Reacción a "Reactions to an analysis of the causes of insect decline in Europe"

This is not an experimental study or one that compares past and present data. It is a review of 82 published papers on two unique groups of insects (one of the many families of beetles and butterflies) in a very specific region (Central Europe), with the aim of synthesising the main causes given to explain the decline in the populations of these insects in agricultural landscapes. The quality of the work is determined by the quality of the studies they use and, in my opinion, their conclusions should be based on a more solid treatment of the data. 

There are studies that compare long time series data across the globe. Although there are not many of them, due to the lack of a clear strategy for collecting information on the most hyperdiverse group on Earth, the trend of declining populations is evident. This review does not add much to this picture and is partial, covering only a couple of insect groups and a very specific region, and I believe that the treatment of the data can lead to wrong interpretations. This paper points out that time comparisons can give rise not only to negative population trends but also to positive trends, and also gives little relevance to chemical contamination as a relevant pressure. The action of such chemical agents has been aptly called 'silent death' because of the difficulty in determining the effects of these compounds. 

Complex and costly environmental chemistry studies and laboratory analyses are necessary to detect these substances and to prove their lethality or morbidity. Moreover, without including other variables related to, for example, the age of the studies, their location or the natural conditions of the region, it is bold to comment that a quarter of the studies show positive effects.  

Of course, there are important limitations. The date of the studies reviewed should have been taken into account, as well as the degree of disturbance or naturalness of the regional matrix in which each is located. The authors find that about a quarter of the studies detect positive population trends and it would be interesting to know whether the age of these studies affects the lack of detection of a decline. The location of each study should also be taken into account, as a study conducted in a locality surrounded by natural landscapes may not show a decline in insect populations due to the 'source' effect of regional populations.  

The conclusions of this synthesis paper stress, as does the press release, that the decline in insect populations is related to 'human activities that influence insect habitat', also emphasising the complexity of the effects of the many causal factors that could help to understand this decline. Among the factors cited, little relevance is given to the increased use of agrochemicals in explaining the disappearance and decline of insect populations. The authors highlight 'anthropogenic activity' as the fundamental factor, an overly general concept that does not identify any specific cause. However, there is a wealth of evidence and studies that establish a direct causal relationship between the use of insecticides and herbicides and the decline of insects. How can the massive and indiscriminate use of products manufactured to kill insects and their populations not affect them?  

What is needed are (i) public initiatives capable of providing reliable and standardised time series data, (ii) studies comparing the composition and diversity of insect communities sampled in the past and present, (iii) experimental data on the effects of the three main processes affecting insect populations (chemical pollution, habitat modifications and climate change) and their interactions.  

Carrying out these studies and the production of results should not slow down the immediate implementation of conservation measures.