| Glenea cantor Fabricius,oligophagous insect,is an important pest of kapok trees Bombax ceiba L.and Adansonia digitata L.,which are mainly distributed in southern China,some countries and regions in southeast Asia.As a member of the subfamily named Laminae,it also making scars for oviposition.The oviposition selection behavior of G.cantor was observed,which enabled by successful mass laboratory rearing.In addition,the mechanism of oviposition selection of G.cantor was analyzed by using ultrastructure observation,plant tissue section,biochemistry,insect electrophysiology and molecular biology synthetically.The main results are as follows:(1)G.cantor have an obvious tendency of weak tree selection,and the population rapidly weakened the host by gathering and feeding.Then the pregnant females gathered and oviposited on the main trunk of the host so as to further damage.The adults oviposit from 9:00 to 18:00 every day,and it took499.54±21.67 s to produce one egg.Each beetle can produce 162.28±2.93 eggs in a lifetime.In the process of host location,the frequency of antennal beat was1.58±0.11 times per second,and the frequency of mandible palp detection was3.23±0.16 times per second.In addition,the results showed there was an explosive gathering oviposition phenomenon when the leaves withered and the ambient temperature reached about 25?.The oviposition height decreased as the days of damage increased,the proportion of oviposition on the smooth side of the host was 88.07±2.31%,and the experimental kapok plant(3.0 m)had the highest proportion of oviposition at 0.5-1.0 m,reaching 31.64±0.96%.In addition,the percentage of eggs-laid in common cracks and green cracks of the trunk were the highest,accounting for 54.94±0.31% and 27.92±0.54%respectively.(2)There are 11 kinds of sensillum in each functional organ of G.cantor which play important roles in oviposition behavior,besides five adhesion structures were found in tarsus.Among them,there are four kinds of sensilla in antennae.The olfactory sensilla on antenna are very developed,especially in females.So antenna plays an important role in oviposition location.The main function of the mandible was to make scars,and a small number of sensilla chaetica helped the female to sense the biting force in the process of making oviposition scars.There are 7 kinds of sensilla in labial palpus and mandibular palpus;besides,5 kinds of sensilla at the end of abdomen.These three organs have a large number of temperature & humidity sensilla and olfactory sensilla,which are mainly involved in recognition behavior during oviposition.Each tarsal of fore-leg,mid-leg and hind-leg of G.cantor is mainly responsible for the attachment of beetles to the host surface.At the same time,the roughness of the host surface can be indirectly perceived through the force of grasping.The ovipositor can not only recognize the suitability of the oviposition scar through the sensilla grooved peg,but also use a large number of barbs on its surface to tear apart the fiber layer of the phloem of kapok,insert into the phloem and ovulate.(3)The oviposition scar of G.cantor can be divided into effective scar and empty(ineffective)scar.As for effective scars,there are eggs inside and those scars are covered by jelly secretion.There are significant differences in length(effective scars=4.04±0.05 mm,empty scars=3.62±0.19 mm)and width(effective scars=0.70±0.01 mm,empty scars=0.63±0.02 mm)between the effective scar and the empty scar.There are seven ways to make the empty scar,which is much more complex than the effective scar.Different gradients of temperature,humidity and photoperiod have effects on the efficiency of the ovipositin scars.The results showed that the efficiency was influenced by temperature and humidity,and the highest efficiency were 84.98±1.52% at 25?and 90.03±1.09% at RH 75±5%,respectively.Combined with all the research results,the causes of empty scar can be divided into four types: Unsuitable biting force;The weak host tree;Unsuitable physiological indexes of plant at notch(too much water or too hard cortex).The complex surface structure of the host which accounts for that the ovipositor could not be inserted.(4)The main components of oviposition secretion were protein,reducing sugar and amino acid,and the extracts were terpenoids and alkanes.It was found that the extract of spermatheca and spermathecal gland were the closest to those of oviposition secretion,and it indicated that the oviposition secretion came from spermatheca and spermathecal gland.(5)Nine kinds of odor source(Leaves of healthy plant,weaken plant,mechanically injured plant,Fed plant;Twigs with larval,twigs with eggs and normal twigs;Feces of adult;Egg-surface pheromones)were studied by GC-MS,then combined with the electrophysiological reaction of G.cantor.Nine active substances related to adult behavior were identified: 3-hexanone,butyl acetate,nonanal,2-Hexanol,p-xylene,decanal,hexadecane,ethyl palmitate and oleic acid.The results showed that 3-hexanone was the host location information compound of adult beetles,and then beetles were attracted by nonanal and decanal in the environment gather to kapok for nutrition supplement.Subsequently,the feeding damage of G.cantor population on kapok led to the gradual weakening kapok and secondary metabolites release.Wherein,p-xylene as the main secondary metabolite increased rapidly,which significantly attracted the longicorn population to the weak kapok.At the same time,2-Hexanol,a secondary metabolite,can induce sex,promote the aggregation and mating of male and virgin females,only attracted virgin females and males which increase the number of fertile females.Butyl acetate plays a guiding role in the oviposition location,attracting females to damage the weakened host,and cause the outbreak of oviposition occurred in the host trunk.(6)Based on the high-throughput sequencing platform,151 genes which related to olfactory were identified from the transcriptome of different organs of male and female beetles.It consists of 16 odorant binding protein genes(OBPs),9 chemosensory protein genes(CSPs),2 sensory neuronal membrane protein genes(SNMPs),84 odorant receptor genes(ORs),27 iontropic receptor genes(IRs)and 13 gustatory receptors(GRs).The results showed that there are significant differences in olfactory protein gene expression between male and female,The olfactory protein genes whose expression up-regulated in female compared with male include: 7 OBPs,3 CSPs and 2 SNMPs in antennae,1OBPs and 1 CSPs in head,1 OBPs in chest,1 CSPs in abdomen,2 OBPs in feet,4 OBPs in wing.In addition,the expression of olfactory protein genes are also different among organs of females.There were more genes expression up-regulated in antennae than other genes,including 8 OBPs,8 CSPs and 2SNMPs.Among them,OBP 6,OBP 7 and OBP13 are only expressed in antennae.In conclusion,the action quantification and the functional identification of main organs of G.cantor in oviposition selection have been established in this study.The chemical mechanism of female oviposition selection was revealed and the molecular basis of olfactory oviposition selection was established through the identification of various information compounds and olfactory related genes respectively,combined with the observation of oviposition behavior.The results are meaningful to clarify the chemical information communication mechanism of oviposition selection,and then provide technical support for the green control of G.cantor. |
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