Living things have long needed to find ways to survive wildfires. Some of them, researchers recently discovered, can even build their own flameproof panic rooms.
Galls are outgrowths induced on plants by other organisms. In some instances, they form when parasitic insects like midges, moths and wasps release substances that prompt the plant to produce more cells. Galls shelter the larvae of the insects that made them grow, and they protect newborns from predators, parasitoids and adverse weather conditions. It turns out that this perfect nursery can also protect some insect larvae from the flames and heat of wildfires.
The discovery, announced this month in the journal Ecology, came from Jean Carlos Santos, an ecologist at the Federal University of Sergipe in Brazil, who was working in Minas Gerais, a state in the Cerrado, a region of savannas in the heart of the country. At that time, in 2012, “a massive fire erupted in the area,” he recalled, burning for 24 hours.
While walking through the area devastated by the flames, he cut open the galls of Solanum lycocarpum, a common plant living in the Cerrado that is also known as wolf’s fruit. These galls were made by females of the Boheman weevil, which lay their eggs on the wolf fruit’s shoots, inducing thick, multichambered galls that host many larvae.
To his surprise, weevil larvae were still hanging on inside.
“This was both fantastic and intriguing!” Dr. Santos wrote in an email. “I was eager to understand how this was possible.”
To investigate further, Dr. Santos came back to the area a few days later with his students. They collected dozens of galls from 40 wolf fruits; some had been exposed to the fire and some had not. Back in the lab, the team cut the galls open and checked whether the weevil larvae and pupae survived.
The galls were at a height on the plants where they “were clearly exposed to extreme heat from the fire. All the galls in the burned areas bore signs of charring,” Dr. Santos said. “Initially, we assumed that no insects could have survived within the galls.”
Despite that, the survival rate of larvae sheltering in burned galls was about 66 percent. Inside 20 galls, all larvae survived; in 23, only some of them came out alive; while in nine galls all weevils succumbed to the flames.
“The thicker the epidermis, the greater the weevil survival,” Dr. Santos also said.
Nadir Erbilgin, a forest entomologist at the University of Alberta who was not involved in the study, said the findings align with many other examples of adaptations by plants and insects to survive fires, especially where fires are recurring events. For example, some bark beetles survive fires by sheltering in the galleries they dig beneath a tree’s bark.
“Nature has a lot of these kinds of surprises,” Dr. Erbilgin said.
He added that he would have liked the researchers to focus more on comparing the burned galls where all the weevils survived with the burned galls where only some of them, or none, survived. Doing so, he added, could have offered more clues to how exactly the weevils outlasted the flames.
It’s possible, he added, that such a mechanism has evolved in other parts of the world. However, as the climate shifts, bringing increasing severity and recurrence of fires, those plant and insect adaptations to survive the flames might not be enough in some places. “Climate change screwed up all the balance,” Dr. Erbilgin said.
For example, more frequent, stronger fires might put to the test the gall’s sheltering ability that allowed the Boheman weevils to survive. “Eventually, the system is going to break up,” Dr. Erbilgin said. The fire from the study, in fact, only lasted one day. “If another fire comes next week or the next month, they may not have that survival ability,” he warned.
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