Pervasive sublethal effects of agrochemicals as contributing factors to insect decline

 

Background

The global insect population is declining at a rapid and alarming rate (Wagner et al. 2020). The reduction of their habitats, global warming and the extensive use of pesticides are believed to be the main factors responsible for this general and widespread decline. However, the root, relevance and scope of this problem has rarely been documented systematically. The authors of this preprint use a library of 1024 insecticides and pesticides – at sub-lethal doses on D. melanogaster larvae – in order to gain a systematic understanding of the contribution of these ‘agrochemicals’ to the global decline of insects.

 

Key findings of this preprint

1. Set up of a high throughput screen to monitor the effect of pesticides

Using D. Melanogaster as a model system, the authors focused on the effects of pesticides on larvae. They measured acute (16h) and long term (10 days) lethality as well as behavioural shifts in larvae movements. The concentrations of agrochemical compounds used were 200 uM, 20 uM (both often used for many pesticides) and 2 uM (concentration often detected in the soil). At the lower concentration of 2 uM, only some chemicals caused a high degree of acute toxicity, though long-term toxicity and a behavioural shift were widely detected across the compound library even in non-insecticide pesticides (Fig. 1).

 

Figure 1 – a,b,c) Schematic representation of the screening workflow, compounds used and parameters analyzed. g,h,i,j,k) Representation of acute, long term toxicity and a behavioral shift for each agrochemical compound tested. Non gray colored dots represent compound for which a toxic of behavioral effect was observed.

 

2. Measuring phosphoproteomics changes upon acute exposure of common agrochemical compounds

To quantitatively measure the impact of sub-lethal common agrochemical pesticides, larvae were exposed to 0.2 uM of either Chlorpyrifos, 1,2-dibromoethane, Cyhalothrin, Dodine or Glyphosate. Subsequently, any phosphoproteomic changes were recorded and analysed. Changing the phosphorylation status of proteins is one of the fastest ways in which an organism can adapt to changing environmental conditions. All tested compounds caused behavioural shifts and phosphoproteomic dysregulation in larvae upon acute exposure (Fig. 2). Particularly enriched hits were related to muscular physiology, indicating a potential important stress response axis.

 

Figure 2 – Volcano plots show the deregulation of the phosphoproteome (upper panel) and proteome (lower panel) by agrochemical compounds exposure. Red dots indicate upregulation while blue dots downregulation.

 

3. Increasing the variables of the assay: temperature and compound combinations

The high throughput assay developed by the authors allowed them to study the interaction of pesticides with factors that may also cause insect decline, such as rising global temperatures. As such, they selected a number of compounds and re-tested them at 25°C vs 29°C. Strikingly, an increase of just 4°C strongly impacted the lethality and behavioural effects of many pesticides, indicating that global warming might worsen the effect of agrochemical compounds on insects. Additionally, when the author tested several combinations of chemicals normally present in soil samples, they found some synergistic effects, raising concerns about the safety of agrochemical mixes.

 

4. Validation in other species and natural isolates

To corroborate their findings, the authors also analysed the sensitivity of natural isolates and other insect species to pesticides. Natural isolates showed higher resistance, especially to organophosphates, which might be explained by an adaptive response to chemical exposure. When focusing on other species, in particular the mosquito Anopheles stephensi and the butterfly Vanessa cardui, they also found sub-lethal effects of agrochemicals affecting these species’ behaviour, highlighting the relevance of the findings described in this preprint for different insects.

 

 

Why I chose this preprint

Designing conservation plans and gaining a deep understanding of the global effects of pesticides on insect biodiversity and survival is a major challenge of our time. This preprint offers a great resource to interpretate and expand our knowledge on agrochemical compounds and their effects on insects. By having also generated a database, The Agrotoxin Database (https://agrotoxin.embl.de/), this preprint also offers an important resource freely available to the community.

 

 

Questions to the authors

• Would it be possible to use the assay you developed to also test the sub-lethal effects of agrochemicals directly on adult insect populations rather than larvae?
• What do you think is the most useful way in which your database could be used?

 

 

References

·         Wagner, D. L. Insect Declines in the Anthropocene. Annu Rev Entomol 65, 457–480 (2020).

 

 

Tags: climate change, drosophila, insects, pesticides

doi: https://doi.org/10.1242/prelights.36431

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