QUALITY AND ENVIRONMENTAL-FACTORS AFFECTING TRICHOGRAMMA-BRASSICAE EFFICIENCY UNDER FIELD CONDITIONS

Field parasitism of the egg parasitoid Trichogramma brassicae Bezdenko (Hymenoptera, Trichogrammatidae) (synonymous to T. maidis Pint. et Vo egele) on Ostrinia nubilalis Hubner was compared to four single qualit y parameters (walking speed, fecundity on the factitious host Ephestia keuhniella Zeller, fecundity on the natural host O. nubilalis, and li fe span) previously measured in the laboratory and, a quality index ca lculated from three of the measured parameters. A single quality param eter (fecundity on E. keuhniella) and the calculated quality index sho wed a correlation to ?: brassicae field parasitism, for different T. b rassicae populations. The number of female Trichogramma released clear ly influenced parasitism but not in the same proportion for all popula tions tested, reflecting that numbers released can only to some extent compensate for low quality in Trichogramma. Variation indegree hours above 18 degrees C also influenced field parasitism. When incorporatin g degree hours to the quality index a significant correlation R(2) = 0 .56 (P = 0.01) is obtained. In this work fecundity of T. brassicae on E. keuhniella can be as good an indicator for the potential field perf ormance of T. brassicae, as the quality index which takes into account three quality parameters. Since environmental factors can obscure the potential performance of a population, i.e., one which under optimal laboratory conditions performs well, the quality index gives only a pa rtial indication of how the released strains will perform in the field .