Discover the characteristics of the grasshopper Schistocerca cancellata

The term locust is used to refer to some species of acrylids capable of forming "swarms" or "clouds" under certain conditions (climatic and food), with the ability to move across large areas, causing damage to crops and/or natural vegetation. Among these species is Schistocerca cancellata (Serville 1839), known as the South American locust, a pending pest in Argentina due to its history since the late 1890s. In Argentina, this pest has been classified as a national pest and is under official monitoring and surveillance. There is a national program, which defines strategies and guidelines for its management, corresponding to the National Service for Health and Agri-Food Quality (SENASA), called the National Acricids Program. Establishes mandatory reporting and the execution of control tasks by producers, owners and tenants of agricultural establishments. INTA monitors the program's actions and collaborates with works in the territory, through training and dissemination of information on the characteristics, life cycle, behavior and management of this species of agricultural interest, due to the damage it can cause. 

FAVORABLE CONDITIONS FOR DEVELOPMENT

As predisposing conditions for this species to reach pest status, it is possible to mention benign winters (high temperatures in winter) and adequate rainfall, which can allow the development of up to three generations per year. Locusts, in their permanent breeding environments, reproduce as long as soil, climate and flora conditions are favorable  and they find food available. When contexts change and become unfavorable, the population migrates forming clouds, made up of thousands and thousands of individuals. In breeding areas, rain normally occurs from November to March-April, allowing the development of two annual generations: 1 - spring, short and quick, and 2 - longer summer, in which adults spend the winter in reproductive diapause until maturity. first rain of spring.

BIOLOGY AND ECOLOGY

The gender Schistocerca It is polyphagous and can devour more than 400 species of plants. The particularity of grasshoppers lies in their ability to change their behavior and physiology (color, size and shape) in response to changes in population density, going from a solitary to a gregarious state and vice versa. Apparently, when large groups of individuals of the same species come together, they release appropriate hormones to activate their migratory behavior, develop greater wing growth and thus be able to disperse to other territories, thus avoiding intraspecific competition for food. This ability to actively gather, form clouds and disperse (up to 150 kilometers per day with favorable winds), added to its voracity, poses a great threat to all agricultural activity in the country. Knowledge of the life cycle and morphological characteristics of each stage allows appropriate management and decision-making to control it.

SITUATION IN ARGENTINA

History and current events

Its distribution area covers Central and Northern Argentina (see map), Uruguay, Paraguay, Southern Brazil, Southeast Bolivia, Central and Northern Chile. The area of ​​origin of the demographic explosions (“outbreak area”) extends from the Center-Southeast of Catamarca and La Rioja, to the East of San Juan, to the North of San Luis and Córdoba and to the Southwest of Santiago del Estero (see map) . When locusts reach high population densities, they enter the gregarious (grouped) phase and migrate in clouds to new areas, which is how they can move great distances.

In Argentina, the first records of locust control date back to the mid-19th century, a phenomenon that continues today in several provinces. The invasion recorded in 1932-1933 was considered one of the largest in the country. It came to occupy more than 152 million hectares, that is, more than half of the country's surface. At that time, little was known about pest control and control procedures. Physical barriers (plates, ditches, trenches, etc.) were used around field perimeters to prevent entry of locust nymphs.

In 2010, a phytosanitary emergency was declared throughout the national territory due to the detection of outbreaks in different areas of the provinces of Catamarca, La Rioja and Córdoba.

In 2015, there were records of a locust cloud that caused problems in the province of Santiago del Estero, southeast of the province of Tucumán and Catamarca; Damage was recorded in forests, natural grasslands and, to a lesser extent, in agricultural areas.

In 2017, clouds of locusts were initially recorded in Formosa, then in Chaco, Santiago del Estero, Córdoba, Tucumán and Northwest of the province of Santa Fé. In this province, in 2017, the mango was concentrated on the 28th Parallel, in the area known as Tres Mojones, a sector included in the vicinity of the limits of the three provinces, Santa Fé, Chaco and Santiago del Estero.

Currently, a cloud of locusts returned to Argentina between the end of May and the beginning of June 2020, coming from Paraguay. This cloud crossed the provinces of Formosa, Chaco, Santa Fé, to settle in the province of Corrientes, where it remained from June 19, 2020 until the first days of July 2020.

THE PLAGUE IN URBAN ENVIRONMENTS

These insects only feed on plant material, do not transmit diseases or cause harm to humans or animals, that is, they do not pose a health risk to the city's populations. This pest feeds on any type of plant material and, therefore, generates an economic impact in rural areas, attacking crops, pastures and forests.

MONITORING AND CONTROL

Preventive management of this pest involves permanent monitoring and control. Early detection is essential for proper management. Continuous monitoring should be carried out in locations where clouds have been established, as well as flight paths, oviposition zones, emergence areas and/or the presence of juvenile stages.

Early identification of outbreaks and pest control will contribute to the effectiveness of their management. The opportune time to control this pest is in the nymph stage (juvenile, as it has not yet developed its wings); At this stage, it moves at ground level in the form of jumps, without moving across large territories. Laying sites must be monitored periodically to check for births. Weeds or crop residues are often used to guide monitoring. Chemical control, at this stage, would make it possible to reduce the population density of individuals that can later fly in the form of clouds, avoiding damage to natural vegetation and agricultural crops. In the adult state and in the gregarious phase, they can also be treated by making applications when the cloud is settled. This control requires monitoring the clouds during the day, until the place where they land in the afternoon/night. Controls can be carried out by air or land, manually, using backpacks or using sprayers and cannons.

Products for chemical control of this species must be registered and authorized by the competent authority and, when carrying out treatment, the lowest possible environmental impact must be guaranteed to all non-target control organisms, such as urban locations, apiaries, water reserves, etc. This also implies coordinated actions between organizations such as SENASA, Provincial Ministries of Production, Colleges of Agricultural Engineers, INTA and agricultural producers in the region involved.

Sources for more information in Argentina

SENASA

 http://www.senasa.gob.ar/caden...

acridios@senasa.gob.ar

“Senasa Alerts” App

INTA

https://www.argentina.gob.ar/i...

https://inta.gob.ar/sanidad-ve...

 

Daniela Vitti, Diego Szwarc and Melina Almada, INTA, Reconquista, Santa Fe. Argentina