Population genetics of farmland sawflies

Over the last 50 years or so populations of certain farmland bird species have undergone catastrophic declines. Among the key indicator species are Grey Partridges, Yellowhammers and Corn Buntings. The population declines of these species are generally attributed to “farming intensification”. One of the possible effects of intensive farming prescriptions could be that they affect the supply of insect food to bird populations at critical points in their breeding cycle.

It has been suggested that a key component of the fledgling diet may be the larvae of grassland sawflies (Hymenoptera Symphyta), and that intensification has reduced the numbers of these insects to the extent that they limit the population size of bird species that depend on them. In particular, sawfly populations may be more than usually susceptible to disturbance because firstly their adult stages are poor dispersers and secondly some species are known to possess single locus complementary sex determination (SL-CSD). In combination these characteristics might produce an abundance of sterile males as a result of inbreeding and therefore play an important part in the population decline.

If these suggestions are correct it should be possible to detect poor dispersal and SL-CSD through patterns of genetic variation within and between sawfly populations at a range of spatial scales, and from both intensive and non-intensive farms. Genetic variation will be quantified by the development of microsatellite markers, and the presence/absence of SL-CSD will be determined by flowcytometric analysis of neuronal cell DNA content.