Identification of Diatraea spp. (Lepidoptera: Crambidae) based on cytochrome oxidase II

Development of a bioassay method to test activity of cry insecticidal proteins against Diatraea spp. (Lepidoptera: Crambidae) sugarcane stem borers

The genus Diatraea (Lepidoptera: Crambidae) includes stem borers representing the most critical sugarcane pests in the Americas. Colombia's most widely distributed and damaging Diatraea species include Diatraea saccharalis, D. indigenella, D. busckella, and D. tabernella. The reduced efficacy of biological tools commonly used in controlling several species highlights the importance of evaluating alternative management strategies, such as transgenic plants expressing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt). The selection of optimal Bt insecticidal proteins for Diatraea control depends on bioassays with purified Bt proteins. Because there is no described artificial diet for borer species other than D. saccharalis and availability of most purified Bt toxins is restricted, this study aimed at developing a bioassay method using fresh corn tissue and providing proof of concept by testing susceptibility to the Cry1Ac insecticidal protein from Bt. Toxicity was evaluated with a single Cry1Ac dose applied directly to corn discs. Stem borer mortality after seven days was higher than 90% for all four tested Diatraea species, while control mortality was below 8%. In addition, we observed that Cry1Ac caused more than 90% weight inhibition in all survivors and delayed development. These results validate the use of this method to determine mortality and growth inhibition due to the consumption of the Cry1Ac protein in each of the Diatraea species. Furthermore, this method could be used to assess other entomopathogenic substances to control these insect pests.

Resistance to Diatraea (Lepidoptera: Crambidae) stem borers in sugarcane is independent of species

Evaluation of host-plant resistance on sugarcane to the sugarcane stem borers of Diatraea spp. is normally conducted in Colombia under field conditions, where environmental variations make the study of the insect-plant relationships difficult. Additionally, several species (i.e., D. saccharalis, D. indigenella, D. tabernella, and D. busckella), which are predominant in Colombia, can overlap in their distribution, raising the question of whether different varieties have the same responses to different pest species. The present study conducted evaluations of host-plant resistance under screen house conditions using two contrasting varieties (CC 93-3895, resistant, and CC 93-3826, susceptible) that were infested with the above-mentioned borer species. Observations of pest injury were conducted on internodes, leaves, and spindles. Survival and size (body mass) of the individuals recovered were analyzed and a Damage Survival Ratio (DSR) was proposed. The resistant CC 93-3895 exhibited less stalk injury, less emergence holes on internodes, and lower DSR; additionally, recovery of pest individuals was lower in comparison with CC 93-3826, independent of the borer species. Insect-plant interactions are discussed, as no previous information was available for three of the species tested (i.e., D. tabernella, D. indigenella, and D. busckella). This screen house protocol is proposed to characterize host-plant resistance among several cultivars from the Colombian sugarcane germplasm bank, using CC 93-3826 and CC 93-3895 as contrasting controls and D. saccharalis as the species model.

Biology of the Most Widely Distributed Sugarcane Stem Borers, Diatraea spp. (Lepidoptera: Crambidae), in Colombia

Most studies on insect biology and ecology of sugarcane borers have focused on Diatraea saccharalis (Fabricius), the most widely distributed species in the Americas. Little information is available on the biology of other borer species present in Colombia, such as D. indigenella Dyar & Heinrich, D. busckella Dyar & heinrich, and D. tabernella Dyar, that present greater expansion and damage in sugarcane-growing regions. The biology of all four species was accordingly studied under laboratory conditions. Diatraea saccharalis presented the shortest development time (39.4 days) and D. busckella the longest (58.2 days). Immature survival was higher for D. saccharalis (83%) and D. tabernella (77%), with the latter also presenting the highest pupal weight (256.6 mg). Observations on reproduction indicate that D. tabernella develops a larger number of egg masses per female (67.3) as compared with D. saccharalis (28.7). All three species spent more time in the pupal stage and resulted in greater pupal size than D. saccharalis; in particular, D. indigenella showed longer female longevity than D. saccharalis. High immature survival rate and greater reproductive success in D. tabernella could potentially generate a larger population in the field, whereas D. busckella takes longer to complete its development, thus increasing the chances of causing greater injury to sugarcane plants. Discussion on biology, ecology, and pest management of these little-known species is done using as model the better-known D. saccharalis.

Morphological and molecular characterization of Castniidae (Lepidoptera) associated to sugarcane in Colombia

The giant sugarcane borer, Telchin licus, has been reported as an economically important sugarcane pest in Colombia; however, its taxonomic status has been scarcely investigated and previous reports offer an ambiguous characterization of both the immature and adult stages. The objective of this work is to identify Telchin species affecting sugarcane and alternative hosts in different departments of the country by integrating molecular analysis and conventional morphology. To date, T. licus has been found in the departments of Caquetá, Casanare, and Meta, while T. atymnius has been found in Antioquia, Caldas, Nariño, and Valle del Cauca. Sugarcane, Musaceae, and Heliconiaceae have been found to be hosts to both species. Additionally, the species T. cacica has also been registered in the department of Nariño, affecting heliconias and plantains. Genetic variation within the species allowed differentiation at the molecular level of subspecies of T. licus and T. atymnius, confirming that the subspecies present in Colombia are T. licus magdalena, T. atymnius humboldti, and T. atymnius atymnius. The haplotype diversity of populations is closely related to their geographical distribution, indicating low gene flow between populations and possible speciation inside the country. Analysis of genetic variance showed significant differences among and within T. atymnius populations, which may suggest a high genetic structure along the regions where it is found and the possible presence of additional subspecies to those previously reported. To understand the geographical and environmental conditions that determine the pest's distribution in Colombia, this information needs to be complemented with ecological considerations of possible geographical isolation and association of alternative hosts.

Development of a next generation DNA sequencing-based multi detection assay for detecting and identifying Leishmania parasites, blood sources, plant meals and intestinal microbiome in phlebotomine sand flies

Leishmaniasis is a disease caused by Leishmania parasites transmitted by phlebotomine sand flies (Diptera: Psychodidae). Human infections with different Leishmania species cause characteristic clinical manifestations; cutaneous or visceral leishmaniasis. Here we describe the development and application of a Miseq Next GenerationSequencing (NGS)-based Multi Detection Assay (MDA) designed to characterize metagenomics parameters pertinent to the sand fly vectors which may affect their vectorial capacity for Leishmania. For this purpose, we developed a MDA by which, DNA fragments were amplified through polymerase chain reactions (PCR) and then sequenced by MiSeq/NGS. PCR amplification was achieved using some published and some new primers designed specifically for identifying Leishmania spp. (ITS1), sand fly spp. (cytochrome oxidase I), vertebrate blood (Cytochrome b), plant DNA ribulose-1,5-bisphosphate carboxylase large subunit gene (rbcL), and prokaryotic micobiome (16 s rRNA). This MDA/NGS analysis was performed on two species of wild-caught sand flies that transmit different Leishmania spp. in two ecologically distinct, but geographically neighboring locations. The results were analyzed to identify, quantitate and correlate the measured parameters in order to assess their putative importance in the transmission dynamics of leishmaniasis.

Towards a global DNA barcode reference library for quarantine identifications of lepidopteran stemborers, with an emphasis on sugarcane pests

Lepidopteran stemborers are among the most damaging agricultural pests worldwide, able to reduce crop yields by up to 40%. Sugarcane is the world’s most prolific crop, and several stemborer species from the families Noctuidae, Tortricidae, Crambidae and Pyralidae attack sugarcane. Australia is currently free of the most damaging stemborers, but biosecurity efforts are hampered by the difficulty in morphologically distinguishing stemborer species. Here we assess the utility of DNA barcoding in identifying stemborer pest species. We review the current state of the COI barcode sequence library for sugarcane stemborers, assembling a dataset of 1297 sequences from 64 species. Sequences were from specimens collected and identified in this study, downloaded from BOLD or requested from other authors. We performed species delimitation analyses to assess species diversity and the effectiveness of barcoding in this group. Seven species exhibited <0.03 K2P interspecific diversity, indicating that diagnostic barcoding will work well in most of the studied taxa. We identified 24 instances of identification errors in the online database, which has hampered unambiguous stemborer identification using barcodes. Instances of very high within-species diversity indicate that nuclear markers (e.g. 18S, 28S) and additional morphological data (genitalia dissection of all lineages) are needed to confirm species boundaries.