https://orcid.org/0000-0002-8488-7782
Abstract
Tricolus simplicisWood 1974 (Coleoptera: Curculionidae: Scolytinae) is reported to bore and reproduce on the branches of Robusta coffee (Coffea canephora) in Chiapas, Mexico. This is the first report of T. simplicis associated with Robusta coffee worldwide. The risk this insect poses for coffee production is discussed.
Se informa que Tricolus simplicisWood 1974 (Coleoptera: Curculionidae: Scolytinae) perfora y se reproduce en las ramas del café robusta (Coffea canephora) en Chiapas, México. Este es el primer reporte de T. simplicis asociado con el café robusta a nivel mundial. Se discute el riesgo que este insecto representa para la producción de café.
Introduction
Coffee (Coffea spp.) is native to Africa but is now grown in tropical and subtropical areas around the world, providing important income to producers, especially in developing countries (Harvey et al. 2021). In 2023/2024, the coffee-producing regions were South America (48.34%), Asia and Oceania (29.61%), Mexico, Central America and the Caribbean (11.41%), and Africa (10.64%) (International Coffee Organization [ICO] 2024). The 2 most commercially important coffee species are Coffea arabica L. and Coffea canephora Pierre ex Frohener. In the coffee production year 2023/2024, C. arabica represented 62.4% of the market (ICO 2024). While C. arabica is almost always consumed after roasting and grinding of the beans, C. canephora—or Robusta coffee—is mainly consumed as soluble coffee or mixed with C. arabica (Campuzano-Duque et al. 2021). Coffee is the most consumed beverage in the world after water (Surma and Oparil 2021).
Several members of the Scolytinae subfamily (Coleoptera: Curculionidae) are key coffee pests. The coffee berry borer (Hypothenemus hampei (Ferrari 1867)), for example, is the most important coffee pest worldwide (Vega et al. 2015). Other scolytinid species that adversely affect coffee production are Xylosandrus compactus (Eichhoff 1875), Xylosandrus morigerus (Blandford 1894), and Xylosandrus discolor (Blandford 1898). These species are all ambrosia beetles that live on branches and twigs, mainly of C. canephora (Waller et al. 2007). Xylosandrus compactus and X. morigerus were introduced into the Americas (Equihua et al. 2023). Not only do Xylosandrus species cause physical damage (galleries) to the branches they attack, but they may also act as vectors of phytopathogenic fungi (Vannini et al. 2017). Unlike H. hampei, which is almost exclusively associated with coffee, Xylosandrus species are polyphagous. For X. compactus, more than 200 host species have been reported (CABI 2022).
Tricolus simplicisWood 1974 also belongs to the Scolytinae subfamily. Here we report, for the first time, its association with branches of C. canephora, and we discuss the implications of T. simplices acting as a pest of coffee.
Materials and Methods
Study Site
The study site was located on the coffee farm ‘Alianza’ (15°2’45.44” N, 92°10’19.66” W, 720 to 730 m a.s.l.) in the municipality of Cacahoatán (Chiapas, Mexico). Alianza is conventionally managed and grows Robusta coffee under full-sun conditions, although the farm also grows coffee under tree-shade conditions in some smaller patches. The study site area was approximately 14 hectares of coffee field planted with Nestlé clones 06 and 07 (10- to 12-year-old plants), spaced 2 m between plants and 4 m between rows. In 2023 and 2024, traps were set up to capture coffee berry borers and other scolytinids, including X. compactus and X. morigerus, which had been detected previously on the farm (Barrera et al. 2024). No insecticides were applied at the study site during the research.
Dissection of Perforated Branches
From February 14, 2023, to January 12, 2024, each week 20 to 22 plagiotropic and orthotropic Robusta coffee tree branches were collected that exhibited perforation patterns typical for Xylosandrus spp. (collected mainly in shaded areas of the study site). The branches were sent to the Laboratorio de Control Biológico y Manejo de Plagas of the El Colegio de-la Frontera Sur in Tapachula (Chiapas, Mexico) for examination. Branches were opened with a knife and dissecting needles, and recovered insect individuals were examined. Examination of infested branches and insects was conducted with the use of a stereomicroscope (Olympus SZ51, Olympus Latin America, Inc., Miami, FL).
Insect Trapping
Sixty ECO-IAPAR artisanal traps were installed in approximately 2.7 hectares (22 traps/ha) in the study site from March 2, 2023, to January 9, 2024. The traps were baited with an attractant mixture containing methanol and ethanol (3:1, both chemical grade) and installed at the study site under full-sun conditions. Traps were made from disposable soft drink bottles that were provided with an opening for the entry of insects (Barrera 2008). Traps were charged with a 10% propylene glycol (USP food grade) solution in tap water to retain and preserve the captured insects and were suspended from branches at 1.20 to 1.50 m above ground level. They were placed in rows of 6 and spaced 14.0 m apart. Captured scolytinids were collected weekly and transferred to the laboratory, where they were counted by morphospecies and examined under a stereomicroscope (Olympus SZ51, Olympus Latin America, Inc.).
Identification of Scolytinids
Scolytinid specimens recovered from branches and traps were separated into morphospecies. Specimens of interest were sent to the Colegio de Postgraduados in Montecillo (State of Mexico, Mexico) for identification.
Results and Discussion
One of the scolytinid species recovered from the galleries of perforated branches was different from X. compactus and X. morigerus, species that previously had been observed to bore into the branches of Robusta coffee trees in the study area. After closer examination, the species in question was identified as T. simplicis (Fig. 1).
Tricolus simplicis in Robusta coffee (Coffea canephora). a) Attacked branch; b) dorsal view of female; c) longitudinal cut of branch with female beginning to bore a gallery tunnel; d) posterior view of female in the entrance of the perforation; e) longitudinal section of branch with female in new gallery (symbiont fungus in white); f) longitudinal cut of branch with female and immature stages in the gallery; g) longitudinal section of branch with pupa (ventral view); h) lateral view of female and pupa; i) longitudinal section of branch with females in old gallery. Photos by J.F. Barrera (a, i), J. Valdez and A. Equihua-Martínez (b), J. de-la Rosa and J. Cruz (c–h).
Two specimens of T. simplicis were detected for the first time on February 14, 2023, in a gallery in one of the 22 dissected branches. The first individuals captured in traps (71 in total, or 1.18 ± 0.22 individuals per trap on average [±standard error]) were recovered on March 9, 2023. Re-examination of samples collected from 60 traps in previous studies carried out at the same study site revealed the presence of T. simplicis on December 6 and 13, 2022 (176 and 150 individuals, respectively).
We found T. simplicis in orthotropic (n = 15) as well as plagiotropic (n = 26) branches. All stages of development of T. simplicis were present in the galleries, indicating that this species develops and reproduces in Robusta coffee trees. However, we found relatively few galleries with immature stages (12/41), which could mean that this species is in the process of adapting itself to this plant. The number of T. simplicis individuals per gallery was almost always lower than the number of Xylosandrus spp. Of 54 perforated plagiotropic branches collected on February 1, 2024, the galleries of 15 (8.1%), 7 (3.8%), and 5 (2.7%) branches had the presence of at least 1 adult per branch of X. compactus, X. morigerus, and T. simplisis, respectively; the galleries of the other half of the collected branches were empty. To date, no male specimens have been detected in the galleries. At least 1 gallery bored by T. simplicis and 1 by X. morigerus were found in the same branch, indicating possible interactions between Xylosandrus species and T. simplicis.
The genus Tricolus is distributed across the Americas, from Mexico to Brazil. This genus includes 52 species, 11 of which have been recorded from Mexico (Wood 1982, Equihua and Burgos 2002, Atkinson 2024). These ambrosia beetles live in tropical climates. In Mexico, Tricolus has been reported from Nayarit to Chiapas, although the genus remains relatively poorly known.
Tricolus simplicis was described by Wood (1974) from Palin (Esquintla, Guatemala) based on specimens collected on May 16, 1964, from twigs (1.0 cm diameter) of Ficus sp. (Moraceae). The insect has a light brown color, is 1.8 mm long, and is 2.8 times longer than it is wide (Fig. 1). Its reported distribution includes Costa Rica (Puntarenas) and Mexico (Guerrero). Previous to our report, only Ficus sp. and Ardisia sp. (Myrsinaceae) (Atkinson 2024) had been documented as hosts of T. simplicis.
Tricolus simplicis is morphologically characterized by an impressed area on elytral declivity subcircular outline. Spine 1 at the base of the declivity is small and sharply pointed. The frons is coarsely aciculate, except for a small, central, weakly raised granulated area (Wood 1982). Tricolus simplicis is closely related to Tricolus inornatusWood 1974 and Tricolus inaffectusWood 1974, and can be morphologically distinguished from these species by the impressed elytral declivity, which is conspicuously longer than it is wide. Also, spine 1 of these 2 species is characterized by a small rounded granule or almost absent (Wood 1982).
It is worth noting that T. simplicis has previously been recognized in Mexico in the state of Guerrero. The species was collected by A. Burgos-Solorio and T. H. Atkinson in 1982 and 2019, respectively, but their reports have not entered the published literature.
The management of this new insect pest possibly will be like the current pest control tactics used for controlling Xylosandrus spp. (pruning and destruction of infested branches, mainly; Barrera 2008), since they belong to the same group of ambrosia beetles. However, the presence of T. simplicis in coffee plantations will complicate the identification, damage assessment, monitoring, and control of the Xylosandrus complex, which until now has been the most important pest group affecting the branches of C. canephora. Dissection of the branches will be required as part of the pest identification process, which will increase the costs associated with pest management.
In conclusion, Robusta coffee is reported for the first time worldwide as a host plant for T. simplicis. Regarding Mexico, this is the first report of T. simplicis for the state of Chiapas, and the second for Mexico (after the state of Guerrero).
Acknowledgements
We thank Mr. Carlos Gordillo, administrator of the ‘Alianza’ coffee farm, for all the facilities he gave us to carry out this research.
Author contributions
Juan Barrera (Conceptualization [lead], Data curation [equal], Formal analysis [lead], Funding acquisition [lead], Investigation [equal], Methodology [lead], Project administration [lead], Resources [equal], Software [lead], Supervision [lead], Validation [equal], Visualization [equal], Writing—original draft [lead], Writing—review & editing [equal]), Jassmin Cruz-Bustos (Data curation [equal], Investigation [equal], Validation [equal], Writing—review & editing [equal]), Javier de-la-Rosa-Cancino (Data curation [equal], Investigation [equal], Validation [equal], Writing—review & editing [equal]), and Armando Equihua Martinez (Conceptualization [equal], Data curation [equal], Investigation [equal], Methodology [equal], Supervision [equal], Validation [equal], Writing—review & editing [equal])
Funding
None declared.
Conflicts of interest. None declared.
