revulsion in
the UK to eating them – but in future insects
may become an important source of protein
for people all over the world.
Man and Super… organism?
Another group of insects which fascinate
people, provide food, cause problems and act
as experimental model organisms for
biologists are the social insects such as the
ants. The tasks in the nest are divided so that
different castes forage for food, look after the
The control of behaviour
Animal behaviour is controlled by:
The nervous system: a system made up
of interconnected neurones specialised
for the rapid transmission of impulses
through the organism.
The endocrine system: a system based
on chemical coordination by hormones.
These are chemicals made in endocrine
glands and released into the blood, or
body fluids which cause a change in
cells or tissues in another part of the
body and may affect behaviour
Pheromones: These are chemicals
which are secreted by one organism
which are detected by and affect the
behaviour of another organism, usually
but not always of the same species.
These three systems often work together to
produce a particular piece of behaviour – for
example a pheromone message is detected
using the nervous system and this may affect
behaviour directly or by stimulating the
release of a hormone.
Ants are known to use chemical signals to
influence the behaviour of other ants by laying
down foraging trails. These external chemical
signals are proving to be very important in
controlling the behaviour of ants. For example
rock ants (Temnothorax albipennis) are small
ants which live in rocky cracks. If the nest is
damaged (and this often happens) the ants
have to find another suitable home very
quickly before the queen and the brood (the
young ants) dry out or get eaten. This can be
replicated in the lab using glass slides removing one of the slides means the ants
lose their home.
Further reading
Scientists have shown that the surface area of
the new home is very important in the choice
of a new nest site – but how do ants measure
surface area?
http://www.infocusmagazine.org/6.3/
env_pollinators.html
An ant enters a prospective site and walks
around it for a fixed length of time, leaving a
chemical (pheromone) trail. She then re-enters
the potential nest site and walks round again
for a set time period, detecting when her new
path crosses the original path. The number of
times she crosses that path is a good
approximation to the surface area of the
potential nest site. A number of ants check out
the site in this way until a critical number
approve when a new nest is built and the
queen and brood are transported to their new
home.
Insects provide us as biologists with a rich
variety of experimental models and examples.
The insights into insect lives provided here are
just the tip of the iceberg. Finding out more
about insects can help open our eyes to the
biology of the whole living world.
Bees v elephants
The Biologist October 2012
Adam and the ants
The Biologist October 2012
What’s bugging George?
The Biologist August 2012
http://rfcarchives.org.au/Next/CaringForTrees/
Pollination1-88.htm
Web resource showing the type of pollination
used by a number of different rare fruits and
tropical crops
The National academies populations bees
http://www.chinadialogue.net/article/show/
single/en/5193
Pollinator populations and China
http://www.bbc.co.uk/nature/18339797
Honey bee virus and Varroa mites
http://www.ncbi.nlm.nih.gov/pmc/articles/
PMC2686636/
Cross referenced journal looking at medical
uses of honey
http://www.genome.gov/10005835
Drosophila and human DNA
http://genome.wellcome.ac.uk/
doc_WTD020807.html
Model organisms
http://www.bbc.co.uk/nature/life/
African_Bush_Elephant#p00qj34x
Video of bee fence
http://www.societyofbiology.org/
newsandevents/biologyweek/flyingantsurvey
Society of Biology flying ant survey 2012