Midge

Abstract: To the Editor: In autumn 2011, an unidentified disease of livestock was reported on both sides of the Dutch–Germany border. By using metagenomics, the etiologic agent of this disease was identified as a novel orthobunyavirus and named Schmallenberg virus (SBV) (1). Other members of the genus Orthobunyavirus (e.g., Akabane virus) are widespread in Africa and Asia; biting midges (Culicoides spp.) and mosquitoes are responsible for transmitting these viruses. Hence, we reasonably assumed that European culicoids might be responsible for transmitting SBV within Europe. We present evidence that culicoids captured October 2011 in Denmark contained SBV RNA and most likely are vectors for this agent. In autumn 2011, culicoids were collected from several sites within Denmark. One site, a chicken farm in Hokkerup (Figure A1), was selected for study because of its location close (6 km) to the German border and proximity (<10 km) to an SBV-infected sheep farm in Germany, as reported on March 9, 2012, by the Friedrich Loeffler Institute surveillance website (www.fli.bund.de). The culicoids were collected during October 14–16 by using a Mosquito Magnet Independence trap (Mosquito Magnet, Lititz, PA, USA) baited with carbon dioxide and octenol. Midges were sorted manually into 91 specimens of the C. obsoletus group (comprising C. obsoletus, C. chiopterus, C. dewulfi, and C. scoticus) and 17 of the C. punctatus sensu stricto group, then stored at −20°C. Pools of culicoids were homogenized in water (100 µL) by using a 3-mm stainless steel bead (Dejay Distribution Ltd., Launceston, UK) in a TissueLyser II (QIAGEN, Hilden, Germany) for 1 min at 25 Hz (2). After homogenization, additional water (100 µL) was added to the samples, and then the mixture was centrifuged at 3,000 × g for 5 min. Nucleic acids were extracted from the supernatant (100 µL) by using a MagNA pure LC Total Nucleic Acid Isolation Kit on a MagNA pure LC (Roche Diagnostics, Basel, Switzerland) and eluted in water (50 µL). Two separate 1-step reverse transcription quantitative PCRs (RT-qPCRs), targeting the L segment and the S segment of SBV RNA, were performed according to protocols provided by the Friedrich Loeffler Institute in Germany (1) on the extracted nucleic acids by using a Mx3005p qPCR system (Agilent Technologies, Palo Alto, CA, USA). Another RT-qPCR targeting ruminant β-actin mRNA was performed as an internal endogenous control (3). Two of 22 pools tested strongly positive for the large (L) and small (S) segments of SBV RNA. Each positive sample was derived from 5 midges of the C. obsoletus group. One pool produced cycle threshold (Ct) values of 26.4 and 24.5 (in the L segment– and S segment–specific assays, respectively), whereas the second positive pool gave Ct values of 28.8 (L segment) and 27.6 (S segment). These pools were negative for the internal endogenous control that targeted the bovine/ovine β-actin mRNA. This result makes it unlikely that the detection of SBV RNA within the midges resulted from recent blood meals from infected animals remaining within the culicoids and suggests the virus has replicated within the midges. The PCR amplicons (145 bp; Figure) from the L segment–specific RT-qPCR were sequenced by using BigDye 1.1 chemistry on an ABI 3500 Genetic Analyzer (Applied Biosystems, Foster City, CA, USA). The sequences of 80 bp from the amplicons, excluding the primer sequences, had 100% identity with the expected region of the SBV segment L (1). Figure RNA extracted from pools of Culicoides obsoletus group midges was tested in 1-step reverse transcription quantitative PCRs (RT-qPCRs) for the Schmallenberg virus large segment, and the products were analyzed by agarose gel electrophoresis. Lanes 1–8, ... Reported Ct values generated by using the same assays from blood of naturally infected cattle were 24–35 (1). Usually, ≈100 µL of bovine/ovine blood is used for virus detection, whereas <1 µL of blood remains in a midge after a blood meal. This uptake of blood should therefore lead to a Ct value that is at least 6–7 units higher (≈100-fold lower level of RNA) when a single midge is tested by RT-qPCR (4). Thus, even if all 5 culicoids in a pool had recently taken a blood meal from a viremic animal, the Ct values observed here strongly suggest replication of SBV within the C. obsoletus group midges. However, in principle, other hosts of SBV could have a much higher level of viremia than cattle and could provide the levels of SBV RNA detected. C. punctatus s.s. midges cannot be ruled out as a possible vector of SBV because of the limited number of insects tested. Our study demonstrates the presence of SBV RNA in C. obsoletus group midges caught in Denmark during October 2011. The low Ct values (i.e., high SBV RNA levels) and the absence of ruminant β-actin mRNA in these samples strongly suggest that SBV replicates in these midges and hence that the C. obsoletus group midges are natural vectors for this virus.

Abstract: Freshwater midges, consisting of Chironomidae, Chaoboridae and Ceratopogonidae, were assessed as a biological proxy for palaeoclimate in eastern Beringia. The northwest North American training set consists of midge assemblages and data for 17 environmental variables collected from 145 lakes in Alaska, British Columbia, Yukon, Northwest Territories, and the Canadian Arctic Islands. Canonical correspondence analyses (CCA) revealed that mean July air temperature, lake depth, arctic tundra vegetation, alpine tundra vegetation, pH, dissolved organic carbon, lichen woodland vegetation and surface area contributed significantly to explaining midge distribution. Weighted averaging partial least squares (WA-PLS) was used to develop midge inference models for mean July air temperature (r boot 2 = 0.818, RMSEP = 1.46°C), and transformed depth (ln (x+1); r boot 2 = 0.38, and RMSEP = 0.58).

Abstract: Despite the speciose fauna of gall-inducing insects in the Neotropical region, little is known about their taxonomy. On the other hand, gall morphotypes associated with host species have been extensively used as a surrogate of the inducer species worldwide. This study reviewed the described gall midges and their galls to test the generalization on the use of gall morphotypes as surrogates of gall midge species in the Brazilian fauna. We compiled taxonomic and biological data for 196 gall midge species recorded on 128 host plant species. Ninety two percent of those species were monophagous, inducing galls on a single host plant species, whereas only 5.6% species were oligophagous, inducing galls on more than one congeneric host plant species. Only four species induced galls on more than one host plant genus. We conclude that gall morphotypes associated with information on the host plant species and attacked organs are reliable surrogates of the gall-inducing species.

Abstract: Despite a recent emphasis on understanding cross-habitat interactions, few studies have examined the ecological linkages between lakes and surrounding terrestrial habitats. The current paradigm of land–lake interactions is typically unidirectional: the view is that nutrients and matter are transported downslope from the surrounding watershed to their ultimate lacustrine destination. Emergent aquatic insects, which spend their larval stages in lake sediments and emerge as adults to mate over land, can act as vectors of material, energy and nutrients from aquatic to terrestrial habitats. In this study, we document a gradient of midge (Diptera: Chironomidae) infall rates into terrestrial habitats (measured as g dw midges m−2 d−1) surrounding eight lakes in Northern Iceland (≈66°N latitude). Lakes ranged from having virtually no midge infall (for example, Helluvaðstjorn, 0.03 g m−2 d−1) to extreme levels (for example, Mývatn, 19 g m−2 d−1) with abundances of midges decreasing logarithmically with distance from shore. Annual midge input rates are estimated as high as 1200–2500 kg midges ha−1 y−1. As midges are approximately 9.2% total N, this can result in a significant fertilization effect of terrestrial habitats with consequences for plant quality and community structure. In addition, we used naturally-occurring δ13C and δ15N isotopes to examine food web structure and diet sources of terrestrial arthropod consumers surrounding lakes with differing amounts of midge input. Terrestrial arthropods showed increased utilization of aquatic-derived (that is, midge) C relative to terrestrial sources as midge infall increased. This pattern was particularly pronounced for predators, such as spiders and opiliones, and some detritivores (Collembola). These findings suggest that, despite being largely ignored, aquatic-to-terrestrial linkages can be large and midges can fuel terrestrial communities by directly serving as resources for predators and decomposers.