Bioinputs for biological control of sugarcane insect pests

Sugarcane cultivation is of great importance to the Brazilian economy and has expanded in different regions of the country. This reduces natural barriers such as native vegetation, allowing the appearance or increase of different insect pests. Ideally, integrated management of these pests should be carried out. And biological control is one of the methods that is part of this integrated management. It consists of pest control using natural enemies, which we can call bioinputs, to keep the population levels of these pests in balance, without causing economic losses to the rural producer.

Fortunately, the sugarcane crop in Brazil is one of the crops that uses biological control the most. Currently, some type of biological pest control is used on 4,5 million hectares of sugarcane. In the 2022/23 harvest, 8,13 million hectares of sugar cane are being cultivated in Brazil. The state of São Paulo stands out as the largest producer, followed by Goiás and Minas Gerais.

There are several insect pests that attack sugarcane. Among them, the cane root leafhoppers stand out. Mahanarva spp, the sugarcane weevil Sphenophorus levis and the sugarcane borer Diatraea saccharalis. In addition to these, there is an attack by leaf-cutter ants of the genus Atta (saúvas), which has also caused damage to sugarcane fields.

Both the nymphs (young form) and the adults of sugarcane root sharpshooters suck the plant's sap, and the adult, in addition to sucking, injects a toxin into the leaves, causing yellowing of the leaves and drying of the tips, decreasing sugarcane productivity between 15 and 80% per hectare, depending on the intensity of the attack.

The bioinput most used to control sugarcane leafhoppers is that produced based on the fungus Metarhikum anisopliae. This fungus has been used in Brazil since the 1970s. Over time, new, more efficient strains of this fungus were selected and produced on a larger scale, in addition to an evolution in the formulation of bio-inputs and field application techniques.

The oldest formulation is the granulated one, with the fungus developed in the rice grains and which can also be washed to separate the fungus spores from the grains and be applied through tractor sprayers or through agricultural planes, with the addition of a spreader. sticker. The other formulation is the wettable powder type, which is composed of pure, dry spores mixed with some inert material to give greater volume. It is mixed with water and also applied with the help of tractor sprayers or agricultural planes.

The third type of formulation is that which uses emulsifiable adjuvant oil. It is called an oily dispersion or even an emulsifiable or concentrated suspension. This formulation has several advantages such as: greater efficiency in killing the targeted insect pest; greater adhesiveness on the foliage and body of the insect pest; greater protection of spores against ultraviolet radiation; less evaporation of the applied solution; greater spread on the foliage and body of the insect pest, which increases the area of ​​contact with the pest; longer storage time at room temperature; and ease of transport and application. It is also applied using tractor sprayers or agricultural planes.

The cane weevil Sphenophorus levis Perhaps it is currently the main sugarcane pest, especially in the state of São Paulo. It works as follows: after mating, the females pierce the healthy tissues of the sugarcane rhizome with their jaws, at the base of the shoots, below ground level. They insert the eggs individually up to four mm inside the stalks. This causes losses of 20-30 tons of sugarcane per hectare/year and reduces the longevity of the sugarcane field. The level of economic damage is a maximum of 3% of stumps attacked. Sugarcane fields with more than 30% of stumps attacked will be repaired immediately. The most used bioinput to control this pest is the fungus beauveria bassiana which can be purchased in different formulations and applied with tractor-driven equipment called a ratoon cutter or with spray bars with hydraulic nozzles on pendants along the sugarcane line.

Another important pest in sugarcane cultivation is the sugarcane borer Diatraea saccharalis. This pest can cause direct and indirect damage to sugarcane cultivation. Direct damage: causes interference with the growth of shoots and tillers, death of buds, toppling of plants, drying out of tips (dead hearts), formation of lateral shoots and aerial rooting. The bioinputs used to control the sugarcane borer are based on wasps parasitic on the borer or egg parasites of the sugarcane moth. Diatraea saccharalis. The wasp cotesia flavipes It is used in more than 4.000.000 ha of sugarcane fields to control the sugarcane borer, where it parasitizes in the caterpillar stage.

Monitoring of Diatraea saccharalis moths is done using a pheromone trap with females and female pupae. Cotesia releases must begin 21 days after the detection of 10 males in 30% of the traps. There are three releases spaced seven days apart at a dose of eight tubes/ha. Each tube contains 15 masses with 50 individuals, giving a total of 750 wasps per tube, or 6.000 wasps/ha.

Now the wasp Trichogramma galloi It is a parasite of moth eggs. Diatraea saccharalis. Moth monitoring is also carried out with pheromone traps with females and female pupae. Releases must begin when 10 males are detected in 30% of the traps. There are three releases spaced seven days apart (the first after five days of reading the trap) and the dose is 50.000 individuals per hectare. The release of these two wasps in the sugarcane field is currently done using drones, which provide a more efficient distribution of this type of bio-input in the field.

New bioinput - Leaf-cutter ants or fungus-growing ants represent one of the most evolved groups of insects in the world. Living in large colonies (anthills) where they cultivate and feed on a mutualistic fungus that develops on the most diverse plant substrates gives these insects polyphagy, protection and food availability all year round. These ants occur throughout the American continent, especially in tropical and subtropical areas, which includes the entire Brazilian territory. In sugarcane cultivation, an adult sauveiro can cause a loss of 3,2 tons of sugarcane/ha. In pastures, in the Cerrado, 10 five-year-old sauveiros occupy an area of ​​715 square meters and consume around 21 kg of grass per day, which is equivalent to the consumption of an ox.

Due to the importance of leafcutter ants, several control methods have been developed, including the use of toxic baits, thermofogging and dry powders. Toxic baits are the most used due to their practicality where the ants themselves carry toxic substrates into the nest. The main problem with using chemical baits is related to the contamination of applicators and residues that can persist in the environment for many years, contaminate groundwater and be assimilated by cultivated plants, animals and even man himself.

Due to this reality and, as there is no truly biological bait on the Brazilian market to control leaf-cutter ants, Embrapa Cerrados decided to invest in research in search of an efficient biological alternative for controlling leaf-cutter ants in sugarcane. The process used to develop biological baits involves a production line for bait masses in the final format for use and a production line for highly virulent fungal spores that will be incorporated into the baits already mentioned. Once ready, the bait is easy to apply, is non-toxic to the environment, food and humans and can be used in different Brazilian crops.

Among the main advantages are that this biological bait is non-toxic to the environment, food and humans; they can be used in both organic crops (which is a constantly growing market) and conventional ones; can be used in annual crops (soybeans, corn, cotton, beans, wheat, vegetables, etc.), perennial crops (reforestation, fruit trees, rubber trees, etc.), semi-perennial crops (sugar cane, cassava, etc.) or in parks and public or private gardens without any problems.

These bio-inputs can be found in the Mapa/Embrapa application called BioInsumos, available free of charge on the Google Play / Play Store and Apple Store platforms.

By Roberto Teixeira Alves, researcher at Embrapa Cerrados