CONDON’S CORNER
Learn from Nature on Earth Day
I
was born with a love of nature. My very earliest memories consist solely of
outdoor experiences, such as seeing a Red Fox and nearby areas of wildflowers
when visiting my grandparents’ farm, as well as finding a lovely blue robin’s
egg in my yard and trying not to step on the large red-and-black ants traveling
the city sidewalks near my home.
As a young child, I simply observed the natural world unobtrusively and committed to memory what I saw; I didn’t think about the whys and wherefores of what I witnessed. That activity came later, when, as a scientifically minded young adult wanting to learn as much as possible about the natural world, I started writing notes to document my observations. Then came the wildlife photography—all of these activities being done for my own learning and enjoyment.
Now, many decades later, I’ve amassed a huge amount of data and thousands of photographs, slides, and electronic pictures. Consequently, I am well able to recognize when inaccurate information is published about the natural world.
For example, some years ago I watched an interesting video online that showed, by use of fluorescent light, the chemical response inside a plant being eaten by a caterpillar. The scientist performing the experiment considered the reaction to tissue damage to be a “defense response” to help the plant deter insects from further feeding upon it.
Apparently, plant scientists have been doing these types of experiments for so many years now that this scientific explanation for this phenomenon is accepted without question as true—except, in my experience, it isn’t.
If it were true, gardeners wouldn’t experience defoliation (loss of leaves) of their plants, which is quite common. Nor would scientists have needed to worry so much about forest defoliation in the last decades of of the 20th century by Lymantria dispar dispar, the Spongey (formerly known known as Gypsy) moth caterpillars.
Consider the following situations that have occurred in my yard and elsewhere, but would be unlikely if the scientific “defense” explanation above was, indeed, valid.
In the summer of 2018, a
volunteer Common Boneset (Eupatorium perfoliatum)
came up and grew tall at a corner of my house, where I walked by it every day
on my way to the compost bin. By August, that plant held nary a leaf because
caterpillars had fed upon every last one.
 |
| Every single leaf of this Common Boneset (Eupatorium perfoliatum) in the author’s yard was eaten by caterpillars, but as seen here, the plant simply began to re-leaf, none-the-worse for the supposed “injury” it had endured. |
And every year, my Wingstem (Verbesina alternifolia) is fed upon by caterpillars of the Silvery Checkerspot butterfly, and—of course—Common Milkweed (Asclepias syriaca) feeds Monarch “cats”. Both plants are often defoliated if enough caterpillars manage to avoid predation long enough.
 |
| Silvery Checkerspot butterfly caterpillars have been feeding upon this Wingstem plant (Verbesina alternifolia) outside the author’s greenhouse for years. A perennial plant that is often defoliated, it has survived and come back in a healthy state in each successive year. |
Away from my yard, I have
walked many times on the Waynesboro (Virginia) Greenway, where I’ve witnessed
defoliation of Northern Catalpa trees (Catalpa speciosa) by caterpillars
of the Catalpa Sphinx moth (Ceratomia
catalpa) in September. In spring (other than the past few years because tent
caterpillar numbers are down), Black Cherry trees (Prunus serotina) are usually defoliated by the larvae of the
Eastern Tent Caterpillar moth (Malacosoma
americanum).
It’s so easy to see plants defoliated by insects that one has to wonder how the idea of plant defensiveness against herbivory could ever take hold in scientific circles. I contacted the scientist who made the video mentioned at the beginning of this column. He felt confident providing this explanation for his own experiment because it was “built on a large body of research from a lot of other labs” that purportedly have shown that wounding (by a caterpillar, or just by cutting a leaf) triggers a suite of responses that deter insects from feeding on a plant.
This scientist was so assured
of the accuracy of this interpretation that when I asked, “Did you subsequently
confirm that a cabbage butterfly caterpillar [the species he was working with]
would not eat the section of plant that showed the response?”, he honestly
replied that he had not bothered to do so. And perhaps therein lies the reason
for the discrepancy I see between reality and lab results. Scientists in the
biological sciences often do not use the real world as their laboratory, and
they do not verify that their lab results correspond to it.
However, it’s also
puzzling that scientists do not give thought (apparently) to the evolutionary
consequences of their assumptions. In this case, the accepted explanation is fatally flawed.
As I’ve written countless
times before, plants exist to feed animals. Therefore, it makes no sense that plants
would need to defend themselves against being eaten. If they prevented animals
from feeding upon them, how would animals survive to perpetuate their species? Therefore,
the whole notion of plant “defensiveness” lacks logic.
It also lacks merit because
the real world doesn’t behave in the manner suggested by the scientific
explanation for the chemical response seen under florescent lighting. And
that’s perfectly reasonable because plants don’t need to act defensively; they
can survive defoliation quite well. People don’t realize it because they never
allow it to happen. But in my yard, and in the natural world, the only
deterrence necessary is accomplished by way of predators that naturally limit
the numbers of caterpillars feeding upon a given plant.
That Common Boneset at the
corner of my house, and the Wingstem and Common Milkweed plants in my yard all regrow.
I can guarantee it because I’ve seen it happen year after year as I don’t
interfere with natural processes.
The catalpa trees will leaf
out just fine next spring in Waynesboro, and although people pay attention to
the tents in Black Cherry trees every spring, they tend not to notice that the
trees survive the early-spring feeding of caterpillars, fully leafing out again
as soon as the caterpillars have grown beyond their feeding stage.
It’s unfortunate that people,
even scientists, do not really understand how the natural world works. The
overconcern with animals harming plants has resulted in much unnecessary
poisoning of the Earth with pesticides, and the killing of wildlife in
unwarranted efforts to “save” plants that, in fact, don’t need saving.
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