A warming world could make insect bites worse for plants

1 Februari 2020

Insects play a vital part in the life of plants by serving as pollinators. Yet insects can also wreak havoc with plants by feasting on them. And as temperatures worldwide continue to rise, plants may end up suffering more damage inflicted on them by creepy-crawlies.

Increased temperatures speed up the metabolism of insects, making them more voracious. A rise of 1 Celsius could increase crop yield lost to insects by up to 25%, explain scientists at Michigan State University in the United States who have published a study.

In addition, warmer temperatures will allow insects to spread farther afield, affecting more cultivated plants than before. Worse: many crop plants infested by voracious insects don’t adapt well to rising temperatures in the first place, which lowers their productivity. The result could be significant drops in crop yields.

“We know that there are constraints that prevent plants from dealing with two stresses simultaneously,” explains Gregg Howe, a professor at the university’s Plant Research Laboratory. “In this case, little is known about how plants cope with increased temperature and insect attack at the same time, so we wanted to try and fill that gap,” he warns.

Plants have built-in mechanisms for fighting off feeding insects. When a caterpillar begins biting a leaf, for instance, plants produce a hormone called jasmonate (JA), which triggers the production of compounds that stymie the caterpillar.

Yet in warmer temperatures such defensive mechanisms might no longer suffice adequately. A researcher at the university discovered this when he began cultivating tomato plants in hot growth chambers with temperatures set at 38 degrees Celsius. Nathan Havko, a postdoctoral researcher, also grew tomato plants in normal temperatures. He then set caterpillars loose on both sets of plants.

“I was shocked when I opened the doors to the growth chamber where the two sets of plants were growing at ‘normal’ and ‘high’ temperatures. The caterpillars in the warmer space were much bigger; they had almost wiped the plant out,” Havko says.

“When temperatures are higher, a wounded tomato plant cranks out even more JA, leading to a stronger defense response,” he elucidates. “Somehow, that does not deter the caterpillars. Moreover, we found that JA blocks the plant’s ability to cool itself down, it can’t lift its leaves or sweat.”

An arms race between insects and plants like tomatoes could escalate with potentially disastrous consequences. “We see photosynthesis, which is how crops produce biomass, is strongly impaired in these [affected] plants,” Havko says. “The resources to produce biomass are there, but somehow they aren’t used properly and crop productivity decreases.”

Having said that, several unknowns remain, not the least of which involves the prospects of insects themselves. In recent years, largely owing to our wanton use of insecticides and pesticides, insect populations have been brought to the edge of collapse across much of the world. It remains to be seen whether they will be able to muster the ability to recover.

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