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Bradford pear in bloom, attracting numerous
pollinators
© 2014 Beatriz Moisset
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Spring finally arrived, although a little later than usual. At
the end of April, the Bradford pear trees in
front of the Abington Library were in full bloom, white clouds against a
sapphire sky. Hordes of little bees eagerly visited the sweet flowers.
Pollinators were not the only visitors to the trees.
Surprisingly, life was also present in places you wouldn't think to look at. A
cluster of bright yellow dots in a bark's crevice caught my eye just by chance.
Afterwards, I began to see many similar clusters, partially hidden by the
bark's irregularities. I knew them as lady beetle eggs, so I wasn't surprised
to see some adult lady beetles engaged in romance or in search of potential
nurseries for their babies.
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Lady beetle eggs
© 2014 Beatriz Moisset
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A solitary green aphid painstakingly climbed the tree trunk,
probably in search of tender shoots to feed on its juices. What was it doing so
far from its traditional food? Perhaps, it had fallen to the ground and,
obstinately, was engaged in the arduous voyage back to distant branch tips.
I puzzled at the lady beetles' choice of egg-laying sites. The
tree trunk may offer refuge for the eggs, but not food for the newborns. The tiny
larvae would have a long way to go to find nutritious aphids. Perhaps, just
like the lost aphid, they could manage the perilous trek successfully.
I visited the trees a week later. They were still blooming,
although slightly past their peak. I looked for the lady beetle eggs and found
many of the clusters still in place. Some had darkened, a sure sign that the
larvae inside would soon emerge, hungry for aphids. Others had become food for
unknown predators and were gone.
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An incipient aphid colony
© 2014 Beatriz Moisset
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Once again, I wondered where they would find food and looked
at the new growth, the clusters of flowers which were already beginning to leaf
out. Aha! Just as I suspected, the green aphids were there, small colonies of
young and adults, wingless and even some winged ones. I would have never
noticed them if I hadn't suspected their presence because of the lady beetles.
Aphids have a way of multiplying at great speed. One female
can produce many babies in a mere week and the babies start reproducing in an
equally short time. The small colonies I observed would become huge by the time
the new leaves reached full size. They would be numerous enough to damage the
new growth.
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Aphid in search of food
© 2014 Beatriz Moisset
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Would something keep the aphids in check? The mentioned lady
beetles had their job cut out for them. But they would need lots of help and I
was pleased to see other aphid enemies. I caught a glimpse of a parasitic wasp.
These tiny wasps lay their eggs inside aphids and their larvae feed and kill
their hosts in the process. Another great helper became apparent later on, on
further observation. Some minute greenish grubs were thrashing about in the midst
of the aphid colony. A syrphid fly had chosen this place to lay her eggs. The recently
emerged blind and apparently helpless larvae were busy devouring their favorite
food, juicy aphids. They grow fast on this nutritious diet and soon
metamorphose into small flies, ready to lay more eggs.
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Syrphid fly maggot feeding on aphids
© 2014 Beatriz Moisset
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The accidental sight of the lady beetle eggs led me to the
related findings, aphids and their predators—an entire mini-ecosystem well
hidden in bark cracks and flower clusters of a pear tree. A month later, I
visited the trees again and found no traces of this entire food chain. The
stems appeared too tough for the aphids; the winged ones had moved
elsewhere. The lady beetles and other predators also took their leave in their
perennial search for nourishment.
Aphids in the web of life
List of articles
© Beatriz Moisset. 2014
