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The Unique Challenges of Responding to Desert Locust Outbreaks

desert locust Schistocerca gregaria

The recent plague of desert locusts in Africa and the Middle East cost $1.3 billion in damage in 23 countries. A report from Pakistan describes the difficult logistical and social hurdles to adequately managing this fast-moving entomological threat. (Public domain image by Adrian Pingstone, via Wikimedia Commons)

By Jody Green, Ph.D.

Jody Green, Ph.D.

Jody Green, Ph.D.

The depth and breadth of destruction due to the recent desert locust plague is unfathomable to those who have not witnessed the impact. Millions of people living in parts of Africa, Asia, and the Middle East are food insecure and living in poverty. This is an entomological story because this insect is the most destructive migratory pest in the world, devouring crops for human consumption and fodder for livestock. However, the problem is exacerbated by human behavior and other compounding complexities, which many do not understand.

The desert locust Schistocerca gregaria is a short-horned grasshopper in the family Acrididae, found in parts of East Africa and South Asia. They are normally solitary, short-winged grasshoppers that feed locally on vegetation in their native range. When conditions occur that favor swarm development—a period of prolonged drought followed by heavy rains—desert locusts enter a gregarious, social phase, where ecological factors and insect pheromones transform millions into long-winged, migratory, crop-destroying machines.

Allan Showler, Ph.D.

Allan Showler, Ph.D.

The recent locust plague is estimated to have affected 25 million people and cost $1.3 billion in damage in 23 countries. An effective strategy for locust management is called proaction, an intervention based on precision timing using insecticides with short residual activity. During the initial stage or early gregarization (i.e., when they begin to become gregarious, exploding in number), locusts can be successfully suppressed by terrestrial or aerial insecticide application. When targeted properly, extreme damage to vegetation can be prevented because swarms are stopped before an upsurge and the development of plagues.

Sounds simple, right? Wrong.

desert locust swarm, Morocco

Desert locusts enter outbreak stage when small bands of wingless hoppers crowded in an area trigger the formation (via pheromone) of large swarms of winged locusts. This transformation is both behavioral and physiological and may progress into an upsurge, which occurs over a period of months through successive generations of high-density breeding. If the upsurge continues, it may progress into a plague. A plague develops from multiple outbreaks and an upsurge, takes at least a year develop, and causes simultaneous damage to many regions. Shown here is an outbreak of desert locusts in Morocco in 2004. (Photo by Magnus Ullman, via Wikimedia Commons, CC BY-SA 3.0)

Much of the challenge of desert locust management comes with surveillance and early detection. “Desert locusts are uniquely complex, owing to the blending of economic, social, logistical, safety, geographical, political, and climatic issuessays Allan Showler, Ph.D., research entomologist at the U.S. Department of Agriculture’s Knipling-Bushland U.S. Livestock Insects Research Laboratory in Kerrville, Texas. Showler has experience working in Africa with various agencies and cites armed conflict as one of the most uniquely challenging aspects of desert locust control. “These remote areas are largely inaccessible unless you have special equipment, including aircraft, and scouts to navigate the dangerous terrain,” he says. Territorial conflict prevents surveillance during and between locust episodes, and political intricacies often impede regional coordination.

desert locust outbreaks in Pakistan, 2018-2021

Nearly all provinces of Pakistan have been affected by the ongoing desert locust plague between 2018 and 2021. Red zones indicate affected areas; province borders also shown. (Image originally published in Showler et al 2022, Journal of Integrated Pest Management)

An account of the recent episode of desert locust plague in Pakistan was published by Showler and colleagues in Pakistan this month in the open access Journal of Integrated Pest Management. The article describes the desert locust swarm as it began in Saudi Arabia in 2018 and progressed into Africa and east to Pakistan, making it the worst locust attack in 27 years. In February 2020, Pakistan declared a National Emergency, and its National Action Plan was employed. (The JIPM article follows a 2019 article on locust control Showler authored in American Entomologist.)

Prior to a locust outbreak, the Food and Agriculture Organization (FAO) of the United Nations issues a “Desert Locust Threat.” Some threats become outbreaks and small bands of wingless hoppers crowded in an area trigger the formation (via pheromone) of large swarms of winged locusts. This transformation is both behavioral and physiological and may progress into what is called an upsurge. Upsurges occur over a period of months through successive generations of high-density breeding. Locusts swarms become bigger and spread into different regions, devouring all vegetation. If the upsurge continues, it may progress into a plague. A plague develops from multiple outbreaks and an upsurge, takes at least a year develop, and causes simultaneous damage to many regions.

The changing climate has the potential to produce more frequent outbreaks, bigger swarms, and widespread food insecurity. Preparation, surveillance, emergency funding, new technologies, weather information, geographic information systems, historical records, communication, and cooperative proaction are all necessary to achieve locust-free zones for the future. This is a very intricate situation that is misunderstood. The desert locust crisis is less about the insect and more about conflict and insecurity among people. It is a story that demonstrates what can happen when countries do not coordinate enough among one another.

Jody Green, Ph.D., is an urban entomology extension educator at the University of Nebraska-Lincoln and a subject editor and communications editor for the Journal of Integrated Pest Management. Twitter: @JodyBugsMeUNL. Email: jgreen17@unl.edu.

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