Could the Locust Upsurge in the Western Indian Ocean Weaken Regional Food Security?

24 March 2020 Mervyn Piesse, Research Manager, Global Food and Water Crises Research Programme Download PDF

Key Points

  • An outbreak of desert locusts in parts of East Africa, the Middle East and South Asia is the largest in 25 years. Without effective containment measures, about 20 million people could face a food crisis as a result.
  • Regional food security is not immediately threatened, but without effective containment measures during the planting season, swarms could destroy crops and weaken food security.
  • Stronger positive Indian Ocean Dipole events and more frequent and severe tropical cyclones in the western Indian Ocean could increase the potential for locust swarms to form in the Arabian Peninsula and East Africa in the future.
  • Chemical pesticides remain the most effective tool against locust swarms as they can be easily acquired and rapidly deployed. Biopesticides present a lower environmental risk, but in most cases, it is too late to use them.



Swarms of desert locusts have spread across parts of South Asia and East Africa from the Arabian Peninsula. Some 20 million people in affected regions could face a food crisis, in addition to the tens of millions who already experience food insecurity. According to the Food and Agriculture Organization (FAO), the outbreak is the largest in the region in 25 years, but for some countries, such as Kenya, it is the worst infestation in at least 70. The affected regions do not face an immediate food security challenge, as the swarms are arriving between the crop harvest and planting seasons. If the swarms are not brought under control during the planting season, which runs from March to May, however, there is a chance of increased food insecurity in the region.



The desert locust is  ‘the most dangerous of all migratory pest species in the world due to its ability to reproduce rapidly, migrate long distances, and devastate crops.’ It usually lives a solitary life in the deserts of North Africa, the Middle East and South Asia, but when a large number of desert locusts gather in a constrained area, they develop group behaviour and act in unison. Swarms usually form after periods of heavy rain, because locusts need moist soil to lay eggs. Rough estimates suggest that a swarm of one billion insects covers about 20 square kilometres and is capable of consuming 2,000 tonnes of vegetation each day. An average swarm can travel up to 150km and consume enough food to feed 34 million people per day. Many of the swarms in East Africa are significantly larger than average and could come to pose a significant threat to regional food security.

Swarms of desert locusts in the Middle East and East Africa originated in the Empty Quarter of the southern Arabian Peninsula during the 2018-19 winter, when heavy rains created optimal conditions for breeding. Small swarms of locusts then spread into Yemen, Saudi Arabia and Iran. Mainly due to civil conflict and political instability, Yemen was not in a position to conduct preventative control measures. Attempts to control the swarms also largely failed in Iran. By the end of 2019, swarms had reached the Indo-Pakistan border from Iran, while other swarms had crossed the Red Sea to Somalia and Ethiopia. The number of locusts continued to rise in those locations and swarms spread into Eritrea, Djibouti, Kenya and Sudan. The October to December 2019 rainfall season in East Africa was one of the wettest in 40 years, which led to an increase in soil moisture and above-normal levels of vegetation, all of which supported a rapid increase in the number of locusts in the region.

The Food and Agriculture Organization warns that if the swarms in Kenya, Ethiopia and Somalia are left unchecked, the number of locusts in the Horn of Africa could increase 500 fold by June. It also states that the situation could present ‘an unprecedented threat to food security and livelihoods at the beginning of the upcoming cropping season.’

Preliminary crop production estimates for East Africa suggest, however, that cereal harvests are broadly near average to slightly above average. It is unlikely that the region faces immediate food security concerns as a result of the locust infestation. As Mark Green, the Administrator of the US Agency for International Development, notes, ‘the timing could have been worse in the sense that harvests are in, so this doesn’t have the worst-case scenario effect.’ As long as another wave of locusts does not eventuate and disrupt the planting season between March and May, it is unlikely that the swarms will severely affect food security in East Africa. The floods that occurred after a prolonged drought could, however, reduce access to food in some parts of the region.

Locust swarms have not reached plague proportions. The number of locusts is currently larger than an outbreak and, as swarms are forming independently in a number of unconnected geographical locations, it is officially declared an “upsurge”. Plagues usually affect an entire continent, while upsurges usually only affect multiple countries or an entire region. A plague will be declared if swarms spread over a larger geographical area and continue to increase in number. It is expected that ecological conditions will remain favourable for the locusts in Ethiopia, Somalia and Kenya until June. If that occurs, locust numbers could surge to plague proportions before dying off due to the arrival of drier conditions.

There has been a major decline in the frequency of severe locust infestations since the 1960s. In the six decades prior to that there were five major plagues, lasting up to 14 years. Plagues now only occur once every ten to 15 years and are usually over within three years. The decline is attributable to a number of factors including:

the introduction of chemical pesticides, improved transportation and infrastructure, and advances in technologies related to precision spraying, communications, geopositioning, spatial analysis, remote sensing, and early warning.

The last major locust upsurge that threatened to grow to plague proportions originated in West Africa in 2003 and spread across 23 countries in Africa and the Middle East. It took almost two years, more than US$500 million and the spraying of 13 million hectares of land to bring the situation under control. Even with those measures, however, cereal crop losses of up to 100 per cent were recorded in some areas. Locust plagues usually take several years to develop and once they reach their peak, they decline very rapidly, usually within six months when appropriate control measures are implemented.

Climatic conditions were ideal for the formation of locust swarms over the last two years. Successive positive Indian Ocean Dipole (IOD) events in 2018 and 2019 were one of the main factors in higher than average rainfall in parts of the Arabian Peninsula and East Africa. The IOD is a measure of the difference in sea surface temperature between the tropical western and eastern regions of the Indian Ocean. During a positive phase, the western region is warmer than normal and the eastern region is cooler than normal. That leads to strong moist winds being directed towards East Africa and drier than usual conditions in Australia. The Australian Bureau of Meteorology states that:

It is unusual but not unprecedented to have successive positive IOD events (based on the Bureau of Meteorology’s criteria, the last known occurrence of consecutive positive IOD events was in 1982 and 1983). While the IOD is a natural mode of variability, its behaviour is changing in response to climate change. Research suggests that the frequency of positive IOD events, and particularly the occurrence of consecutive events will increase as global temperatures rise.

The 2019 IOD was one of the strongest on record and, while it has weakened to neutral, sea surface temperatures off the coast of East Africa remain elevated. They are expected to return to more normal levels over the next few months, however, possibly reducing the potential for a third consecutive positive IOD event.

Warmer sea surface temperatures contributed to the formation of extremely severe cyclonic storms in the Arabian Sea in the last five years, which also increases the chances of large locust swarms forming. In recent years there has been an increase in the frequency of extremely severe cyclonic storms in the Arabian Sea and climate change is the most likely cause. Stronger IOD events and more frequent and severe tropical cyclones could increase the potential for locust plagues to form in the Arabian Peninsula and East Africa in the future.

Crop production and food security is likely to decline significantly across East Africa in the event that a severe locust plague occurs during the 2020 crop season. Keith Cressman, the FAO Senior Locust Forecasting Officer, stated that the potential for a humanitarian catastrophe to occur as a result of the locust upsurge in the Horn of Africa

is very high at this moment because of those good rains and also because of the large number of swarms that have formed in the past few months and the size of these swarms. Some of these swarms are just enormous, for example one swarm in north-east Kenya about a month ago [in January 2020] was about 60 kilometres long by 40 kilometres wide.

According to Mr Cressman, a swarm that is one square kilometre in size is able to consume the same amount of food as 35,000 people per day. The swarm in north-east Kenya is, therefore, capable of consuming approximately the same amount of food as 84 million people per day. A typical swarm would usually only cover about 100 square kilometres, with the ability to consume the equivalent of what 3.5 million people would eat in a day. As 25 million people in the wider region were already severely food insecure before the locust upsurge, a further decline in food production could further weaken food security in the region. Aerial control measures are underway in the region, but are restricted in north-east Kenya and southern Somalia due to the weak security situation in those regions.

Most countries in the Middle East and South Asia are likely to fare better than those in Africa. Outbreaks of desert locusts are more common in those regions and most countries are better equipped to confront the threat.

The conflict in Yemen, which already has one of the most dire food security situations in the world, is preventing sufficient locust control operations to occur. Locust control centres are split between the government and the Houthi rebels, with neither side able to address the outbreak effectively on their own.

Iran, which is already confronting one of the world’s largest outbreaks of COVID-19, is also dealing with a large outbreak of locusts. Southern Iran is often affected by swarms of locusts and it is likely that the five provinces most affected will be able to contain the outbreak. Biological control measures have already been implemented on more than 32,000 hectares of affected farmland. As previous control measures were not sufficient to prevent the locusts from spreading into Pakistan and India, however, there is some uncertainty about Iran’s containment capabilities.

The first large wave of locusts reached Pakistan in November 2019 and, according to one report, up to 40 per cent of crops were destroyed in Sindh province alone. Pakistan declared a national emergency in response to the outbreak on 1 February, after it determined that this is the worst infestation since 1993. It has received 50,000 litres of malathion and 14 air-powered high-efficiency remote sprayers from China. Beijing has also indicated that it will consider further, long-term assistance to help confront future outbreaks in Pakistan. The government has reassured Pakistanis that there are sufficient food stockpiles to outlast any downturn in food production this year. In remote areas of the country, however, warehouse operators have warned that their supplies are old and poorly stored and are probably not sufficient to meet local requirements. Food security could be undermined in Pakistan in the event of a large locust outbreak.

Aerial spraying is the most effective method to reduce locust numbers, according to the FAO. There are concerns that the use of chemicals, such as the widely used insecticide chlorpyrifos, could be harmful to humans and the environment. The use of biopesticides, such as fungi, is likely to present a lower risk to other organisms and the wider environment. The FAO is trialling fungal biopesticides that only kill locusts and related grasshoppers in parts of Somalia, but biopesticides are more effective against young locusts that have not developed wings and they are often not available in sufficiently large quantities at short notice. Chemical sprays also work more rapidly than fungal solutions, making them more effective at containing outbreaks quickly.

The upsurge in locust numbers does not present an immediate threat to food security in East Africa, the Middle East or South Asia. If effective containment measures are implemented now and throughout the planting season, it is probable that locust numbers will be sufficiently reduced to avoid severe crop damage. Given the severity of the outbreak, chemical pesticides are the most effective response measure currently available to the region. Regional food security is unlikely to be significantly reduced if aerial spraying of the most affected areas is conducted until locust swarms disperse. Further monitoring will also be necessary to ensure that they do not reform.

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