Exploring the impact of climate change on the development and functioning of a leafcutter ant pest species, Acromyrmex octospinosus.
Leafcutter ants are social insects which live in a colony founded by a single queen ant. Individuals carry out specific jobs based on their size; there are two main divisions of workers, large ants which perform foraging and defence and small ants which carry out brood care. Leafcutter ants are known to have a complex colony life due to their co-dependency with a fungus garden. Using the leaves they forage, leafcutter ants grow and protect the fungus from parasites and in return, the fungus provides nutrients. This is known as mutualism, as both parties involved benefit from the relationship.
Leafcutter ants live in large colonies underground with their fungus garden, this results in vast amounts of waste being produced. The organisation of this waste is vital to prevent parasitic fungi and bacteria infecting the mutualistic fungus garden that the ants rely on for food. Leafcutter ants are particularly susceptible to a specialised, aggressive garden fungal parasite called Escovopsis. Protection from this parasite is extremely important and as such, the ants have developed defensive behaviours to prevent the parasite destroying their fungus garden. These behaviours include, removing any spores from individual ants by cleaning themselves or other workers and weeding the fungus garden by removing any infected areas. These actions help limit the spread of parasitic spores and allow the colony to grow successfully.
The evolution of leafcutter ants has allowed them to dominate a number of different environments across the world as ecosystem engineers. This has resulted in them being responsible for up to 50% of losses in forestry production and field crops across Latin America, due to the large quantity of plant material they collect (Boulogene et al., 2011; Samuels et al., 2013). They also impact ecosystem functioning by disturbing soil structure and account for 25% of all herbivory in rainforests, foraging 10-15% of leaves in their nest range (Swanson et al., 2019). It is estimated that several million dollars of damage per year is caused by leafcutter ants in the USA and Brazil, making them one of the most serious pests of tropical and subtropical America (Boulogne et al., 2018). This destructive behaviour, combined with their complex living structure, has resulted in leafcutter ants dominating their habitat as many control methods have proven ineffective.
My study hopes to shed some light on the future of this pest species; specifically, how a predicted 2°C increase in annual temperature across areas like Trinidad where leafcutter ants are native, might result in a significant increase in this pests foraging behaviour. This may then result in serious food shortages, as 90% of leafcutter ant attacks are on vegetable and fruit crops. This, combined with warmer, drier conditions could lead to devastating consequences to local economies and ecosystems. No studies have yet to explore the effect of climate change on this species of leafcutter ant (Acromyrmex octospinosus), nor considered the insects behavioural changes that could occur as a result.
Therefore, it is important to understand how leafcutter ant colonies develop and persist, as well as how they manage waste and defend against parasitic fungi, to better develop an understanding on how to control them. It is vital to see how predicted climate change could further increase the pests destructive behaviour and how it could impact the defensive success against common threats.
To do this, I will set up 18 mini leafcutter ant colonies in two temperature rooms (24°C and 26°C) with different weights of fungus garden (0.5g, 1.5g and 2.5g), to test how the stage of colony development is affected by temperature. I will then perform three threats on all the mini colonies in both temperature conditions. These threats will include, crushing individual ant heads to release alarm pheromones, disturbing the colonies waste piles and exposure to talcum powder which safely mimics parasitic spores. While carrying these out, I will observe and note down any behaviours which result from the threats. Examples of these behaviours can be seen below:
From this behavioural experiment, certain analysis can be performed which will hopefully lead to conclusive results on how climate change impacts leafcutter ant colony development and functioning. Unfortunately, so far the experimental process of my project has been put on hold due to the current Covid-19 pandemic. This has lead to some serious challenges in my projects progress, as over two months of time which was originally planned to carry out my behavioural experiments has been lost. The plan going forward is still hopeful that some lab-based experiments will be carried out before Easter, provided safety can be ensured, which will allow some level of results to be concluded. In the meantime, a lot of reading and writing is occurring instead.
Despite the set-back and challenging conditions, I would still choose to perform a behaviour lab-based project as I have always been fascinated in the complex and bizarre behaviours of the animal kingdom, particularly social insects. Ants are such a fundamental part of the world, most of which is hidden from us and being able to explore and reveal their processes is an incredible opportunity, particularly when considering the future and climate change.
Animal Introductions 