Pant Growth Hormones in Ether Extracts of the Greenbug, Toxoptera graminum, and the Pea Aphid, Macrosiphum pisi, Fed on Selected Tolerant and Susceptible Host Plants1

Abstract

Free auxins were detected and identified in extracts of homogenized aphids using paper chromatography in conjunction with a modified Avena coleoptile bioassay method. Variations in auxin content of extracts of the green bug, Toxoptera graminum (Rondani), and pea aphid, Macrosiphum pisi (Harris) feeding on susceptible or tolerant hosts were measured and possible relationship to the tolerance component of resistance investigated. The following auxins were detected in significant amounts and identified by RF values in the extract of the aphids feeding on the following susceptible and tolerant hosts: (1) susceptible Reno barley—3-indoleacetic acid (IAA), 3-indolebutyrie acid (IBA); (2) tolerant Dicktoo barley—auxins not present in significant amounts; (3) susceptible Pawnee wheat—indolepyruvic acid (IPA); (4) tolerant Dickinson wheat—auxins not present in significant amounts, growth inhibition present Extract of pea aphids that had previously fed on susceptible broad bean tissue contained 3-indoleacetic acid (IAA) in significant amounts. Auxins were found in significant amounts in extract of aphids that had fed on susceptible plants but absent in aphids fed on tolerant varieties. Auxins present in green bugs and pea aphids were significantly reduced by a short starvation period prior to analyses, which indicated that auxins present in aphids were plant derived rather than synthesized by the aphids. NO evidence that insects can produce auxins was found. Determining growth substances present in the salivary glands of aphids would provide valuable information as to whether the toxin in salivary juices are plant-derived axons or inhibitors in toxic concentrations or whether the toxins have their source from pertinacious material synthesized by the aphids. The tolerance component of resistance is closely associated with the free-auxin content of plants and the ability of certain aphids to extract and concentrate these growth substances.