GENETIC DIVERSITY OF THE GREENBUG APHID, SCHIZAPHIS GRAMINUM, IN THE OLD WORLD
Wheat, Peanut and Other Field Crops Research
2012 Annual Report
1a.Objectives (from AD-416):
The objective of this cooperative research project is to quantify the genetic relatedness and diversity of greenbug aphid (Schizaphis graminum) populations in Europe, the Middle East, North Africa, and the US.
1b.Approach (from AD-416):
Greenbug aphids will be collected from crop and non-crop hosts in three regions of the Old World: Europe, the Middle East, and North Africa. mtDNA and nDNA from each aphid will be sequenced. DNA sequences will be used to determine the degree of relatedness of greenbug populations. This information will be used to determine if the greenbug found in the US and Old World are the same species, and/or how closely related they are. The geographical origin of S. graminum will be determined, i.e., Palearctic or Nearctic.
The objective of the work is to compare UK and US specimens to help determine the identity of the UK specimens and hence their threat to UK agriculture. Mitochondrial gene sequences from UK specimens showed them to be very similar, and in some cases identical, to US specimens and to match the three genetic groupings reported from the US. Large numbers of a Schizaphis species were found on Holcus lanatus L. (Yorkshire fog grass) in Hertfordshire and Bedfordshire (UK). Laboratory clones were established and various aspects of their biology were studied in order to address the questions that have been raised on the taxonomic status and damage potential. At present it seems likely that UK specimens from H. lanatus correspond with Schizaphis holci, which is not a threat to crops. Some of the field samples from H. lanatus had identical DNA sequences to some of the suction trap samples, but it seems likely that the suction trap samples comprised more than one species or subspecies. Schizaphis graminum s. l. from the UK were very closely related to S. graminum s. s. as found in the US. Nuclear DNA sequencing supported this relationship. It thus appears that there is a potential threat to UK crops, and further work is needed to confirm species identity, to explain why the greenbug has not yet been found in UK crops and to explain the dramatic increase noted in Schizaphis species found in suction traps.