A FUNCTIONAL SCHEME FOR PREDICTING THE OUTBREAK POTENTIAL OF HERBIVOROUS INSECTS UNDER GLOBAL ATMOSPHERIC CHANGE

There are many possible ways in which changes in the global atmosphere could influence the outbreak potential of herbivorous insects; we clarify these by developing a scheme for analysing insect populations in terms of functional attributes that are both important in population regulation and responsive to global change. This analysis shows that elevated CO2 is not likely to have a major influence on probability of insect outbreak, except possibly in systems in which nitrogen-based defensive compounds are produced by plants in response to herbivory. Systems that will have high potential to outbreak, if climatic conditions become more favourable for plant growth and responses are not constrained by other resources, include those in which both herbivorous insects and host plants have highly flexible growth patterns and activity cues. Global changes that increase environmental stress on host plants are most likely to favour sap-feeding insects. Critical enemy (predator or parasitoid) control of the dormant phase of herbivorous insects may be very important in preventing or allowing outbreaks, but is often poorly understood.