How to Fight Asia’s Locust Invasions

Swarms of locusts have devastated farms in some parts of Asia in recent years. Photo: ADB
Swarms of locusts have devastated farms in some parts of Asia in recent years. Photo: ADB

By Noriko Sato, David Hunter, Chris Adriaansen

Farmers in parts of Asia have experienced devastating locust infestations in recent years, threatening national and local food security. A dedicated, well-funded team is needed to monitor the pests and take the fight to them.  

Locusts are a worldwide pest that can cause substantial crop damage and threaten a country’s food security. The ability of locusts to rapidly increase, particularly during monsoon season, and migrate to previously uninfested areas, can mean that farmers are suddenly faced with a pest that can destroy their crops within a few days and overwhelm their ability to protect these vital food sources.

Pakistan and India have had almost annual locust invasions since 2018.  Increased locust outbreaks, including in usually dry desert areas, are expected due to periods of higher rainfall caused by climate change. To meet this threat, countries need to have 21st century management techniques in place.

In Pakistan, there are regular surveys of locust infestation conducted as part of a joint Iran-Pakistan program. Combined with funding and a national action plan, a locust upsurge in early 2020 was supressed by the end of the year.

During all locust treatment programs, the safe and effective use of pesticides has become increasingly important, ensuring safety for both spray operators and agricultural products. Reducing the use of chemical pesticides, using innovative techniques such as strip spraying and including biopesticides in treatment programs, is increasingly necessary to meet national and international sanitary and phytosanitary standards.

Such treatment programs would benefit from applying a number of international best practices:

 Treatment programs should concentrate on treating locusts when they are flightless juveniles (hopper bands) before they reach the very damaging and very mobile adult stage. But bands are difficult to locate from the ground, particularly in desert areas where access is limited, so the best practice is to detect bands from an aircraft flying overhead.

Because the densest bands are most visible, areas with the most locusts can be seen and rapidly treated, and the same system was adapted for the desert locust in East Africa during 2021, leading to a rapid treatment of locust bands.

Bands march hundreds of meters per day, so placing chemical pesticide in strips every 300–500 meters leads to very high mortality. The locusts march into the treated strips within a day or two, pick up a lethal dose and die. Strip treatments lead to a much-reduced use of chemical pesticide, leading to substantially lower monetary and environmental costs.

This system was used to apply insect growth regulators (insecticides that disrupt how insects grow and reproduce) in east Africa during 2021, providing over 95% mortality within 10 days of application. Because insect growth regulators are specific to insects, there is a much-reduced effect on non-target organisms, further limiting side effects on the environment. 

Biopesticides containing the naturally occurring fungus Metarhizium acridum have been used in Australia for over 20 years, and in the People’s Republic of China for nearly as long, and were used in Africa during the recent upsurge. The use against juvenile bands is common but it has also been used against adult swarms, and the latter was particularly successful in East Africa in 2021.

 Critical to these treatment programs is to have a system of preventive management that aims to reduce the size of locust infestations and the crop damage that can result. Preventive management has proven to be most successful when there are readily available resources for rapid response, often provided by a reserve fund, so that early intervention treatments of significant infestations are conducted.

Desert locusts are a serious pest of agriculture, though upsurges only occur from time to time. Effective management depends on a small permanent locust unit that conducts regular surveys and treats any locust outbreaks detected using the latest techniques.

And whenever large populations arise, the unit must have the resources in reserve for the rapid increase in treatments that will be required as part of protecting crops and ensuring food security.

This blog is based on a high-level two-day knowledge sharing webinar on international best practices on locust and management that was held in January 2022 at the Department of Plant Protection in Karachi, Pakistan, with the Asian Development Bank and Pakistan’s Ministry of National Food Security and Research, in collaboration with the Australian Plague Locust Commission.