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Introduction
Much of our knowledge of biodiversity patterns and changes comes from the data based on mammals, birds and vascular plants (e.g., Gillison et al., 2013). Yet these taxa represent only a fraction of biodiversity; the major component of terrestrial biodiversity comprises insects (Mora et al., 2011). A recent meta-analysis of biodiversity studies revealed the dearth of information about most of the world's tropical biota (Gillison et al., 2013), highlighting the fact that in order to decipher biodiversity patterns and change the major component can no longer be ignored. The absence of data on insects in biodiversity surveys, with the exception of small groups of charismatic taxa such as butterflies, dragonflies and dung beetles (e.g., Korasaki et al., 2013; Hart et al., 2014; Zografou et al., 2014), reflects the taxonomic challenges associated with the huge diversity of this group of relatively small-sized organisms (Floyd et al., 2009). Obtaining insect samples is not an obstacle to collecting this data as many efficient sampling techniques have been developed (e.g., Russo et al., 2011, and in particular Malaise traps) but the investment required to sort and classify these samples is prohibitive. Fortunately, modern technology is addressing this impediment. First, conventional (single specimen) DNA barcoding, the use of short cytochrome c oxidase I mtDNA (COI) sequences as species identification tags (Hebert et al., 2003), has been applied to rapidly accelerate biodiversity surveys in hyperdiverse insect groups (e.g., ants of Madagascar; Smith et al., 2005). Now, with next-generation-sequencing technologies allowing simultaneously sequencing of DNA fragments from multiple specimens in a bulk mixture of diverse taxa, termed metabarcoding (Yu et al., 2012), the impediment is being alleviated further.
Metabarcoding is simply the pairing of DNA-based species recognition with high-throughput (next-generation) DNA sequencing (HTS) (Ji et al., 2013). Consequently, metabarcoding, like conventional DNA barcoding, relies on 'universal' polymerase chain reaction (PCR) primers that can amplify a fragment of a standard DNA region from diverse taxa (Ji et al., 2013). Due to the limitations in the size of DNA fragments sequenced by HTS platforms (see Shokralla et al., 2014), metabarcoding has typically been restricted to targeting short fragments of the COI DNA barcode (e.g., Hajibabaei et al.