Tunisia - Iresa

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ut they are not generally considered as citrus pests, and there are few reports of any of these species damaging this crop. For example, in Southern Italy and in Cyprus, Frankliniella occidentalis dominate the thrips fauna of citrus but is not considered as a pest of citrus (14). In Tunisia, damages attributed to thrips on several varieties of citrus fruits have been reported during these last years. A recent work made in 2008 on citrus, in the region of Mraïssa (Cap-Bon) showed the presence of 8 species among which P. kellyanus which is economically very harmful on citrus fruits (21). However, until now, there is not any measure to control thrips citrus which were considered as secondary pests. In contrast, this species causes in Australia important damages on young and mature fruits by scurfing (or halo) marking and rind bleaching that depreciate fruit quality (4). P. kellyanus population can be reduced by insecticide applications (4, 28). Various insecticides were evaluated in field trials against larval stages I and II. Among these, the organophosphate chlorpyrifos, the carbamate methomyl, and the neonicotinoid acetamiprid were the most effective (28). However, repeated chemical treatments can lead to development of resistance, as it has been reported to chlorpyrifos in South Australia, resulting in control failures (3, 24). In Tunisia, works on thrips in citrus orchards are rare because until the last years, these pests were considered as secondary and probably because of the difficulties to study these minute and hidden insects. Thus, the objective of this work is a better knowledge of the species living in citrus orchards and their status. Moreover, it aims to determine the most widespread species in two regions of the North of Tunisia: Cap-Bon and Bizerte, and especially to confirm the presence of P. kellyanus. We also tried to estimate the damages caused by thrips on several varieties of citrus fruits, in relation with the frequency of the phytosanitary treatments. MATERIALS AND METHODS Trial sites. Twenty three orchards, 10 of the region of Cap-Bon (localities of Mraïssa, Menzel Bouzelfa, Goba and Beni Khalled) and 13 of the region of Bizerte (localities of Alia, Azib, Ras- Jebel and Sounine), have been surveyed from December 2009 to March 2010 to try to estimate the thrips damage. Estimation of thrips damage. In these orchards, with a surface nearly of 1 ha, several varieties have been considered: Grape-fruit, Orange (Thomson, Maltaise, Valencia-late, Double-fine, Navel and Meski), Clementine (Hermandina, MA3, Kassar) and Lemon. On all of them, we estimated at the harvest the proportion of scarred fruits caused either by thrips or by other factors; because we noticed that for an unexperienced person it was difficult to separate accurately the scarred fruits by the thrips and those damaged by others factors. The total number of fruits examined was about 450 for all the varieties encountered in the orchard. Then, we calculated the infestation rate that is: (Number of scarred fruits × 100) / Total number of examined fruits. Besides, an investigation was made about the treatments applied in the orchards to relate them to the recorded damages. Thrips species in citrus orchards. Thrips were collected in the orchards where the infestation rate was the highest in both regions, because we supposed that the thrips species and densities would be highest in these Tunisian Journal of Plant Protection 44 Vol. 7, No. 1, 2012
orchards. Thus, 7 orchards from the 23 prospected were chosen: 3 orchards in the region of Cap-Bon and 4 orchards in the region of Bizerte. The thrips were collected from 25 March to 29 April 2010 during bloom stages, fall of petals and at the beginning of fruit formation. The sample was obtained by beating tray of the branches on a white cloth of 50 cm × 50 cm tightened on a wooden frame. Forty branches per variety of citrus were beaten and for each tree, a branch orientation was hitten. The thrips fallen on the cloth were got back by a little aspirator, and then maintained in alcohol 10% until their identification. Then, in the laboratory, the adults were separated from larvae under binocular magnifying glass, and some microscopic preparations were made of them. The protocols used were those Strassen (5) and Mound and Tree (18). Finally, insects were mounted in balm of Canada. The identification of genus and species was made after observation of several morphological criteria under microscope. The main studied morphological characters were the wing nervation, the projection of the head, the number of antennal segments, the sensorias on the antennal segments 3 and 4, the pronotum chetotaxy, the mesothoracic fork and the shape of the abdominal segment 10. The identification was based on the keys of Palmer et al. (22) and Moritz (19). The species were confirmed by Mrs V. Balmes from the National Laboratory of Plant Protection (LNPV) of Montpellier. RESULTS Thrips species and distribution in citrus orchards. Thrips species in citrus orchards. Thrips collected in citrus orchards were identified as 13 species, 12 among them belong to the sub-order of Terebrantia namely Thrips sp., T. angusticeps, T. tabaci, T. major, Frankliniella occidentalis, Odontothrips karnyi, Limothrips cerealium, Aptinothrips elegans, Stenothrips graminum, Pezothrips kellyanus, Melanthrips fuscus and Aeolothrips citricinctus. One was identified as Haplothrips sp. which is a tubuliferan thrips. Twelve species of the thrips collected are phytophagous and only one, A. citricinctus, is predator. Distribution of thrips in the citrus orchards. The Table 1 shows that 6 of the 13 thrips species collected (Thrips sp., O. karnyi, L. cerealium, F. occidentalis, M. fuscus and A. elegans) have been reported in both biotopes while the 7 others have been found only in Cap-Bon (A. citricinctus, T. major, T. tabaci, S. graminum, Haplothrips sp. and T. angusticeps) or only in Bizerte (P. kellyanus). The genus Thrips occurred in the whole of the orchards of both biotopes on the varieties of oranges Valentia Late, Maltaise, Double fine, Thomson, Meski, and Lemon. The species O. karnyi was recorded in 4 orchards of 7 on the varieties of oranges Thomson, Valentia Late and Meski and on the clementine MA3, and Kassar. The species F. occidentalis, which has been already observed in Tunisia on several crops (15), was found in 3 orchards of 7 on several varieties of citrus fruits: oranges Thomson, Maltaise and Valentia Late and the variety of clementine MA3. P. kellyanus was found in the region of Azib in Bizerte (Table 1). Tunisian Journal of Plant Protection 45 Vol. 7, No. 1, 2012
Page 1: Inventory of Thrips Species in Citr
Page 5 and 6: Thrips damages in citrus orchards.
Page 7 and 8: Bizerte, are Thrips sp., O. karnyi,
Page 9 and 10: abundance, fruit damage and monitor

Tunisia - Iresa

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