If a mild winter comes, then questions about the effects on insects are sure to arise in the minds of gardeners.
Yet the answers are far from simple. Yes, some insects survive better in mild winters, meaning that some of our six-legged plant pests might be enhanced come the growing season. We even have useful models for some insects. For example, the average temperature of winter months directly relates to the survival of corn flea beetles that harbor the bacteria that cause Stewart’s wilt of corn.
However, in other cases the situation is more complex. One factor is how winter temperatures affect the survival of certain beneficial insects that feed on other insects; survival of natural enemies affects survival of pests.
A quote on a T-shirt recently worn by OSU graduate student Jed Stinner from John Muir’s book My First Summer in Sierra reminds us of the interconnectedness central to nature: “When we try to pick out anything by itself, we find it hitched to everything else in the Universe,”
But let’s get back to trying to predict the future of insect pest problems this summer based on the past few mild months and today’s pleasant present.
In addition to variable environmental factors relative to winter insect survival, such as the extent of snow cover that can protect insect eggs, pupa and larvae or the effect of sudden temperature swings in the winter months that can affect survival, there is one other key reason that prognostications are problematical. The warning comes from none other than baseball hall of famer Yogi Berra and should be a reminder to us all: “It ain’t over till it’s over.”
Our changing temperatures surely are having effects on the expansion of the range and size of populations northward of certain pests, such as the mountain pine beetle (Dendroctonus ponderosae) out West. I was in Colorado recently, and the devastation there is very noticeable on mountainsides.
Mountain pine beetle, a pest native to the United States, nevertheless behaves as an invasive exotic pest when expanding into new ranges because of greater survivability in warmer winters that are occurring over time from global warming. This beetle is causing damage now well into Canada, with serious effects not only on the pines but also on animals that depend on pines, on natural resource cycling, and on the ecological arrays that, as John Muir noted, are interconnected. Check out articles on Google and Google Scholar to learn more about this pest.
These pines in Colorado reminded me of one of the frequent talks I have been giving and updating lately, The Pervasiveness of Invasiveness. It is interesting how much invasion biology pervades our discussions of plants, forests, landscaping, gardening, wildlife and health.
Examples include Dutch elm disease and chestnut blight, caused by fungi native to Asia; gypsy moths; the emerald ash borer and Asian longhorned beetles. Zebra mussels plague waterways. The fungus Geomyces destuctans, which causes white nose syndrome, is thought to originate in Europe and is devastating bat populations in many areas of the United States. Don’t like bats? Then you must love mosquitoes!
On and on it goes to garlic mustard and even hogweed, originally brought in from lands far, far away by gardeners. No question about it, exotic invasive species and expanding ranges of native species are a big deal. David Pimentel of Cornell University estimated economic damage from invasives at $138 million back in 2000, but invasives just keep on coming.
Most recently, Ohioans learned of hemlock woolly adelgid insects found in Meigs County forests nd Ohio boxwood producers are concerned about Cylindrocladium boxwood blight disease, which came from England and is now found in Eastern states, but not yet Ohio. It matters because boxwood is a multimillion-dollar crop in Ohio’s multibillion-dollar green industry.
So this invasive species issue is pervasive, but it is important to keep in perspective; there are very few purists when it comes to native and non-native species. We cannot and should not see all non-native plants in a negative and regulatory light. Our major earthworm in the northern United States is from Europe — it is too late to change that fact. Honeybees are of European origin. As Jeff Gillman and Eric Heberlig point out in their book, How the Government Got in Your Backyard, 99 percent of the crops planted in the United States are not native.
Nature, over time equilibrates, though at the same time, sometimes we can and should help prevent or limit the occurrence and spread of invasives, such as with Asian longhorned beetle (ALB). This insect is potentially devastating to maples and many other tree species and slow-moving enough that successful eradications have occurred — for example, in Chicago. Hopefully, we will be successful with ALB eradication in Clermont County, the only location in Ohio where this insect has been found.
Like all of nature, invasive species biology is complicated. Non-native tamarisks out West, once condemned by all as a water thief and invasive intruder, is now seen by some as crucial in human-modified river-bed ecosystems. It is considered now the preferred nesting host for a native species of bird that is endangered, the southwestern willow flycatcher.
Mark Davis of Macalester College in St. Paul, Minn., and his colleagues note in an article in the June 2011 journal Nature:
“We are not suggesting that conservationists abandon their efforts to mitigate serious problems caused by some introduced species, or that governments should stop trying to prevent potentially harmful species from entering their countries. But we urge conservationists and land managers to organize priorities around whether species are producing benefits or harm to biodiversity, human health, ecological services and economies. Nearly two centuries on from the introduction of the concept of nativeness, it is time for conservationists to focus much more on the functions of species, and much less on where they originated.”
Let’s channel Yogi Berra: Ain’t nature grand?
Jim Chatfield is a horticultural educator with Ohio State University Extension. If you have questions about caring for your garden, write: Jim Chatfield, Plant Lovers’ Almanac, Ohio State University Extension, 1680 Madison Ave., Wooster, OH 44691. Send email to chatfield.1@cfaes.osu.edu or call 330-466-0270. Please include your phone number if you write.
