Ability of the Hessian Fly to Stunt Winter Wheat. 2. Paper Chromatography of Extracts of Freeze-Dried Larvae and Wheat Plants123

Paper chromatography of freeze-dried larvae of Mayetiola destructor (Say) in a solvent system of 1-butanol:methanol:water, 80:5:15, isolated a peak of plant-growth-promoting substance at Rt 0.15-0.25. This growth promoter was detected also on chromatograms of stomachs and carcasses of fresh larvae but was absent from chromatograms of larvae collected from ‘Knox 62’ wheat, Triticum aestivum L., a cultivar resistant to the Hessian fly, or from chromatograms of larvae that had never fed. Paper chromatograms of ethanol extracts of both infested and uninfested wheat plants revealed that feeding by the larvae did not reduce the amount of the growth promoter, but benzene extracts of infested plants produced chromatograms with more peaks of growth-inhibiting substances than did benzene extracts of uninfested plants. The inhibitors in the benzene extracts of infested plants may be the reaction of the wheat plant to secretions introduced into the plant by the feeding larvae. Therefore, the most likely cause of stunting of winter wheat by the Hessian fly is the result of something discharged into the plant by the Hessian fly larva as it feeds.