Warming has already boosted insect breeding

Museum records, publications suggest extra generations at same time as temperature increases

Summertime and the insect breeding is easy.

That old song rings especially true for 44 species of moths and butterflies in Central Europe, according to an analysis by ecologist Florian Altermatt of the University of California, Davis. As the region has warmed since the 1980s, some of these species have added an extra generation during the summer for the first time on record in that location.

TWO AND MORE Two butterfly species, the small heath (left) and common blue (right), have become more likely since 1980 to have multiple generations in Central Europe in the same year, as a long-term warming trend has picked up pace. Photos: F. Altermatt

Among the 263 species already known to have a second or third generation there during toasty times, 190 have grown more likely to do so since 1980, Altermatt reports online December 22 in Proceedings of the Royal Society B.

Only a rough third or so of all the species Altermatt reviewed show the capacity to breed more than once a year. What warming is probably doing for them, he speculates, is jolting the insects’ overwintering form into action early and also speeding up insect development. These head starts may allow time for a bonus generation before a non-temperature cue, atumnal day length, plays its role in shutting down insects for winter.

“From a pest perspective it’s an important issue,” says population ecologist Patrick Tobin based in Morgantown, W.Va., for the Forest Service Northern Research Station. Tobin has studied a warmth-related extra generation in a North American pest, the grape berry moth. He points out that an extra surge of attacking pests in the growing season means yet another headache, expense and round of damage for farmers.

Extra insect generations are important for ecosystems too, Tobin says, though predicting those ripples of consequences will be “extraordinarily complex.” An additional generation of insects might boost a population of the predators that feed on them and thus make life tougher for the other species the predators attack. Or an extra annual generation of an endangered insect might give the species an extra push toward recovery.

When creatures manage an extra generation in a year, evolutionary processes happen faster, Altermatt says. Those species that do get an extra, successful generation win a little uptick in their chances of adapting. He’s not predicting that the effect will be enough for species to cope with widespread habitat loss or climate change, but, he says, “It’s maybe a little hope.”

The possibility for climate-triggered extra generations hasn’t gotten the research attention paid to other kinds of insecty side effects of global change, Tobin says. Insects expanding their ranges northward or upslope have been the focus of more work, in part because data aren’t as scarce.

Especially rare are studies of many species over decades. Altermatt based his analyses on field work plus a review of all the museum records and publications of butterflies and moths collected within roughly 30 kilometers of Basel, Switzerland. In researching a book, Altermatt and three colleagues gleaned 182,664 records dating from 1818 to the present and describing a total of 1,117 species of butterfly. Altermatt mined the data for information about reactions to climate change.

A long-standing weather station in Basel let researchers check local temperatures for different time periods. Trends followed the recent pronounced warming in Central Europe. There, other researchers have said, mean annual temperature has increased some 1.5 degrees during the last three decades.

Altermatt compared insect records before and after that temperature upswing. For species with decent records, he looked for the numbers of butterflies and moths recorded by date. Peak numbers at a particular time gave him the rough date when a new generation was maturing. When he saw multiple peaks in a year, he noted multiple generations.

“I can’t say if the generations were successful,” he says. One peril of warming is that, when doing a little extra development, insects may not reach a winter-hardy phase.

Susan Milius

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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