GRASSHOPPER CROP AND MIDGUT EXTRACT EFFECTS ON PLANTS - AN EXAMPLE OFREWARD FEEDBACK

Acid extracts and a resultant fraction from solid-phase extraction (SP E) of Romalea guttata crop and midgut tissues induce sorghum (Sorghum bicolor var. Rio) coleoptile growth in 23-h incubations an average of 49% above untreated controls. When combined with plant auxin, indole-3 -acetic acid (IAA), the SPE fraction shows a synergistic reaction, yie lding increases in coleoptile growth that average 295% above untreated controls and 8% above IAA standards. The interaction lowered the poin t of maximum sensitivity of IAA 3 orders of magnitude, resulting in a new IAA physiological set point at 10(-7) g/ml. This synergism suggest s that contents in animal regurgitants making their way into plant tis sue during feeding may produce a positive feedback in plant growth and development following herbivory. Such a process, also known as reward feedback, may exert major controls on ecosystem-level relationships i n nature.