Inheritance patterns of secondary symbionts during sexual reproduction of pea aphid biotypes

Herbivorous insects frequently harbor bacterial symbionts that affect their ecol- ogy and evolution. Aphids host the obligatory endosymbiont Buchnera, which is requiredfor reproduction, together with facultative symbionts whose frequencies vary across aphid populations. These maternally transmitted secondary symbionts have been particularlystudied in the pea aphid, Acyrthosiphon pisum, which harbors at least 8 distinct bacterial species （not counting Buchnera） having environmentally dependent effects on host fitness.In particular, these symbiont species are associated with pea aphid populations feeding on specific plants. Although they are maternally inherited, these bacteria are occasionallytransferred across insect lineages. One mechanism of such nonmaternal transfer is paternal transmission to the progeny during sexual reproduction. To date, transmission of secondarysymbionts during sexual reproduction of aphids has been investigated in only a handful of aphid lineages and 3 symbiont species. To better characterize this process, we investigatedinheritance patterns of 7 symbiont species during sexual reproduction of pea aphids through a crossing experiment involving 49 clones belonging to 9 host-specialized biotypes, and117 crosses. Symbiont species in the progeny were detected with diagnostic qualitative PCR at the fundatrix stage hatching from eggs and in later parthenogenetic generations.We found no confirmed case of paternal transmission of symbionts to the progeny, and we observed that maternal transmission of a particular symbiont species （Serratia symbiotica）was quite inefficient. We discuss these observations in respect to the ecology of the pea aphid.

Plant-herbivorous insect networks: who is eating what revealed by long barcodes using high-throughput sequencing and Trinity assembly

Interactions between plants and insects are among the most important life functions for all organism at a particular natural community.Usually a large number of samples are required to identify insect diets in food web studies.Previously,Sanger sequencing and next generation sequencing(NGS)with short DNA barcodes were used,resulting in low species-level identification;meanwhile the costs of Sanger sequencing are expensive for metabarcoding together with more samples.Here,we present a fast and effective sequencing strategy to identify larvae of Lepidoptera and their diets at the same time without increasing the cost on Illumina platform in a single HiSeq run,with long-multiplexmetabarcoding(COI for insects,rbcL,matK,ITS and trnL for plants)obtained by Trinity assembly(SHMMT).Meanwhile,Sanger sequencing(for single individuals)and NGS(for polyphagous)were used to verify the reliability of the SHMMT approach.Furthermore,we show that SHMMT approach is fast and reliable,with most high-quality sequences of five DNA barcodes of 63 larvae individuals(54 species)recovered(full length of 100%of the COI gene and 98.3%of plant DNA barcodes)using Trinity assembly(up-sized to 1015 bp).For larvae diets identification,95%are reliable;the other 5%failed because their guts were empty.The diets identified by SHMMT approach are 100%consistent with the host plants that the larvae were feeding on during our collection.Our study demonstrates that SHMMT approach is reliable and cost-effective for insect-plants network studies.This will facilitate insect-host plant studies that generally contain a huge number of samples.