| Both Trichogramma dendrolimi and T.dendrolimi have been mass-produced and widely released against Ostrinia furnacalis in China.The control efficiency of O.furnacalis by T.ostriniae is stable,however,the efficiency varied greatly among areas when T.dendrolimi were released.The differences among areas and between the two Trichogramma species possibly resulted from the preference of Trichogramma to host and the suitability of host for Trichogramma.The developmental stage of O.furnacalis eggs affects the parasitizaition of Trichogramma,non-fertilized eggs or those of which the development was arrested may be suitable for parasitization by affecting the behavior of Trichogramma.In present study,the fertilized and non-fertilized eggs of O.furnacalis were chose as hosts.The behavior and suitability of offspring of two Trichogramma species,T.ostriniae,which can parasitize O.furnacalis eggs well,and T.dendrolimi which parasitize O.furnacalis eggs at low parasitism,were investigated in the laboratory.The results are as follows:(1)Non-experienced T dendrolimi spend more time(25.2 s)in searching fertilized eggs of O.furnacalis than that(17.4 s)in non-fertilized eggs.Experienced T.dendrolimi spend less time(11.3 s)in examining surface of fertilized host eggs than that(13.7 s)of non-fertilized host eggs.For T.ostriniae,the similar behavior was observed.However,times spent in host searching,host surface examining,ovipositing,and total parasitization behavior of T.ostrinia was more than that of T dendrolimi,respectively,whatever on fertilized or non-fertilized host eggs.The non-experienced Trichogramam wasps spent more time in completing the parasitization that experienced ones did.(2)One parasitization behavior of both the Trichogramma species can result in 0,1 or 2 wasp eggs in the host egg.The proportion(54.68%)of no wasp eggs laid in fertilized eggs by T.dendrolimi was significantly higher than that(37.68%)in non-fertilized eggs,and the proportion(55.07%)of one wasp eggs laid in fertilized host eggs was higher than that(37.51%)in non-fertilized host eggs.However,the results for T.ostriniae on fertilized host eggs and non-fertilized eggs was contrary to those of T.dendrolimi.There were no significant differences between non-experienced wasps and experienced ones.(3)In choice test,T dendrolimi tended significantly to parasitize non-fertilized host eggs than fertilized ones.Parasitism(33.81%)of non-fertilized host eggs by T.dendrolimi was significantly higher than that(7.77%)of fertilized host eggs.However,T.ostriniae did not exhibit preference to any of the two kinds of host eggs.Non-experienced wasps of both Trichogramma species preferred non-fertilized host eggs to fertilized ones,however,when the wasps made second choice,T.dendrolimi preferred non-fertilized host eggs whereas T.ostriniae preferred fertilized ones.(4)The incidence rate(79.92%)of T.dendrolimi on non-fertilized host eggs was significantly higher than on fertilized(54.47%)and UVF(60.83%)eggs.In contrast,the incidence rate(65.63%)of T.ostriniae on non-fertilized eggs was significantly lower than on fertilized eggs(99.91%)and UVF eggs(100%).The parasitism rate(41.24%)of non-fertilized eggs by and non-emergence percent(10.56%)of T.dendrolimi was significantly higher than that on fertilized eggs(23.25%and 4.62%,resp.)and UVF eggs(28.42%and 4.51%,resp.);however,the parasitism rate(29.59%)of non-fertilized eggs by and non-emergence percent(4.57%)of T.ostriniae was significantly lower than fertilized eggs(56.46%and 7.67%,resp.)and UVF eggs(67.65%and 5.86%,resp.).T.dendrolimi had lower emergence rate(92.33%)on non-fertilized eggs than fertilized eggs(97.46%).There were no significant differences in female proportion,developmental time,egg load and hind tibia length of offspring between the two Trichogramma species.Trichogramma can distinguish the fertilization status of the host eggs,and the fertilization status of O.furnacalis eggs has a significant impact on the host selection,parasitism behavior and fitness of the two Trichogramma species. |
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