When walking through the woods on a sunlit day, admiring the new flowers and occasional buzzing bee, it’s easy to forget that the organisms surrounding us are at war with one another. The trees are competing for sunlight, nutrients and water, the wasps are trying to paralyze caterpillars to feed the youngsters back home, and somewhere, a fungal spore just landed on an insect and is about to germinate.
My coworker, Ryan, returned from the field last week, carrying a big tree branch full of leaves. Ryan is a fungus guy. Not a guy made of fungus, but a guy who studies it. He’s spent tons of time scanning the ground, trees, and even insects, for different fungi, and with this tree branch, he’d hit the jackpot. The tree had been blowing around in the breeze, which flipped up some leaves, exposing suspect spots underneath.
And on closer inspection of one such spot:
It’s was a fly, and although it looked, at a glance, to be in good shape, an even closer look revealed white fungus growing out of its body.
The culprit? An entomophthorales fungus. (Ento-mop-thor-A-lees) Fungi in this group, whose name means “insect-destroyer,” produce spores on the dead insect that are often shot off like missiles. This type of spore is even referred to as “ballistic.” Once the spores are shot into the air, the wind carries them to whatever destiny may have in store for them. With luck, a spore will land on a suitable insect and germinate, starting the life cycle again.
Sometimes, when the weather is perfect and the host insects are around in abundance, you can get an epizootic episode. Then, the fungus is able to reproduce in mass quantities and launch a full scale war at the insects. Such was the battlefield on Ryan’s tree branch:
Such naturally occurring insect diseases can be used to our advantage when we find one that attacks an insect we consider to be a particular nuisance. If the fungus (or nematode or bacteria, for just a few examples) can be cultured and is suitably host-specific, it can be used for the biological control of the pest. Even if the disease in question isn’t cultured for release to control the pest, the pest population can be monitored so that we know when a natural outbreak of the disease is likely. This knowledge can help farmers save money by not spraying pesticides for an insect that would probably be killed anyway by an epizootic episode.
Those people that work in the field of insect pathology focus on finding these pathogens in nature, investigating the biology of how they cause disease, and developing practical uses for their findings. But it all starts with an eye for suspect spots.
Good eye, Ryan!