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Galls found to shield Boheman weevil larvae from wildfire heat in Brazil

A team of ecologists and entomologists affiliated with several institutions in Brazil, working with a colleague from Mexico, has observed the first instance of galls providing protection against fire to gall-inducing Boheman weevil larvae. In their paper in the journal Ecology, the group describes how they discovered weevil larvae alive in some of the galls on Solanum lycocarpum plants after a fire on a farm in Minas Gerais, Brazil.

Galls are bulbous outgrowths on some plants that are produced as a result of an insect releasing a substance through their epidermis. The move is intentional—after releasing the substance, the insect drops eggs into the gall, which grow into larvae.

Galls provide a home for the larvae, and quite often a food source. Prior research has shown that the galls also provide protection against the elements and predators. In this new study, the team has found that for at least one type of insect, they may also provide protection from wildfires.

The researchers made the discovery as one of their members was walking around in a tract of recently burnt savannah in Brazil. The researcher, Jean Carlos Santos, happened upon a burnt wolf apple plant (Solanum lycocarpum), with still identifiable galls on it. Curious, he cut one of the galls open and found a larva inside that was still alive. It had somehow managed to survive the intense heat from the fire.

The find by Santos led to a study of the larva found inside the plant—a Boheman weevil—and whether the initial find was a one-of-a-kind observation. He and his team returned to the burnt savannah and collected multiple samples that they took back to their lab for study.

Boheman weevils induce multichambered galls with each chamber containing one larva. In 20 of the galls, all the larvae had survived the fire. Another 23 contained at least one dead larva, and in another nine, none of the larvae had survived. The researchers noted it was the thickness of the epidermis that made the difference—the thicker it was, the more likely the larvae inside were likely to survive.