Aphid Predictions

Early season aphid activity in 2018

Prolonged exposure to low winter temperatures are known to have lethal and sub-lethal effects on populations of M. persicae which, in Scotland, overwinters as larvae or apterous adults.  Poor over-winter survival delays the build up of populations of this species in the forthcoming growing season.  Prior to 2011, SASA has used the mean temperatures for January and February to predict when M. persicae will become active in the summer.  In 2011, following an extremely cold December 2010, SASA predicted early season aphid activity have been based on the mean temperatures during the three-month period of December-February.  We intend to continue to use the model based on the three month period.

During winter 2017-18, the mean temperatures were slightly below the mean over the last 50 years:  3.6°C at SASA (Edinburgh; mean = 4.0°C) and 3.1°C at JHI (Dundee; mean = 3.7°C).  These winter temperatures rank the 33rd warmest from the last 50 years at Edinburgh and the 37th warmest from the last 52 years at Dundee.  Based on these figures, the predictions for the first flight of M. persicae is 21 June at Edinburgh (average date of first catch is 15 June) and 23 June at Dundee (average date of first catch is 16 June).  Therefore, M. persicae activity in 2017 is expected to commence about 1 week later than in an average summer.

In 2017, the first M. persicae at Edinburgh was recorded on 17 May, 29 days earlier than the average date of first catch and 5 days earlier than predicted.  The first M. persicae at Dundee was recorded on 12 May, 35 days earlier than the average date and 17 days earlier than predicted.  First arrival dates for both sites were well within the 75% confidence limits of predictions.

The predictions for the Potato aphid Macrosiphum euphorbiae, Rose-Grain aphid Metopolophium dirhodum and the Grain aphid Sitobion avenae are provided by Rothamsted Research and are based on mean temperatures over January and February 2018.

Table 1

  2018 Prediction 75% Confidence Limits 2017 Obs'n

2018 Obs'n

Edinburgh
Myzus persicae 21 June 30 May - 12 July 17 May -
Macrosiphum euphorbiae 28 May 6 May - 19 June 9 May 25 May
Metopolophium dirhodum 29 May 5 May - 22 June 28 April -
Sitobion avenae 4 June 15 May - 25 June 24 May -
Dundee
Myzus periscae 23 June 28 May - 18 July 12 May -
Macrosiphum euphorbiae 9 June 16 May - 4 July 29 April 24 May
Metopolophium dirhodum 11 June 20 May - 4 July 29 April 9 May
Sitobion avenae 12 June 24 May - 1 July 16 May -

The slightly cooler than average temperatures over 2017-18 winter indicate that the first flights of M. persicae should be about a week later than on average, and some 6 weeks later than in 2017.  Consequently, they are less likely to develop to population levels that would significantly threaten the virus health of seed crops (see table above).  The prediction for the total of M. persicae caught by 31 July is 16 at Dundee and 12 at Edinburgh.  The 75% confidence intervals for these predictions are 4 at the lower end for Dundee and 2 at the lower end for Edinburgh, and 55 at the upper for Dundee and 46 at Edinburgh.  Therefore, populations of M. persicae should be relatively low during the growing season for potatoes in 2018.  Therefore, there is little scope for significant risk of leaf roll transmission in potato crops, so a low risk of the 2019 crop exhibiting significantly higher levels of leaf roll than the 0.7% predicted for 2018. 

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