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Early season aphid activity in 2015
Prolonged exposure to low winter temperatures are known to have lethal and sub-lethal effects on populations of M. persicae which, in Scotland, overwinters in the larval stage. 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 2014-15, the mean temperatures were close to the average for the last 50 years: 4.23°C at SASA (Edinburgh; mean = 3.88°C) and 3.55°C at JHI (Dundee; mean = 3.64°C). The winter temperatures for 2014-15 rank the 24th warmest over the past 47 years at Edinburgh and 29th warmest over the past 49 years at Dundee. Based on these figures, the predictions for the first flight of M. persicae is 10 June (average date of first catch is 11 June) at Edinburgh and 15 June (average date of first catch is 15 June) at Dundee. Therefore, M. persicae activity in 2015 is expected to commence at a similar time as in an average summer.
In 2014, the first M. persicae at Edinburgh was recorded on 12 June, one day later than the average date of first catch, and at Dundee on 18 June, three days later than the average date. Despite the relatively warm spring, the predicted early flights failed to materialise.
The predictions for the 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 2015.
|2015 Prediction||75% Confidence Limits||2014 Obs'n||
|Myzus persicae||10 June||20 May - 7 July||2 July||4 June|
|Macrosiphum euphorbiae||21 May||30 April - 10 June||29 April||4 June|
|Metopolophium dirhodum||24 May||29 April -18 June||28 April||9 June|
|Sitobion avenae||28 May||7 May - 19 June||23 May||11 June|
|Myzus periscae||15 June||21 May - 10 July||18 June|
|Macrosiphum euphorbiae||31 May||6 May - 25 June||17 May||22 June|
|Metopolophium dirhodum||4 June||12 May - 27 June||17 May||1 June|
|Sitobion avenae||5 June||17 May - 24 June||25 May||2 June|
The average temperatures over the 2014-15 winter indicate that the first flights of M. persicae should be close to the mean dates in mid-June. Consequently, they are less likely to develop to significantly high poulation levels. The prediction for the total of M. persicae caught by 31 July is 15 at both Dundee and Edinburgh. The 75% confidence intervals for these predictions are 4 at the lower end and 53 at the upper for Dundee and 4 at the lower end and 55 at the upper for Edinburgh. Therefore, populations of M. persicae are not expected to build up to significant levels during 2015. Therefore, it is unlikely that there will be a high risk of leafroll transmission, even in crops of potato varieties that are highly susceptible. M. persicae is also a vector of PVY but it appears that only in exceptional years do populations of this species develop within crops to such an extent as to present a risk comparable to that provided by the usually much more numerous cereal aphids. This is unlikely to occur in 2015.
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