This was a field-record study rather than an experiment. The researchers did not directly test the causes of the new geographic distribution or establish whether the German populations have become persistent. The four confirmed records were made between May and August 2022. The authors withheld precise locality information for the fig trees to reduce the risk of vandalism, while making the underlying data available on request.

Wasps were collected from male fig fruits at different locations. Specimens were either immersed in ethanol or died dry before being sent for examination to the Museum Koenig Bonn or the SNSB-Zoologische Staatssammlung München. At Museum Koenig, the researchers processed 21 specimens from Radolfzell, Sasbach im Kaiserstuhl and Bochum. They extracted DNA and initially attempted to amplify the mitochondrial CO1 barcode region, but the original primer pair produced no sequences.

The researchers then used a newly designed forward primer, Heloridae-CV-F, with the HCO 2198-JJ reverse primer to amplify a 619-base-pair fragment. Twenty of the 21 specimens were successfully sequenced. Eighteen barcodes met the stated German Barcode of Life gold-standard criteria, including chromatogram quality and no more than 1% ambiguities or disagreement between contig sequences. The successful barcodes were uploaded to BOLD in dataset DS-DEBLPSEN.

The researchers aligned the new sequences with one B. psenes sequence and four outgroup sequences downloaded from BOLD, then calculated a neighbour-joining tree using the Tamura–Nei distance model. The analyses supported conspecificity among the German specimens and the B. psenes reference sequence. The maximum intraspecific difference was 1.1%. Specimens from Sasbach im Kaiserstuhl differed by 0.6–1.1% from those from Bochum and Radolfzell, while differences within each cluster reached a maximum of 0.5%. Morphologically, the authors considered all German specimens conspecific. The barcode differences might indicate different source populations, but the study did not establish their origins.

Blastophaga psenes is the sole pollinator of the edible fig, Ficus carica, and its reproduction depends on a coordinated cycle involving male and female trees and several generations of fruit. Male caprifigs contain short-styled gall flowers that host the wasps’ eggs and larvae together with male flowers that supply pollen. Female trees bear long-styled flowers and produce edible fruit. Depending on the cultivar, F. carica can produce up to three fruit generations per year.

The association is obligatory but does not mean that every edible fig cultivar requires pollination. Common-type cultivars, sometimes called Adriatic, can grow and ripen all fruit generations without pollination, although pollination may occur. Smyrna-type cultivars produce only pollinated fruits, while San Pedro-type cultivars can ripen Breba without pollination but require pollination for ripe Fichi. Reproduction of the wasp requires male caprifigs with fruit at the appropriate stages, so warmer conditions alone would not be sufficient to support it in a new area. The increasing availability of male caprifigs in central Europe may therefore have created opportunities for the wasp to reproduce alongside cultivated female trees.

Beyond the four confirmed localities, the study mapped less conclusive observations. Members of a Ficus carica Facebook group reported large numbers of wasps entering fig ostioles or emerging from caprifigs in Würzburg, Karlsruhe and Kippenheim near Offenburg in 2023, but those observations lacked detailed species identification and vouchers. The authors considered them reliable and mapped them separately. Pollinated Main Crop fruits from cultivars requiring pollination were also recorded in Riegel am Kaiserstuhl and Freiburg im Breisgau in 2022 and 2023, and in Wattenscheid, Essen and Rheinfelden in 2023; these observations did not include identified or vouchered wasps.

The authors identified climate change as a possible contributing factor, while emphasizing the wasps’ specialised relationship with F. carica. Unpublished 2023 observations from fig enthusiasts in Alsace, Ghent, The Hague, Graz and Klagenfurt suggested a possible stepwise expansion from western and eastern populations along the Rhine, Danube and Rhône corridors, but these were not part of the verified German dataset. The German populations have not previously been compared with specimens across Europe, leaving the routes and origins of the range extension uncertain. Because the 2022 observations involved wasps produced by successful reproduction and further records were made in 2023, establishment is possible but not demonstrated.

Historical introduction attempts illustrate the uncertainty. B. psenes was successfully introduced in southern California in 1889 to pollinate Smyrna figs, but no subsequent range expansion was observed, while attempts in Texas, southern Arizona and Florida failed. The study therefore provides verified first records and a baseline for monitoring the fig–wasp interaction in Germany. Whether the populations will persist, spread further or alter fig cultivation remains unresolved.

Subject of Research: First verified records and genetic identification of the obligate fig pollinator Blastophaga psenes in Germany

Article Title: The obligate fig-pollinator family Agaonidae in Germany ( Hymenoptera , Chalcidoidea )

Article References: Rehberger, S., Vogel, J., Müller, B., Vasilita, C., Krogmann, L., Schmidt, S., & Peters, R. S. (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

Image Credits: AI Generated

DOI: 10.3897/dez.71.117640

Keywords: Blastophaga psenes, Agaonidae, fig wasps, Ficus carica, caprifigs, DNA barcoding, citizen science, Germany, pollination, range expansion, obligate, fig-pollinator

The team used inter-simple sequence repeat markers, known as ISSR markers, to probe the genomes of the collected trees. ISSR markers target short repeated DNA sequences scattered throughout the genome, amplifying the stretches between them to produce a fingerprint of bands that can be compared across individuals. Because these microsatellite-flanking regions mutate relatively quickly, ISSR markers are sensitive tools for detecting variation even among closely related cultivars of the same crop. In this study, 14 ISSR primers generated 214 scorable bands across the 93 cultivars, and a striking 184 of those bands, or 85.98 percent, were polymorphic, meaning they differed among at least some of the trees sampled.

Those numbers translate into exceptionally high genetic diversity for a cultivated fruit tree. The researchers calculated a resolving power of 8.00 for their marker set, a Nei’s gene diversity index of 0.34, a polymorphism information content of 0.52, and a Shannon information index of 0.34. Each of these metrics describes a different facet of variation, from how well the markers distinguish individual genotypes to how much uncertainty remains when guessing the genetic makeup of a randomly chosen tree. A PIC value above 0.5 is generally considered highly informative, indicating that the ISSR system captured substantial discriminating power across the Moroccan fig collection.

Perhaps the most consequential finding came from the analysis of molecular variance, or AMOVA, a statistical framework that partitions genetic variation into components within and between groups. The results showed that 89 percent of the total genetic variation resided within groups of cultivars, while only 11 percent was found between groups. In practical terms, this means that a farmer’s orchard in one valley may contain nearly as much hidden genetic variation as an entire region hundreds of kilometers away. Traditional agroecosystems, where multiple varieties are grown side by side and exchanged informally among neighbors, appear to be incubators of diversity rather than mere repositories of it.

Cluster analysis reinforced this picture of diffuse, locally rich diversity. Using UPGMA, a hierarchical clustering method that groups genotypes according to overall band-sharing similarity, the researchers organized the 93 cultivars into five main groups. The edible female figs from the Beni Mellal-Khenifra region showed particularly high genetic dispersion, scattering across the clustering diagram rather than gathering into a tight regional cluster. That dispersion suggests extensive exchange of planting material, seedling selection by farmers, and possibly multiple historical introductions of fig germplasm into the region, which historically served as a crossroads for trans-Saharan trade routes.

The caprifigs told a very different story. Caprifigs are the male, inedible figs that produce pollen and host the tiny fig wasp, Blastophaga psenes, which pollinates female fig flowers in a symbiosis so ancient and so intimate that neither partner can reproduce without the other. In the study, caprifigs formed a distinct and homogeneous cluster regardless of where they had been collected, separating cleanly from the edible female cultivars. This clear genetic split mirrors the gynodioecious breeding system of Ficus carica, in which male and female functional forms are genetically differentiated, and it validates the use of molecular markers to distinguish caprifig germplasm for breeding and pollination management.

The significance of this work extends well beyond Morocco’s borders. The fig is one of the oldest domesticated fruit trees in the world, and its center of diversity lies in the Middle East and Mediterranean basin, with Morocco recognized as a rich secondary reservoir. Earlier studies using microsatellite and other marker systems have documented diversity in Turkish, Tunisian, Algerian, and Jordanian fig germplasm, and Moroccan collections have been characterized morphologically and with SSR markers in previous work. What this new study adds is a broad, marker-based survey that explicitly spans both the mountain agroecosystems of the Atlas and the desert oases of the south, two environments that impose very different pressures on the trees growing in them.

That environmental breadth matters for conservation planning. Oases are fragile systems threatened by water scarcity, salinization, and rural depopulation, while mountain terraces face their own pressures from land abandonment and climate shifts. When genetic variation is distributed mostly within rather than between sites, losing any single site erodes a meaningful slice of the species’ total diversity. The authors argue that their results underline the value of ISSR markers for conservation and breeding programs, providing a cost-effective way to identify unique genotypes, avoid duplicating accessions in germplasm collections, and select parents for crosses that maximize genetic gain in fruit quality, drought tolerance, or disease resistance.

The study also fits into a growing body of work by the same research group at Sultan Moulay Slimane University, which has applied ISSR markers to Moroccan walnuts, plums, apples, and the endemic resin spurge Euphorbia resinifera. Together with companion studies by Mardoume and colleagues on the sugar profiles, organic acids, antioxidant activity, and phenotypic variability of Moroccan figs, the molecular data sketch a crop that is not only genetically rich but also chemically and morphologically diverse. For breeders seeking climate-resilient cultivars, such multidimensional diversity is raw material that cannot be recreated once lost.

For now, the message from the oases and mountains of Morocco is a hopeful one: centuries of traditional farming have quietly assembled one of the most genetically diverse fig populations ever surveyed with molecular markers. The challenge ahead is to document and conserve that diversity before the agroecosystems that sustain it disappear. With 85.98 percent of their marker bands polymorphic and nearly nine-tenths of the variation locked within local groups, Moroccan figs demonstrate that the future of food security under global change may depend as much on the smallholdings of traditional farmers as on any high-tech gene bank.

Subject of Research: Genetic diversity of fig tree (Ficus carica) cultivars and caprifigs in Moroccan oases and Atlas regions assessed with ISSR molecular markers

Article Title: Genetic diversity of Caprifigs and female fig (Ficus carica) from Moroccan oases and Atlas Regions revealed by ISSR markers

Article References: Mardoume, I., Bouda, S., Khachtib, Y., Zaggoumi, H., Neg, I., Ait Bella, Y., & Haddioui, A. (2026). Genetic diversity of Caprifigs and female fig (Ficus carica) from Moroccan oases and Atlas Regions revealed by ISSR markers. Plant Biosystems, 160(4), Article 216. https://doi.org/10.1007/s44473-026-00221-6

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00221-6

Keywords: Ficus carica, genetic diversity, ISSR markers, Morocco, caprifigs, oases, Atlas Mountains, AMOVA, agroecosystems, germplasm conservation, plant breeding, molecular markers