Biological Control 135 (2019) 110–116 Contents lists available at ScienceDirect Biological Control journal homepage: www.elsevier.com/locate/ybcon Host range testing of Tamarixia dryi (Hymenoptera: Eulophidae) sourced from South Africa for classical biological control of Trioza erytreae T (Hemiptera: Psyllidae) in Europe ⁎ Pablo Urbaneja-Bernata,b, , Jesica Pérez-Rodrígueza,c, Kerstin Krügerd, José Catalána, Rositta Rizzae, Estrella Hernández-Suáreze, Alberto Urbanejaa, Alejandro Tenaa a Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Moncada, Spain b Grupo TRAGSA (Empresa de Transformació Agraria, S.A), Spain c Departament de Zoologia, Universitat de València, València, Spain d Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa e Departamento de Protección Vegetal, Instituto Canario de Investigaciones Agrarias (ICIA), Tenerife, Spain GRAPHICAL ABSTRACT ARTICLE INFO ABSTRACT Keywords: The African citrus psyllid, Trioza erytreae, vectors citrus greening or huanglongbing (HLB) disease. The psyllid Citrus has been reported from mainland Europe, where it is rapidly spreading from the northwest to the southwest of HLB the Iberian Peninsula. In order to reduce its spread and population levels, a classical biological control program Greening disease with the parasitoid Tamarixia dryi is under development in Spain. We evaluated the host specificity of T. dryi Host-specificity using 11 non-target psyllid (NTP) species, including five species of the genus Trioza. The psyllids were selected Non-reproductive effects based on phylogenetic and ecological criteria. Tamarixia dryi exhibited a high host specificity. Females did not Risk assessment parasitize any of the 11 NTPs tested, except for one nymph of a gall-forming Trioza species closely related to Trioza montanetana. Tamarixia dryi only laid one egg on a nymph when it was removed from the gall on Convolvulus canariensis and exposed directly to the parasitoid. However, the immature parasitoid died before emerging. We further confirmed that T. dryi did not parasitize a representative triozid species, Trioza laurisilvae, of the endemic Canarian fauna after long time exposure. Our results demonstrate that T. dryi is a highly specific parasitoid and its introduction, release and establishment in Europe within the classical biological control program of T. erytreae should not affect other psyllid species. Therefore, no significant environmental impact is expected. ⁎ Corresponding author at: Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Moncada, Spain. E-mail address: [email protected] (P. Urbaneja-Bernat). https://doi.org/10.1016/j.biocontrol.2019.04.018 Received 26 February 2019; Received in revised form 15 April 2019; Accepted 29 April 2019 Available online 10 May 2019 1049-9644/ © 2019 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/). P. Urbaneja-Bernat, et al. Biological Control 135 (2019) 110–116 1. Introduction in the test. Since some psyllid nymphs are protected by galls, the nymphs both within the galls and removed from their galls were offered The African citrus psyllid, Trioza erytreae (Del Guercio) (Hemiptera: to T. dryi females. Finally, behavioral and long-time exposure experi- Triozidae), is the latest citrus key pest recorded from mainland Europe. ments were carried out using Trioza laurisilvae Hodkinson (Hemiptera: It was detected in the northwest of Spain in 2014 (Pérez-Otero et al., Triozidae) as NTP representative of the endemic Canarian fauna. This 2015; Cocuzza et al., 2017) and, since then, has spread towards the work presents the results from mandated host specificity testing of T. southwest of the Portuguese coast reaching Lisbon (DGAV, 2018). dryi in quarantine before its release and establishment in the Canary Trioza erytreae heavily infests citrus trees in private gardens in Galicia Islands and mainland Europe for the classical biological control of T. and Portugal. This psyllid transmits the citrus greening or huan- erytreae. glongbing (HLB) disease, the most devastating citrus disease in the world (Bové, 2006; Gottwald, 2007). The disease is associated with 2. Material and methods three phloem α-proteobacterias, “Candidatus Liberibacer asiaticus” (CLas), “Ca. Liberibacter americanus” (CLam) and “Ca. Liberibacter 2.1. Insect cultures and collections africanus” (CLaf). Trioza erytreae is associated with CLaf (Bové, 2006). Since its first record from South Africa in 1929 (Jagoueix et al., 1994; Li Host range tests were carried out at the University of Pretoria (South et al., 2006), HLB has been reported from Sub-Saharan Africa, Yemen Africa) and ICIA (Tenerife, Spain). The collection and management of and a few Atlantic Ocean islands (Bové, 2006; Duran-Vila et al., 2014). the plants and insects varied slightly between the two places. Although HLB has not yet been detected in European countries (Pérez- Otero et al., 2015; Siverio et al., 2017; Cocuzza et al., 2017), the mere 2.1.1. Trioza erytreae presence of the psyllid is a major threat for the Mediterranean citrus For the establishment of two T. erytreae cultures, one in South Africa industry. and one in the Canary Islands, approximately 40 adults were collected Since T. erytreae has already spread through the west of the Iberian from 12 pesticide-free lemon trees at the Pretoria University Farm Peninsula (Galicia-Spain and Portugal), its eradication is impossible and (25°44′52.1″S 28°15′33.6″E) (South Africa) and in di fferent orchards of consequently a series of strategies need to be implemented urgently. pesticide-free lemon trees in the Canary Islands (10 km around Nowadays, classical biological control is the most feasible approach 28°31′29′'N 16° 22′12′'W) (Spain), respectively. Adult psyllids were because no native parasitoids have been recovered from T. erytreae collected using a manual aspirator from young flushes and placed in during different surveys carried out in both the Atlantic islands and the 120 ml plastic tubes with a muslin cover. They were transported to the Iberian Peninsula (Fernandes and Aguiar, 2002; Cocuzza et al., 2017). laboratory and identified using a dissecting microscope. Once identified Tamarixia dryi (Waterson) (synonym Tetrastichus dryi) (Hymenoptera: to species level, adult psyllids were released into corresponding species- Eulophidae) is the most abundant and effective biological control agent specific cultures on citrus. Citrus plants with nymphs suitable for of T. erytreae in its area of origin (Catling, 1969; Mc Daniel and Moran, parasitism (3rd to 5th instar) were collected 12 days after T. erytreae 1972; Van den Berg and Greenland, 2000; Tamesse and Messi, 2002). It adults were released. The plants were used for both maintaining the T. is a solitary koinobiont ectoparasitoid parasitizing 3rd to 5th nymphal dryi cultures and for experiments. instars of the psyllid. Tamarixia dryi has been used successfully in In South Africa, one-year-old pesticide-free grapefruit plants (Citrus classical biological control programs in Reunion Island and Mauritius paradisi Macf.) were used as host plants for T. erytreae. Plants were kept (Etienne and Aubert, 1980; Aubert and Quilici, 1985). In these islands, in 20 cm in diameter pots in bug dorms in a 60 × 60 × 60 cm plastic T. dryi is able to control the psyllid populations effectively (Etienne and cage (BugDorm-2 insect tents; MegaView Science Co., Ltd., Taichung, Aubert, 1980). Taking into consideration these successes and in order to Taiwan) in a climate chamber at 25 ± 2 °C, 60 ± 10% relative hu- reduce the spread of the psyllid, the Instituto Valenciano de In- midity (RH) and 14L: 10D h photoperiod. The plants were watered vestigaciones Agrarias (IVIA) in collaboration with the Instituto Ca- twice per week. nario de Investigaciones Agrarias (ICIA) applied for the permits to in- In the Canary Islands, two-year-old pesticide-free lemon plants troduce T. dryi into the Canary Islands and mainland Spain. The (Citrus limon (L). Burm.f.) were used as host plants for T. erytreae. Plants parasitoid was collected in several citrus orchards from Pretoria (South were grown on vermiculite and peat (1:3; vol:vol) in 20 cm diameter Africa) (Pérez-Rodríguez et al., submitted). pots and were kept in a greenhouse at 23 ± 2 °C, 70 ± 10% RH and In the past, several introductions of parasitoids have undesirable natural photoperiod. Plants were watered twice per week and fertilized negative effects on non-target insects (Heimpel and Mills, 2017). In once per week using a modified Hoagland's solution. order to avoid negative effects of parasitoid introductions, environ- In both countries, young trees were pruned to obtain homogeneous mental agencies and scientists have developed ecological risk assess- young flushes. The optimal state for the introduction of these plants ments (EPPO, 2014). Testing host specificity is the most common into the T. erytreae rearing units was reached when the oldest leaves of method used to determine whether non-target species are attacked by the new flushes measured about 4 cm. This aspect is critical because T. the proposed parasitoid and to assess ecological risks (Hokkanen et al., erytreae females lay their eggs in the axis of very young leaves (Moran 2003; Van Lenteren et al., 2006; Heimpel and Mills, 2017). and Buchan, 1975). One of the key points in host-specificity tests is to define the list of non-target species to be evaluated. Since parasitoid species tend to 2.1.2. Non target psyllid (NTP) for host specificity testing parasitize and develop in or on hosts phylogenetically close to their Multiple criteria were used for the selection of 11 representative target host (Percy et al., 2018), the phylogenetic pattern is a major NTP species for host specificity testing (Table 1). NTPs were collected determinant in host-specificity tests (Dijkerman, 1990; Godfray, 1994; from their respective host plant species by cutting the twigs or leaves Brodeur et al., 1996; Van Driesche et al., 2004; Kuhlmann et al., 2005; where they were settled.