Grasshopper crop and midgut extract effects on plants: an example of reward feedback

A study has been conducted to show that insect herbivores contain peptides that induce plant responses. Acid extracts from crop and midgut tissues of the grasshopper, Romalea guttata, induced coleoptile growth in sorghum 49% above untreated controls. Combining the extracts with indole-3-acetic acid (IAA) showed increases in growth 295% above untreated controls and 8% above IAA standards. These results suggest a synergistic activity between the acid extract and the plant hormone, suggesting that a positive feedback mechanism exists between insects and plants.