The battle between plants and insects in the Caatinga Region

Every year the arid, thorny Caatinga environment, which makes life difficult for the people of the sertão in its driest seasons, is rapidly altered by a process that starts at the first sign of the rainy season and completely transforms the landscape. That environment, which was unfavorable to life before, now offers abundant resources for this same life to appear in different colors, forms and sounds. 

Although there are leaves, fruit and flowers available, they are only accessible for a brief period, during which the insects must fulfill their cycle. For that reason, during the rainy season, one can hardly go past a tree without seeing that several leaves are cut up or have small pieces missing.   

In general, these pieces are removed by herbivorous insects, which use this plant tissue as food. This process, known as herbivority, is well studied in other regions of the planet; however, little is know about its extent and effects, and the agents involved, in the Caatinga region.

You may think that all this happens in a very simple manner, but a real battle is fought throughout the process. In order to feed, herbivorous insects need to overcome various problems and face many hazards.   

The first of these problems that must be overcome are the physical barriers present in the plants. These defenses act at a level that may be noticed by many of us: the thorns present in Juremas, trichomas (short hairs) present on the leaves and stems of the mallow, and even the urticating spicules present in Faveleiras, are examples of the plants’ attempts to make insects’ lives more difficult; in spite of that, the insects manage to bypass these physical barriers.

Once this problem is overcome, another is found in the very source of food. Although they display apparent passivity, vegetables have other strategies to prevent the loss of their leaf area, producing chemical defenses that may act by making the food unpalatable, causing digestive problems, or even causing the death of those that eat them. In addition, for an insect, the Caatinga region may be a very dangerous place, because these animals still have to worry about the predatory insects that move freely and represent a constant threat.   

Although this theory seems to be very simple and clear, the truth is that little – or almost nothing – is known about how interactive processes among plants, insects and the environment work in the Caatinga region.

Data about the herbivority levels, the fauna of free-living herbivorous and predatory insects, and the composition of the chemical defenses of trees in the Caatinga are scarce or non-existent. All this is the reflection of the little attention that the scientific community has given, in recent years, to this biome, which is the only exclusively Brazilian one. 

In order to study these characteristics so as to fill in this scientific gap and to understand better how our biome works, the project “Biodiversity and polytrophic interactions among herbivores and plants in successional Caatinga environments”, which is being carried out by Cláudio Magalhães under the guidance of Dr. Jarcilene Almeida-Cortez, proposes an integrated approach to herbivority levels, the composition of chemical defenses and a survey of the fauna of herbivorous and predatory insects in the Caatinga.