SELECTION OF EFFECTIVE STRAINS OF EGG PARASITES OF THE GENUS TRICHOGRAMMA (HYM, TRICHOGRAMMATIDAE) TO CONTROL THE EUROPEAN CORN-BORER OSTRINIA-NUBILALIS HB (LEP, PYRALIDAE)

Trichogramma strains were compared for their suitability to control the European corn borer Ostrinia nubilalis Hb. The host preference was tested in laboratory experiments by offering single parasite females the choice between eggs of the target pest and eggs of the replacement mass rearing host Angoumois grain moth Sitotroga cerealella. Only the following three strains, from a total of 20 tested, showed preference to and/or satisfactorily parasitized the corn borer eggs, in order of effectiveness: Trichogramma ostriniae from China P.R. (strain 62), Trichogramma evanescens from Moldavia, USSR (strain 10) and T. evanescens from Germany F.R. (strain 105). The number of parasite eggs laid in the corn borer and that laid in the Sitotroga eggs were 17.6 and 5.83 for strain 62; 9.1 and 12.73 for strain 10; and 3.73 and 16.1 for strain 105. The remaining 17 strains almost completely ignored the Ostrinia eggs and only parasitized the grain moth eggs. The searching capacity of T. ostriniae and T. evanescens was compared by conducting parasite release experiments on corn plants in cages. No significant differences between the two species were found. The results of these experiments confirmed that the choice of the two species T. ostriniae and T. evanescens (Moldavia), that are presently being used in practice to control the corn borers in Asia and Europe is justified. The simple laboratory method to test the host preference used in these experiments was found to be suitable for the selection of effective species of the genus Trichogramma for biological control.