Download The Co-evolution of Insects and Plants

The Co-evolution of Insects and Plants
Pamela A Hunter
Plants and insects have evolved a complex but mutually beneficial relationship
It was not until the Cretaceous Period
(135–65 million years ago) that there
was a massive parallel development of
flowering plants and insects, including
ants, wasps, solitary bees and
stingless bees. During this period the
plants evolved to attract insects to
ensure pollination and the insects
evolved to use plants as a food
source. Some of these adaptations in
both plants and insects are both
complex and ingenious. The honey
bees (Apis) and bumble bees
(Bombus) developed approximately 55
million yeas ago.
Steve Alton
The typical insect body plan of head,
thorax and abdomen
Page 8 Bee Craft Digital September 2011
Karin Alton
BOTH PLANTS and insects evolved
over many millions of years but the
earliest examples were quite unlike
present day species, with wingless
insects believed to be present as
long ago as 400 million years.
Fossil records are fragmentary but
there is evidence of ancestors of
Hymenoptera (the group to which
ants, wasps and bees belong) in the
Jurassic period. The earliest
flowering plants also appeared
during this period.
The hoverfly Scaeva pyrastri receives payment for its services
What are Insects?
Pollination and Fertilisation
Insects are invertebrates which have 6
legs, three distinct body parts (head,
thorax and abdomen) and most have
one or two pairs of wings. There are
numerous orders including beetles
(the most common), dragonflies,
mayflies, butterflies, moths, flies,
wasps, ants and bees. Of these many
groups of varied insects it is the bees
that have developed the most complex
methods of utilising and collecting the
nectar and pollen produced by
flowering plants. Unlike many other
groups of insects they do not damage
plants but just collect the plant
products.
Flowering plants have male and
female organs. The pollen is the male
part or gamete (the equivalent of a
sperm) and is contained in an anther,
which is suspended by a filament –
this makes up the stamen.
In addition to honey bees and
bumblebees, there are many other
species of solitary bees, including
carpenter, mason, mining and
leaf cutters. These are all
valuable pollinators. Many
other insects act as pollinators,
including butterflies, moths, flies and
hoverflies.
The female organs consist of a stigma,
which is designed to receive the
pollen grains. These grains need to
germinate and produce a pollen tube
on the surface of the stigma – this is
termed pollination. This tube grows
down a structure called a style, which
may be quite long in some flowers,
until it reaches the ovules contained
within an ovary. When the pollen grain
nucleus fuses with that of the ovule,
this is termed fertilisation.
Cross Pollination
Many plants have both the male and
the female parts in the same flower so
self pollination would be easy and is
generally very efficient but in spite of
this, many species have developed
ways of ensuring that self pollination