Mar. 21, 2019
By Leonardo Gottems, reporter for AgroPages
Research developed by Embrapa Meio Ambiente (a Brazilian agricultural research company) is using weed extracts as insecticides. The discovery
seems to point to the best of the world in agriculture - the use of weed without commercial value and the emergence of a new natural defensive, which can be used in organic crops.
Scientists evaluated the extracts of the plant species Flaming Glorybower (Clerodendrum splendens), Horseweed (Conyza canadensis), Mexican sunflower (Tithonia diversifolia) and Vernonanthura westiniana. The results pointed to a surprising insecticidal effect of these four plants in the control of Helicoverpa armigera and Anticarsia gemmatalis, two of the most feared agricultural pests.
Against A. gemmatalis, for example, the bioactivity of the Vernonanthura westiniana weed caused up to 80% mortality. The bioinsecticide based on Clerodendrum splendens, in turn, eliminated more than 60% of the population of the pest, based on the reduction of the weight gain of larvae and pupae.
Embrapa researcher Jeanne Marinho-Prado, one of the authors of the study, explains that the relationship between insects and plants is regulated by substances called allelochemicals. When released by plants, they can act as stimuli on insect behavior or change characteristics of their cycle. The pest may be stimulated to continue feeding (phage-stimulating) or to stop feeding (phage inhibition).
"The objective was to evaluate if the extracts made with each one of the four species of plants present insecticidal or harmful action to the development of H. armigera and A. gemmatalis caterpillars through ingestion," says Marinho-Prado. She commands which includes three other scientists: Sonia Queiroz, Simone Prado and Marta Assis.
The discovery by the Brazilians offers hope against a serious problem faced by conventional agriculture: the resistance of insects to current agrochemicals. Even transgenic plants with Bacillus thuringiensis
(Cry1Ac) have displayed the first signs that they may lose their protection against caterpillars, since hybrid insects are emerging from the cross between Helicoverpa armigera
and Helicoverpa zea
that attacked genetically modified soybeans in Brazil.
And it is precisely Helicoverpa armigera that is the next target of Embrapa research. In the first tests, V. westiniana weed caused only a 20% mortality rate among the evaluated population of caterpillars of this species. The next steps in the trials will cover the identification of those molecules responsible for the action of antibiosis - which causes mortality or reduction in size, weight, longevity and fecundity.
"Insecticides with a high degree of toxicity or high persistence in the environment have been banned in several countries, and there is an increase in the occurrence of insect populations resistant to products that remain regulated. In addition, it has increased the amount of insects resistant to transgenic plants, reducing the efficiency of this technology. These factors motivate the search for molecules that serve as the basis for the development of new products to be used in pest control, with different research opportunities aimed at the rotation of active compounds within integrated pest management. In addition, there is a growing interest in organic food production, which may benefit from the identification of new plant extracts with potential for application against insect pests," according to the study