Studies On Control Techniques And Mechanisms By Entomophilic Nematode And Sex Pheromone For The Beet Armyworm, Spodopter Exigua

The beet armyworm, Spodoptera exigua (Hubner), has been an important insect pest of economic crops in China for more than ten years. Great yield and economic losses was resulted in due to the serious outbreaks of beet armyworm national wide. Furthermore, chemical control mean has lost its function in suppressing the damage of beet armyworm due to its low control efficiency and highly resistance developed by the beet armyworm. Therefore, beet armyworm is not only the major destructive insect pest, but also a great threaten factor to the sustainable development of agriculture and animal husbandry in China. In this paper, results relevant to theory and practice benefit to the development of other non-chemical control means for beet armyworm were studied. The major contents included parasitism of the entomophilic nematode, Ovomermis sinensis and its variation in different environmental conditions, the mating behavior and capacity of the adult beet armyworm, the influence of mating age and number of female and mating sequence of male on the fecundity of female and hatching rate of the eggs laid, application of sex pheromone trapping techniques to monitor and suppress populations of beet armyworm in the field. The major results obtained were as follows.The parasitism of entomophilic nematode, O. sinensis was determined in the laboratory condition. It was showed that the larval beet armyworm was very sensitive to the attack of O. sinensis and a parasitic rate around 80% was usually obtained. In comparison to the normal non-parasitic larvae with same age, the infested host larvae exhibited a syndrome deceased the amount of food intake, and growth rate and increased contents of protein in the haemolymph. Larval developmental duration was also postponed for the infested host larvae. The infested host larvae began to die at the 8th day after the infestation when nematodes were shed out from the host larval bodies. The parasitism rate of the nematode was highly influenced by the environmental factors, like temperature, ratios of nematode larvae to host (beet armyworm) larvae and thecontacting time. The nematodes could infest host larvae at the temperature from 20℃ to 32 ℃, and the highest and lowest parasitism rate were obtained at 28 ℃and 32 ℃ respectively. Parasitism rate was the highest at the ratio of 20 (nematodes) to 1 (host larva) but decreased when the ratios of nematode numbers to 1 host larva was at 10, 30 and 40. The parasitism rate was around 49% when the larval beet armyworms were treated by nematodes for 30 minutes, and increased linearly when the treating duration postponed. There was no significant difference in the parasitism rate for the 3rd to 5th instar larvae of the host, indicating that this nematode could infect various instars of the host larvae. All these results imply that O. sinensis is a valuable micro-control agent for the beet armyworm although its control efficacy in the field was unable to study in this thesis.The mating behavior and ability of adult beet armyworm were investigated under laboratory conditions (27 ℃ , L14:D10). Results obtained from this study demonstrated that males and females were able to mate on the first night after emergence. The mating frequency on the first three nights were higher (>82%), but decreased significantly on the fourth night and afterwards. The diel mating activity occurred from 23:15 to 05:30, and peaked from 01:30 to 02:30 and from 03:00 to 04:00, with a higher frequency in the first peak. Lifetime mating duration of the moths lasted from 30 to 60 minutes (40.8%, n=97), followed by 60 to 90 minutes (19.4%), and some of them (10.2%) lasted more than 180 minutes. However, mating durations were highly associated with the age of the moths. That is, mating duration for the older moths was significantly longer than that for younger ones. Lifetime number of mating for a male was from 1 to 11, with an average of 4.97 times. However, the mating capacity of a male was significantly associated with the sex ratio of the moths. Lifetime number of mat...