Research confirms new records of insect pests of cassava crops

Taxonomic studies with lace bug, collected from cassava plantations in Acre, confirmed the first official record of the species Vatiga manihotae e Vatiga illudens to the State, and Gargaphia opima for Brazil, associated with culture. Found in fields in the Kaxinawá Indigenous Land of Nova Olinda, municipality of Feijó, these insect pests attack the leaves of the plant and, in high populations, can cause production losses. Published in the journal EntomoBrasilis, the results contribute to increasing knowledge about the geographic distribution of these species in the country.

The discovery is the result of insect prospecting research, carried out with the aim of identifying the main pests of indigenous agriculture and guiding control alternatives, through the project “Ethnoknowledge and Agrobiodiversity among the Kaxinawá of Nova Olinda – Phase II”, carried out by Embrapa Acre (Rio Branco) and partner institutions, between 2015 and 2018. According to researcher Rodrigo Santos, coordinator of the studies, during fieldwork different species of insect pests were collected in indigenous fields, but three species of stink bug were collected. income caught the team’s attention. “We screened the captured insects and selected 21 specimens for analysis. We sent this material preserved in 70% alcohol to the Federal University of Rio de Janeiro (UFRJ), a reference in insect taxonomy, for species identification,” he says.

Identification and confirmation

The taxonomic study to determine the identification of the lace bug was based on the use of dichotomous keys that involve different morphological parameters, that is, descriptions of the external morphology of the order, genus and species of the insects. These studies enable comparative assessments and indicate paths to be followed in the process. According to UFRJ professor Luci Boa Nova Coelho, although these insects have lacy wings as a common characteristic, there is great variation in the morphology of the species.

“We analyzed the shape of the back and wings, positioning of antennas and the shape of the narrowing of the abdomen, where the sexual apparatus of males and females is located, among other characteristics of the body's structural composition, essential for the identification of insects, comparing with species of lace bug already described in the literature. The analyzes allowed us to confirm the species Vatiga manihotae e Vatiga illudens, for the first time recorded in the state of Acre, and the first record of the species Gargaphia opima in Brazilian territory”, says the entomologist.

The experts also carried out comparative studies with species from official entomological collections, maintained in Universities and museums in Brazil and other countries, and with images of insects contained in scientific literature. “The use of dichotomous analytical keys is a very efficient method of identifying insects, but the variation in characters present in each key and the lack of scientific information about some species not yet recognized by Science, among other issues, can make analysis difficult. To avoid errors of interpretation, as a general rule, after identification, we always seek confirmation of the species by comparing the physical specimen with figures and photographs of insects already scientifically determined”, explains Santos.

First registration in Acre

Research reveals that the gender Vatiga includes different species of lace bug, found in the Neotropical region (part of North, South and Central America), associated with different plants of the genus manihot. The species identified in Acre already occur in other locations in Brazil, associated with cassava cultivation. Vatiga illudens it was registered in Bahia, Mato Grosso do Sul, Ceará, Rio Grande do Norte, Federal District and Paraná. Vatiga manihotae was reported in Amazonas, Pará, Mato Grosso do Sul, Paraná and Santa Catarina.

According to Santos, in the context of the Indigenous Land, these species occur in low population density, due to the specificities of the agricultural systems adopted, such as small-scale production and the implementation of fields close to areas of native forest, a practice that contributes to the presence of natural enemies in crops and works as a control method. Under these conditions, these insect pests do not pose any risks to the crop, but we need to investigate how they will behave in extensive areas of monoculture in the state of Acre,” he emphasizes.

First registration in Brazil

Native to the Americas, the genus Gargaphia It is found in Colombia, Ecuador, Peru and Bolivia, with species associated with economically important crops such as passion fruit, jack beans and okra. Until then, only the Gargaphia lunulata (Mayr) had been registered in Brazil, related to cassava. The researchers' hypothesis is that the species Gargaphia opima Drake migrated from neighboring countries, due to Acre's proximity to the Bolivian and Peruvian borders.

The first scientific record of the new species of lace bug in Brazil will make it possible to update the official list of insect pests associated with cassava cultivation, which is the responsibility of the Ministry of Agriculture, Livestock and Supply (Mapa). “This inclusion in the list of agricultural pests in the country will also support the carrying out of prospecting research to identify new areas of occurrence of the insect, understand aspects of population behavior and measure the impacts on production”, says Santos.

Control strategies

Consumed by almost a million people around the world, cassava has been considered, by international organizations, one of the crops that can contribute to reducing hunger on the planet. Cultivated in more than 100 countries, it serves as food for rural and urban populations who consume the root fresh and transformed into flour, kisses and bread, among other by-products. Despite their economic and social importance, crops around the world are susceptible to various diseases caused by fungi, bacteria, viruses or protozoa and pests that can decimate crops, such as the mandarin caterpillar and leaf-cutter ants, as well as pests of lesser economic importance. like lace bugs.

Santos explains that these sucking insects are secondary pests of the crop, however, as they feed on the sap of the leaves, especially the younger ones, removing part of the chlorophyll, at high population levels they harm the productive performance of the crops. Damage caused to the leaves reduces the plant's photosynthesis capacity, compromising the production of starch (sugars) and root development, resulting in losses for farmers.

According to the researcher, the main strategy to avoid attacks and minimize losses is monitoring the population in cassava plantations. Carrying out regular inspections of plantations makes it possible to adopt effective control measures when the first outbreaks of insects are detected, based on the use of products and dosages recommended by the research, an aspect that helps to preserve insects beneficial to the crop. “In addition, generating scientific information about the identified species is essential for the implementation of Integrated Pest Management (IPM) programs, whether at the state or national level”, he highlights.