Lack of an induced response following fire and herbivory of two chemotypes of Melaleuca quinquenervia and its effect on two biological control agents

Induced responses following damage from herbivory or fire may reduce the nutritional quality of plants for subsequent herbivores. If compatible, the combination of fire and biological control has the potential of effectively controlling invasive weeds. Potentially plants subjected to previous herbivory from biological control agents or damage from fire, either natural or deliberate, will be less susceptible to biological control because of decreases in the nutritional quality of the plant from changes in physical defenses and/or accumulated secondary compounds. In the fire-adapted species, Melaleuca quinquenervia, the impact of previous herbivory by the weevil biological control agent Oxyops vitiosa and burning by a propane torch was studied on the first replacement leaves produced following damage. Two chemical variants or chemotypes of M. quinquenervia responded similarly with decreased leaf toughness in leaves produced following burning; little change was found in the levels of foliar nitrogen or volatile constituents in response to treatments. Moreover, survival decreased when the burn replacement leaves were fed to O. vitiosa larvae and Boreioglycaspis melaleucae psyllid nymphs; growth and development time were not affected. These results indicate that although survival will decrease in both species fed the first replacement leaves following burning, previous herbivory by weevils is compatible with subsequent damage by both biological control agents.