Effects Of Inducible Resistance In Zea Maize On Related Physiological And Behavioral Performance Of Spodoptera Exigua (Lepidoptera: Noctuidae) And Microplitis Pallidipes (Hymenoptera: Braconidae)

Responses of plant to herbivores involve diverse traits that allow plants to escape, defend, or tolerate herbivore attack. Much attention has been given to constitutive and inducible chemical defenses including toxins, repellents, antifeedants and digestibility reducers. In addition to these direct defenses, plants also rely on indirect defenses mediated by parasitoids that facilitate control of herbivores. Study on inducible resistance in plants plays important role in understanding the correlation between/among plant, herbivore and the natural enemy, and clarifying the mechanism and function of inducible resistance to herbivores. The beet armyworm (BAW), Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) is a serious pest of crops. This dissertation focused on the interaction of host plant- maize, BAW, and parasitoid wasp Microplitis pallidipes Szepligeti (Hymenoptera: Braconidae), by ecological, physiological and molecular biological technique. The emphasis of study was the plant biochemical responses to exogenous elicitors and influence of induced resistance on behaviour, development, survival and fecundity of BAW and it braconid larvae parasitoid M. pallidipes;the objective was to provide more detailed analyses on how plant-herbivore interactions are mediated. The roles of inducible resistance in plant in biological control of the beet armyworm were discussed. The main results were summarized as follows:Main elicitors of inducing resistance of maize contain exogenous JA (0.01 μ M/seedling), BAW-oral secretion (BAWOS) and attack by BAW. The maize treated by these elicitor exhibited a significant decrease of attractiveness to BAW. But the plant induced with 10 μ M/seedling JA had a significant increase of attractiveness to BAW female moth oviposition. JA-induced seedling of maize exhibited obvious influences on the body-mass and mortality of BAW larvae, but showed diverse effects on different age BAW larvae: significantly affecting both growth and mortality for 2 instar BAW larvae, but only affecting the mortality for 5 instar BAW larvae.The effect of maize induced by exogenous JA and BAWOS on proteinase inhibitors (PIs) activity in the leaves was studied. JA significantly induced PIs activity in the leaves of maize. But, the quantity increase of induced PIs didn't correlation with the concentration of JA treated dosage. The concentration of 0.01 μ M/seedling, BAWOS treated and BAW-damaged plant have the strongest induced function, and the content of PIs were higher than that of control and 0.1, 0.5, 1, 5, 10 μ M/seedling of JA treated plants.The BAW larvae were raised with the leaves of maize induced with 0.01 μ M/seedling of JA and the growth and midgut proteinase activity of BAW larvae were studied. The total midgut proteinase activity was significantly inhibited. On the other hand, the 5-instar BAW larvae fed on leaves of maize treated with JA, the total midgut proteinase activity were significantly activated. The physiological test result shows that the activities of the high alkaline trypsin-like enzyme, chymotrypsin-like enzyme and alkaline trypsin-like enzyme were significantly inhibited in midgut of 3 instar larva feed with JA leaves, however, significantly improved in 5 instar larva. This change of responses shows that the JA-treatedmaize may resist BAW larvae, but later, BAW larva could be adapt to the plant resistance induced by JA.The expression profiles of defence-related genes in herbivore-infested. BAWOS and JA treated maize leaves were analyzed using RT-PCR. The results showed that the lipoxygenase {LOX) and allene oxide synthase (AOS) genes were induced in maize seedling treated by S. exigua infestation, BAWOS and JA. But mechanical damage did not induce the expression of LOX gene and AOS gene. The expression of wound-induced proteinase inhibitor (WIPI) was analyzed using real-time quantitative PCR (RQ-PCR) and found it expressed in all treated maize. The WIPI copy numbers in induced maize seedling were calculated by comparing quantitative PCR results of the WIPI genes with those of the internal standard, ACT. With optimized PCR conditions, we achieved significantly accurate estimates of WIPI copy in different induced maize seedling. Analysis of the results showed that BAW-damaged plant has the strongest induced function on the expression of WIPI. WIPI was amplified based on the cDNA reverse transcript from total RNA, then cloned into prokaryotic expression vector PET-21b and expressed successfully in E. coli BL21 (DE3) plysS.Based on the systematical observation of several aspects of M. pattidipes biology, the preference of parasitoid to host larval stage was observed by uniform design in laboratory. The results showed that M. pallidipes parasitized l-3rd instar larvae of BAW and Mythimna separata, especially the end of 1st instar larvae and the beginning of 2nd instar larva of M. separata (Lepidoptera: Noctuidae) (OAW). The larvae parasitized by M. pallidipes in early 2nd instar larvae of BAW prolonged their instar duration, and consumed less food than non-parasitized host larvae. The parasitoid finished growth, bit away from the late 3-instar of early 4-instar host larvae and killed host larvae. Parasitizing on BAW fed on induced seedling of maize treated with JA and BAWOS, the duration of parasitoid were prolonged remarkably and the mortality rate of host larvae on JA- and BAWOS-treated maize were higher than those that parasitized on control plant. JA, BAWOS and BAW-damaged treated plants exhibited a significant increase of attractiveness to female adults of M. pallidipes, but there was no difference among these three treatments.Inorder to study further function of the antenna of this wasp, we observed the ultra structure and distribution of sensilla on the antennae of both sexes by scanning electron microscope (SEM) and transmission electron microscope (TEM). Results showed that the antenna of M. pallidipes was threadlike, and the flagellum was composed of 16 sub-segments in both sexes, though the length and diameter of antenna on female were larger than those of the male. However, there were no distinct morphological difference in sensory receptors between the male and female. Six types of sensilla were found on the antennae of female. They were sensillum(s) trichodea, s. basiconica I, basiconica II, elongated s. placodea, s. coeloconicum, and s. chaetica. S. trichodea was the most abundant sensillum and distributed over the whole antennae;s. basiconica I and II, s. coeloconicum, and elongated s. placodea presented only on the flagellum;s. chaetica only presented on the scape and pedicle and in low numbers. The morphology, structure and distribution of these sensilla were described. Sexualdifferences appeared only in sensilla placodea numbers. The males have a larger number and a higher density of sensilla placodea than females. TEM investigations showed that, s. basiconica II and elongated s. placodea sensillum wall were porous. The peg-like s. coeloconicum stalk consisted of 11 fingerlike projections that join at the tip. We discussed the significance of these findings on the light of existed literature.