Integrated control of wheat blossom midge - HGCA

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SummaryThe orange wheat blossom midge, Sitodiplosis mosellana, is a common and increasingly important pest ofwheat in the Northern Hemisphere, causing severe yield losses in years of high infestation. In an outbreak inthe UK in 2004, crop losses were estimated to have exceeded £60 million. Larval feeding on the developingseeds causes shriveling and pre-sprouting damage and also facilitates secondary fungal attack by Fusariumgraminearum and Septoria nodorum. This affects both the yield and quality of grain harvested. Due todifficulties in detection of S. mosellana the actual degree of damage to crops is often underestimated.The impact of damage has been shown to vary considerably between varieties and recently a gene conferringresistance against the pest has been identified in Canada. We have tested for differences in vulnerability interms of numbers of larvae produced by a given infestation of female orange wheat blossom midge (wbm)and the degree of tolerance of feeding by the larvae exhibited. The degree of development of survivinglarvae was also assessed to determine whether the variety was resistant to attack.WBM has a very patchy spatial distribution and also varies from year to year depending on climaticconditions. In the UK, precipitation causing moist soil conditions at the end of May, followed by warm stillweather in late May/early June can lead to serious midge outbreaks. The egg-laying female is a small insectwhich can remain well hidden in the crop canopy. The larvae are also hidden within the wheat ear which is acryptic position, as well as a difficult spray target. Thus, to achieve effective control any insecticideapplication has to be applied promptly before larvae burrow in-between the lemma and palea. Detectionproblems mean that it is hard to predict when infestations that would warrant insecticide treatment have builtup. There is considerable grower demand for a reliable monitoring system which would reduce theunnecessary use of pesticides against lower levels of midge infestation and allow populations of beneficialinsects to increase providing a greater level of natural control. To address this we have carried out 3 years offield trials of semiochemical baited traps.Varietal testing (Technical reports 1 and 2)A range of winter wheat varieties selected to cover the main groups and traits in the UK was tested at fivesites over three years to establish whether the exhibited differences in vulnerability, tolerance and resistancewere related to wbm damage and how these traits could be most effectively assessed.A critical factor influencing the number of larvae developing on each variety is the degree of coincidencebetween the vulnerable ear emergence growth stages (GS 53-59) with the egg-laying activity of female wbmat each site. All the varieties grown were assessed for the timing of ear emergence, which ranged between 92
and 14 days after Soissons for the other varieties on the current Recommended List tested. In 2002, wbmactivity was biased towards later emerging varieties at all sites. In 2004, the main bias was towards earlyemerging varieties and sites. The 2003 year differed in this respect with some having an early bias and somea late bias. Over the three years of experiments the bias evened out allowing an assessment of anyunderlying differences in vulnerability; however, the results highlight the danger of drawing conclusionsabout this trait from the results from single sites or years. An examination of the results for those varietiesgrown over all three cropping years showed that there were significant differences between varieties in termsof vulnerability (Table 1), with the most vulnerable variety twice as vulnerable as the least.Table 1. Mean numbers of larvae found compared to mean of controls.Variety Larval score Significance*ECO 22 139.3 dOption (C) 121.9 cdXi 19 108.3 bcTanker (C) 105.3 bcSolstice 99.6 bcMalacca (C) 94.7 abcConsort (C) 89.7 abClaire (C) 88.5 abEinstein 73.3 aPennant 73.0 aNb. Values followed by the same letter do differ at the 5% significance level.ToleranceThe intention to measure tolerance by introducing plots treated with chlorpyrifos was confounded by veryvariable control on different varieties and by the incidental control of aphid infestations which decreasedyields on untreated plots at some sites. The discovery of resistant varieties with their yields unaffected bythe degree of midge infestation at each site allowed an alternative method of assessing yield loss againstnumbers of larvae found. The results were still subject to a large variation between sites, which may havemasked any differences between varieties due to tolerance of damage.The relative ranking of the different causes in variation between sites was: coincidence > vulnerability >tolerance.3
Page 1 and 2: Project Report No. 363March 2005Pri
Page 3: AbstractThe orange wheat blossom mi
Page 7 and 8: 1210Time (min)86420treatedcontrol m
Page 9 and 10: 987treatedcontrol6Time (min)5432103
Page 11 and 12: AcknowledgementsFunding for this pr
Page 13 and 14: Table 1. Genotype : wbm interaction
Page 15 and 16: MATERIALS AND METHODSVarietiesExper
Page 17 and 18: Table 4. Varieties tested in each h
Page 19 and 20: varieties. For example at Boxworth
Page 21 and 22: Table 7. Larvae per 100 grains on u
Page 23 and 24: Table 9. Numbers of larvae on chlor
Page 25 and 26: Table 11. Numbers of larvae on chlo
Page 27 and 28: Table 13 Untreated yields in 2002/0
Page 29 and 30: Table 15. Untreated yields (t/ha) i
Page 31 and 32: Table 14. Chlorpyrifos treated yiel
Page 33 and 34: analysed by ANOVA and by a Friedman
Page 35 and 36: To this end we would recommend:1. U
Page 37 and 38: Technical detail 2.Genetic Analysis
Page 39 and 40: Marker AnalysisA molecular genetic
Page 41 and 42: escape, it is not independent of ot
Page 43 and 44: Figure 1 : Levels of range blossom
Page 45 and 46: Figure 3 : Levels of orange blossom
Page 47 and 48: Figure 5: Marker analysis of a samp
Page 49 and 50: 2. MATERIALS & METHODS2.1. Synthesi
Page 51 and 52: GC column is simultaneously directe
Page 53 and 54: In 2003 field experiments were carr
Page 55 and 56:
Table 2 Field Trapping Experiments
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3.1.3. Field Trapping Experiments3.
Page 59 and 60:
Fig. 6. Expt 1A 2003: pheromone dos
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3.1.3.3. 2004 Pheromone Trap Experi
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Fig. 13. Summary of Expt 2 20046005
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attractive (Fig. 16). In addition,
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5. REFERENCESBirkett, M. A., Bruce,
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Integrated control of wheat blossom midge - HGCA

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