Effects Of Different Host Plants On The Growth And Development Of Spodoptera Exigua (H(u|··)bner) And Chemical Mechanisms Of The Host Preference Of S. Exigua

The beet armyworm, Spodoptera exigua (Hubner), belongs to Lepidoptera:Noctuidae. It is a kind of worldwide herbivorous pest with a wide range of host plants and strong migratory ability. The host plant selection and the chemical mechanism in herbivorous pests are the hot issues in the field of insect-plant coevolution so far, and they are also significant to agricultural production. In this research, four plants:celery, Apium graveolens; wild amaranth, Amaranthus retroflexus; shallot, Allium ascalonicum; cabbage, Brassica chinensis were chosen to feed the beet armyworm, and the development and reproduction of the beet armyworm were evaluated. The host preferences of oviposition for female adults and foraging selection for larvae were also tested. At last, we carried out the EAG dose-dependent responses and the Y-tube olfactomerter bioassays to the main substances of the volatiles of these plants. The main results are as follows:1. Effects of host plants on development and reproduction of S. exigua.Effects of different host plants on development and reproduction of S. exigua were determined by feeding the neonates with leaf tissue of the four host plants. The result showed that S. exigua individuals fed on wild amaranth had shortest larval periods and highest larval survival rate, which were 10.3d and 67.0% respectively. The larvae fed on cabbage showed the heaviest pupal, the longest adult lifespan, maximum egg per female, and the highest egg hatching rate, which were 92.50mg,8.5d,460.4 eggs per female and 77.2% respectively. The larval fed on shallot showed the longest larval periods, the lowest larval survival rate, and the shortest pupal period, but the highest emergence rate, which were 13.9d,55.4%,60.83 mg,6.3d, and 83.7% respectively. The larval fed on celery showed the lowest egg laying amount and egg hatching rate, which were 204.3 per female and 36.6% respectively.2. Oviposition selection and foraging selection of S. exigua to different host plants.The mated female adults laid eggs in the cages within which four host plants were randomly put. The result of S. exigua oviposition selection test showed that the preferences ranked as wild amaranth, which was 222.1 egg per female; shallot, which was 181.6 egg per female; celery, which was 96.3 egg per female; cabbage, which was 26.2 egg per female.In larvae foraging selection test, larvae choosing cabbage were more than those choosing the other three hosts, and fewest larvae chose shallot; host select on ability for the 3th instar larvae was better than that of the 5th instar larvae.3. Identification of host plant volatiles, EAG and olfactory behavioral responses of S. exigua to different substances of host plant volatiles.Volatiles of 4 host plants were identified by using GC-MS, and 10 main substances were selected to determine EAG and olfactory behavioral responses. The results showed that 1,3-dimethyl-benzene, (1S)-(+)-3-carene, naphthalene, undecane, decanal, (1R)-(+)-a-pinene, p-xylene, and nonanal can arouse obvious EAG response. In addition 1,3-dimethyl-benzene, naphthalene, decanal and (1R)-(+)-a-pinene can also apparently cause pregnant S. exigua’s orientation response.