Study On The Head Sensilla Of Eutectona Machaeralis And Its Host Volatile Compounds

The leaf skeletonizer,Eutectona machaeralis(Walker)(Lepidoptera:Crambidae),is a severe insect pest of the noble teak trees(Tectona grandis)in China.The pest has a large occurrence during the heavy infestation,long damage period,short generation period and overlapping generations,which seriously affect the growth,management and cultivation of teak.As the pest brings huge economic losses to human beings,an efficient environmentally-friendly protection measure is highly in need.In this study,scanning electron microscope(SEM)and transmission electron microscope(TEM)were used to observe the head of the mature larva of E.machaeralis as well as the antenna of male and female adults in order to demonstrate the morphology of the antennae and the types,distribution and number of the sensilla.Meanwhile,dynamic headspace adsorption and GC-MS were first used to extract,analyze,and identify the composition and diurnal variation of volatile components in the leaves of teak from two different origins,Burmese provenance teak and Indian provenance teak.The differences of volatile compounds induced by healthy leaves and pest-harmed leaves were analysed and the main physiological volatiles were screened out.Fianlly the electrophysiological response of some main teak volatile components to the antenna of E.machaeralis was measured by electroantennogram(EAG).This study aims to clarify the chemical sensory mechanism of host selection of E.machaeralis,and provide a certain theoretical reference for the effective control of the pest by using natural active substances.The main findings are as follows:(1)The head structure type of the larvae was hypognathous.There are a pair of antennae on the head of the larvae,and six kinds of chemoreceptors were found on the antennae,namely sensillum trichodea,short sensillum trichodea,sensillum basiconica,sensillum styloconica,sensillum chaeticum and small sensillum basiconica.Three sensillum styloconica were found on the maxilla and maxillary palpus;one sensillum chaeticum was found on labial palpus;one sensillum chaeticum was found on the front of each side of fusula.(2)The shape and structure of antennae were similar between males and females,both being filiform and segmented into a scape,a pedicel,and a distal flagellum.Eight morphological sensilla types in total,including B(?)hm bristles(Bb),sensilla trichodea(St),sensilla basiconica(Sb),sensilla chaetica(Sc),sensilla styloconica(Ss),sensilla coeloconica(Sco),sensilla auricillica(Sa)and sensilla squamiformia(Ssq),were observed on both sexes.Significant sexual dimorphism of the sensilla dimensions between the sexes was found,especially the length difference.However,the type,morphology and distribution of the sensilla are not dimorphic.(3)After extraction and analysis by dynamic headspace adsorption method and GC-MS,a total of 92 kinds of volatiles from the healthy leaves of Burmese provenance teak and 74 types of volatiles from the healthy leaves of Indian provenance teak were detected.Both types contain the same types of compounds,most of which are hydrocarbons,followed by esters,alcohols and terpenes,and there are some aldehydes,phenols,amides,ketones and a small amount of ethers and other impurities.The types and content of each type of compounds are slightly different.After the E.machaeralis larvae were damaged,some types of compounds remained the same but the contents were changed,either increased or decreased,and some consistent compounds were produced in different time periods.At the same time,some herbivore-induced plant volatiles(HIPVs)were induced.The newly added HIPVs for the Burmese provenance teak are mainly terpenes,alcohols and aldehydes,and terpenes,aldehydes,alcohols and esters for the Indian provenance teak.Relatively speaking,the HIPVs of Burmese provenance teak increased more,and the material daily rhythm changed more obviously.(4)Both male and female adults of E.machaeralis have obvious EAG reactions to certain concentrations of nonanal and linalool;in short,the response to tridecane and tetradecane is generally weak.The tentacle responses of male and female adult E.machaeralis to linalool and nonanal at different concentrations of 0.001 μg/ml,0.01 μg/ml and 0.1 μg/ml were significantly different,and the response of female moths was significantly higher than that of male moths.