Effects Of Differently Induced Resistance In Brassica Campestris L. On Physiological And Biological Characteristics Of Spodoptera Exigua(Lepidoptera:Noctuidae) And Meteorus Pulchricornis(Hymenoptera:Braconidae)

Plants effectively combat herbivorous insects through innate defense strategies, and the defense responses can be induced by external factors. Studies have shown that plant induced resistance can affect the preference and performance of herbivores and the natural enemies of herbivores. However, few studies have explored how plant induced resistance influence parasitoids. The beet armyworm, Spodoptera exigua(Hübner), is an important crop pest in China. As a generalist parasitoid, Meteorus pulchricornis(Wesmael) is known to attack a variety of hosts in Lepidoptera, which is important for biological control. In order to investigate the effects of plant induced resistance on plant–herbivores–parasitoid interactions, the following questions are addressed: ⑴ Induction of herbivory damage, mechanical damage and exogenous methyl jasmonate(Me JA) on Brassica campestris. ⑵ Effects of different induced resistance on biological characteristics of both S. exigua and M. pulchricornis. ⑶Effects of different induced resistance on the physiological metabolism of S. exigua, as well as the interactions between plant defense enzyme and insect detoxification enzyme. ⑷ Effects of selective pressure of both induced resistance and parasitism on activity of protective enzyme and immune function of S. exigua. The results showed as follows:1. Induced resistance showed a significant effect on biological characteristics of both S. exigua and M. pulchricornis. The induced plant resistance treated by herbivory damage and exogenous methyl jasmonate can have negative impact on S. exigua larvae in survival and body size, which consequently have negative effect on the parasitoid M. pulchricornis in developmental parameters.2. The activities of phenylalanine ammonialyase(PAL), polyphenol oxidase(PPO) and peroxidase(POD) in leaves measured at 24 h after treatment were significantly higher than that of control. Meanwhile, the activities of caboxylesterase and Glutathione –S transferase of larval S. exigua midgut were affected when feeding on different treated plants. Detoxification enzyme influenced by both defense enzyme and feeding time. The time that detoxification enzyme activities increased treated by 0.1mmol/L Me JA were earlier than that treated by herbivory damage.3. Induced resistance had significant effects on immune function of S. exigua larval. The activity of phenoloxidase was suppressed when treated with herbivore damage and Me JA. Induced resistance effects on larval immune function were overwhelmed by the effects of parasitism by M. pulchricornis, and parasitism became dominate factor. The hemocytes count and protein concentration of larval S. exigua declined obviously while the activity of phenoloxidase rised remarkably 48 h after parasitism.