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      Characterization of Hymenopteran Parasitoids of Aphis fabae in An African Smallholder Bean Farming System Through Sequencing of COI ‘Mini-barcodes’

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          Abstract

          Parasitoids are among the most frequently reported natural enemies of insect pests, particularly aphids. The efficacy of parasitoids as biocontrol agents is influenced by biotic and abiotic factors. For example, hyperparasitoids can reduce the abundance of the primary parasitoids as well as modify their behavior. A field study was conducted at three contrasting elevations on Mount Kilimanjaro, Tanzania, to identify the parasitoids of aphids in smallholder bean farming agroecosystems. Sentinel aphids ( Aphis fabae) on potted bean plants ( Phaseolus vulgaris) were exposed in 15 bean fields at three elevations for 2 days. The sentinel aphids were then kept in cages in a greenhouse until emergence of the parasitoids, which were collected and preserved in 98% ethanol for identification. Of the 214 parasitoids that emerged from sentinel aphids, the greatest abundance (44.86%) were from those placed at intermediate elevations (1000–1500 m a.s.l), compared to 42.52% from the lowest elevations and only 12.62% from the highest elevation farms. Morphological identification of the parasitoids that emerged from parasitized aphids showed that 90% were Aphidius species (Hymenoptera: Braconidae: Aphidiinae). Further characterization by sequencing DNA ‘mini-barcodes’ identified parasitoids with ≥99% sequence similarity to Aphidius colemani, 94–95% sequence similarity to Pachyneuron aphidis and 90% similarity to a Charipinae sp. in the National Center for Biotechnology Information (NCBI) database. These results confidently identified A. colemani as the dominant primary aphid parasitoid of A. fabae in the study area. A Pachyneuron sp., which was most closely related to P. aphidis, and a Charipinae sp. occurred as hyperparasitoids. Thus, interventions to improve landscapes and farming practice should monitor specifically how to augment populations of A. colemani, to ensure any changes enhance the delivery of natural pest regulation. Further studies are needed for continuous monitoring of the hyperparasitism levels and the dynamics of aphids, primary parasitoids, and secondary parasitoids in different cropping seasons and their implications in aphid control.

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            Extreme diversity of tropical parasitoid wasps exposed by iterative integration of natural history, DNA barcoding, morphology, and collections.

            We DNA barcoded 2,597 parasitoid wasps belonging to 6 microgastrine braconid genera reared from parapatric tropical dry forest, cloud forest, and rain forest in Area de Conservación Guanacaste (ACG) in northwestern Costa Rica and combined these data with records of caterpillar hosts and morphological analyses. We asked whether barcoding and morphology discover the same provisional species and whether the biological entities revealed by our analysis are congruent with wasp host specificity. Morphological analysis revealed 171 provisional species, but barcoding exposed an additional 142 provisional species; 95% of the total is likely to be undescribed. These 313 provisional species are extraordinarily host specific; more than 90% attack only 1 or 2 species of caterpillars out of more than 3,500 species sampled. The most extreme case of overlooked diversity is the morphospecies Apanteles leucostigmus. This minute black wasp with a distinctive white wing stigma was thought to parasitize 32 species of ACG hesperiid caterpillars, but barcoding revealed 36 provisional species, each attacking one or a very few closely related species of caterpillars. When host records and/or within-ACG distributions suggested that DNA barcoding had missed a species-pair, or when provisional species were separated only by slight differences in their barcodes, we examined nuclear sequences to test hypotheses of presumptive species boundaries and to further probe host specificity. Our iterative process of combining morphological analysis, ecology, and DNA barcoding and reiteratively using specimens maintained in permanent collections has resulted in a much more fine-scaled understanding of parasitoid diversity and host specificity than any one of these elements could have produced on its own.
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              Counting animal species with DNA barcodes: Canadian insects

              Recent estimates suggest that the global insect fauna includes fewer than six million species, but this projection is very uncertain because taxonomic work has been limited on some highly diverse groups. Validation of current estimates minimally requires the investigation of all lineages that are diverse enough to have a substantial impact on the final species count. This study represents a first step in this direction; it employs DNA barcoding to evaluate patterns of species richness in 27 orders of Canadian insects. The analysis of over one million specimens revealed species counts congruent with earlier results for most orders. However, Diptera and Hymenoptera were unexpectedly diverse, representing two-thirds of the 46 937 barcode index numbers (=species) detected. Correspondence checks between known species and barcoded taxa showed that sampling was incomplete, a result confirmed by extrapolations from the barcode results which suggest the occurrence of at least 94 000 species of insects in Canada, a near doubling from the prior estimate of 54 000 species. One dipteran family, the Cecidomyiidae, was extraordinarily diverse with an estimated 16 000 species, a 10-fold increase from its predicted diversity. If Canada possesses about 1% of the global fauna, as it does for known taxa, the results of this study suggest the presence of 10 million insect species with about 1.8 million of these taxa in the Cecidomyiidae. If so, the global species count for this fly family may exceed the combined total for all 142 beetle families. If extended to more geographical regions and to all hyperdiverse groups, DNA barcoding can rapidly resolve the current uncertainty surrounding a species count for the animal kingdom. A newly detailed understanding of species diversity may illuminate processes important in speciation, as suggested by the discovery that the most diverse insect lineages in Canada employ an unusual mode of reproduction, haplodiploidy. This article is part of the themed issue ‘From DNA barcodes to biomes’.
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                Author and article information

                Journal
                Insects
                Insects
                insects
                Insects
                MDPI
                2075-4450
                02 October 2019
                October 2019
                : 10
                : 10
                : 331
                Affiliations
                [1 ]Department of Sustainable Agriculture, Biodiversity and Ecosystems Management, The Nelson Mandela African Institution of Science and Technology, Arusha PO Box 447, Tanzania; mayoprisca@ 123456gmail.com (P.A.M.); patrick.ndakidemi@ 123456nm-aist.ac.tz (P.A.N.)
                [2 ]Graham Centre for Agricultural Innovation, Charles Sturt University, PO Box 883, Orange, NSW 2800, Australia; GGurr@ 123456csu.edu.au
                [3 ]Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent ME4 4TB, UK; P.C.Stevenson@ 123456greenwich.ac.uk (P.C.S.); S.E.J.Arnold@ 123456greenwich.ac.uk (S.E.J.A.); S.R.Belmain@ 123456greenwich.ac.uk (S.R.B.)
                [4 ]Royal Botanic Gardens, Kew, Richmond Surrey, TW9 3AB, UK
                [5 ]Department of Research, Plant Protection Division, Tropical Pesticide Research Institute (TPRI), Arusha PO Box 3024, Tanzania; maneno.chidege@ 123456tpri.go.tz
                [6 ]Institute of Applied Ecology, Fujian Agriculture and Forestry University, Fuzhou 35002, China
                Author notes
                Author information
                https://orcid.org/0000-0002-7958-6934
                https://orcid.org/0000-0002-9439-6856
                Article
                insects-10-00331
                10.3390/insects10100331
                6835700
                31581700
                83bbbc99-8689-4dec-9382-161417302970
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 26 August 2019
                : 29 September 2019
                Categories
                Communication

                primary parasitoids,hyperparasitoids,aphidius colemani,phaseolus vulgaris,natural pest regulation,dna barcoding

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