Discovery of new species of sugarcane pest may facilitate management and reduce losses

Analyses show that a sugarcane spittlebug, found in the Southeast and South of Brazil since the 1960s, was mistaken for other species that are similar to the naked eye.

By André Julião  |  Agência FAPESP – In 2015, Professor Gervásio Silva Carvalho of the Pontifical Catholic University of Rio Grande do Sul (PUC-RS) in the South region of Brazil received several specimens of sugarcane spittlebugs (Mahanarva sp.) for identification.

The insects came from different sugarcane plantations in the South and Southeast of Brazil, where an insecticide commonly used to control the pest had been applied but was not producing the expected results.

The idea was that the researcher’s expertise in insect taxonomy could determine whether those sugarcane spittlebugs were different from the species best known for attacking sugarcane fields based on the characteristics of the animal’s body (morphology).

Shortly thereafter, unbeknownst to the researcher, Professor Diogo Cavalcanti Cabral-de-Mello from the Institute of Biosciences at São Paulo State University (IB-UNESP) in Rio Claro also received several specimens of the insect from the same person. Some had even been analyzed by Carvalho.

Cabral-de-Mello, a specialist in cytogenetics and genomics (fields that study the chromosomes and genetic information of organisms), noticed some differences that might indicate a new species. However, without knowing about the analyses carried out by Carvalho’s group, which would provide morphological evidence, he could not make a categorical statement.

After learning about each other’s work, the researchers joined forces, increasing the number of specimens analyzed to cover most of Brazil. They were then able to describe the new species, Mahanarva diakantha, in a study supported by FAPESP and published in the Bulletin of Entomological Research.

The description paves the way for a series of studies since, until now, Mahanarva diakantha was treated as one of its close relatives, such as Mahanarva fimbriolata and Mahanarva spectabilis. It may have a different life cycle, interact differently with its environment and hosts, and even have greater resistance to commonly used insecticides. These differences could affect its control and sugarcane productivity.

“This genus of sugarcane spittlebug has species that are very similar to each other, which we call cryptic. At that time, after dissecting the insects, we saw that some had different male genitalia, which could indicate a new species. Then, at a scientific event, we met other people working with this organism and decided to go ahead with the idea of describing it,” says Andressa Paladini, first author of the study and currently a professor at the Federal University of Paraná (UFPR). At the time, she was doing postdoctoral research under Carvalho’s supervision at PUC-RS.

“We isolated a specific sequence of mitochondrial DNA, known by the acronym COI [from cytochrome C oxidase], which varies between species and is therefore widely used to differentiate them from one another. However, the difference was so small that we couldn’t have described it as a new species without morphological evidence,” Cabral-de-Mello explains.

The study was supported by FAPESP through two projects coordinated by the researcher: “Investigating the evolution of satellite DNA in holocentric chromosomes of insect pests” and “Structure and evolution of repetitive DNA in Lepidoptera species and its relationship with karyotypic and sex chromosome diversification”. 

Distribution map of the three species and the area where they overlap (figure: Andressa Paladini/UFPR)

Cryptic diversity

The new species is impossible to differentiate from the two closest species, Mahanarva fimbriolata and Mahanarva spectabilis, to the naked eye. Complicating matters further, the three species share an overlapping range in the South and Southeast of Brazil.

The only way to differentiate them without COI gene sequencing is by dissecting the males. The tip of the genitalia of the new species is differentiated in males by being bifurcated, which gave rise to its scientific name, M. diakantha, meaning “two thorns” in Greek.

To eliminate any doubt, the researchers applied a third method of species differentiation: geometric morphometrics, a technique that has been widely used in recent years to study insects. In this method, the researchers compared the shape of the hind wing of the three species of sugarcane spittlebugs. The results of the comparison showed significant statistical differences between the species.

“We don’t know exactly how long ago, but everything indicates that the species differentiated recently. This is very evident in the genetic and morphological analyses,” says Cabral-de-Mello.

With the description of the new species, previous studies with similar species must be reevaluated. While examining sugarcane spittlebug specimens in biological collections, the researchers found individuals of the new species that had been collected decades ago and misidentified as other species. One specimen dated from 1961 and had been misidentified as M. fimbriolata. Some studies do not detail how the analyzed species were identified, which leads us to believe that different species may have been treated as a single species.

One of the next steps for the researchers is to increase sampling to more accurately verify the distribution of the new species in the country and its impact on crops. Another goal is to better understand the genetic diversity of the species, which is essential for developing management strategies.

“Now that it’s been described as a new species, a range of new possibilities has opened up,” Paladini concludes.

The article “Shades of red: several lines of evidence reveal a pest of sugarcane as a new species of Mahanarva (Hemiptera: Auchenorrhyncha: Cercopidae)” can be read at doi.org/10.1017/S0007485325100503.