PARASITIZATION PERFORMANCE OF TRICHOGRAMMA SPP. (HYM., TRICHOGRAMMATIDAE) REARED ON EGGS OF SITOTROGA-CEREALELLA OLIVER (LEP., GELECHIIDAE), STORED AT FREEZING AND SUBFREEZING CONDITIONS

To study the influence of freezing and subfreezing storage conditions of eggs of Sitotroga cerealella on the parasitization performance of T richogramma pretiosum Riley three different storage conditions were te sted: 8 degrees C (refrigerator), - 20 degrees C (freezer) and - 196 d egrees C (liquid nitrogen). During the parasitization step, for the eg gs stored 30 and 130 days in liquid N2, two further variables were con sidered: (a) two parasitization temperatures (21 degrees C and 26 degr ees C) and (b) addition of 'kairomones'. An alternative thawing method was tested (water bath at 50 degrees C during 30 min) for eggs stored during 130 days. Storage in a conventional freezer proved to be compl etely unsuccessful. In the refrigerator, 80% to 90% of the eggs kept i n storage for 10 to 13 days, exposed to parasitoids, turned black (egg s with a Trichogramma pupa inside). This percentage declined to 60% fo r eggs stored during 20 to 25 days and after 35 days the percentage wa s lower than 30%. The percentage of emergence and the sex ratio were n ot significantly different among eggs stored during 5 to 25 days but t he emergence decreased for eggs stored longer than 25 days. For the se x ratio the only difference was found between the stored and non-store d eggs. Liquid nitrogen proved to be a good storing method provided th at a high amount of parasitoids is not immediately required. The perce ntage of parasitised eggs (strictly pupation of the paraisitoid) was n ot significantly different among the treatments (20, 30 or 130 days). Thawing the eggs in a warm water bath plus a raise in temperature duri ng the parasitization increased significantly the yield of parasitoids . Two hypotheses are put forth to explain the probable reasons of the outcomes of the experiments. All in all, if a high performance of the host eggs is required no more than 10 days at approximately 8 degrees C are recommended but if a long term storage is needed, conservation i n N21 accompanied by an appropriate thawing method and a good parasiti zation temperature, proved to be satisfactory.