by Maria Alejandra Parreño
Humanity has a large impact on Earth. Agriculture is one of the major drivers of negative impacts, second only to fossil fuels and mineral extraction. In some way, we could say society started with agriculture and still today is the backbone of our subsistence. The farm is a unique socio-ecological system; fishermen don’t live in the middle of the sea, but farmers mostly live in their farms. In that way, many worlds coexist and collide in the farm: producers, consumers, farm or domestic animals, crop species, “weeds”, rodents, birds, water and nutrient cycles; the list is long. One of the main worlds in this system, are insects.
Who are they?
Insects are small arthropods of 6 legs, 3 defined body parts and an external skeleton; the one that makes a characteristic “pop” when we step over one of them. But that is almost all that insects have in common. For the rest, the 900 thousand species of known insects, out of the between 2 and 30 million estimated to exist, are quite different.1 This wonderful diversity, the largest of all animal groups, is what makes any species that comes to our mind, a poor example to generalize on the rest. Insects can pollinate or be vectors of diseases, they can be predators or prey, they can be parasites or symbionts, they can be disgusting or beautiful, they can be eaten or kill you. While their role might differ, they are all relevant for ecosystem functioning, directly or indirectly.
In the farm, we can group insects as beneficial or harmful, according to their direct impact on agriculture; these are insects of economic importance. Beneficial insects are mainly: 1) pollinators, that help plants reproduce, 2) predators and parasitoids, that help control pests, 3) scavengers and decomposers, that help to break down matter and 4) insects that produce economically valuable products, like honey or silk. Harmful insects (pests) are mainly: 1) herbivores, that eat crops, 2) insects with endo-parasitic larvae that develops inside fruits, and 3) disease vectors of plant, animal or human diseases.
Indirect effects of insects in the farm are mainly related to the functioning of the ecosystem that the farm is embedded in, usually grasslands. Seemingly “neutral” insects still have a relevant role through their participation in resources cycles and food webs that keep the ecosystem stable and productive. Many of them can even be used as bio-indicators of environmental quality .
Are they indestructible?
Insects are relatively small and reproduce in high rates compared to other animals. Therefore, we might be tempted to think of their populations as being sort of indestructible. As if their resilience would allow them to always recover from environmental damage or to always find a new space to resettle. The fact that there is often some redundancy in their roles (e.g.: many species pollinating one plant), can sometimes lead us to think that the non-natural extinction of a species will not be major in the overall ecosystem network.
This is far from true. Insect populations are highly sensible to changes in their environment. For example, small temperature increases can modify the developmental time of parasitoids. When timing mismatches occur between the development of parasitoids and their host, pest control efficiency is reduced.2 Another example is the presence of insecticides aimed at reducing harmful insects like mosquitoes, that have shown a collateral effect on bumblebees even in low doses, hindering their colony growth.3 Recent studies have raised concerns of an alarming insect population decline worldwide, even in protected areas. This is not only a threat for nature but also for economy: conservative figures put the economical value of native insects’ work in the fields of the USA at $0.38 billion for dung burial, $3.07 billion for pollination and $4.49 billion for pest control.4 Globally, this is of course a much larger figure.
What are the threats and what can I do about it?
The main threats for insects in agriculture are loss of habitat, climate change and contamination through chemicals, like herbicides and pesticides. Habitats get lost when we eliminate the places where insects develop, reproduce and feed, like marshes, ponds, bushes and “weeds”, so as to increase arable and grazing land, which goes into intensive constant management. Climate change is exacerbated by the destruction of carbon sinking sources (like forests), meat production and water contamination through runoff from the fields. Herbicides and pesticides kill adult insects or affect their development severely.
Addressing these 3 sources of damage can seem daunting. However, it all starts at home. Small changes add up to a better quality of life for insect populations and a healthier production system overall. Providing hedges in farms, synching mowing to insect developmental and reproduction times, synching pesticide application to daily insect rhythms to avoid their exposure, providing safe shelters for insects nearby farms, increasing landscape connectivity with corridors and urban ecology; these are feasible actions. Most importantly, acknowledging our impact and the existence of our little neighbors will help us make informed economical and political decisions. For instance, do you know where the different types of insects mentioned in this essay live?
At times, it may seem that we don’t have enough information to make decisions. It is true; there is much we don’t know about the complex insect world. But this we know: it takes more time and money to repair a damaged ecosystem, than to prevent its damage. This should be enough to apply a precautionary principle and provide a space in agriculture for insects to be happy. Many worlds coexist and collide in the farm. A healthy farm in the long term will only be possible if the scale inclines more on coexistence, than collision.
1. Smithsonian. Numbers of Insects (Species and Individuals). at <https://www.si.edu/spotlight/buginfo/bugnos>;
2. JEFFS, C. T. & LEWIS, O. T. Effects of climate warming on host–parasitoid interactions. Ecol. Entomol. 38, 209–218 (2013).
3. Whitehorn, P. R., O’Connor, S., Wackers, F. L. & Goulson, D. Neonicotinoid Pesticide Reduces Bumble Bee Colony Growth and Queen Production. Science (2012). doi:10.1126/science.1215025
4. Losey, J. E. & Vaughan, M. The Economic Value of Ecological Services Provided by Insects. BioScience 56, 311–323 (2006).