Ten years after the first record of the cotton boll weevil, Anthonomus grandis Boheman (Coleoptera, Curculionidae), in Argentina, the insect arrived in the cotton area of Chaco. Molecular studies on populations from Argentina, Brazil and Paraguay, and possible source populations from USA and Mexico, provided helpful information to control the pest. RAPD technique (Random Analysis of Polymorphic DNA) and sequencing of Cytochrome Oxidase I and II mitochondrial genes, allowed to differentiate two main lineages: a) lineages with scarce or null variability measured by heterocigosis and haplotypic diversity, considered recent colonizers, and associated with xerophytic environments and cotton areas (Formosa province); b) lineages with high genetic variability and haplotypic diversity, considered ancestral, and associated with areas of wild vegetation as the subtropical forests of Misiones (Iguazú National Park). Both lineages probably have different origins, adaptations and host preferences, and at present would be hibridizing in ecotonal areas. We propose that the boll weevil probably occurs in South America as a consequence of a natural dispersal associated to wild hosts, mainly of the genera Gossypium and Cienfuegosia, probably since Pleistocene times. On the other hand, there is a possibility of introductions from USA to Brazil, trough the commercial exchange. Extensive cotton cultivation and deforestation, with formation of corridors connecting fragments of forests would explain the rapid dispersal of the pest during the last 20 years, in cotton and/or non cotton areas under environmental impact, such as the Misiones province.

Después de diez años del primer registro del picudo del algodonero, Anthonomus grandis Boheman (Coleoptera, Curculionidae), en la Argentina, el insecto ha llegado a la zona algodonera del Chaco. Los estudios moleculares realizados sobre poblaciones de la Argentina, Brasil y Paraguay, y posibles poblaciones fuente de EE.UU y México, han aportado información relevante para el control de la plaga. Se aplicaron las técnicas de RAPD (Polimorfismos del ADN Amplificados al Azar) y de secuenciación de los genes mitocondriales de la Citocromo Oxidasa I y II, las cuales permitieron identificar dos linajes principales de picudos: a) linajes con escasa o nula variabilidad medida en términos de heterocigosis y diversidad haplotípica, considerados colonizadores recientes, y asociados con ambientes xerófilos y cultivos de algodón (provincia de Formosa); b) linajes con una elevada variabilidad y diversidad haplotípica, considerados ancestrales, y asociados con áreas de vegetación nativa de la selva misionera (Parque Nacional Iguazú). Se supone que ambos linajes tendrían diferentes orígenes, adaptaciones y preferencias de huéspedes, y que en este momento se estarían hidridando en zonas de ecotono. Se postula que el picudo se hallaría presente en América del Sur como consecuencia de una dispersión natural asociada principalmente con sus huéspedes silvestres de los géneros Gossypium y Cienfuegosia, probablemente desde el Pleistoceno. Por otra parte no se descarta la posibilidad de una o más introducciones desde EE.UU. hacia Brasil, mediante el comercio del algodón. Se destaca la importancia del cultivo extensivo del algodón, y de la deforestación y formación de corredores entre fragmentos de selva, para explicar la dispersión rápida de la plaga durante los últimos 20 años, en áreas algodoneras y/o no algodoneras pero afectadas por serios disturbios ambientales, como por ejemplo la provincia de Misiones.

The present study is a revision of our work on evolutionary cytogenetics of the genus Zea, including several new experiments which give a deeper insight into the nature of the DNA sequences involved in telomeric regions of Zea luxurians. These new experiments, based on the Southern blotting technique and in situ hybridization, have demonstrated the following: 1) in situ hybridization (FISH) demonstrated the presence of the 180-bp repeat maize-knob-repeat-sequence in DAPI-positive terminal heterochromatic blocks of Z. luxurians (ZL-THB region); 2) Southern blot analysis confirmed that the 180-bp repeat present in maize is also present in Z. diploperennis, Z. luxurians and Tripsacum dactyloides, but not in Z. perennis; 3) another sequence with targeted sites for endonucleases, but without recognition sites for the 180-bp repeat, may be interspersed with the 180-bp repeat in a tandem array sited in the ZL-THB region; 4) in situ hybridization (GISH) of probes and blocking-probes with chromosomes of Z. luxurians (using Z. luxurians as a probe and Z. diploperennis or Z. perennis as a blocking-probe) gave strong fluorescence in both cases. Since Z. diploperennis possesses the 180-bp repeat, fluorescence on Z. luxurians chromosomes was not expected. These results can be explained if the ZL-THB regions are composed not only of 180-bp repeats interspersed with other sequences, but also of other tandem arrays unique to Z. luxurians, which, according to our GISH results, are probably located at the subterminal position.