The magnitude of local host specificity for phytophagous insects and its implications for estimates of global species richness

Estimates of the global number of arthropod species range from 2 million to more than 30 million species. One of the most critical assumptions affecti ng the higher of these estimates is the assumed magnitude of host specifici ty of phytophagous insects, which varies considerably. Difficulties in esti mating this value are caused by both lack of satisfactory data sets and lac k of methods for its objective calculation. We provide a new method for pre dicting host specificity for phytophagous insects at a local scale based on the concept of effective specialization. When the insect-plant host associ ations of a restricted number of plant species are known, we can predict th e magnitude of host specificity when more plant species are included. Based on 2561 host observations of 697 beetle species on 50 plant species in the canopies of a tropical dry forest in Panama, we predict that host specific ity for adult phytophagous beetles in this forest range from 7% to 10%. The se values suggest that the higher estimates of global species richness are not tenable.