Effects of cultivar and egg density on a colonizing vine weevil (Otiorhynchus sulcatus) population and its impacts on red raspberry growth and yield

Black vine weevil (Otiorhynchus sulcatus) is regarded as a damaging pest of horticultural crops, yet empirical data about its population dynamics and effects on crop yield are largely lacking. This paper reports a four year (2007-2010) field study that simulated colonisation by O. sulcatus in a red raspberry (Rubus idaeus) plantation comprising two cultivars (Glen Ample and Glen Rosa). The study tested whether adult O. sulcatus abundance was affected by cultivar or original egg distribution. Total population estimates were also made using mark and recapture methods. Finally, the effects of O. sulcatus on plant growth and berry yield were quantified. O. sulcatus abundance was significantly higher on Glen Ample than Glen Rosa, with the difference becoming even greater in 2009 compared to 2008. The abundance of O. sulcatus adults on particular plants was not related to original egg density. Mark and recapture based estimates suggested that the overall O. sulcatus population reached 3500 in 2008 and 44,100 in 2009. O. sulcatus abundance on plants was negatively related to plant height. Comparing plants with greatest and lowest O. sulcatus burdens showed that the heavily infested plants had lower shoot and root biomass in both Glen Ample (62% and 60%, respectively) and Glen Rosa (50% and 12%, respectively), significantly smaller berries (5.1g and 2.8g, respectively, in Glen Ample and 3.3g and 2.7g, respectively, in Glen Rosa) and smaller yields (2.93kg and 0.99kg in Glen Ample and 2.80kg-1.71kg in Glen Rosa, respectively). While cane fruits like raspberry were thought to tolerate O. sulcatus attack due to extensive root systems, this study suggests that damage can be extensive, particularly on cultivars such as Glen Ample.