Resumen de Bioecology of the chestnut gall wasp, "Dryocosmus kuriphilus" Yasumatsu and biological and biotechnological control methods
- español
El castaño Castanea spp. Mill. (Familia Fagaceae) tiene una gran importancia socioeconómica, medioambiental y paisajística en muchas zonas del mundo, desempeñando un papel polivalente de producción de frutos y madera, coproducción agroforestal (por ejemplo, setas comestibles o miel) y actividades de tiempo libre (Bounous, 2005; Monteiro, 2007).
Las castañas se producen un poco por todo el mundo, aunque algunos países tienen una cuota de mercado mucho mayor. China es el mayor productor mundial, con una producción cercana al 80% del total mundial en 2022. Portugal fue el 8º mayor productor en el mismo período (Lima, 2024).
En Europa, la mayoría de los castaños tienen más de 100 años, ya que este cultivo fue muy importante en el siglo XIX. La producción de castañas sufrió un notable descenso con la aparición de enfermedades fitosanitarias. Hasta entonces, la castaña era un alimento básico para las poblaciones rurales, sustituida por la patata y los cereales (AREFLH, 2012).
En Portugal, las exportaciones representan más de 1/3 de las castañas producidas a nivel nacional, e invertir en su desarrollo es importante no solo por la comercialización del fruto, también para aumentar su valor añadido. En 2023, se exportaron 12.121 toneladas, con un precio medio por kg de 2,36 euros. En el mercado nacional, el precio por kg baja a 1,50 euros. Los principales destinos de las castañas portuguesas son España (5.433 tn), Italia (4.099 tn), Francia (1.448 tn) y Brasil (450 tn). (GPP, 2024) Aunque el castaño es un árbol bastante rustico, es atacado por diferentes organismos que perjudican su desarrollo, tanto en lo que se refiere a enfermedades como a plagas. Entre los principales enemigos del cultivo podemos identificar como plagas clave la avispilla del castaño, D. kuriphilus, el tortrix del castaño, Laspeyresia (= Cydia) splendana y el gorgojo del castaño, Curculio (=Balaninus) elephas Gyllenhal) (Santos et al., 2017) Como ya se ha mencionado, el tortrix del castaño y el gorgojo del castaño son plagas de gran importancia económica. En años normales, causan pérdidas de entre el 30 y el 40% de la producción total de castañas, lo que se traduce en una pérdida significativa para el productor (Santos et al., 2020). Entre las plagas, se debe prestar especial atención al tortrix del castaño, debido a la cantidad de daños que causa y a que sus niveles de población en la región de Trás-os-Montes son considerables (Bento et al., 2007; Pombo et al., 2018; Navarro, 2019).
D. kuriphilus (clase Insecta, orden Hymenoptera, familia Cynipidae) es un organismo originario de China, se detectó por primera vez en 2012 en España y en 2014 en Portugal y ataca a especies del género Castanea (Santos et al., 2017) Esta plaga sólo tiene una generación anual. Los primeros adultos aparecen a principios de junio y siguen saliendo de las agallas hasta principios de septiembre, dependiendo de las condiciones climáticas de la región. Viven unos 10 días y ponen aproximadamente 100 huevos en las yemas del castaño (Bonsignore et al., 2019).
El medio más eficaz para combatir la plaga ha sido el uso de sueltas de T. sinensis. Al igual que la avispilla del castaño, este parasitoide es univoltino, es decir, tiene una sola generación al año y su ciclo vital está sincronizado con el de D. kuriphilus (Nieves-Aldrey et al., 2019). T. sinensis es un parasitoide originario de China, perteneciente a la superfamilia Chalcidoidea y al orden Hymenoptera. Las características que lo hacen tan eficaz son el hecho de que es específico de la avispilla del castaño y que su ciclo biológico está sincronizado con el de esta plaga (Ferracini et al., 2022; Nieves-Aldrey et al., 2019; A. Santos et al., 2017).
La existencia y promoción de parasitoides nativos es una forma indirecta de control, ya que pueden tener un efecto importante en la reducción de las poblaciones de la plaga (Lobo Santos et al., 2024).
La fauna autóctona de Portugal es diversa en especies, con 11 especies identificadas hasta la fecha, pertenecientes a cinco familias: Torymidae, Pteromalidae, Ormyridae, Eupelmidae y Eurytomidae (Lobo Santos et al., 2024). Los resultados obtenidos en Portugal están en consonancia con los de otros países, concretamente Italia, Croacia, Japón, Corea, Eslovenia, Hungría y EE.UU., tanto en lo que respecta a las especies observadas y su importancia como, sobre todo, a las familias presentes, todas ellas pertenecientes a la superfamilia Chalcidoidea (Aebi et al., 2007; Murakami et al., 1995; Stone et al., 2002). Las especies Eupelmus uruzonus Dalman, Eurytoma brunniventris Ratzeburg y Ormyrus pomaceus Geoffroy están presentes en prácticamente todos los países mencionados, siendo E. uruzonus la especie más común en toda Europa (A. Santos et al., 2017). La mayoría de estos parasitoides también están asociados a otras agallas, especialmente del roble.
- English
The chestnut tree Castanea spp. Mill. (Family Fagaceae) has a great socio-economic, environmental and landscape importance in many areas of the world, playing a multipurpose role of fruit and wood production, agro-forestry co-production (e.g., edible mushrooms or honey) and spare time activities.
Chestnuts are produced practically all over the world, although some countries have a much larger share of the market. China is the world's largest producer, having produced around 80 per cent of the world total in 2022. Portugal was the 8th largest producer in the same period (Lima, 2024).
The chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu, is an insect that attacks species of the Castanea genus, inducing the formation of galls on the buds and leaves, which can severely reduce the growth, fruiting and consequently the production of chestnut trees. D. kuriphilus is a species native to China. Torymus sinensis Kamijo is a parasitoid that also comes from China and is specific to the pest D. kuriphilus and is currently the most effective means of controlling this pest.
This research focused on two distinct areas of action: (i) the bioecology of D. kuriphilus and (ii) the evaluation of the efficacy of biological and biotechnological control methods against D. kuriphilus. To achieve the objectives defined in this study, the following working methodology were used: D. kuriphilus biology: Execution of harvests at different stages of the life cycle of D. kuriphilus to evaluate the period of the postures, how immature states develop over time (eggs, larvae and pupae) and emergence of adults period. This evaluation begun in the spring (depending on climatic conditions and evolution of the chestnut tree's phenological state in the region). Harvests were done weekly during the active phase of the cycle and monthly during the remaining period and the galls or buds were dissected in the laboratory for evaluation; Native parasitoids: Harvesting of galls during the month of June in order to study the native parasitoids that can act in this pest control. The harvests were held in Trancoso, Minho and Vinhais. In each region were harvested in 6 different locations. In each site, 240 galls were collected, which were placed in two emergency boxes, each with 120 galls. At the beginning of autumn and the following spring, the boxes were opened in the laboratory and the galls cleaned with a brush and put back into the box. All insects found were collected and placed in Eppendorf tubes identified with the box number. Subsequently the quantification and identification of the insects were carried out with the aid of identification keys; Native parasitism rate: Harvesting of galls during the month of June and dissection of the same in order to evaluate the natural parasitism rates in Trancoso, Minho and Vinhais. In each region, four chestnut orchards were selected, where 100 gall/orchard were harvested. The galls were sectioned and observed under a binocular microscope for counting the chambers and identification of the individuals (D. kuriphilus and parasitoids). Subsequently, the rate of parasitism was calculated; Biological control methods: In the spring, T. sinensis were released in test fields where the pest was installed with some intensity. At the beginning of following spring, the galls of the previous year were harvested and placed in emergency boxes which were monitored weekly to assess whether the parasitoid has established in the plot and what was the rate of parasitism; Biotechnological control methods: Selection and pulverization of test fields in Vinhais with repellent substances. In the test fields, four treatments were applied: control, kaolin, repellent and insect repellent mixture. Each treatment had at least 6 replicates (trees). The evaluation of the results of these treatments were carried out in the following spring on 50 buds in four branches/tree/treatment by harvesting all the galls, counting and dissecting them to evaluate the number of pupation chambers available; and The biotechnological control effect in auxiliary fauna: Evaluation of the possible effect of chemical substances on the auxiliary fauna present in the chestnut orchards, using the beating technic before and after the treatment has been applied (T0; T1; T2, T3 e T3.1). In each test field, 25 trees were selected and arthropods collected, transported into the laboratory and frozen. After that, arthropods were sorted under a binocular microscope and identified to family, genus or species level.
The main results of this research showed that 92% of D. kuriphilus adults emerged between June and July, with emergences occurring until September. We also obtained adults in winter, so it is important to study, in future works, the hypothesis of this pest performing diapause. Regarding the study of native parasitoids, compared to other countries, the same families emerged, with good rates of natural parasitism, although with fluctuations over the years. In the three municipalities under study, 11 species were identified (Eupelmus azureus Ratzeburg, Eupelmus urozonus Dalman, Eurytoma brunniventris Ratzeburg, Megastigmus dorsalis (Fabricius), Ormyrus pomaceus (Geoffroy), Sycophila iracemae Nieves Aldrey, Sycophila variegata (Curtis), Sycophila biguttata (Swederus), Torymus flavipes (Walker), Torymus auratus (Mueller), and Torymus notatus (Walker)). The average parasitism rates varied between 1.92% and 10.68%. Regarding T. sinensis releases, average parasitism rates in year n0 ranged from 7.37% to 33%, and in the municipality of Bragança, in year n0, between 2020 and 2023, the average number of T. sinensis collected was between 45 and 664 individuals per civil parish. Regarding the evolution of the rates over four years after the parasitoid was released, the rates in year n0 (2020) were between 0% and 31.5%, and in the fourth year of monitoring (2023) they were between 15.3% and 50.4%. In the case of the parish of Coelhoso, there were no more galls to monitor in 2023. Regarding the test with different repellent and insecticide substances, this work concluded that kaolin was the most effective treatment in reducing the number of galls and chambers. However, there was a significant impact on the non-target arthropods, especially the orders Coleoptera, Araneae, Heteroptera, Hymenoptera and Diptera.
To conclude, knowledge of the life cycle of the chestnut gall wasp is fundamental to successfully combating it. Native parasitoids play an important role in controlling this pest, but releases of the parasitoid T. sinensis are the most effective means of combating it. Kaolin could be a complement as a control mean against this pest, but it is important to better assess the impact on non-target insects.
