https://orcid.org/0000-0002-4463-8749
Abstract
Gonipterus platensis Marelli (Coleoptera: Curculionidae) has been detected for the first time in the Caazapá Department, Paraguay. This species is closely related to the eucalyptus snout beetle, which is an invasive pest native to Australia, that causes serious damage to eucalyptus plantations. Gonipterus platensis belongs to a complex of cryptic species (Gonipterus scutellatus species complex) that share morphological similarities, making species differentiation challenging. In addition, oothecae parasitized by Anaphes nitens Girault (Hymenoptera: Mymaridae) were found. This record highlights the importance of conducting further studies on the biology and establishment of G. platensis in Paraguay as well as exploring the potential of biological control using A. nitens as a part of an integrated pest management strategy.
Una de las varias especies de gorgojos defoliadores del eucalipto, Gonipterus platensis, fue detectada por primera vez en el Departamento de Caazapá, Paraguay. Esta plaga causa serios daños en las plantaciones de eucalipto, poniendo en riesgo su valor comercial. Se detectaron además varias ootecas de G. platensis parasitadas por Anaphes nitens, un micro-himenóptero que podría ser utilizado como agente de control biológico como parte de una estrategia de manejo integrado de plagas del gorgojo del eucalipto.
Alt text: Picture showing Gonipterus platensis mating in natural conditions and its egg parasitoid Anaphes nitens.
Introduction
Eucalyptus trees are the most extensively planted species in the forestry industry, covering more than 20 million hectares worldwide (Zhang and Wang 2021). Various species and their hybrids serve as a primary source for wood, fiber, bioenergy, and other applications. In recent years, eucalyptus plantations in Paraguay have expanded significantly, increasing from 55,000 hectares in 2008 to 260,000 hectares by 2022, with approximately 20% located in Caazapá Department (MAG 2022). These plantations play a significant role in Paraguay’s economy, generating income through the export of products to the United States, the United Kingdom, Brazil, and several other countries (INFONA 2025).
Eucalyptus plantations globally face significant challenges due to Gonipterus scutellatus, commonly known as the Australian eucalyptus snout beetle. This invasive pest is part of a species complex including at least 4 described species: Gonipterus platensis, G. scutellatus stricto sensu, G. pulverulentus, and G. balteatus (Mapondera et al. 2012, Schröder et al. 2021). This complex has been reported in eucalyptus-producing regions across all 5 continents, emphasizing its widespread impact, posing a serious threat to the sustainability of these plantations (Schröder et al. 2020). The feeding habits of these insects lead to a reduction in leaf area, decreasing photosynthetic capacity, and negatively affecting plant health and productivity (Reis et al. 2012).
Many countries list G. scutellatus as a quarantine pest, either as a single species or as an entire complex. However, the most recent recommendations are to consider this species complex unified in the same pest category (EPPO 2005; Jeger et al. 2018). These cryptic species share many morphological features, making differentiation difficult using taxonomic keys (Mapondera et al. 2012).
Gonipterus platensis was first described by Marelli (1926), based on specimens found on Eucalyptus globulus in La Plata, Argentina. Originated in Australia, it has since spread across the globe and has been reported in several countries including Argentina, Brazil, Chile, Colombia, Ecuador, and Uruguay (Marelli 1926, Lanfranco and Dungey 2001, Wilcken and Oliveira 2015, Rodas 2018, Schröder et al. 2020, Nanini et al. 2022, Crespo‐Pérez et al. 2023, Ribeiro et al. 2023). In Brazil, it was detected in 1979 in the State of Paraná, and later in Rio Grande do Sul, Santa Catarina, Sao Paulo, Minas Gerais, and Espirito Santo (Wilcken and Oliveira 2015, de Oliveira et al. 2022, Nanini et al. 2022, Ribeiro et al. 2023). Notably, the susceptibility of eucalyptus hybrids to these pests varies and, in some cases, host associations are dependent on the eucalyptus species (Souza et al. 2021). However, G. platensis has demonstrated no specific preference for either genotype, putting all commercial plantations at risk (de Oliveira et al. 2022, Gamarra Bustamente and Rin Uribe 2024).
Various strategies have been developed to manage the global incidence of Gonipterus scutellatus species complex, with biological control emerging as the most studied and effective method. Several natural enemies were evaluated in this respect, including entomopathogenic fungi and insects (Ferreira Valente 2018, Hurley et al. 2023, Mejía et al. 2024). Among these natural enemies, parasitoids play a pivotal role and have been integrated into pest management strategies for several years (Tribe 2005, Garcia et al. 2019, Schröder et al. 2021). This pest complex can be naturally regulated by different species of parasitoids present naturally in the field, but they can also be reared and released. The most prevalent parasitoids identified in natural populations include Anaphes nitens Girault (Hymenoptera: Mymaridae), Centrodora damoni Girault (Hymenoptera: Aphelinidae), and Euderus spp. (Schröder et al. 2021). Anaphes nitens is an Australian fairyfly that parasitizes solely Gonipterus spp. eggs (Santolamazza-Carbone et al. 2009). Several publications mention that A. nitens shares the same spreading pattern with its host (Rivera and Carbone 2003, Schröder et al. 2021, Ribeiro et al. 2023, Salazar-Basurto et al. 2023). In different countries, such as Spain, Portugal, and Australia, this parasitoid is being used as a biological control agent of the Gonipterus species complex with successful results (Rivera et al. 1999, Rivera and Carbone 2003, Ferreira Valente 2018, Schröder et al. 2021).
Materials and Methods
In January 2023, the presence of a defoliating weevil (Fig. 1) was reported in eucalyptus plantations (Eucalyptus urophila × Eucalyptus camaldulensis VM01 hybrid clones) located in Puerto Bertoni and Maciel, Caazapá Department, Paraguay (Fig. 2). Sample collection was conducted at the infested area. The species was identified based on morphology and genitalia using keys developed by Halstead (1986) and detailed by Mapondera et al. (2012). For genitalia mounting, the tissues were immersed in 10% KOH and heated in a water bath for 10 min. Genitalia was transferred to microscope slides with a few drops of Hoyer’s solution and covered with a coverslip. Finally, they were placed in a drying oven at 60 °C for 3 days, and sealed for observation.
Gonipterus platensis on eucalyptus. A) Early instar larvae. B) Dorsal view of late instar larvae feeding on eucalyptus leaves. C) Field sampling. D) Adult stage mounted. E) Leaf showing damage signs.
Map of eucalyptus plantations in Paraguay and detection of Gonipterus platensis in Caazapá Department.
Species confirmation was performed by mtDNA Cytochrome Oxidase subunit I (COI) gene fragment sequencing. Genomic DNA was extracted from 2 individuals, named PY1 and PY2, using the ThermoScientific GeneJET Genomic DNA Purification Kit according to the manufacturer’s instructions. PCR amplification of COI fragment was conducted with the GoTaq Colorless Master Mix, using the primers C1-J-2183 (5’-CAA CAT TTA TTT TGA TTT TTG G-3’) and TL2-N-3014 (5’-TCC AAT GCA CTA ATC TGC CAT ATT A-3’), previously described by Simon et al. (1994). PCR mixtures (50 μl final volume) contained 2 μl of genomic DNA and 0.4 μM of each primer. Cycling conditions were as follows: 95 °C for 5 min; 35 cycles of 94 °C for 30 s, 46 °C for 30 s, and 72 °C for 30 s; followed by a final extension at 72 °C for 7 min. PCR products were purified using the ThermoScientific GeneJET PCR Purification Kit and then sequenced (Macrogen Inc., Seoul, South Korea).
The sequencing reads were processed using the R programming language package IsolateR with default parameters, which include the sequence trimming method with a Phred score threshold of 20 (default), applied to remove low-quality bases. The processed sequences were compared using the BLASTn tool to find homologous sequences available in the GenBank database. The sequences were aligned using MEGA software version 11, employing the CLUSTALW algorithm with default parameters (Altschul et al. 1990, Rambaut 2018, Stecher et al. 2020, Tamura et al. 2021, Sayers et al. 2023, Daisley et al. 2024).
Results and Discussion
Male specimens showed its aedeagus structure narrow, with a squarely truncate apex and a large and sinuate internal sclerite (Fig. 3A). Female genital structure showed a round, pigmented apical margin, with long, abundant, erect hairs along its entire length (Fig. 3B). Also presented lateral basal extremities descending in a straight line, without sinuosities or curvatures. Their ventral spicule was apically forked, with 2 sub-arms of equal size, sharpened distally, forming an open angle. These findings are consistent with the genitalia described for Gonipterus species (Rosado-Neto and Marques 1996, Santolamazza-Carbone and Rivera 1998, Mapondera et al. 2012).
Genitalia of Gonipterus platensis. A) Male (♂) aedeagus. B) Female (♀).
COI fragment sequences showed the best homology with G. platensis. Several Gonipterus spp. sequences were selected from the GenBank database to perform the phylogenetic analysis, which revealed that PY1 and PY2 specimens grouped in 2 different clades of G. platensis (Fig. 4), confirming the suspected species.
Phylogenetic analysis of Gonipterus platensis based on Cytochrome Oxidase subunit I (COI) sequence. The phylogenetic tree was constructed using the maximum likelihood method. Bootstrap resampling method with 1,000 repetitions was applied to assess the reliability of the branches. Customization of the tree was done using FigTree software. Coccinella septempunctata was used as the outgroup (*). The GenBank accession numbers of the submitted COI sequences are PQ670295 (PY1) and PQ670296 (PY2). Diamonds represent PY1 and PY2 specimens collected at Maciel district.
Leaf-attached oothecae of G. platensis were found in several samples. They showed a dark color, excrement shape, and 4 to 5 yellowish small eggs inside. No larvae hatched from the analyzed oothecae but many adult micro-hymenoptera emerged (Fig. 5), confirming that the eggs were parasitized. Anaphes nitens was identified as the parasitoid using the taxonomic key developed by Nieves-Aldrey et al. (2006).
Anaphes nitens on ootechae of Gonipterus platensis A) and B) and adult of Anaphes nitens C).
These findings are consistent with those reported by Nanini et al. (2022) who found a high predominance of G. platensis in several Brazilian States bordering the Caazapá Department. This could be a probable source of natural dispersion of this species to Paraguay. Recently, Crespo‐Pérez et al. (2023) conducted a study predicting the potential distribution of the Gonipterus scutellatus species complex in South America, highlighting the southern region of Paraguay as a suitable habitat for these species. As formerly reported in Brazil, the detection of G. platensis also led to the finding of A. nitens (Ribeiro et al. 2023). The increase in eucalyptus cultivation in Paraguay has contributed to the emergence of new reports of exotic eucalyptus-associated insect species (Benitez Diaz et al. 2013, 2014).
Although damage observed in the field was not severe, an affected producer with 15,000 hectares of eucalyptus plantation faced potential risks. Currently, there is a significant gap in our knowledge concerning G. platensis incidence establishment and spreading patterns. Further research is needed to address those gaps and to better understand and manage the impacts of G. platensis on eucalyptus plantations.
The discovery of A. nitens suggests the simultaneous dispersal of both insects along borders. The high parasitism rate aligns with findings by Reis et al. (2012), who reported an increase in parasitism under high temperatures, which are the prevailing climate conditions in Paraguay. The detection of A. nitens naturally parasitizing G. platensis provides key insights into its potential as a biological control agent in the main eucalyptus-producing area of Caazapá, Paraguay.
As this represents the first record of G. platensis and A. nitens in Paraguay, comprehensive studies should be conducted to assess the feasibility of integrated pest management (IPM) strategies. Implementing IPM is crucial to mitigate significant losses in wood production and to safeguard access to export markets. Our findings serve as a valuable indicator of the potential of biological control of G. platensis with A. nitens as a part of those strategies in Paraguay. The use of A. nitens as a biological control agent could contribute to the sustainability of eucalyptus cultivation while ensuring economic viability for growers.
Acknowledgments
The authors would like to thank Pastor Emilio Soria Melo and Jadiyi Torales, President and Technical Director of SENAVE, as well as all the staff at SENAVE Laboratories and the SENAVE Regional Office of Caazapá, for their support and contributions.
Author contributions
Edgar Benítez Díaz (Conceptualization, Investigation, Methodology, Supervision, Writing—original draft [lead]), Yeruti Mongelós-Franco (Investigation, Validation [equal]), Liz Ojeda (Investigation [equal], Writing—original draft [supporting]), Lino Ramirez-Ayala (Data curation [lead], Investigation [equal]), Deisi Acosta (Investigation [supporting]), Bolivar Garcete-Barrett (Validation [equal]), Blanca Coronel (Resources, Supervision [equal]), Alfredo Gryciuk-Almeida (Project administration [lead], Resources [equal]), and Marcelo Alborno-Jover (Conceptualization, Investigation, Methodology, Supervision [equal], Visualization, Writing—review & editing [lead])
Conflicts of interest. None declared.
