Sampling methods and construction of life tables for Sitona humeralis populations (Col., Curculionidae) in Mediterranean climatic areas.
Abstract
Criteria for selecting sites are described and the various sampling, rearing and identification techniques used to investigate field populations of Sitona humeralis Steph. (a pest of lucerne and annual species of Medicago recently introduced into Australia from the Mediterranean area) are discussed. Each developmental stage of the weevil was collected in southern France directly from the host-plant (lucerne) or extracted with simple equipment in a mobile laboratory, and the population densities were estimated realistically with acceptable accuracy. A life-table was constructed from regular sampling and observations in the same site over a 6-year period. It demonstrated that the population reduction caused by each entomophagous species rarely exceeded 20%. The greatest mortality of up to 99% occurred immediately after hatching. A comparison of life-table data from Australia and Europe showed that numbers, particularly of late-instar larvae and young adults of S. humeralis, are greater in Australia than in southern Europe. Hence natural enemies attacking the pre-imaginal stages or depressing the weevil's fecundity should be given first priority for release in Australia.