The biodiversity of terrestrial insects in Brazil, which includes animals such as butterflies, bees and beetles, shows a downward trend. This is one of the results of a study conducted by researchers from the State University of Campinas (Unicamp) and the federal universities of São Carlos and Rio Grande do Sul. The information was compiled from 45 scientific studies on the subject, as well as questionnaires sent to researchers who have been studying insects over the years.
“If you kill the insects, you break all of nature’s food chains at the base. If there are no caterpillars for the birds to eat, the birds will decline. If there are no insects for the wasps to feed on, they will decrease and begin to cause an imbalance that can cause, for example, an increase in pests, both in cities and in agriculture”, warns André Freitas, professor at the Institute of Unicamp Biology and one of the project researchers.
The study presents 75 trends, most of them downward, over 22 years for terrestrial insects. For aquatic insects, the study presents 75 trends over an average of 11 years. Most indicate a reduction in the number of animals. The work was supported by the Research Support Foundation of the State of São Paulo (FAPESP) and by the National Council for Scientific and Technological Development (CNPq). The text has been published this week in the international magazine Biology Letters.
Among terrestrial insects, for example, studies have shown a trend of population decline or loss of species diversity. The situation is different in aquatic groups, where the number of individuals or species has remained stable or, in some cases, has increased. The researchers, however, note that this difference needs to be reassessed in the future.
Global trend
Freitas points out that other studies, especially in the United States and Europe, had already shown the decline of insects in these regions, but there was little information on the situation in tropical countries.
“There they have data collected over decades, which shows that there is a decline of all types, not just pollinators,” he says. He recalls that the diversity of insects is much greater in tropical countries, with a variety of species between 10 and 20 times greater compared to countries with a temperate climate.
The researcher explains that, in order to understand the situation of insects, it is essential to have long-term studies, since these animals have short life cycles. “The analysis of an insect is almost like an electrocardiogram, full of peaks and valleys. So it will always be a zig zag line with large amplitudes, but you can see if it’s going up or down. To have that, very long time series are needed, and we had very little in Brazil”, he explains.
In this sense, studies with at least five years of analysis were considered. “What we noticed is that most studies indicate that there is indeed a decrease in insects in Brazil. There are several jobs that indicate stability, including some that show an increase. But the worrying thing is, if we look only at the number of studies that show an increase, a stability or a drop, those that show a drop are more common, ”says Freitas.
The reasons that explain the decrease are not part of the study, but the researcher presents some hypotheses considering data already found in other parts of the world. He cites: “the indiscriminate use of pesticides; the increase in cities and agricultural and livestock areas, which reduce the area of native habitat; and, near big cities, street lighting, because insects tend to be attracted to light bulbs, they turn around and die”.
insects and the environment
The researcher acknowledges that insects are usually associated with negative things, such as the transmission of diseases, but it is essential to remember the importance of these animals for the balance of the environment.
“The decrease in insects, in general, will favor a few pest species. These, yes, will have a much greater impact on our lives, ”she warns. He reminds that large imbalances can leave only pests associated with humans, such as cockroaches, mosquitoes and certain ants, since they will have food and environment available.
Bee pollination is the best known example of the role of insects in maintaining biodiversity. However, there are other benefits of insects for the environment, such as the fact that they are the first step in the decomposition of organic matter.
“Whether it’s leaves falling to the ground or dead animals. Various beetles, ants and termites do the first degradation of this material. Without insects, for example, forests would have more and more trunks and leaves accumulated one on top of the other, because the bacteria that carry out the final decomposition depend on a first fragmentation”, explains Freitas.