Insects and climate change: The study of phenology

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It turns out that life is more predictable than you might think — well, at least plant and insect life at any rate. Phenology is a jaw-dropping science that examines recurring plant and animal lifecycle events and their connection to the weather. Plants and insects don’t use clocks. Instead they use the conditions of their environment to keep time. The growth and development of both plants and insects is intimately connected to temperature. Phenological events like the blooming of a maple tree, a songbird’s spring arrival, the migration of a monarch, and the egg hatch of Eastern tent caterpillars are all tied to environmental conditions. Nearly all natural phenomena are.

A special clock
Phenological events are amazing timekeepers. Natural events occur in the exact same order every year, many times with plant-based phenological events corresponding to the appearance of particular insects. For example, in Ohio, black vine weevil adults always emerge a few days after the American yellowwood trees are at full bloom, the eggs of Eastern tent caterpillars always hatch just as the first forsythia flower opens, and greater peach tree borers emerge as adults exactly when the Northern catalpa tree begins to flower. Interestingly, the phenological sequence in one region often shows few deviations from that in other regions containing the same plant and insect species; and the phenological order remains the same even when weather conditions differ. In warmer springs, phenological events may be advanced by a few weeks, but they still happen in the exact same chronological order.

For thousands of years, humans were also intimately connected to the sequence of biological events. Before calendars, we tracked the passage of time by watching nature. We needed the predictability of phenological events to get an idea of what would happen next. Early agriculture depended on it. But now, most humans don’t have a clue about the precise order of natural events. Even most gardeners are blind to it.

Special timekeepers
Scientists (and citizens) have been tracking and recording phenological events for centuries. Plants and insects are precise timekeepers, so these recorded emergence and event dates tell us a lot about changes in both long- and short-term weather patterns. Because of these records, we know that insects are changing their distributions and certain insects are now occurring where they didn’t before–most are moving north. We are also seeing insects that used to produce only one generation per year, now producing two or even three. The data also tells us that over the past 30 to 40 years there has been a change in insect emergence times. Many insects are emerging significantly earlier than they did in the 1970’s and that creates a challenge for pest management. Many phenological events in temperate climates have advanced 2.5 days per decade since 1971. That means that the seasonal development of plants and animals has generally advanced by about 10 days since the early 70’s. The phenological records kept for many years by numerous scientists around the world provide very valuable information for tracking climate change. There’s no doubt that our changing climate is affecting insects and the plants they rely on.

Though changes in lifecycles and distribution are big concerns, another potential problem is in phenological synchronization. Plants and insects go together, and if they respond differently to climate change, then the timing of when the insect is active versus when the plant is flowering could get disrupted. This could have lots of ecological consequences. For now, the data on all this is mixed. Some scientists are finding that the plants and insects are changing together while others studies are showing a decoupling of plant and insect species.

There are so many cascading effects of climate change on insect life. And, over time, its crippling effects will not just negatively influence insects and plants, but also humans.

Helping scientists
If you’d to track phenological events in your world and pass that information along to the scientists working to understand these changes, organizations like the U.S.A. National Phenology Network, The Leopold Phenology Project, and Project BudBurst invite gardeners across North America to join them in collecting data about phenological observations. Sign on with one or more of them and help make a difference.

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