Integrated Control of Citrus Pests in the Mediterranean Region

< p>The origin and spread of citrus in the Mediterranean Region are briefly discussed, together with the fundamental characteristics of the main species, cultivars and rootstocks grown in the Region. The choice of the genotypes, the plant propagation, the sanitary control, and the cultural management (planting systems, nutrition and fertilization, irrigation and management of water, soil and ground soil management, harvesting and fruit quality) are presented. In conclusion, the future perspectives and genetic improvement for the Mediterranean citriculture are discussed.< /p> < p>< /p> < p>< /p> < p>< /p> 3174938 978-1-60805-294-3 3 18 0003.pdf Paolo Inglese, Giovanni Pensabene Bellavia, Dipartimento di Colture Arboree, Universita degli Studi di Palermo, Viale delle Scienze, 90128, Palermo, Italy Citriculture, Mediterranean Region, fruit, rootstock, orchard management,

The origins of biological control, the influence of its early successes, and relevant observations and experiments conducted in the late 19th and early 20th centuries in the Californian citrus industry are briefly presented. These practices, along with the growing disappointment with chemical control, naturally led to the move from strict biological control to the concept of Integrated Pest Management (IPM). The history of IPM in the Mediterranean citriculture throughout that period is presented against this background, and the most important projects of classic and augmentative biological control carried out in the region are discussed. Brief information on the role of international institutions (IOBC, EU, FAO) and the scientific community in the development of IPM is also provided.

In this chapter the goals of Integrated Pest Management (IPM) are discussed, along with the steps necessary for their implementation in citriculture. Pest prevention is treated first, and then available choices and horticultural practices, climate monitoring, the identification of pests and their natural enemies, the sampling and monitoring of pest populations, the prediction by Degree-Days (°D) and related decision tools and finally calculation of the Economic Injury Level (EIL) and Economic Threshold (ET) and a general approach to the Action Threshold (AT). A discussion of the means of pest control completes the chapter.

The correct identification of pest species is a prerequisite for the implementation of Integrated Pest Management (IPM) programs. Towards this aim a key is presented for the identification of the classes, orders and families of the most important pests infesting citrus in the Mediterranean Region.

The major natural enemies of the citrus pests in the Mediterranean Region are briefly presented. The complexity of the topic has led to a simplification of the treatment. The more common Hemiptera, Neuroptera, Lepidoptera, Diptera, Coleoptera, Hymenoptera and Acari are discussed, along with the general features of each group.

Eleven mite (Acari) species in four families are serious pests of citrus in the Mediterranean Region. These include Aceria sheldoni (Ewing), Phyllocoptruta oleivora (Ashmead) and Aculops pelekassi (Keifer) in the family Eriophyidae; Brevipalpus californicus (Banks), B. lewisi McGregor, B. obovatus Donnadieu and B. phoenicis (Geijskes) in the Tenuipalpidae; Polyphagotarsonemus latus (Banks) in the Tarsonemidae and Eutetranychus orientalis (Klein), Panonychus citri (McGregor) and Tetranychus urticae (Koch) in the family Tetranychidae. Diagnostic characters and illustrations are provided for each species, along with data on their life history, economic importance and management.

Eleven Thysanoptera (thrips) species, all included in the family Thripidae, are listed as pests on citrus in the Mediterranean region, and a diagnostic dichotomic key is provided for them. For each species the main morphological characters, biological features and data on the economic importance are reported. Amongst them, five species i.e. Chaetanaphothrips signipennis Bagnall, Frankliniella bispinosa Morgan, Scirtothrips aurantii Faure, S. citri (Moulton) and S. dorsalis Hood are quarantine species that are not yet present in the Mediterranean countries; however, Heliothrips haemorrhoidalis (Bouche), Pezothrips kellyanus Bagnall, Thrips flavus Schrank and T. tabaci Lindeman are common pests on citrus. Data on pest activity due to F. occidentalis (Pergande) are not yet known, whereas literature reports on its spread onto new hosts, have only very recently become available from a few Mediterranean countries.

The large hemipteran family Cicadellidae, or leafhoppers, has more than 2300 species described in 338 genera in the Palearctic region. Many are world-wide pests of crops. Sixty-one leafhopper species were collected in citrus orchards in the Mediterranean Region, but many have low economic importance. Asymmetrasca decedens (Paoli), Empoasca alsiosa Ribaut, and E. decipiens Paoli are common and devastating cicadellids. They live on vegetables, vineyards and cotton in summer, moving to citrus later on, when other host-plants are no longer available. On the other hand, members of the Circulifer haematoceps (Mulsant and Rey) complex are less common than the three aforementioned species, but are capable of transmitting Spiroplasma citri Saglio et al., the causal agent of citrus stubborn disease. Many parasitoids and predators of cicadellids have been identified. Gonatopus lunatus Klug on Circulifer haematoceps and Aphelopus sp. on Asymmetrasca decedens and Empoasca decipiens were effective parasitoids (Hymenoptera: Dryinidae). Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae), Deraeocoris pallens (Rt.) (Hemiptera: Miridae), Nabis ferus (L.) (Hemiptera: Nabidae), Geocoris sp. (Hemiptera: Geocoridae), Paederus f.c. kalalovae Curtis (Coleoptera: Staphylinidae) are common predators feeding on cicadellids in citrus orchards.

The Aphididae, or aphids, is a large family of nearly 4000 small and soft-bodied insects in the superfamily Aphidoidea. More than 25 aphid species have been found in citrus orchards throughout the world, of which some are of economic importance and others probably occur there sporadically. The aphids infesting citrus in the Mediterranean Region reach their maximal numbers in spring, attaining another, lower peak in autumn, and sometimes a third, of minor importance, during summer. Some of the citrus aphids, like Aphis craccivora Koch, A. fabae Scopoli, Macrosiphum euphorbiae (Thomas), and Myzus persicae (Sulzer), never reach high population levels due to the activity of their natural enemies. The others, Aphis gossypii Glover, A. spiraecola Patch, Toxoptera aurantii (Boyer de Fonscolombe) and T. citricida (Kirkaldy), are serious pests, either because they occur in very large numbers or due to their ability to transmit many virus diseases, including citrus tristeza virus (CTV). Their management is mostly by their many natural enemies. These include parasitoids of the subfamily Aphidiinae (Hymenoptera, Braconidae) and many predators of the families Coccinellidae (Coleoptera), Syrphidae (Diptera); Cecidomyiidae, Chamaemyiidae (Diptera); Anthocoridae, Lygaeidae, Miridae, and Nabidae (Hemiptera) and Chrysopidae (Neuroptera).

The chapter presents a brief historical account on citrus cultivation in the Mediterranean basin and on major epidemics that affected citriculture in the past. The citrus industries mostly survived these serious drawbacks by changing about 150 years ago their horticultural practices from non-grafted to grafting trees on the sour orange rootstock which produced a stionic combination highly resistant to fungal root-rots. Basing the industry on the sour orange eventually turned into the road map for the emergence of a subsequent major global pandemic caused by the aphid borne Citrus tristeza virus (CTV). This led growers to shift to new stionic combinations based on a variety of rootstocks that provided not only tolerance to the disease along with adaption to a variety of edaphic conditions. Adaptability is an ongoing process as recently experienced in certain parts of Brazil, where the Rangpur lime rootstock which for almost half a century has been successfully providing both drought and CTV tolerance is succumbing to a recent localized epidemic caused by citrus sudden death, a new vector borne disease caused by an infectious agent that is still not sufficiently characterized. Rootstock replacement is however not an universal remedy for all citrus mainly because some threatening diseases such as greening /huanglobing (HLB), Citrus variegated chlorosis (CVC), witches broom and stem pitting isolates of CTV damage directly the scion part and thus not helped by rootstock-replacement. The chapter focuses on three vector-borne pathogenic agents that cause three important citrus diseases, stubborn, CTV and citrus greening/HLB respectively representing three types of disease problems (i) endemic, (ii) emerging and (iii) threatening of concern for Mediterranean growers. Some possible ways to minimize the damaging impacts of these diseases on the future of citrus production in the Mediterranean Region are discussed and some measures validated by past experience with endemic disease are used to obtain an estimate on the potential damage of two disease problems threatening the Mediterranean citrus industries, the spread of Toxoptera citricidus, the most effective vector of CTV and the possible spread and emergence of greening/HLB epidemic in the area. Information on other vector born citrus diseases as citrus variegated chlorosis, citrus sudden death, citrus leprosis, Omani lime witches broom disease, in relation to their potential threats to Mediterranean citriculture is provided. Essentially the message is simple and follows the slogan “better safe than sorry” as a clear indication that the Mediterranean citrus industries must place high priorities both on national and regional certification and R&D programs to prevent the spread of these potentially devastating diseases.

The adults of the Aleyrodidae (whiteflies) are small winged insects usually yellow-white in colour; some species bear grey marks on the wings or are darker, even brown-black. Immatures may be misidentified as aphids or scale insects, but the “vasiform orifice” will help in separating whiteflies from other groups in slide mounted and red-stained puparia. All instars secrete wax, in the shape of powder, curls, threads or as vitreous layers. They are called “whiteflies” due to their general whitish appearance. They are mostly bisexual, but several species or “strains” show both arrhenotokous and thelytokous parthenogenesis, usually in relation to insemination. The post-embryonic development is neometabolic, consisting of four larval instars, pupae (immotile and not-feeding) and adults. Whiteflies share with other Sternorrhyncha the piercing-sucking mouthparts and the specialized “filter chamber” mid gut. They suck plant sap, killing their host plants in heavy infestations and excreting abundant liquid faeces as honeydew drops. These drops cover infested plants, which then blacken because of colonization by sooty mold fungi. The blackened plants or products are untradeable due to the sooty mold. Whiteflies may also cause physiological changes and transmit viruses. In the Mediterranean Region whiteflies live mostly on woody perennial plants. Natural or classical biological control programmes have successfully controlled current or potential pest species by the introduction of effective natural enemies. Aleurocanthus spiniferus Quaintance is currently of major concern to citriculture in the Mediterranean Region because it was recently introduced and no indigenous natural enemies seem to control it. As in the past, unwanted, introduced whiteflies may become key pests of citrus in the Mediterranean Region.

The families Pseudococcidae (mealybugs) and Monophlebidae include small scale insects (Coccoidea: Hemiptera) that suck out plant sap. The bodies of young instars and adult females are covered with a wax secretion, whereas adult males carry a pair of small wings. Feeding by these pests can cause premature leaf, flower, and fruit drop, reduce plant vigour and discolour tissues. In addition, they secrete honeydew upon which sooty-mould fungi grow, reducing photosynthesis and the market value of the product. Six species of Pseudococcidae, namely Planococcus citri (Risso), Pseudococcus cryptus Hempel, Ps. longispinus (Targioni Tozzetti), Ps. calceolariae (Maskell), Ps. viburni (Signoret) and Nipaecoccus viridis (Newstead) are economic pests of citrus in the Mediterranean area, along with Icerya purchasi Maskell, in the family Monophlebidae.

Soft scale insects (Hemiptera: Coccidae) are important citrus pests. They are sessile insects that damage citrus by sucking plant sap, thus reducing plant vigor. They also excrete copious amounts of honeydew that promotes the development of sooty mold fungi, which hinder the photosynthetic ability of the plant and directly reduce the market value of the fruit. In the Mediterranean Region six species are of economic importance for citrus production: Coccus hesperidum (Linnaeus), Coccus pseudomagnoliarum (Kuwana), Saissetia oleae (Olivier), Ceroplastes rusci (Linnaeus), Ceroplastes floridensis Comstock, and Ceroplastes sinensis Del Guercio. Field and microscopic identification keys are provided and notes on their biology and current practices of pest management are also reviewed.

The Diaspididae, like all Coccoidea (Hemiptera), feed on plants and may at times become pests. Nine species are important pests of citrus in the Mediterranean Region. They consist of Aonidiella aurantii (Maskell), Aspidiotus nerii Bouche, Chrysomphalus aonidum (Linnaeus), C. dictyospermi (Morgan), Lepidosaphes beckii (Newman), L. gloverii (Packard), Parlatoria cinerea Hadden, P. pergandii Comstock, and P. ziziphi (Lucas). Field and microscopic keys for these pests are provided, along with diagnostic characters, life history details, economic importance data and management methods for each species.

Two tephritid species are important pests of citrus in the Mediterranean Region. The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), is widely distributed, whereas the peach fruit fly, Bactrocera zonata (Saunders), has only recently been recorded in Egypt. Both are multivoltine and polyphagous that can cause direct losses in fruit production and impede international trade. Descriptions, host plants, life history, effects of hosts and climatic factors, biotic mortality factors and population dynamics are discussed, along with the most important control methods of both species.

Four species of moths are harmful to citrus in the Mediterranean Region. They are assigned to the families Gracillariidae (Phyllocnistis citrella Stainton), Yponomeutidae (Prays citri Milliere) and Pyralidae [Cryptoblabes gnidiella Milliere and Ectomyelois ceratoniae (Zeller)]. The first two are direct pests, whereas the others inhabit and damage citrus only when attracted there by mealybug honeydew. A key to the identification of the three families and to the larval stages of the 4 species are provided. Diagnostic characters, life history data, economic damage and management recommendations are provided for each species.

The economic importance of the Formicidae (ants) in agriculture is mainly due to their interactions with honeydew-producing Hemipterans, which reduce the abundance of beneficial arthropods in the canopies, thus hindering the biological control of pests. Argentine ant [Linepithema humile (Mayr, 1868)] and native ants (of the genera Camponotus, Formica, Lasius, Pheidole, Plagiolepis, Tapinoma, Tetramorium) are the most common ant species that aggressively protect and attend Hemipterans in the Mediterranean Region. Although many ants occur in citrus groves, very few species directly damage the plants. A brief review of the important species and guidelines for their management in citrus groves are presented.

Herein we treat secondary pests that occasionally infest citrus in the Mediterranean Region. Many of these species occur fortuitously, whereas a few may become pests. Some cause economic-level damage only in one or a few countries, being pests during a few years, later disappearing or becoming almost harmless. Therefore this list is probably incomplete, and will require changes in the future. Brief systematic and biological data are provided for each species, with a minimum of references.

In this concluding Chapter we discuss the importance of several basic steps that can optimize the outcome of a citrus IPM program. In particular, we treat the need for stricter quarantine services and determining the Economic Injury Level (EIL) and Action Threshold (AT) for each pest. We emphasize the need to know more about the direct and indirect effects of the various citrus hosts on the pests and on their natural enemies, about the indirect effects of soil conditions and horticultural practices on pests and their enemies, quantitative estimates of the impact of the natural enemies (or any other IPM program) on pest numbers and (even more important) on yield quantity and quality. We also advocate initiating further in-depth studies on the use of indigenous natural enemies, exploring interactions between suites, or guilds, of natural enemies, and a far more extensive application of molecular tools, all of which could provide support for tracking the results of IPM projects. Finally, we suggest the setting up of a centralized database about citrus pests and their natural enemies in the Mediterranean Region.