Inducible Responses in Papaya: Impact on Population Growth Rates of Herbivorous Mites and Powdery Mildew Under Field Conditions

Abstract

Induced plant responses to herbivores and pathogens have been found in many systems. We examined intra- and interspecific interactions among three parasites through induced responses in their shared host plant, papaya. Three key parasites attack papaya foliage in Hawaii: the carmine spider mite, Tetranychus cinnabarinus (Boisduval); the papaya rust mite, Calacarus flagelliseta Fletchmann, De Moraes, and Barbosa; and the powdery mildew causal agent, Oidium caricae F. Noack. Under laboratory conditions, papaya seedlings were first exposed to standardized populations of mites and mildew; the parasites were removed, and the clean, previously infested plants were transplanted into the field to be exposed to colonization by natural populations of plant parasites. Population growth of colonizers was monitored for a period of 3 mo. We found no evidence for induced plant resistance. Rather, our results suggest that papaya expresses a weak form of induced susceptibility after injury from papaya rust mites and powdery mildew. Plants exposed to rust mites as young seedlings subsequently supported larger populations of spider mites, and plants exposed early to powdery mildew subsequently supported larger populations of rust mites.