The Reason Pesticides Aren't Effective: A "Different Species"? One Sugarcane Plant, Three Similar Pests - Discovery of a New Sugarcane Pest Species Changes Control Strategies

The Reason Pesticides Aren't Effective: A "Different Species"? One Sugarcane Plant, Three Similar Pests - Discovery of a New Sugarcane Pest Species Changes Control Strategies

2025年12月04日 10:00

A small insect that has quietly plagued sugarcane fields for many years has been given a new "name" and "face."


A Brazilian research team re-examined specimens of the "root spittlebug," known as a major pest of sugarcane, and discovered that among them was a **new species of pest, "Mahanarva diakantha,"** which had been mistaken for a known species.Phys.org


This discovery is not just academic news.


Sugarcane is a staple crop in Brazil, with exports of sugar and ethanol estimated to exceed $9 billion annually.Entomology Today

 If an "unknown" pest resistant to pesticides is increasing in those fields, identifying the new species is an important step in unraveling the damage mechanism and reducing losses.


The story that began with a sense of "pesticides not working"

The story began in 2015. Researchers received numerous pest specimens from sugarcane farms in southern and southeastern Brazil, accompanied by inquiries about why the usual insecticides were not reducing pest numbers.Phys.org


The specimens were sent to two laboratories.

  • Professor Carvalho's group at PUC-RS (Pontifical Catholic University of Rio Grande do Sul), experts in insect morphological classification (visual characteristics)

  • Professor Cabral de Melo's group at São Paulo State University (UNESP), specializing in chromosomes and genes


Initially, both teams were unaware of each other's existence.
However, as they observed the specimens, they began to feel a strange sense of unease.

"The shape resembles the 'usual' Mahanarva fimbriolata, but the shape of the genitalia (reproductive organs) of some male individuals is slightly different...?"


The morphology team felt this unease, which was also sensed by the genetics team through a different route.
When they analyzed the COI region of mitochondrial DNA (a barcode gene used for species identification), they found similarities to known species, but there was an inexplicable difference.Phys.org


Later, the two teams met by chance at a conference and realized, "Aren't these the same specimens?" This realization accelerated their joint research. They re-collected specimens from across Brazil and began a comprehensive analysis combining morphology, genetics, and "wing shape."Phys.org


Indistinguishable to the naked eye, the third of the "three look-alike brothers"

The focus of this study, the sugarcane spittlebug, is a small insect belonging to the genus Mahanarva.
The main pest species of sugarcane known so far were:

  • Mahanarva fimbriolata (M. fimbriolata)

  • Mahanarva spectabilis (M. spectabilis)

These were the two species. The new species, diakantha (M. diakantha), can be described as the third of the "three look-alike brothers" that looks almost identical to these two species. Phys.org


  • The body color is also similar

  • Their habitats largely overlap in southern to southeastern Brazil

  • Even experts cannot distinguish them based solely on their appearance from the surface of the field


Therefore, it is possible that in the field, they have been collectively labeled as **"all fimbriolata."** In fact, when the research team reviewed museum and university specimen collections, they found cases where individuals collected in 1961 were labeled as fimbriolata, but upon re-examination, they were identified as the new species diakantha.Phys.org


The name's origin is "two thorns": The key to distinguishing them is the "tip of the male"

The new species has been named **"Mahanarva diakantha."**
"Diakantha" is derived from Greek, meaning "two thorns," referring to the bifurcated tip of the male genitalia.Phys.org


There are three main points for distinguishing them:

  1. Subtle differences in the shape of the male genitalia

    • The new species has a bifurcated tip, differing in structure from the two known species.

  2. Differences in COI gene sequences

    • Although the numerical differences are small, phylogenetic analysis revealed a distinct branch, supporting its validity as a separate species.Phys.org

  3. Statistical analysis of hind wing shape (geometric morphometrics)

    • A method that has become widespread in insect research in recent years, quantifying and comparing the "shape" of wing contours and patterns.

    • When analyzing the three species together, statistically significant differences emerged, allowing species identification with nearly 90% accuracy.Phys.org


In other words, this new species is a representative example of a **"cryptic species,"** where **"the genes and shape are almost identical to known species, but overall, it is a different entity."


Why "just classification" is directly linked to farmers' income

So why is the addition of "one more species" important for sugarcane farmers?

In the first place, the root spittlebug (M. fimbriolata) is one of the most important pests of sugarcane in Brazil.


  • Adult insects above ground suck the sap from leaves, and the toxins they secrete cause the leaves to appear scorched yellow or red, significantly reducing photosynthesis and sugar accumulation.

  • Larvae underground absorb nutrients from the roots while wrapped in a foamy secretion, causing the stems to become thin, hollow, and leading to lodging or death.koppert.com.ar

The damage is quite severe when viewed numerically.


  • The decline in raw material quality can be up to 30%.

  • There are reports of yield (tons/hectare) reductions reaching **15-85%**.Revista Cultivar

Another report estimates that root spittlebug damage can lead to a loss of up to 36 tons of sugarcane per hectare. Tridge


When the element of "actually a different species" is added, the situation becomes even more complex.

  • The new species diakantha may have subtle differences from existing species in terms of:

    • Occurrence timing

    • Preferred environmental conditions

    • Sensitivity to pesticides

  • However, since they have been counted together with fimbriolata until now,

    • Occurrence prediction data

    • Pesticide efficacy tests

    • Tests of biological pesticides and natural enemies
      may have actually been "average values of multiple species."Phys.org


"If you misidentify the enemy, the strategy goes awry."
This identification is precisely the starting line for that review.


Revisiting all past data and specimens?

The research team carefully re-examined domestic specimen collections. And then...

  • Among individuals collected in the 1960s, diakantha was mixed in

  • However, the labels were for fimbriolata or another closely related species

Multiple such cases were found.Phys.org


In other words, this new species is not a "newcomer" that suddenly appeared recently, but has likely been in sugarcane fields for at least 60 years, yet has been overlooked.


This fact raises several questions.

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