| Tea green leafhopper,Empoasca onukii Matsuda,is one of significant pests in Asian tea plantations.It is reported that the pest has resistance to a few insecticides,which results in the difficulty for the pest control and the safety of tea drinking.It is urgent to seek the harmless control managements for the pest to replace the chemical control.E.onukii is known for its capacity to move rapidly.It is thought that the impact of insecticide applications for this pest is reduced because of this capacity to move rapidly and seek refuge.In this dissertation,we quantified avoidance behaviour and entrapment of nymphs and adults of the tea green leafhopper(Empoasca onukii)using simulated rainfall onto host plant foliage and made observations of pretarsi,abdomen and wing microstructures,and the hydrophobicity and the adhesion between the insect and water were also tested to explain the mechanism for the different escape behaviours between adults and nymphs.We also tried to explore the harmless control managements according to the different escape behaviours and the different hydrophobilities between adults and nymphs.The primary results are as follows:1)The nymphs and adults of the tea green leafhopper showed different escape behaviours when stimulated by water spraying.Most young nymphs were washed from water-sprayed leaves though older nymphs tended to remain on leaves and subsequently escaped from water droplets.For N2-3 nymphs,only 15%individuals escaped the water droplets with a mean escape time of 48.70 ± 3.05 s after cessation of spraying for 1 min.For the larger N4-5 nymphs,85%of the individuals escaped droplets and did so at a mean of 17.40 ± 2.78 s after cessation of spraying,less than half the time taken by N2-3 nymphs.When stimulated by water spraying in a group,the adults could stand on the gaps between the water droplets on the acrylic hood,while 80%adult insects were adhered to water droplets on the tea leaves and 20%adults trapped o the water film with their wings on the gauze element and could not escape successfully in a short time.Adults responded rapidly to simulated rainfall and escaped by jumping in a response time for 0.29 ± 0.15 s.Comparing the effect of eyes,antennas and wings on the adult escape,we found the successful escape proportional rate of the "covered eyes" team was lowest,with 67%adults trapped in the water spraying district in 1 min we observed.2)The different wetting property of pretarsus between adults and nymphs of E.onukii were related to their morphology difference.E.onukii adults were able to stand on water film whilst most nymphs had multiple penetrating tarsi,which means the hydrophobicity of adult pretarsi were stronger than nymphs.Tea aphid Toxoptera aurantii Boyer and white back planthopper Sogatella furcifera(Horvath)were used as control groups.All legs of T.aurantii dipping into water,regardless of adults or nymphs,and both adults and nymphs of S.furcifera stood on the water surface and skipped freely.From the observation of SEM,the shape of E.onukii adult pretarsi was flatter than nymphs,and with more brochosomes on the surface,while the nymph pretarsi have a pair of cup-like aroliums;the pretarsi of adults and nymphs have the similar structure for T.aurantii and S.furcifera.The pull-off forces(POF)of E.onukii pretarsi from water surface and tea leaf surface were tested by simple straw balance.The POF of nymph pretarsi from water was 108.6 ± 11.9 ?N,and the POF from a tea leaf surface was 96.7 ± 6.9 ?N,which were significantly greater than adults.The results indicated that the cup-like aroliums of nymph pretarsi might have vacuum function to leaf during water spraying,and the flatter pretarsi with numerous brochosomes of adults could lower the adhesion with water,which was in favor of adult quickly escape from the water spraying district.3)The abdomen morphologies varied with life stages,which affected the brochosome distribution and the hydrophobicity.Adults had denser covering of water-repelling brochosomes on abdomen surface than nymphs.When brochosomes were removed by PVS film,six lines of sensory setae were distributed on the dorsal surface of nymph abdomen,and the cuticle was quite glossy,while the dorsal aspect of the adult abdomen had uniform scale structures formed with microtrichia(0.3-0.6?m)but without any sensory setae.The changes also exhibited on ventral abdomen.From younger instars(1st and 2nd)to older instars(3rd to 5th),many micropapillae(0.3-0.8 ?m)on the ventral surface changed into microtrichia(0.7-1.6 ?m)with more brochosomes.The ventral aspect of adult abdomen had uniform scale structures formed with microtrichia(0.7-1.6 ?m).The CAs of adult abdomen surfaces were significantly reduced from an average of 149.10 ± 1.03° to 125.35 ± 0.69° when brochosomes were removed,while the changes on the nymph abdomen were not significant.For both adults and nymphs,the pull-off forces(POF)of brochosome-free abdomens were significantly higher than the values of brochosome-covered integument.With or without brochosomes,the POF values of nymph abdominal surfaces were obviously higher than adults.We speculated the origin of the adhesion between the nymph abdomen and water was related to the insect small size and nonuniform distribution of brochosomes.The small size water droplet was nearly spherical on the nymph abdomen,described as Cassie-Baxter stage,while larger sizewater droplet was disrupted on the nymph abdomen,which was described as Wenzelstage with stronger adhesion.4)Brochosomes could improve the hydrophobicity of E.onukii wings and could also generate high adhesive force with water.Both fore and hind wings of E.onukii were covered with brochosomes uniformly,and the CAs on all the wings were larger than 150°,which could be defined as superhydrophobicity,and was declined definitely when brochosomes were removed.The pull-off force of the wings with water came to 160.3 ± 3.5 ?N,which nearly 33 times as the insect gravity.The wings with superhydrophobicity and high adhesion could be presumed as "petal effect",as micro-spherical brochosomes covered on the wings with nano-honeycomb gaps constituted the microscale and nanoscale hierarchical structures.5)According to the different hydrophobicities,water spray was used to control nymphs,while insecticide spray with tent was applied on adults.First,the insect tolerance to water was studied.Results showed that the tolerance of younger instars(2nd and 3rd)was lowest,with highest mortality 83.3%,while older instars(4th and 5 th)and the adults had lower mortality.For nymphs,we chose spraying water repeatedly until the nymph was passively bilged in vivo with their activity weakened.Considering the water usage,the best treatment was as follows:spraying time 20 min,spraying distance 30?40 cm,and spraying 2 times,which lead an average mortality 75%of nymphs after 72 h.For adults,considering the adhesion between the wings and water film,we developed pesticide droplet dipping bioassay and gauze element film bioassay,comparing with leaf-dip bioassay and centrifuge tube residual bioassay.The bioassays were carried out for three insecticides,azadirachtin,Bacillus thuringiensis,and bifenthrin.All the insecticides had high mortalities at low concentrations by droplet dipping bioassay and gauze element film bioassay.For gauze element film bioassay,as LC50 for azadirachtin was 43.39 ?g/L,equal to the agentia diluted 6.9 × 104 times,and for agritol.LC50 was 447.2 IU/L,equal to the agentia diluted 1.7 × 107 times,and for bifenthrin,LC50 was 0.12 ?g/L,equal to the agentia diluted 2.0 × 108 times.The toxicities on gauze element film bioassay were definitely higher than centrifuge tube residual bioassay.We designed a mobile insecticide spraying film tent with plastic film and gauze element,the control(?)efficiency of azadirachtin spraying in light concentration(diluted 1500 times)with tent was nearly 50%,which has no significant difference with the treatment without tent.More insecticides need to screen to verify the use of insecticide spraying tent could reduce the dosage of insecticide on controlling the tea green leafhopper.Until now,the insect hydrophobicity was study for bionics material development,and how to utilize the insect hydrophobicity on insect pest control would be a new valuable method for exploring. |
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