Fallarmywormherbivoryaffectssilicaaccumulationincornandrice

FlorE.Acevedo1,MichellePeiffer1,DawnLuthe2andGaryFelton11DepartmentofEntomology,and2DepartmentofPlantScience.ThePennsylvaniaStateUniversity,UniversityPark,PA16802.

•  Silica accumulation is an inducible plantdefense mechanism that causes wear on theinsect mandibles and hampers their ability tofeedonplanttissues.

•  Insect herbivores are able to modify itsdevelopment to feedonplantswithhigh silicacontent.

Thisresearchdetermined:1)  The effect of fall armyworm herbivory on the

accumulationofsilicaincornandriceplants.2)  The effect of silica on the fall armyworm

mandiblewear.3)  The fall armyworm adaptations to feed on

plantswithhighsilicacontent.

•  PlantsandinsectsWeusedthecorn,Zeamays inbredlineB73;andthe rice, Oryza sativa japonica cultivarNipponbare. The fall armyworm, Spodopterafrugiperda wereobtainedfromalabcolonyfromtheUSDA-ARSinGainesvilleFlorida.•  Effectofinsectfeedingonplantsilicaaccumulation

Rice and corn plants were exposed to FAWherbivory for 24hours ormechanically damagedwith scissors in a complete randomized design;the new regrowth tissues were used to quantifytheamountofsilicawiththemolybdenumyellowmethod(3).•  CaterpillarmandiblewearMandible wear and mineral composition wasdetermined by X-ray and scanning electronmicroscopy.•  StatisticalanalysisWe used ANOVA to test for differences oftreatment means, followed by the Tukey test atα=0.05.

2. Silica accumulated in plant leaves wears the fall armywormmandibles. This is one of the \irst studies to explore the

dynamic interplaybetween insectherbivoresandsilica accumulation in plants of economicimportance.Threeofthemostimportantcropsforhumankindare grasses (silica-accumulating plants); a betterunderstanding on how silica enhances cropresistance against insect herbivores is of globalimportance.

Plants, especially grasses, accumulate largeamounts of silicon dioxide in their leaves. Silicadeposition plays a role in defense against abioticand biotic stresses including herbivores. Thisresearch determined the effect of the fallarmyworm(FAW)herbivoryintheaccumulationofsilicaincornandriceplants,aswellastheeffectofsilica on the caterpillar mandible durability. Ourresults show that FAW feeding induces silicaaccumulation in rice but not in corn plants. Silicawears the FAW mandibles affecting its feedingability;inresponsetheFAWplasticallymodi\iesitsmorphology and development to feed on silica-containingplants.

1.  HuntJW,DeanAP,WebsterRE, JohnsonJN,andEnnosAR.AnnalsofBotany102:653-656,2008

2.Fürstenberg-HäggJ,ZagrobelnyM,andBakS.Int.J.Mol.Sci.14,10242-10297,2013

3.SaitoK,YamamotoA,SaT,andSaigusaM.SoilSc.PlantNutr.,51,29-36,2005

Fig.1.Fallarmywormlarvafeedingoncorn.

•  Silicon accumulation increases plantresistancetoherbivorousinsectsAmong many other roles, silicon accumulationincreases the abrasiveness of the plant leavesacting as a physical defensemechanism againstphytophagousinsects(1).

• Herbivorous insects face diverse plantdefensemechanismsInsect herbivores adapt their morphology,physiology, development and behavior tocounteractplantdefenses(2).• Researchquestions1)Doesinsectfeedingaffectplantsilica

accumulation?2)Doessilicaaffectstheherbivorefeeding?3) How do insects manage to feed on silica-

containingplants?• Modelsystem Corn,riceandthepolyphagousinsectfallarmyworm,Spodopterafrugiperda(Lepidoptera:Noctuidae)(Fig.1).

Resultsanddiscussion

Rice and corn plantsaccumulate silica intheepidermisoftheirleaves and tips oftrichomes (Fig. 2).Ricecontain~3timesmoresilicathancorn.

3. The fall armyworm plastically modiOies its morphology anddevelopmenttofeedontoughsilica-containingplants.

1.Fallarmywormfeedingaffectsplantsilicaaccumulation.CornRice

Fig.2.Backscatterelectronimageofsilicabodiesinriceandcornleaves.

Fig. 3. Silica accumulation in rice (left) and corn (right) plants aftermechanical damage and insect-feeding treatments. Different lettersindicatesigni\icantdifferencesamongtreatmentmeans(P<0.05).

ArtiOicialdiet-fedRice-fedCorn-fed

Fig.5.Backscatterelectronimageofthefallarmywormmandiblesfromcaterpillarsfedondifferentdiets.Whiterouterareascorrespondtomineral-enrichedregions.

Zn Cl Na

Fig.4.X-raymappingofZn,ClandNaoftheFAWmandibles.

Fig.6.Headcapsulesize(left),mandibularmuscles(center),andmandiblesize(right)ofthefallarmywormlastinstarcaterpillarsrearedonriceandcornleaves.

Corn-fedRice-fed

2.60mm

Rice-fedCorn-fed2.92mm

Rice-fedCorn-fed

Whenfeedingonrice,theFAWundergoesanadditionalmoltincreasingthesizeofitsmandiblesandattachedmusculature(Fig.6).

Methods

Rice Corn

The FAW enhances thehardness of the cuttingedges of its mandibles byincorporating mineralsincludingzinc, chlorineandsodium(Fig.4).

Feedingonrice,ahighsilica-containing plant, destroysmostofthemineralizedareaof the FAW mandibles (Fig.5). Mandible wear hampersthecaterpillarabilitytofeedonplanttissues.

Conversely, inc o r n , t h edeposition ofsilica is thes a m e f o ri n s e c t - f e dplants and foru n t r e a t e dcontrols, botharelowerthanmechanicallyd a m a g e dplants(Fig.3).

The mechanical damage caused by the fall armyworm feeding induces silicaaccumulationinriceplantsby~37.2%comparedwithuntreatedcontrols.

USDA-ARSGainesville,Fl.PennStateMicroscopyfacility.PennStateCollegeofAg.Sciences(CAS)grant.USDA-NIFAgrant#2011-67013-30352.NSF

SigniOicance

Conclusions

References

Acknowledgments

Objectives

Introduction

Abstract