Primer on locust and grasshopper management

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S. piceifrons control by Mario Poot-Pech

Locust and grasshopper management involve strategies and interventions aimed at controlling and mitigating the impact these insects have on agricultural crops and pasture land. Management usually falls on a country's plant protection agency or a branch of their agricultural department. Some countries have specific departments dedicated solely to the management of locusts and grasshoppers (e.g. APLC). There are also special international and regional commissions, non-profits, and intergovernmental organizations (see the United Nations) devoted to monitoring the population dynamics, breeding patterns, and movements of locusts and grasshoppers. This is done mainly through the use of field surveys and remote sensing technologies. Once locusts or grasshoppers populations reach a level that poses a significant threat to crops, control efforts are usually put into place and involve chemical insecticides, biopesticides, and/or manual techniques.

Locust and grasshopper preventative management

©FAO/A. Monard. Exchange between decentralized National Service of Food Safety, Veterinary and Plant Protection staff and farmers and shepherds concerning presence of locusts, Dedoplistskaro area, Georgia, 18 April 2010

Widespread preventive management began in the 1960s and is currently advocated as an approach for reducing, or sometimes preventing outbreaks.[1] [2] [3] [4] [5] [6][7] This approach involves initiating treatments before pest populations escalate to devastating levels and, whenever feasible before they even reach the crops or pasture land. However, in many cases, treatments are initiated only when populations have already reached economically significant levels and crops have been damaged.[7] Although chemical pesticides are commonly used to protect crops, even their widespread application may not effectively prevent substantial harm. Preventative management requires the implementation of carefully orchestrated monitoring and targeted treatments, with a particular focus on suspected breeding areas where the formation of nymph bands, consisting of juvenile grasshoppers without fully-developed wings, is anticipated.

Challenges of preventative management

Although the implementation of enhanced preventive management systems has successfully reduced the extent and duration of agricultural damage, and the development of biopesticides shows potential as an alternative solution, there remain noteworthy obstacles to overcome when adopting any preventative practice, whether chemical-based or otherwise. Showler[8] conducted research on the desert locust and identified a number of interconnected challenges associated with preventive management that are relevant to other species of locusts and grasshoppers. These challenges include [7]:

  • Remote, rugged terrain
  • Poor roads and infrastructure, which impedes access to breeding areas
  • Political insecurity (e.g., rebellions, banditry, war, and minefields)
  • Unpreparedness (which delays detection of breeding populations and population management efforts)
  • Environmental concerns (arising from insecticide applications with associated risks to the environment and human safety)
  • Research impediments (slow progress toward developing proactive and preventive strategies)
  • Political hindrances and false assumptions around management (as most international aid agency representatives have little or no locust or grasshopper campaign experience)

Political regime shifts can lead to the discontinuation of projects, loss of organizational continuity, and the disarray of locust and grasshopper management systems.[7] Instances of this include the independence gained by African nations in the latter half of the 20th century during desert locust plagues [9], as well as the collapse of the Soviet Union in Kazakhstan in the early 1990s, which hindered the response to the 1998–2001 outbreak of Italian and Asiatic migratory locusts [10][7]. In 2018, the geopolitical situation and unusually powerful tropical cyclones in the Arabian Peninsula complicated desert locust monitoring, impeding the detection of nymphal marching bands and allowing three generations of desert locusts to remain undetected and unmanaged.[11]

Apart from direct political obstacles, a significant challenge in managing locusts and grasshoppers is the lack of consistent funding for preventive measures. [7] Numerous authors have criticized the funding pattern typical of locust outbreak management. [12] [13] [14] When a locust crisis subsides, research focus and financial resources decline, creating a gap between the problem and the generation of new ideas not to mention the maintenance of management programs.[7][12] [15] There are also disparities in the willingness and capacity of affected countries to take and sustain effective actions.[16] [17] [18] This inconsistency hampers the development of long-term, successful preventive strategies. Such instances of inconsistency have been repeatedly observed:[7]

  • Prior to the 1987–1988 desert locust outbreak, there was a reduction in funding and infrastructure support.[9] [12]
  • Due to a prolonged absence of locust swarms in the Horn of Africa region, the monitoring and response infrastructure deteriorated, leaving them unprepared for a major desert locust plague in 2019-2021.[20]

Read more about the vicious cycle of locust outbreaks

Vicious cycle Therville et al. 2021[15] and Lecoq 1991[12].

The key to addressing the challenges associated with preventive management lies in fostering collaboration, information sharing, and interdisciplinary cooperation.[7] Successfully coordinating a campaign often entails scientists partnering with government officials and decision-makers, farmers collaborating with locust and grasshopper officers, and stakeholder groups, non-profits, and NGOs working with different components of these systems. Biological research can offer valuable insights into how ecological factors influence treatments and the underlying mechanisms of these interactions. Social science also plays a crucial role in understanding the drivers of human decision-making during management programs and identifying areas where organization and preparedness may falter.

History of locust control

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The history of locust control dates back thousands of years, with evidence of early attempts to manage locust outbreaks found in ancient records and writings. One of the earliest known methods used to control locusts was manual labor, where communities would come together to physically remove and destroy locusts by hand. This method was practiced in various regions, including ancient Egypt and China, where locusts were considered a significant threat to agriculture.

Over time, different cultures developed innovative techniques to combat locusts. For example, in ancient China, the use of fires, drums, and arrows was employed to disperse and scare away locust swarms. Similarly, in ancient Rome, farmers would create noise and smoke by beating drums and burning sulfur to deter locusts from their fields.

With the advancement of civilization, new technologies and methods were introduced to manage locust populations. In the late 19th century, the development of chemical pesticides brought a significant breakthrough in locust control. In 1874, the invention of the insecticide Paris Green (an arsenic-based organic pigment) provided a powerful tool to combat locusts, leading to its widespread use in various parts of the world.

Colonialism and locust control

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The colonial era played a significant role in the history of locust control, particularly in Africa. Colonial administrations often prioritized locust control as a means to protect agricultural production and ensure the stability of their colonies. In Africa, locust control efforts were initiated by colonial authorities, and dedicated locust control departments were established. For example, the Colonial Office of the British government established the Anti-Locust Research Centre (ALRC) in 1945 to address locust outbreaks in British colonies in Africa, including countries like Kenya, Sudan, and Nigeria.

The French colonial administration also implemented locust control measures in their territories. For instance, in French West Africa, the administration established locust control services and conducted research on locust behavior and control methods. The French colonial authorities actively engaged in monitoring locust populations and organizing control campaigns to protect agricultural productivity.

Locust control efforts under colonial rule were not limited to British and French colonies. Other colonial powers, such as the Dutch, Portuguese, and Spanish, also implemented locust control measures in their respective colonies. These efforts included surveillance, research, and interventions to combat locust outbreaks and protect agricultural resources.

During the colonial period, locust control efforts were generally centralized and organized under colonial authorities. The administration would establish dedicated locust control departments or institutions to address locust outbreaks. These departments were responsible for monitoring locust populations, conducting research on locust behavior and control methods, and implementing control measures when necessary.

Colonial powers introduced modern technologies and methods for locust control. The use of aircraft for aerial spraying of insecticides became more widespread during this time, enabling more extensive coverage of locust-infested areas. Colonial authorities also invested in research and development to improve the effectiveness of control measures, including the development of new insecticides and the implementation of systematic monitoring and reporting systems.

Some argue that the primary focus on protecting colonial interests often resulted in neglecting the welfare and needs of the local populations affected by locust outbreaks. Additionally, the extensive use of chemical insecticides during this period raised concerns about the environmental and health impacts of these interventions.

20th century

During the 20th century, as scientific understanding of locust biology and behavior improved, more targeted and efficient control methods were developed. The use of aircraft for aerial spraying of insecticides became a common practice, allowing for broader coverage and faster response to locust outbreaks. Additionally, the development of synthetic pyrethroids in the 1970s and 1980s provided more effective and environmentally friendly insecticides for locust control.

International cooperation and coordination in locust control became increasingly important after World War II and the dissolution of European empires. To address this challenge, the establishment of the Food and Agriculture Organization of the United Nations (FAO) in 1945 introduced a collaborative global framework. Throughout the 1950s the FAO helped set up the Desert Locust Control Committee (DLCC) to promote international locust control cooperation. Since 1955, the FAO ensures the coordination of desert locust monitoring and control activities and plays a major role in the early warning system through its Desert Locust Information Service (DLIS) (managed by the ALRC in London from 1943 to 1978, then by the FAO in Rome).[7] International monitoring, control, and cooperation were gradually implemented, and international organizations were set up for the permanent survey. [21] [22] [23] [9]

During the post-world-war period, in the 1950s and 1960s, similar regional organizations and initiatives were established in other parts of the world to enhance collaboration in monitoring, research, and control efforts.[7]

Jump to history of locust phase change research

Current management techniques

©FAO/Sven Torfinn 31 March 2020 Lewa Wildlife Conservancy airstrip, close to Isiolo, Isiolo county, Kenya. Pilot from Orsmond Aviation, South Africa based company, ready for take off on mission to do aerial spraying.

Chemical control

Chemical control has been widely employed in the management of locusts and grasshoppers. Various methods and insecticides have been utilized to mitigate their populations and minimize agricultural damage. One common approach is the aerial spraying of insecticides, such as organophosphates and pyrethroids, over infested areas. These insecticides effectively target and kill the insects, reducing their numbers and curbing their destructive feeding behavior. Ground-based applications of insecticides are also utilized, especially in localized outbreaks or areas inaccessible to aerial spraying. In recent years, the development of more selective and less environmentally harmful insecticides has gained attention to minimize the impact on non-target organisms.

Baiting

Baiting has been historically used as a method of locust control. Prior to the 1950s, baiting was a popular approach for managing locust infestations. The technique involved mixing insecticide dust with a carrier substance, such as maize meal or wheat bran. The bait mixture would then be spread among or in the path of the locusts. Baiting was considered effective in attracting locusts to the treated areas and poisoning them upon ingestion. It was particularly useful for controlling locust swarms and targeting settled hoppers and adults. However, this method presented several challenges. The significant amount of work involved in preparing, transporting, and applying large quantities of bait was a notable drawback. For instance, it required applying approximately 5-15 kg of bait per hectare for marching bands and over 50 kg per hectare for settled hoppers and adults. Another concern with baiting was the potential risk it posed to non-target organisms, including livestock that might consume the bait. These factors, along with advancements in other control methods and technologies, have led to a decline in the use of baiting in recent years.

Historically, arsenic-based compounds, such as calcium arsenate and lead arsenate, were used in bait formulations for locust control. These formulations were effective in poisoning and eliminating locusts. However, the use of arsenic-based compounds in agricultural practices has significantly declined due to concerns over their environmental and health impacts. Arsenic is a toxic substance, and its accumulation in soil and water can have detrimental effects on ecosystems and human health.

Dusting

Dusting is a method that involves mixing pesticide dust with a substance like powdered chalk or talc and scattering it onto locusts. Similar to baiting, dusting offers the advantage of not requiring specialized application equipment, as a hessian bag filled with dust and beaten with a stick has often been used. However, the use of dusting has diminished in many countries due to certain drawbacks. One challenge is the significant amount of product that needs to be transported and applied, which can reach up to 10 kg per hectare. Additionally, control efficacy can be inadequate, particularly when dealing with later-stage hoppers and adult locusts. Another concern associated with dusting is the health risk posed to operators who might unintentionally inhale the dust. These factors have led to the decreased adoption of dusting as a primary locust control method in recent years.[24]

Spraying

Spraying is widely recognized as the predominant method employed for locust control. This approach entails the utilization of a sprayer to transform a liquid pesticide into fine droplets, which are subsequently dispersed across the designated area. The subsequent pages provide further details on various types of spraying techniques utilized in locust management.[24]

Water-based spraying

Water-based spraying is a common practice in conventional agricultural crop protection. It typically involves the application of large volumes of insecticide/water mixture per hectare, often amounting to hundreds of liters. The insecticide formulation used in water-based spraying is usually an emulsifiable concentrate (EC), although other formulations such as wettable powder (WP) may also be used.[24]

However, when it comes to combating desert locusts, water-based spraying is seldom implemented on a large scale. This is primarily due to the low work rate, which refers to the number of hectares that can be treated per hour. Additionally, finding sufficient volumes of clean water in most desert locust habitats presents a significant challenge.[24]

Ultra low volume (ULV) spraying

The technique of ultra-low volume (ULV) spraying, which utilizes significantly smaller amounts of spray liquid, emerged in the 1950s specifically for combating the desert locust. Over time, it has become the most efficient and widely adopted method for locust control. ULV spraying involves the application of spray liquid at a rate ranging from 0.5 to 5.0 liters per hectare, with a preference for 0.5 to 1.0 liters per hectare in ULV locust control.[24]

Unlike other spraying methods, ULV spraying does not require mixing a concentrated insecticide with water or any other liquid. The insecticide formulation, known as a ULV (or UL) formulation, is typically supplied in a ready-to-spray state, eliminating the need for additional mixing or dilution.[24]

To effectively disperse such small volumes of spray liquid, it is necessary to break the liquid into tiny droplets that are light enough to be effortlessly carried by the wind. In locust control operations, where hot weather conditions are common, it is crucial to prevent these small droplets from evaporating too quickly. Hence, ULV formulations used in such scenarios are oil-based, as opposed to solvents like water or petrol fractions, which tend to be more volatile and prone to rapid evaporation. The use of oil-based formulations helps to ensure that the sprayed droplets remain stable and effective for an extended period.[24]

The small droplets generated in ULV spraying have a tendency to remain airborne and do not readily deposit on surfaces. Due to their slow descent, they are more likely to be carried laterally by the wind rather than settling on horizontal surfaces like rain. Additionally, when the droplets are too small or the wind is too gentle, they have a tendency to bypass objects rather than collide with them, resembling the behavior of smoke (refer to Fig. 3A).[24]

However, when the droplets are of an appropriate size and there is sufficient wind, they can effectively deposit through impact onto vertical surfaces, such as vegetation or locusts. The impaction of these properly sized droplets allows for targeted deposition.[24]

Locust pesticide list

Mechanical control

Mechanical control methods refer to manual practices like digging trenches or using branches to beat hoppers. Digging or plowing up locust eggs in the soil is another approach, but it is labor-intensive and challenging to locate all the locust egg beds without accurate information about previous swarm laying sites. Read more at about edible insects and locusts as more than pests

Biopesticides

Biopesticide methods have proven to be effective in locust control, offering environmentally sustainable alternatives to traditional chemical pesticides. One prominent approach involves the use of entomopathogenic fungi, such as Metarhizium, which infect and kill locusts. Biopesticides containing Metarhizium are typically applied as conidia (spores) in various formulations, including oil, oil-water emulsion, or dry formulations. These formulations are strategically deployed in locust habitats, targeting areas where locust populations are concentrated or during specific stages of their life cycle. Once applied, the Metarhizium conidia adhere to the locusts' bodies, penetrate their exoskeletons, and subsequently infect the insects internally, ultimately leading to their demise. This method provides a targeted and environmentally friendly solution for managing locust populations, reducing the reliance on conventional chemical pesticides and minimizing potential harm to non-target organisms and ecosystems.

View full biopesticide page

Land management strategies

In contrast to the common conception that herbivores are limited by nitrogen and protein [25] [26], many locusts prefer and grow best in low nitrogen environments harboring plants with low protein and high carbohydrates.[27] When soils are depleted through heavy livestock grazing or continuous agriculture, studies are seeing a link to the occurrence of locust outbreaks [28] [29] [30] [31] [32]. Therefore, it is possible to indirectly manage locusts through soil amendments. More nitrogen in the soil translates to plants higher in protien and less likely to fuel locust growth and migration.[31]

Read more on locust ecology

Check out these guides to sustainable locust management

Read about regional practices in locust management by exploring the geography pages

References

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