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Effects of low-intensity microwave radiation on Tribolium castaneum

Effects of low-intensity microwave radiation on Tribolium castaneum
Effects of low-intensity microwave radiation on Tribolium castaneum

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Effects of low-intensity microwave radiation on Tribolium castaneum physiological and biochemical characteristics and survival

Huanghua Lu,Jicheng Zhou,Shanbai Xiong,Siming Zhao *

College of Food Science and Technology,Huazhong Agricultural University,Wuhan,Hubei Province 430070,PR China

1.Introduction

The red ?our beetle,Tribolium castaneum (Coleoptera:Teneb-rionidae),feeds on ?our and stored grain.The scent glands of the adult secrete a malodorous ?uid,imparting a ‘‘mildewed’’smell to infested material,thereby ruining it for consumption.

Phosphine fumigation is the most common control method for mass grain storage (Stephen,2003).However,large-scale and long-term use of fumigant pesticide results in both highly resistant pests and environmental https://www.doczj.com/doc/f93691687.html,e of high-intensity microwaves has a clear insecticidal effect,but affects food quality.

Low-intensity microwave radiation (LIMR; 2.0kW/kg)(Vadi-vambal et al.,2007),however,can kill various pests (Hallman and Sharp,1994),and inhibit mold (Wang et al.,2003).Because LIMR is claimed to have little effect on food quality (Zhao et al.,2007b;Vadivambal et al.,2007)there is considerable interest in this method of controlling stored product pests.

Presently,the ef?ciency of use of LIMR treatments against T.castaneum during storage is still relatively low.To optimize treatment protocols,there is a clear need to understand the actions of LIMR on the insects.Non-thermal effects of microwaves often change the character of microwaved material (Banik et al.,2003).LIMR causes a variety of biophysiological,biochemical and

functional changes.Through its thermal effects on material,heat conduction changes the structure of biological substances in vivo .LIMR can suppress superoxide dismutase activity,which can lead to lipid peroxidation and damage to cell,mitochondrial and lysosome membranes,and cause cell lysis,DNA breaks,and gene mutation;these effects are similar,and related,to those of aging (Paul et al.,2007).

In this study,we investigated the effects of LIMR on the physiological and biochemical characteristics of T.castaneum ,in hopes of providing a theoretical basis for prevention and control of storage pests.

2.Materials and methods 2.1.Materials

T.castaneum were obtained from Henan University of Technology and were maintained on a diet of wheat at our laboratory.Beetles were cultured in wheat medium in 0.3-L glass jars covered with a cotton cloth,and were maintained in a growth chamber at 28?28C and 65?5%relative humidity.

Beetles were fed on wheat ?our (Clever Wife brand re?ned wheat ?our,Wuhan,Yufeng Grain and Oil Food Industry Co.,Ltd.)that had been frozen at à188C for 24h to kill any pest eggs that might have been in the wheat,removed from the refrigerator and allowed to reach room temperature.Robust T.castaneum speci-mens were placed into glass bottles using a clean sterile brush.

Journal of Insect Physiology 56(2010)1356–1361

A R T I C L E I N F O Article history:

Received 31October 2009

Received in revised form 16April 2010Accepted 23April 2010Keywords:Microwave

Tribolium castaneum Survival

DNA damage Peroxidation

Acetylcholinesterase Alkaline phosphatase

A B S T R A C T

The red ?our beetle,Tribolium castaneum (Coleoptera:Tenebrionidae)is a widespread pest that lives in,and feeds on,wheat ?our.Here,we studied the effects of low-intensity microwave radiation (LIMR; 2.0kW/kg)on physiological and biochemical characteristics of T.castaneum ,and compared them to the effects of heat conduction treatment,to provide a theoretical basis for using LIMR for pest control.Lethal model equations with respect to temperature were shown to provide acceptable ?tting accuracy for the effects of LIMR treatment.Semi-lethal and lethal temperatures induced through LIMR (488C and 508C,respectively)for T.castaneum were lower than those induced through heat conduction (508C and 528C).When T.castaneum were subjected to LIMR,the insects’moisture content,pH values,alkaline phosphatase and acetyl cholinesterase activity were all lower than when the insects were subjected to heat conduction.Peroxide values and total free amino acid content were higher,and protein subunits molecular weights were lower when T.castaneum were exposed to LIMR than to heat;moreover,after LIMR exposure,the amino acid composition of T.castaneum was changed and the insect’s DNA was damaged.

?2010Elsevier Ltd.All rights reserved.

*Corresponding author.Tel.:+8602787288375;fax:+8602787288375.E-mail address:zhaosimingjx@https://www.doczj.com/doc/f93691687.html, (S.Zhao).Contents lists available at ScienceDirect

Journal of Insect Physiology

j o u r n a l h om e p ag e :w w w.e l s e v i e r.c o m /l o c a t e /j i n sp h y s

0022-1910/$–see front matter ?2010Elsevier Ltd.All rights reserved.doi:10.1016/j.jinsphys.2010.04.019

300g wheat?our was placed into the glass bottles with30beetles. The bottles were then sealed with a layer of sterile gauze.Glass bottles and samples were placed in an incubator and kept at a constant temperature of28?28C and65?5%relative humidity (Donahaye,1990).

2.2.Test methods

2.2.1.Sample preparation

The wheat?our was frozen atà188C for24h,removed from the refrigerator and allowed to reach room temperature for about 30min,following which100g of wheat?our was transferred into a beaker of250mL.Three replicates were used for each treatment. The bottles were then placed in an incubator and kept at a constant temperature of28?28C and65?5%relative humidity.

For the microwave treatment,samples were irradiated with microwave energy using a QW-15HM microwave oven.The effective length,width and height of the oven were508,420mm and305mm,respectively(Guangzhou Kewei Microwave Oven Energy Ltd.,China;900W capacity;frequency 2.45GHz).The power output of the generator was adjustable from0W to900W. Wheat?our temperatures were measured immediately after irradiation with a JDDA80point thermometer(Wuhan,Jingda Instrument Factory Co.,Ltd.,China)at different times.Five groups of20beetles each were placed in3cm?5cm plastic‘‘zip-top’’bags after weighing.The bags were then each buried inside a glass bottle?lled with100g wheat?our.The bottles were microwaved at rates of0.4kW/kg,0.8kW/kg,1.2kW/kg,1.6kW/kg,or2.0kW/ kg,so as to produce a range of?nal temperatures according to a predetermined standard temperature–time curve.

To determine the effect of conductive heat treatment,20beetles each were placed in a3cm?5cm plastic‘‘zip-top’’bag after weighing.The bag was then buried inside a glass bottle?lled with 100g wheat?our and subjected to a constant temperature of658C in water bath.A point thermometer was used to measure the sample temperature at different times.

After each treatment,the beetles were removed from the bottles in their bags and kept for examination.

2.2.2.Determination and calculation of mortality

After microwave irradiation or conductive heat treatment, adult beetles were separated from the sealed packages and observed for24h to determine whether they were dead.Adult insects were considered dead if no movement was observed. Moribund and surviving adults were observed over the following3 days.Mortality of adults was calculated as

M A?N d

N S

?100%(1)

where M A is%mortality of adults,N d is number of dead adult insects for each trial,and N S is the sum of live and dead adult insects for each trial.Microwave irradiation dosage was the input power of the microwave oven divided by the weight of the irradiated adult beetles which had been placed in the microwave oven.The?nal wheat?our temperature was de?ned as the temperature(8C)of the wheat as it left the microwave oven.

We used Mortality Equation(2)(Zhao et al.,2007a)to describe the relationship between mortality and temperature of T. castaneum at different temperatures in the experiment of Fig.1: Mortality Equation(2)

M?1eT1TT

M?eàA?eT1àT0T=eTàT0T meT0T T1T

M?0eT T0T

(2)

where T0(8C)is the?our temperature at which beetles begin to be killed and T1(8C)is the temperature of?our at which beetles suffer 100%mortality.The constant A is a susceptibility factor,which re?ects how easy the insects are to kill.The constant M is a?tted to the mode2.

2.2.

3.Determination of moisture content

The moisture content of T.castaneum was determined using the classical oven method(Reh et al.,2004;Vogl and Ostermann, 2006).

2.2.4.Determination of pH value

Ten beetles and5mL distilled water were placed in10-mL centrifuge tubes and homogenized in an ice bath,then centrifuged at48C,10,000?g for10min using an Avanti-J26high-speed refrigerated centrifuge(Beckman Corporation,USA);the pH of the supernatant was immediately measured using a FE30Conductivity meter(Mettler-Toledo Instruments Co.Ltd.,China.).

2.2.5.Determination of peroxide value

Peroxide value is de?ned as the milliequalivalents of peroxides per kilogram of sample.This was determined by titration(Owen and Brake,2006).One hundred beetles were crushed using a glass mortar and pestle and placed in a250-mL Erlenmeyer?ask;30mL petroleum ether was added,and the mixture was allowed to sit overnight.The next day,using?lter paper,the mixture was?ltered into a100-mL?ask,and a vacuum distillation method was used to extract the solvent.The fat thus obtained was weighed,and30mL of a40%chloroform/60%glacial acetic acid(v/v)mixture was added;after the sample had completely dissolved,1mL saturated potassium iodide solution was added,the container was immedi-ately sealed,and gently shaken for30s,and kept in the dark for 3min.Next,100mL distilled water was added.The resulting solution was then titrated with sodium thiosulfate standard solution(2000?10à3mol/L Na2S2O3)to pale yellow.At this point, 1mL of starch indicator(soluble starch dissolved in water,10g/L) was added and titration was continued until the blue colour disappeared.Distilled water was used as a titration

control.

Fig. 1.Effects of microwave radiation on Tribolium castaneum mortality.(A) Measured value of microwave on T.castaneum mortality.(B)Microwave treatment mortality observed with analog values(0.4kW/kg).

H.Lu et al./Journal of Insect Physiology56(2010)1356–13611357

2.2.6.Determination of amino acid composition

For amino acid analysis,?fteen milligrams of powdered beetles was treated in a tube with 6mol/L HCl;the sealed tube was allowed to hydrolyze for 24h at 1108C,then distilled water was added to a constant volume to 50mL.Of this solution,1mL was evaporated,dissolved in 0.02mol/L HCl and analyzed on a Hitachi 835-50automatic anion-acid analyzer (Hitachi Ltd.,Tokyo,Japan)(Okahashi et al.,1983).

2.2.7.Determination of DNA damage

DNA damage was measured by the cetyl trimethyl ammonium bromide (CTAB)method (Taylor and Powell,1982;Fang et al.,1992),using phenol–chloroform extraction.Adult beetles were weighed (0.5g),and placed in a small and clean glass mortar;0.9mL extraction buffer (2%cetyl-trimethylammonium bromide [CTAB],1.4M NaCl,20mM EDTA,100mM Tris–HCl pH 8,0.2%polyvinyl-polypyrrolidone [PVPP],0.01%sodium dodecyl sulfate [SDS],0.2%a -mercaptoethanol)was added to the mortar and the beetles fully ground to a paste,which was transferred to a 2-mL centrifuge tube with the tip cut off and replaced with a 0.5-cm blue suction head.After 45min of extraction at room temperature,samples were washed twice with 0.6mL chloroform-isoamyl alcohol (24:1,v/v)followed by centrifugation for 10min (20,000?g ).DNA was precipitated with a half volume of isopropanol for 20min at à208C and pelleted by 20min of centrifugation at 48C.The pellet was washed with 70%cold ethanol,vacuum dried and dissolved in 0.3mL TE buffer (pH 8).After 30min of RNase (0.02m g)treatment at 378C,samples were stored at à208C (Doyle and Doyle,1987).

2.2.8.Determination of alkaline phosphatase activity

We performed a crude enzyme liquid extraction using a previously described method (Chen et al.,1996).We selected 10beetles,and ground them in a mortar with 1:50(w/v)pre-cooled 0.05mol/L Tris–HCl (pH 7.5),which contained 0.1mol/L NaCl,adding 20%(V/V)n-butanol for extraction,so that the combined enzyme was completely released;we then centrifuged it at 4000r/min for 20min,to obtain a crude enzyme solution which was stored at 48C.Enzyme activity was determined using a Nanjing Jiancheng Bio-Engineering Institute Alkaline Phosphatase kit,following the manufacturer’s instructions.

2.2.9.Determination of acetylcholinesterase activity

A crude enzyme liquid extraction was performed using a previously described method (Liu et al.,2006).We took 10beetles,added 1.5mL frozen 0.1mol/L phosphate buffer (pH 7.0),and homogenized them in an ice bath,then transferred the homoge-nate to a 1.5-mL centrifuge tube and spun it at 48C,10,000?g for 20min.The supernatant was stored at 48C.

Acetylcholinesterase (AChE)activity was determined using the method of Ellman et al.(1961).The substrate was 1.5mmol/L thio-acetylcholine iodide (ATChI),which was hydrolyzed to generate

thiocholine and acetic acid.Thiocholine was determined spectro-photometrically using the reagent dithio-bis -nitrobenzoic acid (DTNB; 1.0mmol/L),after adding 20%sodium dodecyl sulfate (SDS)to stop the reaction,and measuring optical density at 412nm.An extinction coef?cient formula was used to convert OD values into ACh E activity (m mol/min mg pro).We then used Ellman’s method (1961)to calculate ACh E activity,expressed as nmol/min/m g:[Ach E activity =(OD ?R ?1000)/(e ?S ?W ?P )],where OD is average absorbency,OD 412nm/min;e is the extinction coef?cient,13,600mol à1cm à1;S is the analyzed sample volume,m L;R is total volume of the reaction,m L;W is the protein content,m g;P is the optical path length (0.6cm in this case).2.3.Data analysis

Data was mapped with Excel2003,using SAS for regression analysis (SAS Institute,1989).Differences were considered signi?cant at P <0.05.3.Results

3.1.Effects of microwave conditions on T.castaneum mortality The effects of heating the medium to different temperatures using different LIMR power rates on the mortality of T.castaneum are illustrated in Fig.1.The effects of LIMR on T.castaneum mortality were negligible below 458C,but sharply increased between 458C and 508C.Nearly 100%mortality was obtained with LIMR treatments that resulted in medium temperatures above 508C.Conductive heating was less effective in killing T.castaneum than LIMR.The fatal effects of heat conduction were almost zero below 488C,but then increased to 100%at 528C.

Table 1shows eigenvalues for the death of T.castaneum under different conditions using Mortality Equation (2).We can see from Table 1that the regression sum of squares is much larger than the remaining sum of squares,indicating that Mortality Equation (2)is highly predictive.

The semi-lethal temperatures of the ?ve different doses of LIMR were all just under 488C and the lethal temperatures were all $508C;the semi-lethal temperature from heat conduction exposure was $508C,and the lethal temperature was $528C.Another factor,A ,is the susceptibility factor;this re?ects how easily the insects are killed by the treatment.We can see from Table 1that A was much larger for LIMR than for heat conduction;the value of A was larger when the intensity of the microwave treatment was lower.This analysis shows that T.castaneum are more susceptible to LIMR than are rice weevils (Zhao et al.,2004).3.2.Effect of microwave conditions on T.castaneum moisture content The effects of LIMR on moisture content of T.castaneum are shown in Fig.2.The moisture content of T.castaneum was reduced

Table 1

Death eigenvalues of Tribolium castaneum .Processing conditions T 0/8C

T 1/8C

A

M

Semi-lethal

temperature (8C)

Lethal

temperature (8C)

Regression sum of squares/remaining sum of squares Microwaves 0.4kW/kg 405012.4?10à314.8847.850.238,720.6/4.40.8kW/kg 40508.70?10à314.8647.750.039,049.2/3.61.2kW/kg 4050 5.12?10à315.5847.649.739,389.3/3.11.6kW/kg 3550 5.03?10à328.5047.549.739,480.3/14.22.0kW/kg 3550 2.11?10à327.3447.449.540,069.4/13.9Heat conduction

40

52

8.59?10à4

39.23

50.1

51.5

21,111.1/11.1

Note :When the mortality is 0.5,semi-lethal temperature can be calculated using Mortality Equation (1).

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after both microwave and heat conduction treatments.Both microwave and heat treatments led to beetles’moisture content lower,and the water loss is less by microwave.The lower the microwave dose,the greater the water loss,probably it is because lower microwave dose took longer to kill pests.3.3.Effect of microwaves on pH of T.castaneum

The effects of microwave conditions on pH of T.castaneum are shown in Fig.3.Heat conduction treatment resulted in decreased pH values;however,as microwave intensity increased,the pH of the beetle extract decreased to a greater extent.When the two kinds of approaches achieved the same physical temperature,the pH values of specimens treated with LIMR were lower than those treated with heat conduction.

3.4.Effects of microwaves on peroxide levels

The effects of LIMR on T.castaneum peroxide levels are shown in Fig.4.As the temperature increased,T.castaneum peroxide levels increased;heat conduction affected peroxide levels more than did LIMR.As the semi-lethal and lethal temperatures for heat conduction treatment were higher than those of LIMR,and the period of exposure was longer,heat conduction resulted in a higher degree of fat oxidation.

3.5.Effects of microwaves on amino acid composition

The effects of microwaves on the amino acid composition of whole T.castaneum beetles are shown in Table 2.Of the 17amino

acids in T.castaneum ,the contents of aspartic acid,glutamic acid,alanine,isoleucine,tryptophan and arginine were signi?cantly increased,while lysine,histidine and proline were signi?cantly reduced,and other amino acids were little changed after LIMR treatment.After heat conduction treatment,the contents of threonine,glutamic acid,glycine,alanine and arginine were signi?cantly increased,while that of proline content was signi?cantly reduced.

3.6.Microwave-induced DNA damage in T.castaneum

Fig.5shows the electrophoresis pattern of T.castaneum DNA.The mobility of the main band of DNA from untreated control beetles was consistent with a molecular size in the range 9416–123,130bp.The effect of lower power LIMR treatments was to shift the main electrophoresis band upward in the gel,as seen in Lanes 2and 3(0.4kW/kg and 0.8kW/kg,respectively)indicating that the main effect of LIMR is to aggregate https://www.doczj.com/doc/f93691687.html,nes 5–7(1.6kW/kg, 2.0kW/kg and heat conduction,respectively)showed both upward and downward shifts,indicating that the effect of the LIMR treatment on DNA was both aggregating and

degrading.

Fig.2.Effects of microwave radiation on moisture

content.

Fig.3.Effects of microwave radiation on pH of Tribolium castaneum .(n =3,ˉx ?SD T.Different capital letters (A and B)express signi?cant differences in pH at the two lethal temperatures under different heat treatment conditions.Different lowercase letters (a–c)indicate signi?cant differences in pH at the same lethal temperature under different heat treatment

conditions.

Fig.4.Effects of microwave radiation on peroxide levels in Tribolium castaneum (n =3,ˉx ?SD T:Different capital letters (A and B)indicate signi?cant differences in peroxide values at the two lethal temperatures under different heat treatment conditions.Different lowercase letters (a–c)indicate signi?cant differences in peroxide levels at the same lethal temperature under different heat treatment conditions.

Table 2

Composition content of Tribolium castaneum amino acids (%,dry basis,n =3,ˉx ?SD T:.Amino acids Control Microwave Heat conductivity Aspartic acid 2.53?0.01b 2.56?0.01a 2.51?0.01b Threonine 1.30?0.01b 1.31?0.00b 1.33?0.01a Serine

1.17?0.01a 1.18?0.00a 1.18?0.00a Glutamic acid 3.61?0.02c 3.81?0.01b 3.89?0.02a Glycine

2.73?0.01b 2.74?0.00b 2.78?0.01a Alanine 2.02?0.00c 2.09?0.00b 2.40?0.01a Valine

2.05?0.00b 2.07?0.01b 2.14?0.00a Methionine 0.71?0.00b 0.71?0.01b 0.74?0.00a Isoleucine 2.48?0.01b 2.55?0.01a 2.50?0.02b Leucine 2.40?0.00b 2.45?0.01a 2.46?0.00a Tyrosine

1.49?0.01b 1.53?0.02a 1.48?0.01b Phenylalanine 1.00?0.02b 1.03?0.00b 1.10?0.02a Lysine

1.87?0.01a 1.84?0.01b 1.87?0.01a Tryptophan

2.80?0.01b

3.01?0.02a 3.24?0.01a Histidine 1.35?0.01a 1.31?0.01b 1.35?0.00a Arginine 1.81?0.00c 1.87?0.01a 1.84?0.00b Proline 2.15?0.00a 1.54?0.01c 1.74?0.00b Total

33.57?0.13b

33.61?0.14b

34.55?0.13a

a Amino acid content signi?cantly differs from control.

b

Amino acid content signi?cantly differs from processing by microwave.c

Amino acid content signi?cantly differs from processing through heat conductivity.

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3.7.Effect of microwave on alkaline phosphatase activity of T.castaneum

The effects of LIMR and heat conduction treatments on alkaline phosphatase activity of T.castaneum are shown in Fig.6.While heat conduction had little effect on alkaline phosphatase activity,alkaline phosphatase activity decreased as the power of the LIMR treatment increased.This indicates that the heat tolerance of T.castaneum may decrease as LIMR power increases.

3.8.Effect of microwaves on T.castaneum acetylcholinesterase activity

The effects of LIMR on AchE activity of T.castaneum are shown in Fig.7.The AChE activity of T.castaneum decreased after exposure to both LIMR and heat conduction.Surprisingly,the effects of LIMR on AChE activity were greatest when the intensity of microwave was smallest,which indicates that LIMR’s effects on AChE activity are not directly related to LIMR intensity,and that less-intense radiation can injure the T.castaneum central nervous system.The effects of LIMR on AChE activity of T.castaneum were larger than those of heat conduction.4.Conclusion

Our mortality exponential model (Eq.(2)),accurately predicted the effects of LIMR on T.castaneum mortality.Semi-lethal and lethal LIMR temperatures (488C and 508C,respectively)were lower than the semi-lethal and lethal temperatures (508C and 528C,respectively)for heat conduction processing.After LIMR treatment,moisture content,pH,alkaline phosphatase and acetylcholinesterase activity of T.castaneum were lower,while peroxide value and the total free amino acid content were increased.Amino acid composition was changed,and DNA was aggregated and degraded compared with the effects of heat conduction.

Albert (1977)and Webber et al.(1980)have reported that microwave radiation signi?cantly affects physiological processes,but does so differently from conventional heating.Different points in physiological temperature ranges are tied to differences in enzyme activity.Microwave radiation has previously been found to lead to increased ornithine decarboxylase activity (Byus et al.,1988),and decreased activity in calcium-dependent protein kinase,Ca 2+Mg 2+-ATPase,lactate dehydrogenase,antioxidant enzymes,alkaline phosphatase (Phelan et al.,1994),acetylcholin-esterase and others,as amino acid levels changed.

In this study we found that the activity of T.castaneum alkaline phosphatase (ALP)was affected by LIMR treatment.This enzyme plays an important role in cell phosphate metabolism and signal peptide transduction.ALP itself is a membrane-bound metal-glycoprotein.Enhancement of alkaline phosphatase activity improves the heat tolerance of cells and helps them maintain normal physiological function (Sowadski et al.,1985).Alkaline phosphatase affects plasma membrane active transport and its function is closely related to the occurrence of disease (Kim and Wyckoff,1991).

Acetylcholinesterase (AChE)is a critical enzyme in biological nerve conduction,and is a well-known target for insecticides.Damage to this enzyme would clearly affect viability.

LIMR also altered amino acid levels in treated beetles.This is a gross measure of protein composition and is not easy to interpret,but may re?ect protein breakdown.Changes in proline level are particularly interesting;as an energy source for insects,proline can be obtained not only from food,but also from the insect’s own fat,through synthesis of alanine.In blow?ies,the product of proline after the rapid dehydrogenation required by ?ight is glutamic acid (Sacktor,1975;Beenakkers et al.,1984;Goldsworthy,1983and Ga

¨de,1992).We speculate that a large amount of proline is consumed through intense exercise by T.castaneum ;perhaps this activity is induced by the treatment.LIMR treatment caused proline levels to decrease more than did heat conduction.

In addition to effects on proteins,LIMR treatment affected a number of physiological variables.Among these was water content.Insects will act to avoid the heat stress and consequent water loss of hot environments (Henry and Prange,1996).Normal water balance in insect cells is destroyed by high

temperatures;

Fig. 5.Electrophoresis of Tribolium castaneum https://www.doczj.com/doc/f93691687.html,ne M:standard;Lane 1:comparison sample;Lane 2:0.4kW/kg;Lane 3:0.8kW/kg;Lane 4:1.2kW/kg;Lane 5:1.6kW/kg;Lane 6:2.0kW/kg;Lane 7:heat

conduction.

Fig.6.Effects of microwave radiation on alkaline phosphatase activity.Different letters (A–D)indicate signi?cant differences in alkaline phosphatase activity in T.castaneum under different processing

methods.

Fig.7.Effect of microwave radiation on acetyl cholinesterase activity.Different letters (A–E)indicate signi?cant differences in acetylcholinesterase activity in T.castaneum under different processing methods.

H.Lu et al./Journal of Insect Physiology 56(2010)1356–1361

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heat increases cell osmotic pressure,leading to increased cell permeability.

The pH of a T.castaneum extract was found to be lowered by LIMR treatment.The cell membrane bilayer structure is formed by protein and phospholipid composition.The cell in vivo H+ concentration can affect the state of cell nucleus macromolecules (proteins and nucleotides)(Hochachka and Somero,1984),thereby affecting the permeability of cell membranes.

Peroxide levels in T.castaneum were increased by microwave treatment.Lipid peroxidation can produce free radicals,sponta-neously or through a chain reaction,thus damaging the body(Njaa and Aksnes,1981).Ionizing radiation and ultraviolet radiation can cause the production of lipid peroxides and free radicals through non-thermal effects(Ramesh et al.,1995).

Microwave heating is based on the transformation of alternat-ing electromagnetic?eld energy into thermal energy by affecting polar molecules of a material so that it can kill the insect at a lower temperature.By using microwave treatment,it is possible to heat pest insects to a lethal temperature while leaving the foodstuff in which they live unaffected,or heated to a lesser extent than the insects themselves.This explains why LMIR killed T.castaneum beetles at medium temperatures that were less than those caused by conductive heat treatment.Both microwave and heat treat-ments led to beetle DNA degradation,but the ability of the microwave treatment to cause DNA aggregation may suggest a possible mechanism for the enhanced ability of LIMR to cause insect lethality.

We conclude that LIMR could eventually present a clean and effective means of controlling this very widespread pest,but further study will be needed.

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na bu gei ma ya kiu 那不给妈呀久儿我 ga xi yi dai gei no 噶西带给路 ma lou xi bu yi mu lei du gei you li da 吗楼西不一木类度给有大 na bu gei ma ya kiu 那不给妈呀久儿我 ga xi yi dai gei no 噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那 na dou na han bu ka qi 那都那汗不卡气 yi jian gu dai a ni ji 一见古带啊你几 ku dai pa la bu miao 苦带怕拉不秒 ca la wu dai ka 擦拉屋带卡 ku niao ti yi ka niao ji 苦鸟提一卡鸟几 ca la gu a gu mi no mu kou 擦拉古啊古米闹木口 cu wu xi wu s ka wo so 粗屋西屋丝卡我收 ku dai han bu ka gei 苦带汗不卡给 yi lu jiur gei you 一路酒给又 nei you mu nu lo 内有木奴咯 yi lu jiu gei you 一路就给又 na bu gei ma ya kiu 那不给妈呀久我 ga xi yi dai gei no 噶西带给路 ma lou xi bu yi mu lei du gei you li da 吗楼西不一木类度给有里大yang gou li ya sang jin dang nei gu wu 羊够里呀桑金当内古 a long da ma de xi gei lei gu li you li da 啊龙大吗的西给类古里有里大ka xi le gong long no yin ku kou qiu 卡西了工龙木因哭口求 na bu li qiu liu ma pu ma xi you so sou 那不里求留吗扑吗西有否搜 na bu gei ga ya piao ka xi dei you nu 那不给妈呀久我噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那 nei ga dou na ba leng dei you 内噶都那吧冷给又 ku dai lu man du la wu 苦带路满度啦舞 ku dan ku miao sa la han gei ji 苦但苦秒撒拉汗给几 na bu gei ma ya kiu 那不给妈呀久我 ga xi yi dai gei no 噶西带给路 ma lou xi bu yi mu lei du gei you li da 吗楼西不一木类度给有里大 yang gou li ya sang jin dang nei gu wu 羊够里呀桑金当内古 a long da ma de xi gei lei gu li you li da 啊龙大吗的西给类古里有里大ka xi le gong long no yin ku kou qiu 卡西了工龙木因哭口求 na bu li qiu liu ma pu ma xi you so sou 那不里求留吗扑吗西有否搜na bu gei ga ya piao ka xi dei you nu 那不给妈呀久我噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那 na bu gei ga ya piao ka xi dei you nu 那不给妈呀久我噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那

主持词 2020年大学毕业晚会主持词

xx年大学毕业晚会主持词 b:让我们静静享受一下挑战,在日复一日与时间的赛跑中,你会变得更加坚强,更加神采奕奕!又一个青春之旅从今晚启航,又一个光阴的故事在今晚讲述 c:亲爱的同窗,不要带着离别的愁绪,因为明天又是一个新的起点,因为我们相信再次相逢,我们还是一首动人的歌!d:很高兴今天能有这个机会同大家相聚一堂,共叙离别。就让今天铭刻在我们心间,让母校留住我们的风采! a:今天,我们也非常荣幸的请到了 b:下面让我们用热烈的掌声有请上台讲话 结束语a:欢快的舞蹈表达不尽我们对母校的敬意 b:热情的赞歌唱不尽我们对母校的一腔深情 c:流火的六月,我们将带着恩师的叮咛,怀着必胜的信心,走向新的征程 d:绚烂的七月,我们将载着母校的祝愿,带着亲人的希望,向着新的征程扬帆起航 a:老师们,同学们,欢送10级毕业生联欢晚会合:到此结束a李:毕业,是一个沉重的动词; 刘:毕业,是一个让人一生难忘的名词; 李:毕业,是感动时流泪的形容词; 刘:毕业,是当我们以后孤寂时候,带着微笑和遗憾去回想时的副词;

李:毕业,是我们夜半梦醒,触碰不到而无限感伤的虚词。 刘:若干年后,假如我们还能够想起那段时光,也许这不属于难忘,也不属于永远,而仅仅是一段记录了成长经历的回忆。 李:尊敬的各位领导老师 刘:亲爱的各位同学们 合:大家晚上好! 李:很荣幸和大家相聚在这激情如火的六月,在这充满忧伤的六月! 刘:很高兴和大家相聚在放心去飞,20年后再相聚毕业晚会现场! 李:我是李扬 刘:我是刘伟清 李:今天晚会现场非常荣幸的邀请到院系的各位领导和老师们。 刘:让我们首先欢迎 李:灿烂的星空曾经铭刻你我的笑容 刘:美丽的海岸曾经珍藏你我的背影。 李:连绵起伏的山川,像一双腾飞的翅膀支撑起我们坚韧不屈的信念, 刘:沸腾的黄海血脉,像千万奔涌的旋律连绵成我们亘古不灭的传说。 李:在这个光荣同梦想交融的时刻,让我们共同祈祷 合:环保的明天更美好!

毕业生晚会主持稿

毕业生晚会主持稿 毕业生晚会主持稿(一) A:青春是一曲荡气回肠的歌,三年前我们怀着彩色梦想走进了鄂大,三年中我们有过欢笑,流过泪水,经历磨炼,得到成长:三年后的今天,我们在这里重温青春过往,因为明天就将各奔天涯。也正因为此,今夜,我们承载了太多的祝福与惦念,寄托了太多的关怀与企盼。 C:今晚,让我们再一次重温,那些感动过我们的人和事:灯火通明的教学楼里用功的身影,篮球场上捍卫集体尊严的男儿霸气,满是欢声笑语的宿舍边不着边际的闲谈 D:又一个三年轮回之后,在同样微凉的夏夜,你是否会记起校园里的梧桐树,你是否会记起日记本里的书签,那些五彩缤纷的日子? A:无数个三年之后,你们的思念是否会有增无减?在你成长的岁月里,在你闯荡社会的每一天,是否会有那么几个瞬间让你渴望回到过去 :让我们静静享受一下挑战,在日复一日与时间的赛跑中,你会变得更加坚强,更加神采奕奕!又一个青春之旅从今晚启航,又一个光阴的故事在今晚讲述 C:亲爱的同窗,不要带着离别的愁绪,因为明天又是一个新的起点,因为我们相信再次相逢,我们还是一首动人的歌!D:很

高兴今天能有这个机会同大家相聚一堂,共叙离别。就让今天铭刻在我们心间,让母校留住我们的风采! A:今天,我们也非常荣幸的请到了 :下面让我们用热烈的掌声有请上台讲话 结束语A:欢快的舞蹈表达不尽我们对母校的敬意 :热情的赞歌唱不尽我们对母校的一腔深情 C:流火的六月,我们将带着恩师的叮咛,怀着必胜的信心,走向新的征程 D:绚烂的七月,我们将载着母校的祝愿,带着亲人的希望,向着新的征程扬帆起航 A:老师们,同学们,欢送10级毕业生联欢晚会合:到此结束 A李:毕业,是一个沉重的动词; 刘:毕业,是一个让人一生难忘的名词; 李:毕业,是感动时流泪的形容词; 刘:毕业,是当我们以后孤寂时候,带着微笑和遗憾去回想时的副词; 李:毕业,是我们夜半梦醒,触碰不到而无限感伤的虚词。 刘:若干年后,假如我们还能够想起那段时光,也许这不属于难忘,也不属于永远,而仅仅是一段记录了成长经历的回忆。 李:尊敬的各位领导老师 刘:亲爱的各位同学们

浅谈小学语文小班化教学的有效性

浅谈小学语文小班化教学的有效性 发表时间:2019-08-21T11:09:06.843Z 来源:《中小学教育》2019年第372期作者:王克文[导读] 新课程改革背景下,对于小学语文教学提出了更高的要求。 甘肃省天水市麦积区五龙中心学校741020 摘要:新课程改革背景下,对于小学语文教学提出了更高的要求。小学语文教师要积极创新教学理念,结合小学生自然天性特点及个体学习能力差异,开展多元化小班教学。以激发学生学习兴趣及参与度,促进学生学习能力和语文综合素养提升,满足新时期教学要求,实现良好语文教学实效。本文结合当前小学语文教学现状,具体阐述了小班化教学策略探究。 关键词:小学语文策略探究小班化教学现状 小学义务教育阶段是小学生语言行为习惯养成,以及人生观、思想观和价值观形成的重要时期。小学语文作为最为重要的基础学科,教师在教学中要结合学生个体学习能力的差异开展小班化教学模式,以激发学生学习兴趣及参与度,促进学生语文综合素养提升,实现良好教学实效。 一、当前小学语文教学现状 1.教学方式传统单一。当前,部分小学语文教师在教学过程中,依然固守传统单一的教学模式。大多采用填鸭式灌输教学,无法激起学生学习兴趣,不利于提升学生的学习成绩和语文核心素养,直接影响教学实效。 2.学生阅读视野狭窄。现阶段,很多学生都存在阅读视野狭窄、阅读量不足的问题。不利于学生累积优秀词汇及大量写作素材,无法有效地提升学生语文核心素养,影响语文教学实效。 3.忽视学生教学主体地位。一些语文教师在教学过程中,完全忽视学生教学主体地位。一味依据既有教案设计和授课节奏,不注重与学生展开互动模式教学。不能有效地提升学生学习兴趣和课堂参与度,直接影响语文教学实效。 二、小学语文小班化教学策略探究 1.应用多媒体形式,促进传统文化教育渗透实效。例如:教师在讲解《父亲的菜园》这一课节时,就应用了多媒体的直观生动优势,将传统文化教育渗透到了语文教学中。首先,教师先引领学生进行全文阅读,以加深课文理解。紧接着,在开始播放课前选取好的对应课文内容的相关在山坡上开垦菜园视频,使学生们可以直观、立体地了解掌握课文内容。在视频中出现暴雨落在山坡菜地画面时,适时诵读“那天,父亲正在吃午饭,把碗一丢,抓起铁锨就冲进了暴雨中。可是,山坡菜地里那薄薄的一层泥土已经被大雨冲了个一干二净,露出大块大块狰狞的岩石来。父亲没有气馁,他在坡地的边缘砌了一道矮墙,再从山脚下把土一筐一筐挑上去,盖住了那可怖的岩石。父亲的双肩红肿,脚板也磨起了泡。看着新菜园终于被开出来了,父亲笑了。”通过视频观看以及教师诵读讲解,学生脑海中浮现出一位坚强刚毅、面对困难永不放弃、辛勤劳动的父亲形象。 2.开展角色扮演,促进情感教学实效。例如:教师在讲解《落花生》这一课节时,分别选取了5位同学扮演课文中的父亲、母亲、哥哥、姐姐和第一人称“我”的角色,并将课前准备好的带壳花生分发给了他们。随后,引领学生诵读全篇课文,帮助学生熟悉课文内容。学生阅读结束后,角色扮演环节开始啦。学生们进行角色扮演时,认真观察着手里的花生,完全投入到了角色情感世界中,良好演绎了课文内容。通过这种角色扮演的教学形式,学生了解到花生的诸多好处,更意识到不要做只讲体面却不能帮助别人的人,要做有用的人。 3.引导学生分组评改作文,促进作文教学实效。教师摒弃以往实行的全程精细作文评改方式,引导学生进行分组评改。不仅可以激发学生学习热情及参与度,更能有效地促进学生作文水平和语文综合素养提升,实现良好作文教学实效。比如:教师在班级内设立“作文评改小能手”分组评改活动。首先将班级学生分成6个小组,首先,在各小组内进行作文评改活动,最后评选出组内评改小能手。然后,教师选出适合的作文习作,让每组的评改小能手进行评改。最后,选出最终的作文评改小能手。在整个作文评改过程中,每个学生都积极主动地参与进来,使学生充满了愉快骄傲的学习热情。 4.参照课文内容改写文本。如:教师在讲解《独坐敬亭山》这一课节时,就可以在学生充分认识理解古诗的创作背景和蕴涵深意后,引导学生进行文体改写。《独坐敬亭山》是我国唐代著名诗人李白的一首五言绝句,诗中表面上叙述了诗人独自游览敬亭山的悠然情趣,实际却是表达自己怀才不遇、孤峰独立,并寄情于山水的真实情感。教师引导学生,以白话体的形式来改写古诗内容,将诗人的孤独感、寄情山水的悠然都生动、直观地表达叙述出来。 5.为学生推荐优秀阅读书籍。比如:《十万个为什么》、《绿叶仙踪》、《海底两万里》、《上下五千年》、《尼尔斯骑鹅旅行记》《中国民间故事》、《三字经》、《昆虫记》、《格列佛游记》、《鲁滨逊漂流记》等优秀阅读书籍。此外,教师还积极鼓励学生在阅读过程中,将书中优美词汇和生动素材整理到笔记本上。 综上所述,本文首先简述了当前小学语文教学现状,随之阐述了小班化教学的具体策略探究。新时期形势下,小学语文教师要积极转换教学理念,结合学生个体学习能力差异开展小班教学模式,以促进学生语文综合素养提升,满足新时期教学要求,实现良好的语文教学实效。 参考文献 [1]邓建恩浅谈小学语文小班化教学的有效性[J].学周刊,2017,11,(18),218-219。 [2]黄佐评小学语文小班化教学策略分析[J].语文课内外,2018,15,(34),307。 [3]韩小磊小学语文小班化课堂教学研究[J].语文天地(小教版),2018,17,(10),92-93。

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