The biodiversity of terrestrial insects in Brazil, which includes animals such as butterflies, bees, and beetles, is on a downward trend. This is one of the results of a survey carried out by researchers from the State University of Campinas (Unicamp) and the federal universities of São Carlos and Rio Grande do Sul. The information was gathered from 45 scientific pieces of research on the theme, besides questionnaires sent to researchers who have been studying insects for years.
“If you wipe out insects, you break all of nature’s food chains at the base. If you don’t have caterpillars for the birds to eat, the birds will decline. If you don’t have insects for wasps to feed on, their number will fall, and once it does, they start to cause an imbalance that can lead, for example, to an increase in pests, both in cities and in agriculture,” André Freitas, professor at the Institute of Biology at Unicamp and one of the project’s researchers, warns.
The study presents 75 trends – most of them decreasing – over 22 years for terrestrial insects. For aquatic insects, the study presents 75 trends over 11 years on average. Most of them indicate a reduction in the number of animals. The work was supported by the São Paulo State Research Foundation (Fapesp) and the National Council for Scientific and Technological Development (CNPq). The text was published this week in the international journal Biology Letters.
Among terrestrial insects, for example, the studies indicated a tendency for population decline or loss of species diversity. The situation is different in aquatic groups, in which the number of individuals or species has remained stable or, in some cases, increased. The researchers, however, emphasize that this difference should be reassessed in the future.
Worldwide trend
Freitas points out that other studies, especially in the United States and Europe, had already shown a decline in the number of insects in these regions, but there was little information about the situation in tropical countries.
“Over there they have decades of data showing that there is a decline of all types, not only of pollinators,” he points out. He explained that the diversity of insects is much greater here, with a variety of species from 10 to 20 to one, compared to temperate countries.
The researcher explains that to understand the situation of insects, long-term studies are fundamental because these animals have short life cycles. “[The analysis of an] insect is almost like an electrocardiogram, full of peaks and valleys. It’s always going to be a zig-zag line with large amplitudes, but you can see if it’s going up or down. To have this [kind of information], you need very long time series, and we had very little [in Brazil],” he says.
In this sense, studies with at least five years of analysis have been considered. “What we have realized is that most of the studies indicate that there is indeed a decline of insects in Brazil. There are several studies that indicate stability, and even some show an increase. But what is worrying is that, if we look only at the number of studies that show an increase, stability or decline, those that show a decline are more common,” Freitas declared.
The reasons that explain the decline are not part of the survey, but the researcher presents some hypotheses for this picture, considering data found in other parts of the world, for instance, “the indiscriminate use of pesticides; the increase in the size of cities, and of agricultural and farming areas, which reduce the native habitat area; and urban lighting in large cities, because insects tend to be attracted by light bulbs, they spin around and die.”
Insects and the environment
The researcher admits that insects are often associated with negative things, such as disease transmission, but it is fundamental to remember the importance of these animals for the balance of the environment.
“The decline of insects, in general, will favor a few pest species. These will have a much greater impact on our lives,” he warns. He reminds us that large imbalances can result that only pests associated with humans, such as cockroaches, mosquitoes, and certain ants remain since they will have food and an available environment.
Pollination by bees is the best-known example of the role of insects in maintaining biodiversity. But there are other benefits of insects to the environment, such as the fact that they are the first step in the decomposition of organic matter.
“Whether it’s leaves that fall to the ground or dead animals, various beetles, ants, and termites do the first degradation of this material. Without insects, for example, the forests would constitute more and more trunks and leaves piled on top of each other, because the bacteria that do the final decomposition depend first on the fragmentation,” explains Freitas.