Variability in quality of Trichogramma brassicae (Hymenoptera: Trichogrammatidae) from commercial suppliers in Germany

The quality of Trichogramma brassicae Bezd. (=T. maidis n. sp.) (Hymenoptera: Trichogrammatidae) produced in 1998 and 1999 by four companies (AMW Nuetzlinge GmbH, Biocare GmbH, BASF, and Landi) to control the European corn borer Ostrinia nubilalis Hubner (Lepidoptera: Pyralidae) was measured. Standard methods developed by the International Organization for Biological Control (IOBC) were used to assess sex ratio, number of females released per hectare, longevity, fecundity, and capacity to parasitize the natural host. The percentage of females was between 50.7 +/- 1.5 and 68.3% +/- 1.9%, always higher than the 50% standard agreed upon by the IOBC. The number of parasitized eggs released per hectare was, with one exception, considerably higher than the standard of 100,000 given by the companies. In five cases, it was over 150,000 parasitized host eggs per hectare. The emergence rate varied from 72.3 +/- 1.3 to 90.6 +/- 0.9%. Therefore, the number of females released per hectare varied between 38,532 and 86,966. The survival rate (to day 7) fluctuated between 16.7 and 66.7% and was much lower than the optimistic IOBC standard of 80%. The fecundity on the mass rearing host Sitotroga cerealella (Olivier) and on the target host O. nubilalis was also often lower than the IOBC standards, and this especially in the first release, which could partly be due to longer storage. The releasing units contained parasitoids in different development stages to prolong the period of adult emergence and thereby extend the duration of treatment. Parasitoid emergence for the two treatments together continued for about 4 weeks (June 30 to July 27, 1998, and June 23 to July 21, 1999). In both test years, the two parasitoid releases produced strongly overlapping periods of adult emergence that coincided with the egg-laying peak of the pest in the field.