Rothamsted Research where knowledge grows Epidemiology and forecasting of BYDV on winter cereals Richard Harrington Rothamsted Insect Survey RETIRED Alnarp 5 th June 2015
Talk content Aphids The suction-trap network BYDV, its vectors, transmission Insecticide resistance Climate change Yield loss and control
Aphids and why they are pests
600 UK species
Telescoping of generations
Fast breeders 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1 50 2,500 125,000 6,250,000 312,500,000 15,625,000,000 149 km layer covering the Earth
Parthenogenesis in action
Sex once a year (for the lucky ones)
Winter eggs
apterous fundatrigenia emigrant apterous exule fundatrix Spring Summer several generations egg Winter Autumn alate exule ovipara apterous exule gynopara male
Host alternation Spindle to Bean Willow to Carrot Bird cherry to Cereals Peach to Potato Blackcurrant to Sowthistle Blackcurrant to Lettuce Plum to Reeds Plum to Hops Rose to Cereals Dogwood to Grass roots Apple to Plantain etc.
Elgin Dundee Gogarbank Ayr Newcastle 1964 2014+ Daily data York Preston Kirton Wellesbourne Broom s Barn Hereford Rothamsted Silwood Park Silwood Starcross Writtle Wye
12.2 m suction traps operating in Europe Dec 2014 Shaded countries are EU members 42 sites in 11 countries Tyrnava Jokioinen Ultuna Viikki Pushkin Elgin II Preston Belfast Broom s Barn Wellesbourne Ayr Dundee Gogarbank Newcastle Tollebeek Colijnsplaat Kirton II Kollumerwaard Ingelstorp Alnarp Bialystok Hereford Rothamsted Starcross Winna Góra Writtle Quedlinburg Žatec Silwood Wye Sosnicowice Gembloux Lipa Libramont Čáslav Orléans Reims Le Rheu Auxerre Changins Vĕrovany u Olomouce Chrlice u Brna
English grain aphid, Sitobion avenae
Bird cherry oat aphid, Rhopalosiphum padi
Virus transmission
Virus transmission BYDV is a persistent (or circulative ) virus 3 2 1 4
Forms of bird cherry oat aphid ASEXUAL PRE-SEXUAL
Proportion of cereal-colonising forms Female R. padi from 12.2m Rothamsted Trap 1986-2014 r 2 = 0.624 P < 0.0001
R padi Sept - Dec Number of R. padi in autumn at Rothamsted vs summer rainfall 1968-2006 10,000 1000 100 P < 0.001 10 40 80 120 160 200 240 Rainfall (mm) June - Aug
Frequency of combination WARM WINTER + WET SUMMER + WARM WINTER 1.0 0.8 0.6 0.4 North west South west North east 0.2 South east Central 0.0 1960 1980 2000 2020 2040 2060 2080 2100 Year
2011/12 SEASON Nothing notable in early autumn in terms of aphid numbers Very warm dry conditions of October to January led to much extended aphid flight, reproduction and movement than usual
HGCA aphid news 25 th November 2011 Activity on the ground should continue apace with development and reproduction possible above 4ºC and walking between plants above 1ºC. The BYDV threat remains high with reports of even the latest crops to emerge being treated this year in some areas. The continuing relatively mild conditions suggests checking untreated crops is still worthwhile. HGCA aphid news 2 nd December 2011 The warm dry conditions through October and November led to a significantly extended autumn flight period and enabled aphids to continue multiplying and moving within crops. These aphids have the potential to spread BYDV and because of the exceptional weather this autumn, crops at risk could include those grown from insecticide treated seed. Aphid news Newsflash 20 th January 2012 Aphids will be multiplying and moving in autumn-sown crops, especially in more southerly areas and, where they were not fully controlled before flights ended in autumn, the risk of virus spread (e.g. BYDV and TuYV) is likely to be high.
Insecticide resistance in grain aphid Some pyrethroid control failure noticed since Summer 2011 Photo: Alan Dewar, Dewar Crop Protection
% kdr-sr aphids English grain aphid % resistant 60 50 40 30 20 2009 2010 2011 2012 2013 2014 10 0 Broom s Barn Kirton Rothamsted Suction-trap Sites * *No data for 2009 and 2010 at Rothamsted 2014 data funded by Potato Council
37 Rhopalosiphum maidis (Corn leaf aphid) and BYDV-RMV R. maidis transmits RMV efficiently and other BYDV strains inefficiently RMV is transmitted by other aphids very inefficiently RMV not currently a problem in UK R. maidis is entirely asexual Prefers maize to wheat and barley But, with warmer conditions
38 Rhopalosiphum maidis (Corn leaf aphid) and BYDV-RMV More maize More successful aphid overwintering R. padi may become more efficient at transmitting RMV (Lucio-Zaveleta et al. (2001) Variation in transmission efficiency among BYDV RMV isolates and clones of the normally inefficient aphid vector, R. padi. Phytopathology 91, 792-796) RMV likely to become an issue
Yield loss Varies considerably with crop species, virus strain and sowing date Example of sowing date effect (1990 winter barley) SOWING % YIELD (t/ha) YIELD (t/ha) YIELD (t/ha) DATE INFECTION untreated treated increase 5 th Sept 32.5 4.42 5.95 1.53 18 th Sept 12.5 6.51 7.77 1.26 29 th Sept 8.7 7.29 7.75 0.46 9 th Oct 6.1 7.40 7.69 0.29 18 th Oct 2.8 7.02 7.42 0.40
Cultural control Clean stubble before preparing seedbed Leave at least 5 weeks between ploughing and sowing new crop Consider a desiccant herbicide if cultivation to sowing < 5 weeks Delay sowing by a week to reduce BYDV spread by up to half Choose a moderately resistant spring barley variety
Chemical control Use of neonic-treated seed can provide about 6 weeks protection In mild seasons the threat of infestation may continue into winter Pyrethroid sprays will kill most wingless aphids Chemical control is usually ineffective in spring-sown crops No satisfactory thresholds for treatment exist
Day-degree (dd) calculation ( t-sum ) Serious spread begins when the second generation after colonisation is produced. A generation takes around 170 dd above 3 deg. C e.g. 17 days if the mean temperature each day is 13 deg. C. A generation later (i.e. 340 dd after colonisation) serious spread is inevitable if there has not been high mortality. Start accumulating the dd sum: 6 weeks after sowing for neonicotinoid-treated crops; date of emergence for other crops; one week after pyrethroid spray treatment.
50 years and counting (aphids)
Acknowledgements All Rothamsted Insect Survey and SASA Group, past and present All trap operators Steve Foster, Martin Williamson, Di Cox (Rothamsted) Lawes Agricultural Trust
Rothamsted Research where knowledge grows THE ROTHAMSTED INSECT SURVEY IS A BBSRC-SUPPORTED NATIONAL CAPABILITY
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