Parasitism And Suitability Of Trichogramma On Fertilized And Non-fertilized Eggs Of Different Host Species

Parasitism and suitability of different hosts are the key factors to screen effective Trichogramma species for controlling insect pests. Trichogramma exhibits different preference not only on eggs of different host species, but also on different stage eggs of the same host species. The parasitism and suitability of fertilized and non-fertilized eggs of host for Trichogramma have not been documented until now. In this study, we selected Trichogramma japonicum, T. chilonis, T. dendrolimi and T. leucaniae as test parasitoid species, and Chilo suppressalis, Corcyra cephalonica and Antheraea pernyi as insect hosts. The main results obtained as followed.1. Parasitism and suitability of fertilized and non-fertilized eggs of C. suppressalis for Trichogramma.Three parasitoid species of T. japonicum, T. chilonis and T. dendrolimi exhibited significant preference on fresh fertilized egg of C. suppressalis. Trichogramma japonicum, T. dendrolimi and T. chilonis parasitized more fertilized eggs(9.3, 8.6, 9.4 eggs) than unfertilized eggs(1.1, 2.1, 2.9 eggs) in 24 h. However, there were no significant differences in percentage of emergence, percentage of female progeny and development time between fertilized eggs and unfertilized eggs. 2. Parasitism and suitability of fertilized and non-fertilized eggs of A. pernyi for Trichogramma.Trichogramma dendrolimi had significant preference to parasitize fertilized eggs of A. pernyi than non-fertilized. When non-fertilized eggs by self produced, self produced and washed with water, obtained with caesarean, obtained with caesarean and washed with water were offered, 60%, 80%, 75% and 60% of host eggs were parasitized. When fertilized eggs by self produced and self produced and washed with water were offered, however, 100% of host eggs were parasitized. Numbers of eggs laid on fertilized eggs by self produced(74.6 eggs)and self produced and washed with water(63.1 eggs) were significantly higher than those of non-fertilized eggs by self produced(39.4 eggs) and obtained with caesarean and washed with water(38.2 eggs). After parasitizing fertilized and non-fertilized eggs of A. pernyi, there were no significant difference in percentage of emergence and percentage of female progeny. 3. Parasitism and suitability of fertilized and non-fertilized eggs of C. cephalonica for Trichogramma.Trichogramma japonicum, T. chilonis and T. dendrolimi parasitized more fertilized eggs of C. cephalonica(32.3, 37.4, 33.8 eggs) than non-fertilized eggs(10.4, 14.5, 17.4 eggs). There was an increasing tendency of development time for T. japonicum(8.7 eggs), T. chilonis(7.9 eggs) and T. dendrolimi(10.0 eggs) on non-fertilized eggs compared with on fertilized eggs(8.4, 7.7, and 9.5 eggs). There were no difference in percentage of emergence and percentage of female progeny between fertilized and non-fertilized eggs. 4. Parasitism and suitability of fertilized eggs of C. cephalonica with ultraviolet inactivation for Trichogramma.Trichogramma chilonis parasitized more fertilized eggs with ultraviolet(UV) inactivation(42.2 eggs) than fertilized eggs without UV inactivation(31.3 eggs). Trichogramma chilonis parasitized more eggs than T. japonicum and T. leucaniae on fertilized eggs with UV inactivation. However, there was no significant difference in number of eggs parasitized on fertilized eggs without UV inactivation among the three Trichogramma species. Each of three Trichogramma species had higher percentage of emergence on fertilized eggs with UV inactivation than on those without UV inactivation. There was no difference in percentage of female progeny on fertilized eggs with or without UV inactivation among the three Trichogramma species. However, T. chilonis had the shortest development time on fertilized eggs with or without UV inactivation, followed by T. japonicum and T. leucaniae. 5. Parasitism and suitability of different aged fertilized and non-fertilized eggs of C. cephalonica for Trichogramma.When different aged fertilized or non-fertilized eggs of C. cephalonica were offered, there was a clear tendency of parasitism increasing with host age increasing for T. chilonis, T. japonicum and T. leucaniae. Generally, various Trichogramma species parasitized more fertilized eggs than non-fertilized eggs on each of host age. There was a tendency of percentage of emergence decreasing with host age increasing for the three Trichogramma species on different aged fertilized eggs. However, there was no difference in percentage of emergence on non-fertilized eggs among the three Trichogramma species. There was a tendency of development time increasing with host age increasing for the three Trichogramma species on different aged non-fertilized eggs. Trichogramma chilonis parasitized most eggs, and had the shortest development time on each of host age eggs compared with other two Trichogramma species.Based on the results of parasitism and suitability of fertilized and non-fertilized eggs of C. suppressalis, C. cephalonica and A. pernyi for four Trichogramma species, we can make a conclusion that Trichogramma prefers to parasitizing fertilized host eggs and has better suitability on fertilized host eggs than on non-fertilized eggs.