Locust cloud monitoring and control measures

A dense cloud of locusts Schistocerca cancellata movement in neighboring Argentina put Brazilian authorities on alert in June. It was the first time in the last 70 years that the pest was so close to the border with the South of the country. The occurrence led the Brazilian government to declare a phytosanitary emergency in the states of Rio Grande do Sul and Santa Catarina. With the capacity to move up to 150 kilometers per day, each square meter occupied by the locust cloud represents thousands of voracious insects, with an appetite to devour vegetables in a volume equivalent to 35 thousand people or up to two thousand cattle.

Entomologist Milton Souza Guerra, who passed away in 2015, already warned about the risk of locusts at the beginning of 2000. He said that the next wave would come from the West, as the Chaco region met many conditions for proliferation and that there was an important population of this type. insect just waiting for some circumstances that would trigger the pest level.

This is not the first time that the insect has appeared in Argentina. Data from the National Health and Food Quality Service (Senasa), which maintains a pest control program, shows that locusts have been causing damage in the country since 1538, when they devastated cassava plantations in the province of Buenos Aires.

During the first half of the 20th century, the migratory grasshopper (Schistocerca cancellata Serville) was the most harmful in Argentina, responsible for economic losses in crops and natural fields, in large regions.

This led Argentina to adopt different control strategies over the years (Box). More recent outbreaks were also recorded in 2010, 2015 and 2017.

The outbreak in 2020

On June 17, 2020, the locust cloud entered the territory of the province of Santa Fé, in Argentina, after having been reported days earlier in the provinces of Chaco and Formosa, in Paraguay. The insect's distribution area includes Paraguay, Bolivia and Brazil, in addition to Argentina (in the Center and Northwest) in provinces such as Córdoba, Santiago del Estero, Catamarca and La Rioja.

Since then, the National Health and Agro-Food Quality Service (Senasa) has carried out several monitoring and spraying actions and announced that it had managed to reduce the locust population. In the first days of July, part of the remaining cloud remained in the department of Curuzú Cuatiá, province of Corrientes, approximately 140 kilometers from Uruguaiana, in Rio Grande do Sul.

Depending on climatic and environmental conditions for dispersal over long distances, the strong cold recorded in the region favored the insects' permanence on Argentine soil.

Since the detection of the latest outbreak in Argentina, the Ministry of Agriculture, Livestock and Supply (Mapa) and state secretariats in southern Brazil have adopted emergency measures and monitor the situation at the border, in contact and cooperation with health authorities in the neighboring country.

Mapa prepared a technical manual with guidance on actions to control the South American locust. The publication, adapted to Brazilian conditions, is supported by scientific data, with training of agents involved in a possible outbreak of the plague in the country.

The material has as references the National Service for Health and Agri-food Quality (Senasa) and the Food and Agriculture Organization of the United Nations (FAO). It informs how to carry out monitoring, the stages of the pest, identification, preventive treatment and general guidance on the use of agrochemicals.

MAIN GUIDELINES OF THE MAPA TECHNICAL MANUAL

It is one of the few species of Schistocerca which truly form dense migratory “clouds”. The wings are lacy and the general coloring involves different shades of brown.

The great migratory tendencies of this Orthoptera leave room for doubts about their real distribution status. Records indicate that Schistocerca cancellata it is adapted to the arid and semi-arid regions of Bolivia and Paraguay. When favorable weather conditions exist, successful breeding occurs, followed by the formation of clouds that can migrate to cultivation regions.

MONITORING AND CONTROL

Monitoring must be carried out in places where locusts with eggs have been recorded. Observe whether there are holes in the ground and confirm the presence of eggs (attention: sometimes there are signs that eggs have been laid, however, the eggs may not have been deposited). An adult grasshopper can lay more than once, approximately between 80 eggs and 120 eggs per clutch.

Control at egg instar is generally complex. In most cases, laying sites must be identified for monitoring and early detection of births and subsequent spraying with insecticides registered on the Map. Only in specific situations can the soil be mechanically turned over to expose the eggs, causing loss of viability.

NYMPHS

Grasshoppers in the juvenile stage, that is, nymphs, do not have the ability to fly, therefore, monitoring is at ground level. Laying sites must be monitored periodically to check for births.

Weeds or damaged crops are often used to guide monitoring. Control of juvenile stages can be carried out on land, and can complement actions by air in certain situations that allow control to be effective ("open locations").

The presence of non-target organisms must be considered when choosing the most appropriate method. Births occur staggered, which must be taken into account when controlling, and the use of insecticides can be effective in certain situations.

COMPARISON OF NYMPHS

Researchers raised locust nymphs in the laboratory, in isolated conditions and in groups. Resulting differences in coloration can be clearly seen.

In the first stages, individuals are more sensitive, this is when they are more densely grouped and there is natural mortality. In general, control at this stage is more effective, with a significant percentage of mortality. Phytosanitary control carried out using knapsack sprayers, boom sprayers and/or atomizers is effective for this work.

PREVENTIVE TREATMENT IN BANDS

Due to the mobility of the pest, it is possible to apply insecticides in bands, as this will considerably reduce the surface to be treated, reducing the environmental and financial impact, in addition to optimizing time. As the nymphs move forward in groups, they will encounter the treated strips, thus avoiding full coverage application. Although the movement of locusts may be irregular, treatment should be carried out perpendicular to the advance of the pest.

Each strip must be approximately 30 meters, if the application is carried out with the wind, or 50 meters if it is against the wind. The distance between the stripes depends on the movement of the pest:

If the pest is already installed in a crop, active ingredients with faster acting power should be used to obtain effective control, and a combination of active ingredients may be used.

ADULTS

Adults can be treated by air or by land using cannon-type atomizers. Application with the locust cloud spatially located is recommended.

Aerial control requires monitoring the “clouds” of locusts during the day, until the location where they land in the afternoon/night. At this time, the surface where the pest is located must be estimated and a polygon marked so that the application can be carried out the next day, first thing in the day. Therefore, there is a reduction in the surface to be treated, less environmental impact, lower application costs and less risk for the applicator.

Early application prevents pest movement due to temperatures. It is necessary to have excellent work coordination and have the necessary supplies, as the decision time is very short, as is the application window.

History of control strategies in Argentina

Defensive struggles (1897 to 1940): at this stage there were no known "fighting" procedures with positive results to control the plague and avoid its socioeconomic damage. The use of physical barriers to prevent the spread of the pest in the nymphal stages was very common.

Offensive struggles (1944 to 1954): characterized by the partial incorporation of synthetic products, but the high density and great dispersion of the pest exceeded the possibilities of control. During this period, locusts seriously affected a large part of the country.

Preventive fights (since 1954): preventive treatments are currently carried out to control the density of the pest. The methodology focuses on detecting and controlling incipient outbreaks of the juvenile stages of the pest. The strategy focuses on continuous prospecting, monitoring and control of outbreaks framed within a holistic view.

About the plague

Scientific name: Schistocerca cancellata Serville

Other scientific names:

Acridium cancellatum;

Schistocerca americana paranensis;

Schistocerca paranensis (Burmeister).

International common names:

Spanish: esperanza; flying lobster;

EPPO code: SHICCH (Schistocerca cancellata).

Taxonomic Tree:

Domain: Eukaryota

Kingdom: Metazoa

Phylum: Arthropoda

Subphylum: Uniramia

Class: Insecta

Order: Orthoptera

Family: Acrididae

Genre: Schistocerca

Species: Schistocerca cancellata

General recommendations - Chemical control

• Use agrochemicals indicated by the Map in a specific act.

• It should not be applied during times of high temperatures, as in these conditions air currents occur that move the insecticide away from the surface to be treated and evaporation is greater. The instars of the pest must be taken into account to achieve good control and consider a margin of time between one application and another.

• Post-treatment mortality needs to be checked to assess its effectiveness.

• In the case of spraying with insecticides, the label of the phytosanitary product purchased must be carefully read in full, in order to respect the precautions and recommendations for its use.

• In case of spraying with insecticides, use personal protective equipment (PPE).

• The application of the phytosanitary product and the final disposal of product remains and empty packaging must be carried out in accordance with current federal and state legislation.

The full Manual of General Procedures for the Control of the Schistocerca cancellata pest is available at here.