Trichogramma are typically purchased as pupae within parasitized eggs. In both years, the vigor of Trichogramma brassicae received from the supplier was good, but the numbers of wasps that emerged varied. In 1992, a total of 429,120 female wasps per hectare were released over 10 dates. In 1993, only 163,680 female wasps per hectare were released over the 10 dates. The researchers cited unexpected emergence during shipping and perhaps low initial parasitism of the commercial material as possible reasons for the reduced emergence in 1993. The wasps killed at least 45% of the corn borer egg masses in both years.
Trichogramma treatments improved the percentage of clean ears over untreated plots. In 1992, Trichogramma plots had 62% clean ears versus 51% in untreated plots. In 1993, Trichogramma plots had 60% clean ears versus 51% in untreated plots. Dipel treatments alone also improved ear quality. The lowest rate of Dipel produced 66% clean ears and at the highest rate 77%, versus only 38% clean ears in untreated plots. However, using both Bt and Trichogramma together did not result in additional insect control compared to either used alone.
B. P. Mertz, S. J. Fleischer, D. D. Calvin and R. L. Ridgway. 1995. Field assessment of Trichogramma
brassicae (Hymenoptera: Trichogrammatidae) and Bacillus thuringiensis for control of Ostrinia nubilalis
(Lepidoptera: Pyralidae) in sweet corn. Journal of Economic Entomology 88: 1616-1625.