Entomopathogenic nematodes (EPN) belonging to the Heterorhabditidae family are lethal parasites of soil-dwelling insects. Two species were reported in Argentina: Heterorhabditis argentinensis and Heterorhabditis bacteriophora characterized mainly by morphometric features. In this work a comparative and phylogenetic study between five Heterorhabditis populations from Argentina was conducted to analyze the variability between strains and to evaluate the taxonomic position of Heterorhabditis argentinensis. The PCA analyses of morphometric characters separated the larger juvenile, female and male H. argentinensis from H. bacteriophora populations. The juvenile (IJs) stage provided the clearest separation of Heterorhabditis populations presenting the least variability between strains. The variable L and MBW were highly related to H. argentinensis IJs. Three groups were separated by this stage considering PC1 and PC2: one formed by H. bacteriophora OLI, RIV and RN strains, (isolates from Córdoba and Río Negro province), one for H. bacteriophora VELI strain (Buenos Aires province) and one for H. argentinensis (Santa Fe province). Heterorhabditis bacteriophora VELI and H. argentinensis isolated from regions with more rainfalls and humidity presented larger values for morphometric features. Molecular analyses showed the Argentinian populations (H. bacteriophora VELI strain and H. argentinensis), forming a same clade, with six other H. bacteriophora populations (not from Argentina) with a genetic similarity between them of 99%. Heterorhabditis argentinensis presented one unique nucleotide that was not present in any of the other species of the clade. Considering the results of this study H. argentinensis would be conspecific to H. bacteriophora, constituting a strain with a great morphometric variation where the host and climatic conditions could have influenced on the measurements.Keywords: entomonematodes, Heterorhabditidae, variability, strains, Argentina. Estudo da variabilidade entomopatogênicos nematóides populações (Heterorhabditidae) da Argentina Resumo
The weevil Phyrdenus muriceus Germar (Coleoptera: Curculionidae) is an emergent pest of eggplant (Solanum melongena L.) crops in the humid Pampa of Argentina. Entomopathogenic nematodes (EPNs) constitute an effective and environmentally safe strategy within integrated pest management. The efficacy of a native EPN Heterorhabditis bacteriophora SUP isolate for the control of P. muriceus was evaluated. Larvae and adults were susceptible to the nematode in laboratory assays. Field evaluations indicated a slight reduction of P. muriceus populations, evidenced after a second application by a decrease of the foliar damage in the eggplant crops. Adults of P. muriceus parasitized by H. bacteriophora were observed in the field one month after the second application. The present study is the first assessment of EPNs against P. muriceus under field conditions, and the first report of their use in the humid Pampa, one of the major agricultural areas of Argentina.
The pampean region in the Buenos Aires province of Argentina is a major horticultural area. Biological pesticides to control pest insects available in the market are scarce in this country and nonexistent based on entomonematodes. In this paper, we characterized a native entomopathogenic nematode isolated from soil in the pampas, and evaluated its infectivity and reproductive capacity in the strawberry sap beetle Lobiopa insularis. Morphological and molecular-genetic analysis determined this isolate to be a nematode of Heterorhabditis bacteriophora, thereafter designated as the VEli strain. A 901-bp genomic-DNA fragment was isolated (GenBank Accesion No KJ575524). The new strain was pathogenic against L. insularis. In 200 ml containers with autoclaved clay soil (100 ml), at concentrations of 1,000; 5,000 and 10, 000 IJs, mortality in larvae ranged from 25 to 77 %. At a concentration of 10,000 IJs, infectivity was higher in larvae and pupae (77 ± 20% and 64 ± 25 %, respectively) than in adults (2.2 ± 1.1 %). The lethal concentration required to kill 50 and 90 % of the larvae (LC50 and LC90) over 10 days was 2,840 and 23,743 IJs. Differences were observed in the parasitism levels and emergence time of IJs between concentrations and stages, although not for production. Heterorhabditis bacteriophora strain VEli is the first entomopathogenic nematode found to infect and kill L. insularis, capable of completing its life cycle in all strawberry sap beetle stages. This availability would enable the establishment and subsequent dispersal of the strain in strawberry fields. Finally, this report constitutes the first presentation of data on the morphological, morphometric, and molecular-genetic characterization of a native entomopathogenic nematode strain from the Buenos Aires province, Argentina.
Este trabajo fue realizado entre el 2006-2010 en campos de trigo de la región pampeana, Argentina. El objetivo fue determinar especies de nemátodos parásitos patógenos de gusanos blancos, plaga importante del suelo. Las muestras fueron tomadas con pala en sitios seleccionados al azar. Larvas de Diloboderus abderus y Cyclocephalla signaticollis (Scarabaeidae) fueron recolectadas del suelo a mano con pala. Trece especies de nemátodos pertenecientes a 5 familias (Mermithidae, Thelastomatidae, Travassosinematidae, Diplogasteridae y Rhabditidae) fueron determinadas. Los valores de riqueza de especies fueron 1 para C. signaticollis y 12 para D. abderus. Los thelastomátidos y rhabdítidos fueron el grupo más numeroso, con un total de tres especies cada uno. Los thelastomátidos fueron muy prevalentes con infecciones que superaron el 60%, seguido de los diplogastéridos que alcanzaron el 36%. Los mermítidos fueron los menos prevalentes con valores cercanos a 10%. La familia Travassosinematidae fue la que presentó la menor abundancia (0.32). Este trabajo aporta por primera vez para la región pampeana de nuestro país una lista de nemátodos parásitos de gusanos blancos.
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