Early instar larvaAdult ovipositingEggsypgWheat Stem RK PetersonWheat Stem SawflyInternal damageW. MorrillPlant LodgingRK PetersonDesign by Shitan Zun• 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, 2002WESTERN TRIANGLE RESEARCH CENTERWESTERN TRIANGLE RESEARCH CENTER30%20%25%30%15%20%5%10%0%INFEST ED CUT PARASIT ISM PATHOGEN` Cutting can be avoided by killing larvae in the stemsH?`How?◦ Planting resistant cultivars◦Parasitoids that attack developing larvaeParasitoids 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)pith does not develop enough (shading)◦ Some larvae may survive to cut the stems` ParasitoidsBracon lissogaster Bracon cephiRK PetersonBracon lissogasterBracon cephiRK PetersonParasitoid lW. MorrillW. MorrillRK PetersonlarvaDesign by Oscar Perez455030354045SITIS202530% PARAS51015%05 6 17 18 21 25 32 38 38 48% STEMS CUTData: Morrill, unpublished- from ten farms in Montana, 1998.` Rates of parasitism in excess of 90% have been reported (Morrill 1997)“Bhidjdifl`“B. cephicaused a major drop in sawfly populations across the Canadian prairies between 1955 and 1957”(Holmes 1982)between 1955 and 1957 (Holmes 1982)`How can we enhance parasitism?`How can we enhance parasitism?` Heavy tillage has more impact on parasitoids than sawflies◦Sawfly overwinter in underground stubs–adapted toSawfly overwinter in underground stubs adapted to digging out ◦ Parasitoids overwinter in above-ground part of stems – not adapted to diggingoutadapted to digging out`Residue height`Residue height ◦ 1/3 conserves parasitoidsPERCENT SAWFLY LARVAE KILLED BY PARASITOIDS IN FIELDS BORDERING TILLED AND UNTILLED FALLOWFIELDS BORDERING TILLED AND UNTILLED FALLOW8090TILLED6070CHEMFALLOW405020300101998199819991999200020012001200119981998199919992000200120012001Reference: Runyon et al. 2002. J. Economic Entomology. 95:1130-1134.` Solid stem◦widely adopted management practice◦widely adopted management practice`Biological control`Biological control◦ research is being conducted to rear, collect and redistribute parasitoidsgrowers can enhance parasitoid numbers with certain crop◦growers can enhance parasitoid numbers with certain crop management practicesHow do these two management practices interact?` Tends to depress parasitoid effectiveness◦ Multiple eggs per stemCannibalism◦Cannibalism◦ Defenseless parasitoid larva` Holmes (1963) and Morrill (1997) both report this phenomenon# Sawflies in cagePercent InfestedPercent of infested stems ih i idwith parasitoid50 82 825 61 815611415611452619The Canadian Entomologist Vol. 95 No. 219561957195819591956195719581959Red Bobs32703040Percent ParasitismRed Bobs32703040Rescue( lid)66983837Th C di E t l i t V l 95 N 2Rescue (solid)66983837The Canadian Entomologist Vol. 95 No. 2` SOLID STEM WHEAT & PARASITOIDS◦ The top 2 management strategies◦ & they work well together!!`Cutting as a measurement of “Resistance” Cgconfounded by the presence of parasitoids` Fungal pathogensFussariuminfested sawflylarvae in wheat stemslarvae in wheat stems` We have◦ Cut stems with overwintering larvae◦ Parasitoid cocoons, and emergence holes in stems◦Solid stems and hollow stems◦Solid stems and hollow stems◦ Sawfly larvae◦ Evidence of sawfly larvae in stemsx