Pheromones, the chemical flags that serve as communication between individuals of the same species, are used by insects to attract the opposite sex for mating, to mark out their territory or even as a warning against danger. When they are synthesized they can be used in traps in the field to capture insects with different objectives, such as identification, population monitoring or even population control. In Brazil, their use is still restricted to just a few crops, like apples, coffee, citrus fruit and sugarcane, but the application potential will tend to expand as the results obtained in research conducted at Embrapa Genetic Resources and Biotechnology in Brasília show; it has led to the chemical synthesis of the sex pheromone of the neotropical brown stinkbug (Euschistus heros), the main pest in soybean crops. Tested experimentally in the field, the technology was transferred to Isca Tecnologia, from Ijuí in the state of Rio Grande do Sul, and is now in the large scale field experiment phase.
In Brazil, producers use around 6 million liters of insecticide every soybean crop just fighting off the stinkbug. “In addition to causing an environmental problem, excessive use of insecticides also does away with insects that are beneficial to the plantation,” says the researcher Miguel Borges, from Embrapa’s Semiochemicals Laboratory, and responsible for the research with pheromones. Soybeans are not the only crop attacked by the brown stinkbug. Corn, wheat and cotton are also targets for the insect’s appetite. “Although there are genetically modified plants, they have been structured to control pests which eat the crops, like caterpillars, and not sucking pests, like the stinkbugs,” says Borges. That is why today they are occupying other niches, in addition to soybeans.
The substances released by the insects are mostly volatile compounds. When male stinkbugs are sexually mature they release a sexual pheromone to attract females for mating. To make its use feasible in the field, the first tasks of the researcher are to identify what these chemical flags that are immediately recognized by females from the same species consist of, and to synthesize the compound in the laboratory. The tests start after recognition and synthesis of the substances that compose the aromatic bouquet. “Placed in a trap in the field, the synthetic pheromone has to release a compound identical to the one released by the insect in order to attract a partner for mating,” says Borges. When he falls into the trap the stinkbug cannot escape and, based on the number of insects found, it is possible to find out whether insecticide needs to be applied or not. “Even when application is necessary it will be done selectively, resulting in a cost reduction for the producer, in addition to protecting the worker and the environment,” says Borges.
The only current method for monitoring stinkbugs is the so-called ‘cloth and beat’ method, where a 1 meter long by 0.5 meter wide cloth or tarpaulin with wooden side supports is placed between two rows of soybeans. The plants are bent over and beaten on to the cloth and the stinkbugs are then counted. However, the reduction in space between plants, the great expanses of soybean crops and the size of some plants, particularly in rainy years, have made this method largely impractical. The crop, which spreads over 16 states and has a planted area greater than 24 million hectares, is responsible for an annual soybean production of 67 million tons in Brazil. “The damage the stinkbug causes in soybeans is irreversible,” says Borges. This is because, unlike caterpillars that merely eat leaves, this insect manages to perforate the plant and suck out the sap and the beans. “Some producers around the Federal District have already had losses of between 80% and 100% of their crop because of this insect,” explains the researcher, who started his work with pheromones in 1989, when he was doing his PhD at the University of Southampton, in England. Currently, control has been carried out by applying insecticides close to the time the plant flowers, without taking into account the dynamics of stinkbugs in the field.
The synthetic pheromone was experimentally tested in crops in Goiás, around the Federal District, in Mato Grosso and in Uberlândia (MG). “The use of traps with pheromone allows us to monitor stinkbug populations more precisely and avoids an outbreak of the pest, principally in the most critical phase when the soybean is filling out,” says Borges. “In one of the experiments carried out in Uberlândia, in the area treated with pheromones the application of insecticide fell by 50%.” The traps were placed every 1 hectare in the plantation and worked perfectly. “If they were placed every 200 meters the cost/benefit would be very large.”
The partnership deal with Isca was closed in October 2010, but only now, after the field trials have ended, has the company started more extensive trials with soybean producers in Rio Grande do Sul, Paraná, Mato Grosso, Minas Gerais and the Federal District. The trials began in October this year, the beginning of the soybean crop, and will continue until March, when it ends. “We’re going to compare the traps with pheromones with the ‘cloth and beat’ technique,” says Rafael Borges, Isca’s R&D Manager. The company is also developing three types of trap, with an enhanced capacity for recapturing and retaining insects, and assessing the best concentration of synthetic compounds. “The first challenge is to develop a trap that is commercially viable, which will facilitate introducing the technology in the field.”Republish