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Factors contributing to mortality of wheat stem sawfly



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Eggs Adult ovipositing p g Early y instar larva Wheat Stem Sawfly RK Peterson Design by Shitan Zun Plant Lodging RK Peterson W Morrill Internal damage Lodged stems cannot be harvested Damage to vascular tissue reduces head weight 3 22 Trapped nutrients below node Lodging cutting provides evidence of infestation but no lodging does not necessarily mean no infestation SAWFLY INFESTATION 2002 WESTERN TRIANGLE RESEARCH CENTER 30 25 20 15 10 5 0 INFESTED CUT PARASITISM PATHOGEN Cutting can be avoided by killing larvae in the stems H How Planting resistant cultivars Parasitoids that attack developing larvae Disease fungal pathogens What is the mechanism of resistance Solid stem wheat Reduce lodging Reduce head weight loss Under heavy sawfly pressure or if the pith does not develop enough shading Some larvae may survive to cut the stems Parasitoids Bracon lissogaster Bracon cephi RK Peterson RK Peterson Bracon cephi Bracon lissogaster Parasitoid l larva RK Peterson Design by Oscar Perez W Morrill W Morrill PARAS SITIS 50 45 40 35 30 25 20 15 10 5 0 5 6 17 18 21 25 32 38 38 48 STEMS CUT Data Morrill unpublished from ten farms in Montana 1998 Rates of parasitism in excess of 90 have been reported Morrill 1997 B B cephi hi caused d a major j d drop iin sawfly fl populations across the Canadian prairies between 1955 and 1957 1957 Holmes 1982 How can we enhance parasitism Heavy tillage has more impact on parasitoids than sawflies Sawfly overwinter in underground stubs adapted to digging out Parasitoids overwinter in above ground part of stems not adapted to digging out Residue height 1 3 conserves parasitoids PERCENT SAWFLY LARVAE KILLED BY PARASITOIDS IN FIELDS BORDERING TILLED AND UNTILLED FALLOW 90 T IL L E D 80 C H EM F AL LO W 70 60 50 40 30 20 10 0 1 9 98 19 98 19 9 9 19 9 9 20 0 0 2 00 1 2 00 1 2 00 1 Reference Runyon et al 2002 J Economic Entomology 95 1130 1134 Solid stem Biological control widely adopted management practice research is being conducted to rear collect



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