Responses Of Coleophora Obducta (Meyrick) To Host Plant Volatiles And Ultrastructures On Antennal Sensilla

Coleophora obducta(Meyrick)(Lepidoptera:Coleophoridae),a kind of larch defoliators exclusively latent in leaves,frequently break out in larch forest of northeast China,which appeared burned and resulted in dried up when severely harmed,causing prodigious economic losses,and had no effective methods to control the rampant damage yet.Plant volatiles served as a sort of behavior-implict chemical signals played important roles between plants and insects,moreover,environmental safe insecticides accepted as green and friendly control method had been increasely paid much attention to on practical use.This article studied the responses of C.obducta to host plant volatiles and environmental safe insecticides,observed the ulstructuer of antennal sensilla for the first time,which provided theoretical basises for exploring chemical communications between plants and insects,and developing environmental safe control in field.This article tested the EAG responses of C.obducta to nine kinds of larch volatiles, namely R-α-pinene,S-α-pinene,β-pinene,ocimene,phellandrene,3-carene,myrcene, camphene and phytol.The results showed that,in concentration of 0.4mol L^-1,most volatiles had significant EAG responses compared with the blank(P＜<0.05),except females to R-α-pinene, males to R-α-pinene and phellandrene;Besides,EAG responses between males and females also existed differences.Observations of behavioral responses of C.obducta to the above nine kinds of volatiles in a series of concentrations of 0.0004,0.004,0.04,0.4,0.8mol L.(-1) had been carried out with the application of Y-tube olfactometer.Females were attracted by S-α-pinene 0.004mol L^-1,S-β-pinene 0.0004mol L^-1,phellandrene,phytol 0.04mol L^-1,3-carene 0.0004 and 0.04mol L^-1 (P＜0.05),whereas repelled by S-α-pinene 0.04mol L^-1,phellandrene 0.0004mol L^-1,myrcene 0.004 and 0.8mol L^-1;Males were lured by ocimene,myrcene 0.0004mol L^-1 and phytol 0.004mol L^-1,whereas repulsed by camphene 0.004 and 0.0004mol L^-1(P＜0.05).We adopted volatiles that activated to females,then sprayed them singly to healthy larch seedlings,the results indicated that S-α-pinene 0.004mol L.(-1),S-β-pinene 0.0004mol L.(-1),and 3-carene 0.04mol L^-1 attracted the females(P＜0.05);Whereas,S-α-pinene 0.04mol L.(-1) and myrcene 0.8mol L^-1 repelled the females(P＜0.01);Most larvae that feeding on twigs spyayed with volatiles were dead compared to the blank(P＜0.01) with exception of myrcene 0.004mol L^-1 which had no significance(P＞0.05),the phenomenon suggested that volatiles may be harmful to larvae,thereinto,S-α-pinene 0.04mol L.(-1) caused the most larvae dead,which accounted for 86.677%of total number.Otherwise,sprayed with volatiles could reduce eggs that laid on larch seedlings compared with the blank of mean eggs of 15.79 per female,and among which sprayed with phellandrene 0.0004mol L^-1 and myrcene 0.8mol L^-1 had the least oviposition with mean eggs per female 5.63 and 5.21 respectively,and the two had no significant differences(P＞0.05).In order to expolre the influencese of environmental safe insecticides to C.obducta and effect of control,we tested the tendency and oviposition responses of female C.obducta to seven kinds of environmental safe insecticides,found that,imidacloprid EC 3000 times solution and emamectin benzoate microemulsion 2000 times solution rejected the C.obducta, with repellent rate 75.00%and 68.75%respectively.Eggs that laid on larch seedlings sprayed with environmental safe insecticides were notably depressed in contrast to both the blank and seedlings that sprayed with volatiles(P＜0.05),and among which sprayed with avermectin and imidaclopridhad the least oviposition with mean eggs per female 3.13 and 3.33 respectively, and the two had no significant differences(P＞0.05).Antennae and their sensilla of C.obducta were observed using scanning electron microscopy.Both sexes of antennae were threadlike,and totally,there were eight types of sensilla found:sensilla placodea,sensilla basiconica,sensilla coeloconica,sensilla styloconica, sensilla trichodea,sensilla squamiformia,sensilla furcatea and B6hm bristles,respectively.The shapes,distributions and putative functions of sensilla were described and discussed.Thereinto, sensilla placodea accounted for the most of both moths' antennal sensilla,and sensilla trichodea took second place;Sensilla squamiformia exclusively scattered on the last segment of male and female flagella.Sensilla furcatea were found for the first time,sporadic distributed on female antenna,and the function of this type was not clear yet.Moreover,there were obviously sex dimorphisms,including different antenna sizes,different sensilla shapes,sizes, numbers and distributions.Using transmission electron microscopy(TEM) to illustrate the ultrastructures and possible functions of antennal sensilla of C.obducta.Sensilla placodea,basiconica and trichodea were found to be innervated by sensory neurons,we inferred from their ultrastmctures as chemoreceptors;Besides,the neuron of sensilla styloconica terminated in a tubular body-like structure typified gustatory/mecheanosensory function,and the terminal sensory pegs may function as contact-chemoreceptors because of their location.In a word,larch volatiles and environmental safe insecticides could influence the behaviors of C.obducta such as olfaction,feeding and oviposition to some extent,which providing a new thought to pest control,otherwise,studies on antennal sensilla would also establish a theoretical foundation on further research of insect-plant communication.