The laboratory test described in the present paper assesses pesticide effects on the 'most exposed' life stage of the parasitic wasp Opius concolor, and it has been developed and interpreted according to the guidelines of the IOBC/WPRS Working Group 'Pesticides and Beneficial Organisms'. The evaluation of results is based on longevity and parasitism of adult females exposed to a fresh residue of pesticide on a glass surface. Longevity measurements were based on the time of exposure required to cause 50% mortality (LT50) and were compared to a standard control LT50, in order to calculate the reduction caused by the pesticide. Parasitism was surveyed by means of three sequential determinations: the number of days that females were seen parasitizing, the mean number of attacked hosts and the progeny size per female. These determinations were also compared to a control to calculate the impact of pesticides. Using this 'worst case' situation, pesticides reducing the beneficial capacity of O. concolor below the IOBC threshold for harmlessness may be recommended for field use in combination with this wasp.
