S. TOEPFER, U. KUHLMANN
CABI Bioscience Centre Switzerland, Rue des Grillons 1, 2800 Delémont, Switzerland, stoepfer@cabi-bioscience.ch

The western corn rootworm (Diabrotica virgifera virgifera) is an exotic invasive species and offers the possibility of classical biological control through the search for effective natural enemies in the area of origin.  Life tables will determine mortality factors acting on D. virgifera populations in Hungary and will provide information on the most suitable life stages (egg, three larval instars, pupae and adults) to be attacked by exotic biological control agents.  Additionally, this three-year study investigates the fecundity of the beetles as well as their reproductive period in the laboratory and in the field (EU Project QLK5-CT-1999-01110).  In order to determine mortality factors in the field, several sets of eggs were exposed to winter conditions in two years and recollected during following springs.  Population density and mortality of each larval instar and of pupae were obtained by soil-root sampling in three fields (96 samples per week per field).  Adult density was measured in emergence cages covering 70 plants per study area (0.4 ha).  Diabrotica adults were collected in selected fields in Hungary, Croatia and Yugoslavia and kept in cages in order to determine parasitism.  The population density of each stage was compared and mortality between each stage was calculated.  In a second experiment to determine mortality factors, maize plants were artificially infested by L1 and then L2, L3, pupae and adults were recollected.

Highest mortality was found in diapausing eggs and in the first instar larval stage.  There was some mortality observed in prediapausing eggs but lowest mortality was determined during hatching of larvae, during second and third instar larvae and in adults.  Additional results are provided on the fecundity, longevity and reproductive period of the adults in the field, as well as on the occurrence of D. virgifera natural enemies in Hungary.

In conclusion, the key stages for exotic biological control agents are the late larval instars or the adults of D. virgifera.  CABI Bioscience is conducting investigations on the search for parasitoids in the area of Diabrotica's origin and will test the suitability of exotic parasitoids in Swiss quarantine facilities.