Research Article |
Corresponding author: Ralph S. Peters ( r.peters@leibniz-lib.de ) Academic editor: Silas Bossert
© 2024 Silvan Rehberger, Jonathan Vogel, Björn Müller, Cristina Vasilita, Lars Krogmann, Stefan Schmidt, Ralph S. Peters.
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:
Rehberger S, Vogel J, Müller B, Vasilita C, Krogmann L, Schmidt S, Peters RS (2024) The obligate fig-pollinator family Agaonidae in Germany (Hymenoptera, Chalcidoidea). Deutsche Entomologische Zeitschrift 71(1): 177-183. https://doi.org/10.3897/dez.71.117640
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All native and many cultivated fig plants are pollinated by representatives of the family Agaonidae (fig wasps), which are specialised, secondarily phytophagous relatives of parasitoid wasps that evolved an obligate mutualism with fig trees. So far, distribution of Agaonidae in Europe has been limited to southern, mostly Mediterranean areas, for example, in Greece, Croatia, Hungary, Italy, France, Spain and Portugal. Here, we report the first four records of the family for Germany, all in the form of the widespread species Blastophaga psenes (Linnaeus, 1758). New verified records are from three States in western and south-western Germany, Baden-Wuerttemberg (Radolfzell at Lake Constance and Sasbach am Kaiserstuhl near Freiburg), Saarland (Saarbrücken) and Northrhine-Westalia (Bochum) and all are based on citizen-scientist observations and collections. The new records are considerably more northern than previously recorded localities and, strikingly, geographically distant from these. All records can be attributed to the presence of large male caprifig trees (Ficus carica var. caprificus), whose three generations of fruits host the development stages of Blastophaga psenes. We generated DNA barcode data of specimens from three localities and added them to the national GBOL (German Barcode of Life) database and the international Barcode of Life database (BOLD). The somewhat surprising occurrence of the species/family in Germany might be attributable to increasing temperatures as a result of global warming, but this needs further investigation. Additionally, the presence of fig wasps, assuming it stabilises, could offer new opportunities for fig farming in Germany.
Fig. wasps, Ficus carica, Blastophaga psenes, pollination, first records
All species of the genus Ficus (figs) (Moraceae) depend on obligate pollinators of the wasp family Agaonidae (Hymenoptera, Chalcidoidea). There are about 880 accepted species of figs and many more undescribed (
Ficus carica shows a special type of inflorescence called the syconium, which is built as a fleshy fruit from the stem (
Female fig cultivars are differentiated by their fruit generations into two types: Uniferous cultivars grow mainly Fichi and no or almost no Breba fruits. Biferous cultivars grow both Breba and Fichi. Female fig cultivars are also differentiated by their ability to grow parthenocarpic fruits (i.e. fruits without pollination). The Smyrna type only grows fruits with pollination. The Common type, sometimes also referred to as the Adriatic type, grows and ripens all fruit generations without pollination, though pollination can occur. The San Pedro type grows ripe Breba without pollination, but ripe Fichi only after pollination. Since Blastophaga psenes has, so far, not been present in wide areas of central and western Europe, including Germany, figs are almost exclusively grown as a hobby and not as a commercial fruit. Due to a large number of parthenocarpic Common and San Pedro cultivars, it is possible to grow figs without the pollinator. However, in the main production areas, the so-called caprification has been actively aided for centuries by planting caprifig trees or by hanging male caprifig branches in the fig plantations (
Both species, Ficus carica and Blastophaga psenes, rely on a fine-tuned interaction with three fruit and wasp generations, with male and female figs and on perfect timing. The fig trees in central Europe, for example Germany, that are sometimes just ornamental plants, are usually parthenocarpic female trees. Previously, male fig trees were found only occasionally in Germany, but in recent years, their number has been growing (
Fig. wasps were collected out of male fig tree fruits at different locations in Germany. They were either immersed in ethanol or died dry and were shipped to
At
We complemented our sequences with one Blastophaga psenes sequence downloaded from BOLD (BOLD sequence ID: GBMIN30266-13) and outgroup sequences downloaded from BOLD (Pleistodontes sp., BOLD sequence ID: ASMII11091-22; Blastophaga silvestriana, ID: GBAH19865-19; B. nipponica, ID: GBAH20335-19; B. yeni, ID: GBAH20406-19). All sequences were aligned with the MUSCLE (v. 3.9.425) algorithm allowing for a maximum of eight iterations (
BOLD-IDs of barcoded specimens, along with specimen IDs and depository information.
Specimen ID | Locality | Sex | BOLD-ID | bp-Length (ambiguities) | Depository |
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Bochum | ♀ | GBHYG1886-23 | 619(0) |
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Bochum | ♀ | GBHYG1887-23 | 619(0) |
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Bochum | ♀ | GBHYG1888-23 | 619(0) |
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Bochum | ♀ | GBHYG1889-23 | 619(0) |
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Bochum | ♂ | GBHYG1890-23 | 619(0) |
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Bochum | ♂ | GBHYG1891-23 | 619(0) |
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Bochum | ♂ | GBHYG1892-23 | 619(0) |
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Bochum | ♂ | GBHYG1893-23 | 619(0) |
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Sasbach/Kaiserstuhl | ♀ | GBHYG1894-23 | 619(0) |
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Sasbach/Kaiserstuhl | ♀ | GBHYG1895-23 | 619(0) |
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Sasbach/Kaiserstuhl | ♂ | GBHYG1896-23 | 619(0) |
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Sasbach/Kaiserstuhl | ♂ | GBHYG1897-23 | 619(0) |
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Radolfzell | ♂ | GBHYG1898-23 | 619(0) |
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Radolfzell | ♂ | GBHYG1899-23 | 619(0) |
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Radolfzell | ♀ | GBHYG1900-23 | 619(0) |
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Radolfzell | ♀ | GBHYG1901-23 | 619(0) |
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Radolfzell | ♀ | GBHYG1902-23 | 619(0) |
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Radolfzell | ♀ | GBHYG1903-23 | 619(0) |
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Confirmed records of Blastophaga psenes (those complemented by DNA barcodes marked *) in order of discovery date are:
Note that we do not give more detailed locality data to prevent vandalism of the respective fig trees. Detailed locality data are available from the authors upon reasonable request.
Localities are on display in Fig.
Analyses of DNA barcodes show conspecificity of the specimens with sequences generated herein, as well as with the B. psenes sequence added from BOLD, with a maximum intraspecific difference of 1.1%. There is a notable distance between the specimens from the Kaiserstuhl and the remaining specimens from Bochum and Radolfzell (Fig.
NJ tree, based on DNA barcode data for B. psenes specimens from three localities in Germany, complemented with one B. psenes sequence, three congeneric sequences and one Pleistodontes sp. (Agaonidae) sequence accessed via BOLD. The dotted branches that connect Pleistodontes sp. are not to scale. The support values (bootstrap with 1,000 replicates) are indicated on the respective branches.
The records of the agaonid Blastophaga psenes (Fig.
Higher mean temperatures as a result of climate change are the first obvious explanation for the new records in Germany, as is well known for many other insect taxa – for example, the fig-associated lepidopteran Choreutis nemorana (Hübner, 1799) (
At the moment, we do not know whether or not these populations become established. However, since the 2022 generation of the wasps already was the result of a successful reproduction and since more occurrences were recorded in 2023, it is well possible that these populations will establish and even spread further. Statements have to be made with caution, because B. psenes has not been known to expand its range, but is known to be difficult to establish in new areas. One of the best known examples is the deliberate introduction of B. psenes in southern California for the purpose of cultivating Turkish Smyrna fig cultivars. After many failed attempts with other species of Blastophaga and also some failures with B. psenes they finally succeeded in 1889 (
The multiple records of this extraordinary wasp taxon Agaonidae in Germany are the starting point for more in-depth studies on the details of the extension of the species’ range as well as on their potential to fundamentally change fig plant cultivation in central Europe. In our team of citizen and professional scientists, we will curiously monitor the development over the next years and continue to study the story of this intriguing plant-insect-interaction in Europe.
This paper is dedicated to the memory of our co-author, colleague and friend Stefan Schmidt.
We would like to thank Anja Ruppert, Raphael Gebhard, Stephan Rawer and Nikolaj Spiegel and many other people from the Ficus carica Facebook-Group for their support in searching for Blastophaga psenes populations at male fig trees in their home regions. Song Miaoyu and Huiqin Ma (Agricultural University Beijing, China) provided insights into research concerning Ficus carica and Blastophaga psenes in China. Don Shaw is acknowledged for linguistic help. We thank Vera Rduch (Museum Koenig Bonn) for her constant help with coordination of the GBOL III: Dark Taxa project. J. Vogel, B. Müller and R.S. Peters are supported by a grant from the Federal Ministry of Education and Research (BMBF), Berlin, Germany (FKZ 16LI1901A), for the project ‘GBOL III: Dark Taxa’.