Abundance and survival of a seed-infesting weevil, Pseudanthonomus hamamelidis (Coleoptera: Curculionidae), on its variable-fruiting host plant, witch-hazel ( Hamamelis virginiana )

Abstract

1. The relative importance of seed abundance and of mortality factors in the population biology of Pseudanthonomus hamamelidis , a hostspecific predispersal seed predator on Hamamelis virginiana , is evaluated by analysis of weevil life tables and abundance estimates in three years with markedly different magnitudes of fruit production. 2. Fruit production of marked Hamamelis individuals averaged 336 m -2 in 1978, increased three- to four-fold in 1979, and declined again in 1980. More individuals fruited in 1979 than in the other two years. 3. The early larval stage of P.hamamelidis incurred the greatest mortality, with 42–58% dying from often undeterminable causes. Losses in the egg stage ranged from 22% to 31%. Three parasitoid species each accounted for minor mortality. Generation survival was similar in all three years, ranging from 21% to 28%. 4. The percentage of Hamamelis fruit crops infested by P.hamamelidis was high in 1978, averaging 76%, but was much lower in 1979, the year of abundant fruit. In 1980, when fruit were less abundant again, infestation was nearly complete. Egg densities on fruits were lower in 1979 than in the other two years. 5. The fluctuating fruit crops of Hamamelis are responsible for limitation of P.hamamelidis numbers during poor fruiting years. The occasional highly productive fruiting year results in satiation of weevil populations and concomitant seed escape by Hamamelis . Mortality factors appear less important in influencing weevil population dynamics.