| Tetranychus cinnabarinus is an important agricultural pest which usually causes heavy damage to vegetables and crops,resulting in yield reduction and quality decrease.At present,chemical control of the mite with acaricides is the major measures,supplemented with biological control techniques such as natural enemies.However,disadvantages of chemical control including rapid developing resistance and environmental problems arising in recent years,appealing for efficient and environmentally friendly control methods.It is found that plant volatile compounds can regulate behaviors of herbivores such as insects and mites,which implicates valuable possibility of development of behavior regulators.This study started with the establishment of a mite olfactory electrophysiological test technique,Electrotarsography(ETG).Based on the ETG technique,together with employment of Y-tube olfactometer and electron microscopic scanning of olfactory organs,the study aimed to investigate the olfactory and behavioral responses of T.cinnabarinus female adults to plant volatiles.Main results are as follows.1.Electrophysiological responses of T.cinnabarinus female adults to plant volatilesIn order to explore the specific olfactory responses of T.cinnabarinus female adults,an olfactory electrophysiological test method suitable for T.cinnabarinus female adult’s leg tarsus was established for the first time based on insect Electroantennography techniques.Detailly,the whole body of T.cinnabarinus female adult was applied with conductive gel except leg I.Then the mite body was hold with a fine glass capillary which was filled with conducting solution of KCl.The glass capillary functioned as the holder for mite body and as a reference electrode as well.Then another glass capillary which was filled with conducting solution was connected to tarsus of leg I.Thus a close circuit with the mite body was established and named as Electrotarsography(ETG).Using the ETG,electrophysiological responses of T.cinnabarinus female adults to common solvents such as hexane and acetone were tested and the hexane was then selected as a solvent for plant volatile compounds tested later because of its reliable ETG response from adult mites.Subsequently,ETG responses of T.cinnabarinus to 28 plant volatile compounds were tested and 27compounds elicited responses from the mites.The highest ETG value,1.08±0.02 m V was recorded in Nonanal,followed by Laurene(0.96±0.03 m V),β-ionone(0.91±0.01)m V and Farnesol(0.80±0.003 m V).Hexyl acetate elicited the lowest ETG value,0.42±0.01 m V,which was same as that of the solvent control of hexane.Dose-response effects of 12 compounds with relatively high ETG values were confirmed within a dose range from 10~0 ng to 10~4 ng,which further clarified robust electrophysiological responses of T.cinnabarinus female adults against the tested compounds.2.Behavioral responses of T.cinnabarinus female adults to different plant volatile compoundsBehavioral responses of T.cinnabarinus female adults to 12 ETG active plant volatile compounds were tested with a Y-tube olfactometer.Among the compounds,Nonanal,Farnesol,Methyl Salicylate and Nerolidol showed obvious attracting effects while repellent effects were observed in Geranyl acetone,Myrcene,Linalool andα-terpineol.Remaining 4 compounds including cis-3-hexenyl acetate,β-ionone,Palmitic acid andα-phellandrene elicited no obvious behavioral responses from tested mites.3.Observation of ultrastructure of legs of T.cinnabarinus female adultsA low temperature SEM was used to observe the ultrastructure of mite legs and the number and distribution of setae and solenidion on each leg were analyzed.Results showed that T.cinnabarinus female adults had a large number of mechanical hairs on each leg,which were rough and scaly in surface,simple in structure,sharp in tip and significantly longer in length than solenidion.The tactile setae were evenly distributed in each section of leg,and the number decreased from leg I to legⅣ.In addition,potential chemical sensillum on each leg were observed.Totally there were 3ω-solenidions,2 fastigials and 1φ-solenidion located at the dorsal middle area of tarsal segment(d)and tibial segment of legⅠ,and 2ω-solenidions and 1 fastigial located at the dorsal tarsal segment(d)of letⅡ.Besides,there is only oneω-solenidion was found at the lateral tarsal segment(l)of legⅢand legⅣrespectively.The solenidions sowed an elongated spine shape with a blunt tip and the fastigials were short,prickly and apically spine-shaped,which were mainly distributed at the tarsal area of legⅠand legⅡ,implicating a potential role in mites’chemical sense. |
PDF Full Text Request