| The beet armyworm Spodoptera exigua(Hübner),belongs to Lepidoptera and Noctuidae,has become one of serious pests in China since 1980's and caused severe losses in agricultural production,especially for vegetables.However the traditional usage in chemical pesticide management has resulted in serious resistance development of S.exigua.As a result,to explore the chemical sensor mechanism of S.exigua and clarify the relationship between beet armyworm and its host plants possess important theoretical and practical significance by means of chemical ecology.Based on the theory of insect chemical ecology,the main morphology,characteristics,quantity and distribution of sensilla on the head of both adult and larvae of beet armyworm were systematically studied in this study via a series of techniques and methods such as optical microscope,scanning electron microscopy,EAG,PCR and improvement of indoors breeding;the odorant binding proteins from antenna of beet armyworm were carried out at molecular levels;the electrophysiological responses by EAG were also conducted.Through several years' work,the chemical sensor mechanism of the beet armyworm was systematically studied and the main results were as follows:1.Firstly,the basic laboratory rearing techniques for beet armyworm were improved and the preservation of pupae of beet armyworm was investigated.The results showed that the beet armyworm pupae can not survive in refrigerator(4℃);however under the condition of artificial incubator(16℃) pupae live well and the emergence rote amount to 49.81%t,which was although significantly low from the counterpart of untreated pupae but no effects for the further studies.Besides,the effects of breeding space on population dynamics of the beet armyworm were studied.The results showed that there were significant effects of space on population development of the beet armyworm.Disposable plastic cups were adopted in indoor breeding for beet armyworm and there is a high population trend index with a total of 15 beet armyworms in one cup.Considering that self-mutilation phenomenon exists among old larvae,it is recommended that 10 armyworms should be raised per cup.2.Daily rhythm and circadian rhythm of pupation,emergence,courtship,mating and oviposition for the beet armyworm were observed indoors.The results showed that the sex ratios of both pupation and emergence were close to 1:1;there was an obvious circadian rhythm for emergence,highest emergence rate concentrated between zero to eight o'clock in the morning amounting to over 50 percent of total emergence quantity and significantly different from other time quantum;pupation concentrated during 4- to 8-d pupae(accounting for 95%or so) and there was hysteresis phenomenon for male pupae;most matings occurred after 23:00 in the evening and there was an occurrence rate of 70.44 percent for an mating duration between 40 to 100 min;the eggs laid between zero to five o'clock in the morning amounted to 65.46 percent of the total eggs.3.Sensors on the head of beet armyworm were observed though scanning electron microscope. The results showed that there were longer antenna for female beet armyworm while the quantity of flagellum was more for males;a total of 8 types of sensors were observed in antenna,those incuding Sensilla trichodea,Sensilla chaetica,Sensilla basiconicum,Sensilla coeloconica,Sensilla auricillica, Sensilla squamiformia,Sensilla styloconica and Sensilla ecfloresco Among these sensors,the number of Sensilla trichodea was largest and there was a smallest number of Sensilla ecfloresco.On proboscis and labipalp three types of sensors were observed,Sensilla chaetica,Sensilla basiconicum and Sensilla ecfloresco.4.The sensors on the head of beet armyworm larvae are also abundant and chaetotaxy on the head is one type of Sensilla chaetica.Compared to the counterparts of adult,there are less types and numbers of larvae antenna with only one Sensilla styloconica,five Sensilla basiconicum and 2 Sensilla chaetica.There are 8 sensillum styloconicum on larvae palpus,arranged 3-2-3;2 Sensilla styloconica and 1 Sensilla basiconicum were observed on galea and 4 Sensilla trichodea were founded on palpifer.One Sensilla styloconica and one Sensilla basiconicum were recorded on labipalp.5.PBP1 and PBP2 sequences were firstly obtained from beet armyworm through RT-PCR technique and sequence analysis was conducted subsequently.The sequence analysis showed that cDNA of the beet armyworm PBP1 possess an open reading frame of 492bp encoding 164 amino acids and the first 23 amino acid residues contains the typical characteristics of signal peptides of the secreted proteins in eukaryotes.PBP1 precursor and mature protein contains 164 and 141 amino acid residues,respectively,with an predicted molecular weight of 18.9kD and 16.4kD,an predicted isoelectric point of 5.56 and 5.27.The sequence analysis showed that cDNA of the beet armyworm PBP2 possess an open reading frame of 510bp encoding 170 amino acids and the first 27 amino acid residues contains the typical characteristics of signal peptides of the secreted proteins in eukaryotes. In addition,the common characteristics of eukaryotic pheromone binding peptide were also observed and 6 cysteine residues can form two disulfide bond.PBP2 precursor and mature protein contains 170 and 143 amino acid residues,respectively,with an predicted molecular weight of 18.9kD and 16.1kD,an predicted isoelectric point of 5.5 and 4.98.In addition,the common characteristics of eukaryotic pheromone binding peptide were also observed and 6 cysteine residues can form two disulfide bond.The phylogenetic tree was built and its homology was analyzed subsequently.6.The electrophysiological responses of the beet armyworm antenna to plant volatile substances were determined through EAG technique.The results suggested that EAG peak value of the beet armyworm fluctuated a lot to 6 ordors matter from onion with stonger response recorded in male moths.The response degree of female moths from highest to lowest was in the order of methyl-n-propyl disulfide＞C diene Disulfide-＞b-propyl disulfide＞2-methyl-2-E-aldehyde＞2-Thirteen-＞2-Eleven-one; and the status of male moths was in the order of 2-methyl-2-E-aldehyde＞diallyl disulfide＞n-propyl disulfide b＞methyl-n-propyl disulfide＞2- Eleven-＞2-Thirteen-one. It can be seen that significant difference exists between male and female moths.In general,a systematic study on chemical sensor of the beet armyworm was carried out via the combination of insect physiology,molecular biology and electron physiology.The results above have not only enriched and developed the study content of insect chemical ecology but also provided some useful explorations for clarifying the nature of pest insect behavior response,and they are the basis of application study on integrated pest management.
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