Cassava Entomology
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CASSAVA ENTOMOLOGY Activity 1. Arthropod taxonomic activities on CIAT commodity crops. Taxonomy: The science dealing with the identification, naming and classification of organisms, is a vital component in a pest management program. Identification and classification is the basic approach to any scientific endeavor, and it is often critical to the success of pest management activities. An inaccurate identification of a pest organism can result in an acute loss of time and resources and delay the most appropriate response to pest attack and damage. An example of this is the misidentification between the cassava mealybug Phenacoccus manihoti and P. herreni; this delayed, by four years, the discovery of P. manihoti’s key natural enemy, the parasitoid, Apoanagyrus lopezi, and its subsequent introduction into Africa. Accurate crop pest and natural enemy identification is an essential component in a pest and disease management program. Insect systematics is considered, by some authors, to have begun with the work of Aristotle, who included the Entoma as a subdivision of the Anaima (invertebrates). Within the Entoma Aristotle place the Arthropoda (excluding Crustacea), Echinodermata, and Annelida (Gillott, 1980). For more than 2000 years hence, the identification and classification of arthropods, has been based primarily on external or morphological structures. Some use had also been made physiological, developmental, behavioral, and cytogenetic data. In more recent years, the application of molecular techniques have played an increasingly influential role in the accurate identification of arthropod species and equally important, of biotypes. CIAT has recently implemented the use of molecular techniques, based on PCR, especially for the identification of whitefly species, their biotypes and natural enemies. These techniques can offer an accurate, rapid and relatively low cost method for identifying critical species or complexes. The CIAT IPDM Project (PE-1) provides the service of identifying arthropod pests collected from various crops, but especially to CIAT’s mandate crops and related activities. The project maintains a working collection of arthropod pests and their natural enemies for cassava, beans, rice, tropical pastures and tropical fruits, as well as those collected from related agroecosystems, such as vegetables, legumes, forest environments and others. A database containing information on the individual specimens accompanies the collection and this is made available to collaborating institutions, museums, universities and national research and extension programs. In addition, the project biologist/taxonomist maintains contact with more than 40 recognized taxonomists around the world and relies on their assistance in pest and natural enemy identification. A major activity of the project is the CIAT convened “System wide Tropical Whitefly IPM Project (TWF/IPM).” CIAT provides taxonomic support for whiteflies and their natural enemies collected from different agroecosystems in the neotropics. Whitefly specimens from participating collaborators from numerous countries (approximately 15 in the Americas) are continuously being sent to us for identification. CIAT also maintain a capacity in molecular taxonomic techniques based on PCR for arthropod (especially whiteflies) identification. These techniques 1 offer a rapid method for the precise identification of critical species or species complexes (including biotypes) that are often morphologically indistinguishable during one of its life stages. During the past year, numerous insect and mite species were added to the collection, which now numbers more than 20,000 specimens. The services provided, including access to the database, contributes to numerous CIAT and national program activities. During 2003-04 we continued collecting homopteran species that may be associated with Cassava Frogskin Disease. A description of these collections and identifications are reported in Activity 7. In addition surveys were initiated to determine the Chrysopidae species associated with cassava arthropod pests. The Chrysopidae constitute an important group of generalist predators that are often employed in biological control projects. The results of these surveys are reported in Activity 2. A description of some of the additional activities follows. Project 1 – Whiteflies Objective: Process and identify whitefly specimens collected in El Salvador and Mexico. Methodology El Salvador: CIAT’s TWF/IPM project received 137 whitefly samples collected from the “Valle de Zapotitan” in El Salvador (C.A.). Samples were sent by Ing. Agr. Leopoldo Serrano Cervantes of the Departamento de Protección Vegetal (Facultad de Ciencias Agronómicas, Universidad de El Salvador) during December 2003 and processed during 2004. Twenty, non-parasitized, pupae were selected from each sample; 10 of these were used to determine biotype (Virology Laboratory), and 20 were imbedded in microscope slides for morphological identification. Results: Bemisia tabaci (Gennadius) was the whitefly species identified in 135 of the samples received. These were collected from 17 plant hosts (Table 1). The specimens were mounted on 585 slides and included in the CIAT whitefly collection. Plant hosts included vegetables, legumes, melons, squashes and potato, indicating the wide host range of this pest species. The two remaining samples were identified as Aleurocybotus occiduus Russell, collected from sorghum and maize in Chalatenango (Nueva Concepción, El Salvador). México: Whitefly specimens were received from Tula, Tamaulipas, México and collected from Lycopersicon esculentum (Tomato) and Menta piperita (mint). Specimens were sent by Dr. Raul Díaz, INIFAB-CIR Sureste Campo Experimental Mococha (Merida, Yucatán, México). These specimens were identified as Bemisia tabaci and Trialeurodes vaporariorum. 2 Table 1. Plant hosts of the whitefly Bemisia tabaci collected in Valle de Zapotitan, El Salvador (December, 2003). Crop Scientific Name Squash Cucúrbita moschata Eggplant Solanum melongena Broccoli Brassica oleracea Sunnehemp Crotaliaria guatemalensis Sweet pepper Capsicum annum Beans Phaseolus vulgaris Guisquil Sechium edule Mint Menta piperita Loroco Fernaldia pandurata Melon Cucumis melo Okra Hibiscus esculentus Potato Solanum tuberosum Cucumber Cucumis sativus Pipian (Squash) Cucúrbita mixta Cabbage Brassica oleracea capitara Watermelon Citrullus lanatus Tomato Lycopersicon esculentum Project 2 - Mites Phytophagous mites are an important pest of cassava and other CIAT related crops. Mite collections from cassava have been carried out for nearly 30 years on cassava and the CIAT collections consists of more than 10,000 specimens mounted on microscope slides. These extensive collections provide a unique description of the complex of phytophagous mites associated with cassava, their geographic distribution, alternate hosts and natural enemies. All the aforementioned information is contained in the CIAT maintained database. During 2003-2004 mite collections were carried out in numerous sites in Colombia and Ecuador on cassava, avocado, coffee, citrus, guanábana (custard-apple), mango, coconut, guava, madroño, sweet potato, rice, ornamentals, and others (Table 2). Many of these identifications were done at the request of national institutions such as ICA (El Instituto Colombiano Agropecuario), CENICAFE (El Centro Nacional de Investigaciones del Café), INIAP (Instituto Nacional Autónomo de Investigaciones Agropecuaria), Estación Experimental Portoviejo, Ecuador. CIAT’s expertise in acarology, especially in the identification of phytophagous mites and the mite predators, Phytoseiidae, is recognized in many countries in the Americas. As can be observed in Table 2, an impressive diversity of phytophagous mites were collected from numerous hosts. Samples #2634 and 2635, with the species Tetranychus urticae and Mononychellus tanajoa respectively (both collected from cassava) contained the presence of the entomopathogen fungus, Neozygites sp. This fungus is often observed as an important natural enemy of cassava mites. The mite Steneotarsonemus spinki Smiley (Fam. Tarsonemidae) is reported causing damage to the rice crop in Cuba (Ramos et al, 2001), and more recently in Costa Rica. This species has not yet been reported in Colombia but it is important to monitor rice fields throughout the country to 3 identify species within this family. Samples # 2653 from Santa Roca (Villavicencio) and #2654, from CIAT, Palmira are identified as Tarsonemidos, found in the panicle of sparkled rice grains. Taxonomic observations indicate that these mites are Tarsonemus bilobatus, a species reported as mostly feeding on fungus spores. Table 2. Phytophagous mites collected from cassava and other hosts from Colombia and Ecuador. Sample Country Department Municipality Site Host Species 2622 Colombia Valle Ginebra Ginebra Guava Eriophyidae' mites 2623 Colombia Tolima Espinal Toluva Basil Poliphagotharsonemus latus 2627 Colombia Valle Cali Cali Chiminango Eotetranychus sp 2628 Colombia Atlántico Sto. Tomas El Esfuerzo Coconut Eriophyidae'mites 2629 Colombia Caldas Palestina Montelindo Avocado Allonychus braziliensis 2631 Ecuador Manabí Portoviejo Teodomira Cassava Mononychellus caribbeanae Oligonychus peruvianus 2632 Ecuador Manabí Portoviejo E.E.INIA Cassava Mononychellus caribbeanae 2633 Colombia Valle Palmira CIAT Sweet potato Tetranychus ludeni 2634 Colombia Valle Palmira CIAT Cassava Tetranychus urticae* 2635 Colombia Valle Palmira CIAT Cassava Mononychellus tanajoa*