Global Warming and Insects Bites Threaten Plants from Both Ends. 

Recently, scientists from Michigan State University have developed some models highlighting the plants’ adaptation process as climate warming is on the rise. They become vulnerable to insects’ attack in a hotter climate. A new study focusing on tomato plants shows that the rising temperatures hampered their ability to fight with caterpillars. Both the warm climate and the insects are double threats for the plants. 

The study holds two factors responsible for this. The first one is the temperature rising around the globe. The increased heat has an impact on the insects’ metabolism. They start to eat more when it is too hot. Besides, the hot climate allows the insects to find out hospitable habitats. 

The second factor is how plants react with this constant change in temperature. 

Gregg Howe, a distinguished professor from the DOE Plant Research Laboratory at Michigan State University says, "We know that there are constraints that prevent plants from dealing with two stresses simultaneously. 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."

Plants have also their own metabolism to fight with any threats. Let’s see what happens when caterpillars attack. When a caterpillar attacks the leaves of it, the plant produces a hormone as a defense mechanism of the attack. The name of this hormone is Jasmonate or JA. This hormone can thwart the caterpiller by producing defense compounds quickly.  

The plants also have tricks to fight temperatures. They can keep themselves cool even in hot weather. As they can not take shelter under a tree, they slightly lift up their leaves from the soil that is very hot.

They also sweat like us to cool down their body. We sweat through our skin but they do this by their stomata that are similar to skin pores. By doing so they evaporate and keep the leaves cooler. 

Nathan Havko works in the Howe lab as a postdoctoral researcher. He started growing tomato plants in hot chambers maintaining 38 degrees Celsius. This research paved him the way to a significant breakthrough. Later, he spread hungry caterpillars on them. 

Howe says, "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 stronger defense response. 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."

Staying in the hot chamber, the plants perhaps don’t want to lose water from the attacked areas by the caterpillars. As they can not release sweat, they feel a similar type of heatstroke for this. The caterpillars take advantage of this weakness of the plant and advance their attack. The plants still do not open the pores, the leaves become hotter and help the caterpillars to have healthy growth. 

What are the consequences? 

Havko says, "We see photosynthesis, which is how crops produce biomass, is strongly impaired in these plants. The resources to produce biomass are there, but somehow they aren't used properly and crop productivity decreases."

Still, many questions may arise in our minds. But this very study shows for now that when global temperature rises, plants might change some of their strategies. 

Howe continues, "I think we have yet to appreciate the unexpected tradeoffs between defense responses and plant productivity, especially when other types of environmental stress are present. Turning on the defense response may do more harm than good if the plants face high temperatures or other stresses." 

The National Academy of Sciences published the study. This team from the Howe lab consisted of George Kapali, Michael Das, Gregg Howe, and Nathan Havko. From the Sharkey lab, Thomas Sharkey and Alan McClain supported the team in photosynthesis.