Early season aphid activity in 2013
Prolonged exposure to low winter temperatures are known to have lethal and sub-lethal effects on populations of aphids that sucoverwinter in the larval stage, such as Scottish populations of M. persicae. Poor over-winter survival delays the build up of populations of this species in the forthcoming growing season. Prior to 2011, SASA used the mean temperatures for January and February to predict when M. persicae will become active in the summer. In recent years, following an extremely cold December 2010, SASA predictions of early season aphid activity have been based on the mean temperatures during the three-month period of December-February.
During winter 2012-13, the mean temperatures were close to the average over the past 45 or so years (although a little cooler than most recent winters): 3.7°C at SASA (Edinburgh; mean = 3.8°C) and 3.4°C at JHI (Dundee; mean = 3.5°C). The winter temperatures for 2012-13 rank the 17th coldest over the past 45 years at Edinburgh and 18th coldest over the past 47 years at Dundee.
|2013 Prediction||75% Confidence Limits||2012 Obs'n||
|Myzus persicae||17 June||26 May - 6 July||25 June|
|Macrosiphum euphorbiae||25 May||4 May - 14 June||22 May|
|Metopolophium dirhodum||N/A||24 May|
|Myzus periscae||17 June||23 May - 13 July||27 June|
|Macrosiphum euphorbiae||4 June||12 May - 27 June||23 May|
The 2012-13 winter temperatures suggest that the first flights of M. persicae should be slightly later than average. In 2012, this species was much later than predicted, probably due to the poor spring and early summer weather. Environmental conditions in the months following those used for the predictions are likely to have some influence on aphid activity during the summer. As Metopolophium dirhodum overwinters as an egg, winter temperatures have minimal effect on when this species starts to fly; environmental factors during the weeks prior to flight commencing have a much greater effect.
The prediction for the total of M. persicae caught by 31 July is 14 at Dundee and 10 at Edinburgh. The 75% confidence intervals for these predictions are 3 at the lower end and 49 at the upper for Dundee and 2 at the lower end and 39 at the upper for Edinburgh. Therefore populations of M. persicae are not expected to build up to significant levels during 2013 and seed crops of potato varieties susceptible to leafroll are unlikely to require protection against this aphid during the early part of the 2013 growing season.