Could scorching summer temperatures that continue into the fall be killing off monarch butterflies and armyworms?
Researchers at Western University believe so.
A pair of master’s students working under the supervision of biology professor Jeremy McNeil have been studying the effects of climate change on the two high-profile insects.
Monarch butterflies, which were declared endangered this summer by the International Union for the Conservation of Nature, are meant to migrate to Mexico for the winter. However, research shows the longer-lasting summer heat may be signaling to the butterflies to breed, rather than head south.
Most eggs laid in the fall die as larvae or pupae, and those that survive to become adults “are often deformed and not likely to be able to migrate,” said Campbell McKay, one of the two masters students looking into the ill-effects of climate change on the insects.
He added that for the few normal butterflies that reach adulthood in late October and early November it is too late to make it to Mexico before the cold kills them. They are what’s known as a “dead-population”.
Other factors contributing to the downfall of the monarch is the quality of plant they choose to feed on. The butterfly’s larvae eat only milkweed, of which there are several different species of plant in Ontario. McKay is trying to determine how feeding on the three common types of milkweed affects the size of the dead-end population from year-to-year. He suspects at least one of the milkweed species is slowing monarch development, causing the butterflies to emerge late in the year.
“If we can understand what’s happening to the Monarch, we may also understand better what’s happening to other migratory insect species,” said McKay.
The findings of McKay’s work are expected to be completed by the end of the year and could guide gardeners selecting a species of milkweed to help boost the dwindling monarch population.
McKay’s counterpart, Cailyn McKay, has been examining how the prolonged heat is wreaking havoc for the armyworm.
This insect, known as a crop pest to farmers, spends its summers in Canada and the northern U.S. and its winters in the southern U.S. The insect has trouble when temperatures rise above 30 C, something that is happening more and more through the summer in Canada.
In its larvae and moth states, the insect can move to cooler sites, but at the pupal stage, when it lacks legs or wings, it is left to bake in the sun.
In the lab, Cailyn has been looking into whether the prolonged exposure to high temperatures is reducing the month’s ability to reproduce.
She exposed pupae to 30 C for 48-hour spells at four different times during their metamorphosis. She then compared the reproduction ability of the moths hit with heat to those that weren’t. What she found was the ones that endured the scorching temperatures produced fewer eggs that were less likely to be fertile. She also discovered the heat-treated female moths mated less. She believes the 30 C temps may be affecting how pheromones, the scent used to attract and pick a mate, are emitted by both females and males.
While farmers may rejoice at the idea of fewer armyworms around to destroy their crops, Cailyn reminds they are a native insect to Canada that is important to the ecosystem.
“These guys aren’t invasive. They’re just really bad when they come in large numbers. Birds and spiders eat them so their absence could have a ripple effect on other species.”
