Desert locusts, Famine and Climate Change: The eighth plague sent by man

Updated: Apr 22, 2021

Throughout vast expanses of Eastern Africa, the Middle East and Asia desert locust swarms biblical in proportion continue to ravage the land causing severe food shortages and loss of livelihood.

In June this year, the Food and Agriculture Organization (FAO) locust watch division issued red threat levels in Yemen, Ethiopia, Somalia and Kenya to warn farmers of swarms that covered areas as large as cities and which numbered in the hundreds of millions (1). Throughout much of the Northern hemisphere’s summer, these countries have been subject to these warnings and even now in September, they continue to be issued. Many believe the situation will not see any appreciable improvement until after October by which time the monsoon rains will have subsided (2).

Figures 1 + 2 Threat warnings issued by the FAO locust watch division in June this year (top) and the most recent warnings issued in September (bottom) (3).

According to the FAO, even an average-sized swarm can consume the same amount of food in a day as 2,500 people (4). Each desert locust can consume its bodyweight (2g) of vegetation daily, when this figure is combined with the larger swarm numbers reported - 80 million, the food equivalent of 35,000 people can be consumed in a day (5).

According to Chaundhry Inayatullah, a former scientist at the international centre of Insect physiology and ecology in Nairobi, this year’s locust attacks are the worst in 30 years and are likely the most economically destructive since the 1960s (2). Esther Ndavu, a Kenyan man living the town of Mathyakani told BBC future planet “I have gone through a lot of challenges growing up as an orphan, but this locust invasion is more than a challenge. It is a matter of life and death because it has left us hungry and confused (5).”

Figure 3 - A woman attempts to repel a swarm of locusts in Dongra Ahir village, India (6).

Climate change?

Many scientists believe the intensity of this year’s swarms to be tightly interlinked with Climate Change, more specifically by ocean warming that has resulted in increased rainfall and cyclone commonality across Eastern Africa (2). The rainfall here is largely dependent on an ocean oscillation known as the Indian Ocean Dipole (IOD) – this can be characterised by three states: positive, negative and neutral. Each state describes the movement of warm surface-level water across the Indian ocean and the relative position of this warm water to Australia and Eastern Africa (7). Depending on the state of the IOD, weather patterns across Eastern Africa and surrounding areas can vary hugely.

When the IOD is negative for example, warm ocean water is moved by winds from the west towards Australia leading to rainfall across the country. When the IOD is positive, a lesser amount of warm water is swept towards Australia due to weaker westerly winds. This warm water remains closer to Eastern Africa and results in higher precipitation there. Over recent years due to global warming an intense positive dipole has been observed meaning that Australia has experienced significant lacks in precipitation and Eastern Africa has experienced higher than average precipitation (7). As a result of this (and due to this unnatural imbalance), Australia has experienced intense drought and more intense wildfires and Eastern Africa along with surrounding countries have seen plagues of Desert locusts descend upon the land.

Figure 3 – The positive Indian Ocean Dipole observed over recent years. This positive dipole is characterised by warmer than average water at the east of northern/middle Africa and cooler than average water to the north of Australia. This has resulted in higher than average rainfall in Eastern Africa and less than average rainfall across Australia (7).

How does precipitation influence locust swarms?

According to the FAO locust division the ideal conditions for desert locust population growth are (4):

1) Sand/clay soil with moisture that penetrates 10-15cm below the top ground layer

2) Availability of bare areas for egg-laying

3) Green vegetation for the development of hoppers (young locusts)

Although the FAO locust division stress that the presence of all these three conditions does not automatically lead to plagues of locusts, the satisfaction of any of these does increase the likelihood that they will be able to develop and aggregate. Not only does increased precipitation from the positive Indian dipole lead to moistening of the top ground layer of soil, but this rainfall also leads to the growth of vegetation that young locust hoppers can use to inhabit, consume, grow and develop with.

To understand why precipitation is so important in dictating locust swarms we must understand aspects of their ecology that make rain a signal for emergence. Many believe that locusts have evolved a ‘phenotypic plasticity’ (a physiological/behavioural response) towards their environment due to it being so temperamental and harsh in nature (8). Locusts have evolved to adapt towards conditions that can be Incredibly arid for stretches of years and where resources are scarce due to a lack of water. These years without rain across a larger time period are interrupted by heavy downfalls in very short periods of time. Due to this precipitation pattern – long periods of aridity contrasting with concentrated bursts of intense rainfall, locusts have evolved to respond quickly when downfalls do occur and as a result when vegetation for their consumption becomes available.

The way they have evolved to do this is through the development of two distinct life phases – the solitary, ‘grasshopper phase’ and the ‘gregarious phase’ (6). During arid conditions, locusts are generally in the grasshopper stage – during this period they are not considered to be a pest. They lay dormant, leading solitary lives and do not multiply or cause agricultural damage to any significant degree. When environmental conditions improve, however (usually when rainfall occurs), locusts shift to the gregarious phase and can multiply exponentially, 20-fold over three months in some cases (8). During this gregarious phase, locusts become sociable rather than solitary and swarm together in vast numbers, moving from patch to patch looking for resources to consume as a collective force.

Figure 4 – Locusts can shift from solitary to gregarious at many stages before reaching full maturity or when they are fully mature. Changes in behaviour can reverse or persist after environmental conditions revert back to being less desirable (9).

Locust defences

For the average farmer in afflicted countries, the potential for defending their crops is largely inadequate. With the absence of necessary pesticides/technology required to repel such vast amounts of insects many farmers resort to either starting fires and using smoke as a repellent or by crashing metal plates/hitting drums in the hope that the noise scares them away.

Farmers are largely at the mercy of swarm movements and either hope that the clouds of insects do not descend onto their patch or rely on the limited governmental intervention being provided. The primary method utilised by governments is to spray pesticides – usually organophosphate chemicals in concentrated doses from the air and on the ground over infested areas (10). Though this has been shown to kill vast quantities of locusts, these chemicals have also been demonstrated to have negative side-effects for non-target flora and fauna leading many to look towards alternative methods causing lesser levels of collateral damage.

One potential option being explored is the use of biological pesticides, namely the fungus Metarhizium anisopliae var. acridum which is able to penetrate through the locust cuticle, grow within it and cause eventual death. The benefit of using this is the fungus’ increased specificity when compared to the organophosphate chemicals being used. Widespread implementation would likely result in less severe damage to non-target flora and fauna meaning it could be used in more ecologically sensitive ecosystems such as national parks or specific conservation areas. This said, the current commercial formulas on the market (Green muscle and Green guard) are slow to work and need further field-testing in Africa under the specific climatic conditions of the area to test for efficacy (10).

With Climate Change showing no signal of slowing the conditions across Eastern Africa, the Middle East and Asia look likely to become wetter. As a result of this, the issues of locust swarms and widespread crop destruction look likely to persist and worsen before they improve. In a region already fragile from poor governance, conflict and poverty (in Eastern Africa alone more than 25 million people are experiencing food security issues (4)), the potential for further famine and loss of life is frightening.

Moving forward in the short-term further research and testing of more effective control methods, improvements in tracking/observation of swarms and an overall increase in funding is needed to support practical anti-locust initiatives in the areas most heavily affected. In the long-term, however, in the pursuit of achieving prolonged damage prevention rather than just limitation, Climate Change must be accepted as the prevailing factor and addressed as such on more than just a local level. At its core ocean warming and alterations in the Indian Ocean Dipole are the specific causes for increased precipitation and locust swarms across Eastern Africa, the Middle East and Asia. As a result of this, it is the duty of us all collectively as active contributors towards Climate crises such as this to reduce our carbon footprint and take responsibility for how our daily actions and decisions might influence those more vulnerable than us.

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