The engineer from the Montes department of the Center for Research and Technological Development of Extremadura (Cicytex), Adrián J. Montero-Calvo, and the agricultural engineering doctor from the Plant Health Service of the Department of Agriculture, Livestock and Sustainable Development, Luis M. Torres-Vila, have developed research into advances in knowledge of the sessids associated with Quercus in Extremadura, the results of which have been disseminated in the journal "Montes".
As the study’s managers explain, in recent years "an increase in damage has been detected in our region in holm oaks, cork oaks, and gall oaks caused by larvae of moths from the family of sessids".
Moths from the family of sessids, known popularly as transparent-wing moths, are present in almost all regions of the planet, although their biology continues to be poorly understood outside the specialized field of entomology. More than 1,500 species have been described to date, as the Junta de Extremadura has indicated in an information note.
The review and survey work carried out between 2020 and 2025 analyzes how knowledge of these species in the Extremaduran territory has evolved. It begins with the rollout of automatic monitoring systems in 2021 and extends through detailed studies of distribution, phenology, and daily activity that have been published in 2025.
Ecological impact and damage in Quercus
The ecological impact caused by sessids occurs under the bark of trees and shrubs. Their larvae feed on the inside of living stems, branches, or roots, where they excavate galleries over several years.
Certain species attack fruit or forest trees and, when infestations reach high intensities, they can seriously weaken or even cause the death of the tree, which is why some sessids are cataloged as forest and agricultural pests.
In Extremadura, the lack of specific studies contrasted with on-the-ground confirmation of significant damage in young Quercus plants, whose causes were not clear. For this reason, since 2020, surveying and monitoring efforts have been promoted that have made it possible for the first time to obtain a preliminary knowledge base on these species in the community.
To this end, a network of baited traps with sexual pheromones was installed in 38 representative sites of dehesas, reforestation areas, and natural forest stands. This network was reinforced with automatic detection systems, among which a trap connected via LoRaWAN technology designed by Adrián Montero stands out, which sends real-time alerts of each capture.
The work carried out up to 2023 has also made it possible to verify the presence of 19 species of clearwing moths in Extremadura, four of which have species of the genus Quercus as hosts. These are "Synanthedon conopiformis" —the most abundant— and "Synanthedon vespiformis", followed by "Paranthrene insolita" and "Synanthedon codeti".
Each of these species has a different flight period throughout the year and even specific hours of daily activity. The Board highlights "S. vespiformis", which shows two flight peaks, in spring and autumn, and nearly disappears in summer. Montero and Torres-Vila point out that it could be an adaptive response to the summer heat and drought, increasingly pronounced due to the effect of climate change.
All these species are widely distributed in holm oak groves, cork oak woodlands, and rebollo oak stands, and several of them have been recorded for the first time in the provinces of Badajoz and Cáceres.
The two engineers emphasize that having more precise knowledge about the ecology and regional distribution of these species is key, given their potential phytosanitary impact on the trees of the dehesas of Extremadura.
Along these lines, they consider that the damage detected in reforestations and densification of Quercus makes it necessary to carry out deeper research on aspects such as the complete biological cycle of the species, the rates of parasitism and the action of entomopathogens, the genetic variability of populations, the factors that explain interannual fluctuations in density, and economic damage thresholds under different silvicultural management models.
Finally, they highlight that the results obtained will contribute to optimizing the integrated management of these species. Knowing their periods of greatest activity will make it possible to apply prevention and control measures at the most appropriate time, while identifying where they are located and in what abundance will facilitate delimiting the areas of greatest risk and prioritizing interventions.