Research Article |
Corresponding author: Hugo Miguel Silva ( hmvcsilva@ua.pt ) Academic editor: Laurel B. Symes
© 2024 Hugo Miguel Silva, Laura Avivar-Lozano, Gonçalo Gomes, Howon Rhee, Thomas Dellinger, Dora Aguín-Pombo.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Silva HM, Avivar-Lozano L, Gomes G, Rhee H, Dellinger T, Aguín-Pombo D (2024) New records of Oecanthus species (Orthoptera, Oecanthidae) in the Madeira archipelago. Journal of Orthoptera Research 33(1): 95-102. https://doi.org/10.3897/jor.33.113947
|
The Madeira and Porto Santo Islands have both witnessed substantial habitat loss since their initial colonization. Despite their small size and the degradation of their natural habitats, they harbor a rich diversity of terrestrial invertebrates, including a significant number of endemic species. While research on Orthoptera fauna has predominantly focused on the largest island of Madeira, the smaller island of Porto Santo has remained relatively understudied. Fieldwork on both islands has led to the discovery of Oecanthus dulcisonans Gorochov, 1993 in the Madeira archipelago (Porto Santo and Madeira) for the first time. This species was described based on specimens collected in Tenerife and the Arabian Peninsula. However, its distribution, which includes parts of Africa, Western Asia, and some localities in Southern Europe, remains poorly understood. Oecanthus dulcisonans is morphologically very similar to Oecanthus pellucens (Scopoli, 1763), the only species of this genus previously recorded for the island of Madeira. Due to this resemblance, doubts have arisen regarding which of these two species is present in Madeira. By examining new material of O. pellucens, we have confirmed the presence of this species on Madeira as well. These new findings highlight the fact that, for these species, the Madeira archipelago represents the western limit of their distributional ranges in the Palearctic region.
Macaronesia, Oecanthus dulcisonans, Oecanthus pellucens, Porto Santo Island, tree-cricket
Madeira is a biodiversity hotspot (
Today, only around 20% of the native Laurel Forest area remains on Madeira Island. Natural habitats are primarily restricted to the north coast of Madeira, with a few areas confined to the south coast having been largely converted into urban and agricultural areas. In Porto Santo, the oldest island in this volcanic archipelago (14 million years old), only scattered remnants of its native vegetation survive, primarily on cliffs and mountaintops. Despite these habitat alterations, current environmental threats, and the small size of Porto Santo, both islands still harbor highly diverse terrestrial fauna. According to
A total of 38 publications have been dedicated to studying the Orthoptera of the Madeira archipelago. However, research efforts have been uneven among the five islands of the archipelago. Most publications (33) have focused on Madeira, the largest island, while the much smaller island of Porto Santo (43 km2) has received limited attention (
Research on the Orthoptera fauna for the Madeira and Porto Santo Islands has reported 31 and 12 species, respectively. These include 13 and five from the Acridoidea, nine and two from Tettigonioidea, and nine and five from Grylloidea. Notably, while the papers on Madeira Island contain a few records of Oecanthus pellucens (Scopoli, 1763), there are no documented records of any species from this genus on Porto Santo. Given the size, age, and rich terrestrial fauna of this island, it is plausible that the Orthoptera fauna may be even more diverse than currently reported.
During our various field trips aimed at studying the local Orthoptera in the archipelago, we collected many Orthoptera specimens from the Madeira and Porto Santo Islands. Among these specimens, we found for the first time in the archipelago Oecanthus dulcisonans Gorochov, 1993. Initially described from specimens collected in Tenerife and the Arabian Peninsula, the distribution of this species remains poorly understood. Recent records suggest that it may inhabit the same regions as O. pellucens, a morphologically very similar species often mistaken for it (
The field trips to Madeira and Porto Santo were conducted during two separate periods: from June 14th to 19th, 2023, in Madeira and from October 22nd to 24th, 2022, in Porto Santo. Our primary method for locating crickets was by listening for their songs. In Madeira, we walked along paths through the vegetation between 22:00 and 00:00, while in Porto Santo, we traveled by car at a speed of 15 km/h between 20:00 and 23:00. Upon hearing an individual’s song, we traced the source of the sound and captured the insect either by hand or with the use of a net. The coordinate data were collected using WGS84, with a precision of three meters.
Moreover, we recorded the calling song of O. dulcisonans in Porto Santo using a Xiaomi Redmi 9C NFC smartphone with 48 kHz sampling frequency and 16-bit resolution. As the original recording contained ambient noise due to the field recording conditions, we cut only the clearest part (5 seconds) of the song. Since we lacked audio recordings of O. pellucens, we compared the songs of O. dulcisonans with referenced data for O. pellucens from the Orthoptera Species Files Online (
Finally, we examined two specimens of O. pellucens from Madeira Island that had previously been collected and were held in the University of Madeira Insect Collection (UMACI). Male and female specimens were identified according to
All the material studied has been preserved as dry-pinned specimens and is deposited in the UMACI.
During the present study, we found 21 specimens of O. dulcisonans and four specimens of O. pellucens on Madeira Island. We also found a nymph that, due to its presence at higher altitudes, could be O. pellucens. For Porto Santo Island, we collected one specimen of O. dulcisonans (Fig.
PORTUGAL • 16♂, 1♀; Madeira Island, Machico, Caniçal, Ponta de São Lourenço; 32°44'37"N, 16°42'05"W; 76 m a.s.l.; 16.VI.2023; H. Silva, G. Gomes, T. Dellinger, H. Rhee leg.; on: Hyparrhenia hirta; UMACI • 3♂, 1♀; Madeira Island, Santa Cruz, Caniço, Reis Magos; 32°38'56"N, 16°49'23"W; 38 m a.s.l.; 19.VI.2023; H. Silva, G. Gomes, H. Rhee leg.; on: Hyparrhenia hirta; UMACI • 1♂; Porto Santo Island, Campo de Baixo; 33°2'53.39"N, 16°21'5.86"W; 16 m a.s.l.; 23.X.2022; H. Silva, D. Aguín-Pombo, L. Avivar-Lozano, M. Dias leg.; on: Hyparrhenia hirta; UMACI.
MADEIRA ISLAND – ♂: BL=14.44 ± 0.55 mm (n=19); EL=14.18 ± 0.68 mm (n=19); HW=2.59 ± 0.32 mm (n=19); FL=7.98 ± 0.50 mm (n=19); ♀: BL=14.08 ± 0.39 mm (n=2); EL=14.10 ± 0.55 mm (n=2); FL=7.85 ± 0.63 mm (n=2); OV=5.48 ± 0.32 mm (n=2). PORTO SANTO ISLAND – ♂: BL=17.34 mm (n=1); EL=13.28 mm (n=1); HW=2.00 mm (n=1); FL=7.03 mm (n=1).
The song of the species consists of continuous long echemes without gap, as has been already mentioned (
Oecanthus dulcisonans is primarily distinguished from O. pellucens by the shape of the metasternal plate. In the specimens of O. dulcisonans, this plate is longer and thinner than the metasternal plate of O. pellucens (Fig.
Oecanthus dulcisonans (A, B, D, G) and Oecanthus pellucens (C, E, F, H) from Madeira archipelago. Metasternal plate (the dots represent parts of the structure that were not visible to draw) (A, D, E, F), body in dorsal view (B, C), and epiphallus in dorsal view (G, H). Photos: Thomas Dellinger. Scale bars: 1 mm (A, D, E, F); 10 mm (B, C); 0.5 mm (G, H).
Photos of Oecanthus dulcisonans stridulating (A) and standing (B) on Hyparrhenia hirta E. Fourn at Ponta de São Lourenço, Machico, Madeira Island on June 17, 2023. Photos: Howon Rhee. Oscillograms of songs of O. dulcisonans recorded at 23°C in Porto Santo Island (C) and Oecanthus pellucens recorded at 22.5°C in a laboratory with an individual from Spain by Klaus-Gerhard Heller (D), from the Orthoptera Species Files Online (
Morphometric data on Oecanthus dulcisonans and Oecanthus pellucens. Records from literature references and the specimens studied in this work. n = number of specimens studied, BL = body length, EL = elytra length, FL = posterior femur length, HW = length of posterior hind protruding below elytra, and OV = length of oviscape. All measurements are in millimeters.
Species | Locality | n | Sex | BL | EL | FL | HW | OV | Literature References |
---|---|---|---|---|---|---|---|---|---|
O. dulcisonans | Spain, Tunisia | 6 | ♂♂ | 14.01±0.26 | - | 8.60±0.14 | 3.57±0.20 | - |
|
Spain | 1 | ♀ | - | - | - | - | - | ||
O. dulcisonans | - | - | - | 14.00–17.00 | - | - | 3.50 | - |
|
O. dulcisonans | Spain, Saudi Arabia, Oman, Palestine, Cyprus | 6 | ♂♂ | 15.00–17.00 | 14.00–16.00 | 8.70–10.00 | - | - |
|
Oman | 1 | ♀ | 14.00 | 14.00 | 9.00 | - | 5.20 | ||
O. dulcisonans | - | - | ♂ | 15.00–17.00 | 13.00–16.00 | - | 3.00–4.00 | - |
|
- | ♀ | 14.00 | 14.00 | - | - | 5.20 | |||
O. dulcisonans | Porto Santo Island | 1 | ♂ | 17.34 | 13.28 | 7.03 | 2.00 | - | This work |
O. dulcisonans | Madeira Island | 19 | ♂♂ | 14.44±0.55 | 14.18±0.68 | 7.98±0.50 | 2.59±0.32 | - | This work |
2 | ♀♀ | 14.08±0.39 | 14.10±0.55 | 7.85±0.63 | - | 5.48±0.32 | |||
O. pellucens | Spain | 11 | ♂♂ | 10.80±0.14 | - | 7.60±0.17 | 0.42±0.10 | 6.00–7.50 |
|
7 | ♀♀ | - | - | - | - | - | |||
O. pellucens | - | - | - | 10.00–14.00 | - | - | 1.00 | - |
|
O. pellucens | - | - | ♂ | 10.00–13.00 | 9.00–11.00 | - | 1.00 | - |
|
- | ♀ | 11.00–14.00 | 9.00–11.00 | - | - | 6.00–7.50 | |||
O. pellucens | Madeira Island | 4 | ♂♂ | 12.98±0.11 | 10.93±0.37 | 7.93±0.57 | 1.23±0.37 | - | This work |
Gryllus pellucens Scopoli, 1763: page 139
Oecanthus pellucens:
PORTUGAL • 1♂; Madeira Island, Câmara de Lobos, Boca da Corrida; 32°42'40"N, 16°59'11"W; 1202 m a.s.l.; 25.XI.2020; G. Oliveria, T. Santos leg.; UMACI • 1♂; Madeira Island, Câmara de Lobos, Garachico; 32°40'12"N, 16°59'19"W; 439 m a.s.l.; 28.X.2018; R. Marques leg.; on: Vitis vinifera; UMACI • 2♂; Madeira Island, Calheta, Ponta do Pargo; 32°48'49"N, 17°15'41"W; 317 m a.s.l.; 14.VI.2023; H. Silva, H. Rhee leg.; on: Hyparrhenia hirta E. Fourn; UMACI • 1 Nymph; Madeira Island, Funchal, Parque Ecológico do Funchal; 32°42'25.0"N, 16°55'05.7"W; 1200 m a.s.l.; 01.VIII.2023; H. Silva, L. Soraya leg.; on: Rumex maderensis Lowe; UMACI.
MADEIRA ISLAND - ♂: BL=12.98 ± 0.11 mm (n=2); EL=10.93 ± 0.37 mm (n=4); HW=1.23 ± 0.37 mm (n=4); FL=7.93 ± 0.57 mm (n=4).
Regular gaps occur between each echeme in songs, which is also shown in Cordeo et al. (2009). The echeme repetition rate (the number of echeme per second) is approximately 1.0/s (Fig.
The mean elytra length measurements of the males, averaging 10.93±0.37 mm, align with the reported range of 9.00–11.00 mm provided by
Madeira now has a new Oecanthus species, further contributing to its overall biodiversity. This discovery holds significant value for conservation efforts and the identification of ecologically significant areas. The new records presented in this work expand the list of Orthoptera species in the Madeira archipelago to 29. Specifically, in Madeira, there are 27 species belonging to 21 different genera, while in Porto Santo, there are 13 species from 10 different genera. These records also confirm that the Madeira archipelago and the Canary Islands represent the westernmost limit of the Palearctic distributions for O. dulcisonans and O. pellucens. The presence of both species on Madeira signifies that the range extension for these species within the Palearctic region is larger than previously thought. This finding has implications for biogeographical research and enhances our understanding of the distributional patterns of these insects.
Oecanthus species are often closely associated with specific vegetation types and microhabitats (
Oecanthus pellucens is abundant and widespread, spanning from southern and central Europe to northern Africa and central and western Asia (
Acoustic monitoring and recording of individuals can serve as valuable methods for studying the distribution and population density of these tree crickets (e.g., continuous echemes for O. dulcisonans and non-continuous echemes for O. pellucens). During our field trips to Madeira, we collected only two specimens of O. pellucens on the island’s western point. In contrast, we collected 21 specimens of O. dulcisonans from two different locations, suggesting that the species might be more abundant in certain areas. Additionally, we heard its distinctive stridulations in various places at lower altitudes along the island’s south coast. Similarly, during our field trip to Porto Santo, we observed several individuals of O. dulcisonans engaged in stridulating near Praia do Zimbralinho, Cabeço da Ponta, and Campo de Baixo, suggesting a potentially widespread distribution throughout the island.
Further studies are needed to assess the potential risks confronting Oecanthus species in the Madeira archipelago. In Madeira, the natural vegetation depletion of the south coast, particularly at lower altitudes, has drastically reduced suitable coastal habitats for the species. Additionally, habitat fragmentation at higher altitudes presents significant challenges. It is essential to confirm the presence of the species on the north side of the island to assess the potential risks they encounter in Madeira. In Porto Santo, erosion and nutrient runoff have been impoverishing the soil since the 15th century (
Enhancing our knowledge of the orthopteran fauna in the Madeira archipelago, particularly of Porto Santo Island, remains a priority. Comprehensive research is urgently required to better understand the species inhabiting these increasingly fragile and reduced habitats. Only with a solid understanding of the local fauna can we formulate effective conservation strategies. Similarly, an in-depth investigation of the orthopteran fauna of Madeira Island is essential. Analyzing their ecology and morphological variations will aid in finding externally recognizable characters to facilitate the identification of these variable species and provide valuable insights into their preferred habitats. Furthermore, considering the size variations noted in specimens from the Madeira archipelago, conducting genetic comparisons with specimens from the remainder of Europe can provide additional insights into the populations of Orthoptera in Madeira. Moreover, the discovery of Oecanthus crickets in Madeira offers a unique opportunity to engage the public and students in the importance of biodiversity and conservation. These findings can be used for educational outreach programs to raise awareness about the island’s unique insect fauna.
We express our gratitude to Andrej Gorochov for his generous assistance in confirming the identification of the Oecanthus dulcisonans specimen from Porto Santo. Our appreciation also goes to Tomé Freitas for supplying the habitat photographs from Porto Santo and to Marta Dias for her assistance in collecting the O. dulcisonans specimen on this island. We would like to acknowledge the support of the Orthopterists’ Society in this manuscript and the Instituto das Florestas e Conservação da Natureza da Madeira - IFCN for granting us permission for sampling during our field trips.