Insects in peril: Decline seen locally and nationwide
Massive rainfall in Mid-Ohio Valley could hurt even more
Dave McShaffery is the Ebenezer Baldwin Andrews Chair of Natural Sciences in the department of biology and environmental science at Marietta College. His degree is in entomology – the study of insects – and he has been at the college and lived in the Mid-Ohio Valley for more than 20 years.
McShaffery says that as a general rule it’s true that mild winters tend to create conditions favorable for the proliferation of insects, and this year he is, in some ways, pulling for the bugs.
Within the past year, several studies have shown a worldwide decline in the population of insects, arachnids and pillbugs. Scientists are alarmed at what might be happening, which is apparently more than a localized phenomenon occurring in only certain parts of the world.
McShaffery makes frequent field trips into the wilder areas around Marietta, surveying and observing insect populations, and what he has seen recently, he said, is disturbing.
“Part of it was the wet weather, but even on good days we didn’t see the same numbers as we’ve seen in the past 30 years,” he said. “We were out quite a bit on field trips, and they just weren’t there. It’s kind of weird.”
The entomologist looks for bugs that most ordinary people might not be familiar with, such as the dogsbane leaf beetle and the pelycinid wasp.
“The leaf beetle is really quite beautiful, it has a rainbow color, very polished looking, less than an inch long,” he said. During his journeys around the state during the summer last year, he said, he saw none of them in places where he had seen numbers of the insects before.
The pelycinid wasp is unusual, the females having a long, segmented abdomen they use to probe the ground for June beetle grubs. The parasitic eggs are laid in the grubs, and when they hatch the larval wasps devour the grub.
“At our field station outside Marietta, we normally see hundreds, but last year we didn’t see any. There are also different kinds of caterpillars, and there were a lot of those we didn’t see,” he said. “They feed on plants as caterpillars, but as butterflies they act as pollinators, so it comes back to bite the plant, so to speak.”
Scientists worldwide have viewed the decline of insect populations with alarm and called for projects that will offer more precise data. It is not known whether pesticides, climate change, habitat destruction or a combination of all those could be to blame for the situation. The decline in the migratory monarch butterfly and the collapse of wild bee colonies have captured public attention in recent years, but according to scientific journals and publications, the problem is much more widespread.
Although the populations of some insects are on the rise as they move into new territories, those of many others are on the wane, and according to a Scientific American article from November, overall the insect biomass is in planetary decline.
Lower insect numbers would affect the pollination opportunities for plants and the growth and sustenance of animals such as lizards, frogs and birds that feed on insects.
Locally, McShaffery said, the rainfall could adversely affect insect populations. National Weather Service records show that the four months from September to December dropped precipitation 58 percent above normal levels on the Marietta-Parkersburg area this fall and winter.
Some insects could perish from fungus and mold if they are unable to escape the wet conditions, and others will experience a decline in the energy they can take in because the nectar in flowers they depend on is diluted, he said.
High winter temperatures could partially offset the negative effects of the wet conditions, he said.
“A mild winter might be a good thing for them, but weather events can really throw things off,” he said. “We could still get a pretty good cold snap, and if things go below zero for a couple of days, that would probably affect a lot of them.”
From the agricultural view, however, the mild winter and a big hatch of nuisance insects could be menacing for crops.
Tom Witten of Witten Family Farms near Beverly said insects can affect crops both by eating them and by acting as a vector of diseases that affect crops.
Witten said he’s hoping for some freezing weather.
“We are really looking for something like zero degrees for at least two weeks,” he said. “And snow can provide a lot of insulation. We want the ground to be bare with those cold temperatures. We’ve had it mild so far, but if we can just get that 10-day window below 10 degrees, that really puts the population down.”
Witten said his farm uses crop rotation and other natural management tools to minimize the impact of insects and disease and uses chemicals only as a last resort.
“We don’t spray unless we have to,” he said. “We’re always very wary and try to be as bee-friendly as we can. We have a chart of what’s most harmful to bees.”
Meanwhile, he’s hoping the weather will take care of potential problems. If the cold can limit numbers to start, he said, it also limits the numbers further into the year.
“They can only do so many generations,” he said.
Winter weather in Marietta
•Total rainfall, September through December: 21.33 inches.
•Departure from normal: 12.4 inches, or 58 percent higher.
•Average daily high temperature, September through December: 60.55 degrees.
•Departure from normal: .02 degrees colder.
Source: National Weather Service.