José A. Arroyave

Morphological and mitochondrial DNA marker analyses of whiteflies (Homoptera : Aleyrodidae) colonizing Cassava and beans in Colombia

Abstract Morphology of the third antennal segment and compound eyes of adults of the whitefly species Bemisia tabaci (Gennadius), B. argentifolii Bellows & Perring, B. tuberculata (Bondar), Trialeurodes vaporariorum (Westwood), T. variablilis (Quaintance), and Aleurotrachelus socialis (Bondar) were studied using scanning electron microscopy to aid in identification of adult whiteflies in cassava and beans in Colombia. Random amplified polymorphic DNA polymerase chain reaction markers proved complementary to the morphological identification of whitefly species and the only rapid method to distinguish individuals in the Bemisia tabaci species complex. From each species of whitefly, a region of the mitochondrial 16S rDNA gene was amplified, cloned and the sequence determined. Parsimony and distance analyses were performed and the results were similar to those based on morphology. The distance between the two species of Trialeurodes was greater than expected for two species within the same genus. The combination of morphological and molecular traits is useful in understanding the diversity and evolution of these whitefly species.

Emergence and partial characterization of rice stripe necrosis virus and its fungus vector in South America

A new disease of rice, known as ‘entorchamiento’ (crinkling), was first noticed in the Department of Meta, Colombia, in 1991. Symptoms include seedling death, foliar striping and severe plant malformation. Tissue extracts and purified preparations from diseased rice plants, contained virus-like particles ca. 20 nm in diameter, with a bimodal length of 260 and 360 nm. Particle aggregates were also observed in the cytoplasm of infected rice leaf cells. Electrophoretic analyses of purified preparations and dsRNA extracts, revealed a single protein species of M 22,500, and four dsRNA bands ca. 6300, 4600, 2700 and 1800 bp in size. Cystosori, characteristic of plasmodiophorid fungal vectors of plant viruses, were consistently observed in the roots of diseased rice plants. PCR and sequence analyses of amplified fungal DNA products from infected rice roots, revealed that the putative fungus vector was Polymyxa graminis. A Western blot of tissue extracts obtained from ‘crinkled’ rice plants from Colombia, using antiserum against a West African isolate of rice stripe necrosis furovirus (RSNV), resulted in the detection of a protein band of approximately M 22,000. The RSNV antiserum recognized the Colombian virus isolate in serologically specific electron microscopy tests. These results confirm the presence of RSNV in the Americas.

A little known mode of dispersal of Polyphagotarsonemus latus (Banks)

Abstract Females of Polyphagotarsonemus latus (Banks) were found attached to the tarsi and tibiae of the whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), on beans (Phaseolus vulgaris L.) in screenhouse at CIAT (Centro Internacional de Agricultura Tropical) in Cali, Colombia. Photographs are given.