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Agronomy

Spittlebug attacks

Biological control kills the insect that has become a pest due to the mechanized cutting of the sugarcane

MIGUEL BOYAYANThe spittlebug injects toxins into the leaves and damages the plant’s photosynthesis capabilityMIGUEL BOYAYAN

The gradual restriction towards the burning of the sugarcane stock for harvesting, now determined by a state law, has had as an immediate effect the reduction of the amount of carbon dioxide released into the atmosphere, a considerable environmental and public health relief for the people who live in the sugarcane municipalities of the state of São Paulo. However, the change in the harvesting system, with the consequent adopting of mechanized cutting, allowed the proliferation of new pests to this crop, such as the Mahanarva fimbriola known in Brazil as the cigarrinha-da-raiz (root spittlebug).

Without the burning, which also kills off the insect, these sharpshooters found a favorable environment to live in the organic material accumulated in the soil. The damage done by this little insect, which measures close to one centimeter, is devastating for the largest and most important agro-industrial crop in the state, responsible for an annual production of 148 million tons of raw material, transformed into 9.6 million tons of sugar and 6.4 million cubic meters of alcohol.

In order to control this pest and other natural enemies of sugarcane and also to evaluate the resistance towards the herbicides used during growing, a group composed of twelve researchers has been working since May of 2000 on a thematic project, financed through FAPESP, which has already yielded promising results. Coordinated by professor Antonio Batista Filho, the director of the Experimental Center at the Biological Institute, an organ linked to the São Paulo Agency of Agribusiness Technology of the Secretariat of Agriculture and Supplies of the State of São Paulo, located in Campinas, the group is working with a bio insecticide based on the fungus Metarhizium anisopliae, a pathogen for the sharpshooter, which shows great efficiency in the elimination of this insect.

The technology has already been passed on to four laboratories in the state, established and installed in sugarcane production municipalities: Biocana (Pontal), Biocontrol (Sertãozinho), MethaVida (Catiguá) and Usina Univalem (Valparaíso). The natural insecticide will also be manufactured by Usina Delta, in the town of the same name, in the state of Minas Gerais. All of them will have the support of the Experimental Center at the Biological Institute.

“The action of this bio-insecticide has shown itself to be highly efficient against the nymph (which are the young forms of the sharpshooter), mainly after successive applications”, professor Batista explains. “A good part of the insect population is eliminated during this phase, considered strategic for control.” Batista emphasizes that chemical insecticides have similar performances, or even better in some cases, but cost up to ten times more and cause environmental damage. The cost per hectare with conventional agricultural insecticides is around R$ 150,00 while control using the fungus comes in at R$ 15,00.

The life cycle of the sharpshooter begins with the start of the rainy season, between September and October. The eggs, buried in the soil, give origin to the nymph that live for around fifty to sixty days. Shortly after leaving the egg, they move to the base of the sugarcane and get enveloped in a froth produced by themselves, for their protection, whilst sucking the plant’s sap to feed themselves until their adult phase, when they can fly, breed and generate new eggs.

The adults cause damage by injecting toxins into the leaves, thus interfering in the capacity of the plant’s photosynthesis .The loses can reach as much as 60% in the sugarcane plantation, without taking into consideration the damages in industrial production, due to the reduction in the level of sucrose in the sugarcane. The attack, which can go on as far as a third generation, only ends in March, when the drier season begins. From this moment on the sharpshooter places its eggs in the soil, and they will remain there awaiting the humidity of another humid season, when, once again, a new colony will start up.

Natural control
The studies for the multiplication on an industrial scale of the Metarhizium anisopliae fungus started in the Northeast region of the country some thirty years ago, when the sugarcane producers began to suffer loses with the spittlebug (Mahanarva posticata). The observations that led to the bio-insecticide were carried out in Campos (RJ), where the insect was found in the sugarcane plantations, but did not cause problems because it had been associated to a pathogen entrusted to natural control, the Metarhizium.

The work developed by the Biological Institute in partnership with the Luiz de Queiroz College of Agriculture (Esalq), of the University of São Paulo (USP), and the Center of Agrarian Sciences of the Federal University of São Carlos (UFSCar), involved tests with new strains of the fungus, more aggressive, in different regions of the state, as well as studies with other pathogenic agents that might be incorporated into the control.

One of these work stages for choosing the most efficient fungi, which is still on going, involved tests with eighty strains, of which the best eight were chosen. They are now being tested in the field at the Cerradinho Mill, by Elisangela de Sousa Loureiro from the São Paulo State University (Unesp), at the Botucatu campus, who is working on her doctorate and being supervised by professor Batista. Another experiment linked to the group is being carried out at UFSCar. The master’s degree student, José Francisco Garcia, studying entomology at Esalq, under the supervision of professor Paulo Botelho, of UFSCar, is developing a system for the creation, in the laboratory, of the spittlebug, guaranteeing insects for studies that involve the behavior and the biology of the insect.

The importance of all of this work is in the fact that sugarcane represents almost 30% of the total gross income of agriculture in the state of São Paulo, higher than the value of the production of meat cattle and of the various more important fruit, such as oranges, grapes and tangerines. For this reason the Projeto Cana (Sugarcane Project), as the thematic project is known as by the researchers, will be going even further with experiments dealing with the biological control of the pest. The choice of the most aggressive fungus in combating the spittlebug is only one of the ways. It will be necessary to find the most efficient formula and the best way of applying the fungus.

“The observations carried out up until this moment show that the ideal period to begin biological control are the months of October and November”, explains Batista. During this period, when the average infestation of the sharpshooter is around 0.1 to 0.5 per square meter of sugarcane, considered small, it is much easier to break the cycle. “The problem is that, since the sugarcane is very short, the incidence of solar light is high and the ultraviolet rays kill the fungi”, underlines the researcher José Eduardo Marcondes de Almeida, who also makes up part of the Biological Institute team. The recommendation is that the application should be done in the late afternoon, because darkness and humidity favor the action of the Metarhizium.

The ideal dose per planted hectare, determined through tests carried out at Esalq, is between one and two kilos of fungi. This product is cultivated on rice from which it is extracted, washed and sieved. The field experiments were accompanied by sugar mill workers from the Cosan Group, in the town of Valparaíso (SP); from the Guarani Mill in Olímpia (SP); and from the Cerradinho Mill in Catanduva (SP), who verified the results. The traditional fungus is produced on rice, but the team has studied new methods of cultivating and application. According to Almeida, still as part of the project, they intend to study recipes that give better protection to the fungus, based on oil, as it has already happened with herbicides, so that the application can be carried out during the day.

For the time being, rice is the only crop that has been commercially explored to produce the fungus, but other compounds, such as sugarcane yeast and beer yeast associated to sugars such as dextrose (from corn), may offer excellent conditions for industrial scale production. The researchers are also beginning experiments with water and liquid protein. “We began testing by way of a liquid culture because the risk of contamination through a solid culture, such as rice, is very high plus the fact that it involves a very large volume to work with”, explains Almeida. Only over the period of 2001 to 2002, the São Paulo companies made use of more than 25,000 kilos of rice to produce the Metarhizium fungus, which represents an area of sugarcane of around 20,000 hectares. The application of the bio-insecticide is carried out by tractor, when it is still possible to enter into the plantation, or by aircraft.

Double efficiency
Another pathogen, studied by the group, which shows high efficiency towards soil pests are nematoids, small worms that look like earth worms. In the laboratory they can eliminate 100%, but their production is much more expensive than that of the Metarhizium fungus because in general they are produced using animal protein as a substrate. The research carried out tests of various alternative cultures and economic possibilities. According to the researcher Luís Garrigós Leite, the nematoid worms have the capacity to search out their host by using chemical receptors located on their head.

When they are applied to the soil, they can move themselves about from up to a distance of thirty centimeters, attracted by the carbon dioxide gas emitted by the spittlebug. Furthermore, they work in association with a bacterium, which they carry in their intestine. Thus when they penetrate their host, they liberate the bacterium, which swiftly multiplies and in twenty four hours kills the insect. During this phase, the nematoids feed themselves on the bacterium together with the content of the insect. In order to obtain the nematoids by artificial means, the one hundred most aggressive were selected from two strains for tests that will be carried out in the field during this year.

One of the research lines of the thematic project, conducted by Flávio Martins Garcia Blanco, also from the Biological Institute, is to study the interaction of the Metarhizium fungus with herbicides applied to the soil to kill off weeds, such as sedge, known for the speed with which it can invade crop areas. This plant damages the growth of the sugarcane because it fights for the available water, space and nutrients. In the evaluation done by biologist Blanco, the ideal situation is to use defensive chemicals at least twenty to thirty days before the fungus, so as not to interfere in the biological control.

The studies also discovered that the persistence of the herbicides in the soil and the effects of their permanence. “The results show residues in the field up to six hundred days after the application of a herbicide based on sulfentrazone, widely used to combat sedge, a period of time much greater than that necessary to avoid the appearance of the weed”, Blanco explains. “If it is in the soil, it can contaminate rivers and wells.” Blanco emphasizes that chemical defense needs a residual period, but not so extensive. Before this research, the only available data to understand the behavior of herbicides was from studies of other plants in other countries, which do not reflect the conditions of climate, soil and microorganisms of Brazil.

The deadline established by law to totally eliminate burnings in the sugarcane fields in the state of São Paulo is the year 2020. Although it is still far off, the producers are already working to find the most benign varieties of the plant for mechanized cutting and the most resistant towards new pests that are appearing. “The demands of the planted area were different before mechanization, now everything has changed, it’s another way of growing, another manner of treating the plantation”, explains Amaury da Silva dos Santos, a researcher with the Biological Institute. Over the next few years, the mechanization of the harvesting and of the plantation itself will begin to demand land with low levels of inclination, which is not always available.

Some sugarcane municipalities, such as Piracicaba, are studying new niches in the market in order to adapt themselves to the restrictions imposed by the topography of their land. According to a study carried out by Esalq, close to 70% of the areas in the region slope more than 12%, which impedes the use of cutting machinery. However, the producers have discovered a way out: to transform all of the area into producing organic sugar. This type of produce demands a different type of management, with greater spacing between the planted rows, and no spraying with chemical insecticides or herbicides. Organic sugar is priced three to four times more than traditional sugar on the international market, mainly in North America and Europe. Thus, even with only a small planted area to work with, it still pays off.

The future that is being sketched out for the municipality of Piracicaba reflects the new demands of the sugarcane industry, installed in this country through the system of colonial provinces that began in the 17th century. The research developed at the Biological Institute, USP and UFSCar is fundamental for the producers to adapt themselves to current environmental regulations and to the demands of the consumer. And the results, already demonstrated publicly at itinerant meetings and workshops, show that this is the road to follow for Brazil so as not to lose its position as the world’s largest sugar exporter.

The project
Evaluation and Control of Pests, Illnesses and the Persistence of Herbicides in the Sugarcane Agro Systems using Mechanized Cutting, without Burnings (nº 99/08585-9); Modality Thematic project; Coordinator Antônio Batista Filho – Biological Institute; Investment R$ 228,746.51 and US$ 18,099.66

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