Comparison of Parasitism Behaviors and Study on Interspecific Competition between Trichogramma Ostriniae and Trichogramma Dendrolimi
|School||Nanjing Agricultural College|
|Course||Agricultural Entomology and Pest Control|
|Keywords||Trichogramma ostriniae T. dendrolimi Ostrinia furnacalis Corcyra cephalonica parasitic behavior egg age interspecific competition superparasitism|
Trichogramma ostriniae Pang et Chen and T. dendrolimi (Matsumura) are two most important species of parasitoids to control O. strinia furnacalis(Guenee) in China. The control effect of T. ostriniae is universally accepted, but there are also many disputes about the control effect of T. dendrolimi. The research object of this paper was two Trichogramma species that have different fitness to O. strinia furnacalis (Guenee). We investigated differences of two species in parasitical behavior and interspecific competition between T. ostriniae and T. dendrolimi. Some research results are as follows:(1) The behavior processes of T. ostriniae and T. dendrolimi parasitizing eggs of Corcyra cephalonica and O. furnacalis(Guenee) were grossly similar, but consuming time of the two stages of drilling and oviposition for T. ostriniae was longer than that for T. dendrolimi. For T. ostriniae, the consuming time in parasitizing O. furnacalis eggs was shorter than that in parasitizing Corcyra cephalonica eggs, whereas, for T. dendrolimi there were no significant differences in the consuming time between two hosts. The drilling time for T. ostriniae parasitizing O. furnacalis eggs was shorter than that parasitizing Corcyra cephalonica eggs. On the contrary, the drilling time of T. dendrolimi was just opposite.(2) The coincidence ratio between the parasitization times and the number of eggs loaded in C. cephalonica egg was more than 80%; but the coincidence ratio between the parasitization times and the number of eggs loaded in O. furnacalis egg was less than 60%. Superparasitism of two Trichogramma species occurred and the number of eggs loaded could reach to 5 and 4 per host for C cephalonic and O. furnacalis, respectively. The frequency ratio for 1 or 2 wasp eggs loaded per host (O. furnacalis) by T. ostriniae significantly more than that for 3 or 4 wasp eggs, the total of frequency ratio for 1 and 2 wasp eggs loaded in host was 72.5%. For T. dendrolimi, the frequency ratio of every number of wasp eggs loaded in host (O. furnacalis) successively significantly decreased with increase of the number of wasp eggs loaded in host, and the frequency ratio for 1 wasp eggs loaded in host was 57.8%, significantly higher than others.(3) The ratio of valid drilling for two species in parasitizing C.cephalonica egg was significantly higher than that in parasitizing O. furnacalis egg. The ratio of valid drilling for T. ostriniae parasitizing O. furnacalis egg was significantly higher than that in parasitizing T. dendrolimi egg.(4) The effects of superparasitism on the body size and sex ratio of offsprings of T. ostriniae and T. dendrolimi were studied by using eggs of C. cephalonica as host in the laboratory. Results indicated that the superparasitism occured in two Trichogram- ma species, and 45.5% of host eggs oviposited twice was significantly more than the percentage for other oviposition times on one host in T. dendrolimi. Oviposition times on one host egg significantly affected the percentage of host with emerged wasps and the sex ratio of offspring. Trchigramma species and oviposition times or number of wasp emerged per host significantly affected the body size of offspring. The body size of wasp from host with only one wasp emerged was significantly larger than that of wasp from host with two or three wasps emerged, and the body size of T. dendrolimi wasps from host with two or three wasps emerged was significantly larger than that of correspondent T. ostriniae. There were no significant differences in body size of female/male wasp from host with one wasp emerged between two Trichogramma species, whereas the body size of wasps of T. dendrolimi (female:0.43mm; Male:0.38mm) was significantly larger than that of correspondent wasp of T. ostriniae (Female:0.38mm; Male:0.35mm) in wasps from host with both sex emerged. The female ratio of T. ostriniae offspring was significantly linear correlated with the oviposition times, whereas it was not for T. dendrolimi. These results indicated the suitability of T. ostriniae to superparasitism was weaker than that of T. dendrolimi, and the negative effect of superparasitism on offspring of T. ostriniae was more significant than that on T. dendrolimi.(5) There were significant differences in the amounts of emergence female wasps of T. dendrolimi among different host ages. The amount of emergence female wasps for T. dendrolimi parasitizing 24h host was the most, and it was the least for 12h host. Despite exposed singly to T. ostriniae or T. dendrolimi or both of two parasitoid species together, host ages significantly affected the body size of offspring. The body size of offspring of correspondent parasitoid species was significantly smaller when host were exposed to two parasitoid species simultaneously than that when host of correspondent age were exposed to T. dendrolimi or T. ostriniae. The amounts of died pupae were not significantly different among different host ages for T. ostriniae when O. furnacalis egg was used as host, whereas, it increased with host ages for T. dendrolimi.