ARTICLE IN PRESS. Hong Li a,b,, Stephen H. Futch c, James P. Syvertsen c, Clay W. McCoy c

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1 Soil Biology & Biochemistry 39 (27) Time series forecst nd soil chrcteristics-sed simple nd multivrite liner models for mngement of Diprepes revitus root weevil in citrus Hong Li,,, Stephen H. Futch c, Jmes P. Syvertsen c, Cly W. McCoy c Deprtment of Plnt nd Animl Sciences, Nov Scoti Agriculturl College, P.O. Box 55 Truro, NS, Cnd B2N 5E3 Deprtment of Soil nd Wter Sciences, Chin Agriculturl University, Beijing 194, Chin c Citrus Reserch nd Eduction Center, University of Florid, IFAS, Lke Alfred, FL 3385, USA Received 22 July 26; received in revised form 3 April 27; ccepted 8 April 27 Aville online 3 My 27 Astrct Synthesis of insect nd soil vrile ptterns in spce nd time vi process models would e useful for reducing the cost of field monitoring nd for chieving improved integrted pest mngement. During 21 23, we monitored the Diprepes revitus (L.) root weevil popultion in fltwoods citrus grove contining sndy Alfisol nd lomy Mollisol in Hendry County, South Florid. Our ojectives were to exmine the multi-yer correltions of the Diprepes root weevil with soil chrcteristics, nd to develop time series model nd soil vrile-sed simple nd multivrite liner models for predicting weevil ptterns in spce nd time. Adult weevils were monitored weekly using 1 Tedders trps rrnged in 3 12 m grid. Grvimetric soil wter content (SWC), time-dominreflectory (TDR) volumetric SWC, soil orgnic mtter content (SOM), cly, snd, silt, ph, nd Mehlich-I extrctle P, K, C, Mg, Fe nd Mn concentrtions were determined for ech trp loction. Adult weevil density ws weevils m 2 cross the 3 yers, nd the weevil popultion grew exponentilly (R 2 ¼.81). Ech yer, the weevil ws positively relted to SWC, TDR, cly, SOM, nd soil Mg, C nd K concentrtions (.32oro.65, Po.5). High weevil density, SWC, SOM, nd P, K, Mg nd C levels mtched the Mollisol oundry. The utocorreltion rnges for the weevil nd soil vriles were within the soil type unit. Time series moving verge forecst of Diprepes weevil development ws relted to the 3-yer men weevil density monitored in the field (R 2 ¼.88). The SWC, TDR nd SOM-sed simple nd multivrite liner models explined 45% of the vrince in the weevil ptterns (Po.1). Time series nd soil chrcteristics-sed simple nd multivrite liner models suggest vrile rte nd less frequent spry for future mngement of the weevil in citrus production systems. r 27 Elsevier Ltd. All rights reserved. Keywords: Citrus root weevil control; Liner model; Soil insect reltions; Time series nlysis 1. Introduction Mngement of root weevil pest is often otined y repeted folir ppliction of chemicl tretments when pest densities exceed n economicl threshold tht requires tretment (Grhm et l., 23; Byers nd Cstle, 25). However, the excess use of costly pesticides cn hrm the environment (Byers nd Cstle, 25). The root weevil Corresponding uthor. Deprtment of Plnt nd Animl Sciences, Nov Scoti Agriculturl College, Truro, P.O. Box 55, NS, Cnd B2N 5E3. Tel.: ; fx: E-mil ddress: hli@nsc.c (H. Li). Diprepes revitus (L.) is serious pest of citrus in Florid. Diprepes dult weevils re citrus lef feeders nd femles deposit egg msses glued in the citrus tree cnopies (Grhm et l., 23; McCoy et l., 23). Htching neontes fll onto the soil nd their lrve re soilinhiting root predtors (Li et l., 24). Diprepes lrve feed on citrus tree roots nd grow in the soil. Growth of Diprepes lrve could e n increse of times their weight s 1-dy-old neontes within 3 dys of infesttion on citrus roots (Li et l., 26), nd times within 4 dys of infesttion on citrus roots in the greenhouse (Li et l., 27). The time required for single genertion from oviposition to dult emergence is estimted to e /$ - see front mtter r 27 Elsevier Ltd. All rights reserved. doi:1.116/j.soilio

2 H. Li et l. / Soil Biology & Biochemistry 39 (27) dys t 26 1C in the l (Lpointe, 2). Long period feeding of Diprepes lrve cn rek the resistnce of citrus roots to infection y Phytophthor spp., nd oth lrvl feeding nd disese cn led to tree decline to n unproductive stte or deth y extensive lrvl root injury (Grhm et l., 23). Typiclly, citrus growers control the Diprepes weevil popultion y four pplictions of insecticides ech yer, nd usully uniform rte is pplied over the orchrd (Li et l., 27). Soil wter content (SWC) nd texturl clss influenced plnt growth in different soils (Li et l., 22), nd soil moisture nd nutrients were relted to soil orgnism cycles, lef qulity nd herivorous insect popultion (Klironomos et l., 1999; Lower et l., 23). Since Diprepes lrve, pupe nd tenerl dults re soil-hiting, soil physicl nd chemicl chrcteristics could influence lrvl development nd dult weevil density, exmined in the environmentl controlled greenhouse studies nd in the fields t different citrus grove sites (Li et l., 24, 26, 27, ). Among the most importnt fctors tht could influence citrus tree helth sttus, SWC, soil texture, nd Mg nd C concentrtions were ssocited with Diprepes weevil sptil ptterns (Li et l., 24, 27). Air/soil temperture nd rinfll were the most influentil climte fctors ffecting Diprepes dult weevil density (Li et l., 27c). In other studies, emergence nd growth of gll-insects were only slightly ffected y environmentl vrition (Fy et l., 1996). Susurfce cly content (.2.4 m) ws relted to moisture in the upper soil lyer (.2 m) in which most nemtodes resided (McSorley nd Frederick, 22). Citrus trees were vulnerle to ttck y the Phytophthor Diprepes weevil complex in fine-textured, poorly drined soils (Grhm et l., 23). Field monitoring of insect popultions for tretment determintion could e criticl ecuse of the cost nd lor. Costs for the citrus root weevil nd the ssocited root disese could e s much s $6 h 1 (Grhm et l., 23). Some studies hve shown need to develop mthemticl models using ville field monitoring dt for predicting insect ptterns (Worner, 1991; Toin et l., 21; Crowder nd Onstd, 25; Byers nd Cstle, 25). Models were useful to define prolems, understnd the systems, nd mke predictions for purposes of insect or soil mngement (Worner, 1991; Byers nd Cstle, 25; Li et l., 26, 27). These models included time-step simultion models, non-liner degree-dy models, nd est-fit polynomil nd exponentil regression models (Toin et l., 21; Crowder nd Onstd, 25; Byers nd Cstle, 25; Li et l., 26, 27). In n cidic Mollisol, the Diprepes popultion in citrus grove ws shown to decrese significntly with incresing soil ph nd SWC, estimted using stepwise multivrite liner model (Li et l., 27). Soil units, soil oundries, soil chemicl nd physicl chrcteristics, nd interpoltion techniques were useful for ddressing environmentl concerns in production systems (Alphen Vn nd Stoovogel, 2; Li et l., 22, 24; Fox et l., 24). The development of these kinds of soil-chrcteristics tools hs een the forces of the reserch on integrted pest mngement of the Diprepes root weevil in Florid. New developments hve included delineting mngement zones, mpping soil fctors, nd quntifying soil nd Diprepes weevil sptil correltion rnges (Li et l., 24, 25, 27). Citrus growers need regulr soil testing to determine fertiliztion rtes for tree mngement. If the temporl ptterns of multi-yer Diprepes dult popultions cn e correlted to soil physicl nd chemicl chrcteristics, then these soil vriles could e useful for developing simple or multivrite models for weevil control purposes. We hypothesized tht if the Diprepes root weevil distriution ptterns were ssocited with time nd soil vriles, then mthemticl equtions derived from their correltions in susequent yers would e useful for predicting future Diprepes weevil ptterns in time nd spce. Our ojectives were to (i) exmine multi-yer sptil ssocition processes of Diprepes root weevil vriility with soil wter, texture, SOM, ph, nd mcro nd micronutrients nd (ii) to develop time series model nd soil chrcteristics-sed simple nd multivrite liner models to estimte future Diprepes dult weevil dynmics in spce nd time for weevil control. Mthemticl models could then e comined with soil unit mngement zones, environmentl mpping, nd utocorreltion nlysis for improving mngement of the root weevil. 2. Mterils nd methods 2.1. Soil nd citrus trees t the study site A 3-yer study of the Diprepes dult popultion vrition with time nd spce ws conducted in fltwoods citrus (Citrus sinensis (L.) Os.) grove in Hendry County ( N, W), South Florid, during The grove consisted of Hmlin ornger trees on Swingle citrumelo rootstocks (Citrus prdisi Mcfd Poncirus trifolit (L.) Rf.). Across the study site, there were two soil types, Boc snd nd Choee fine sndy lom (Fig. 1), formed in thick eds of sndy nd lomy mrine sediments (USDA-NRCS, 23). Boc snd zoned etween Choee fine sndy lom (Fig. 1). The Boc soil consisted of deep, poorly drined, modertely permele soil with light snd on the surfce, nd rown sndy lom susurfce overlying limestone. The Boc snd ws clssified s Lomy, Siliceous, Superctive, Hyperthermic Arenic Endoqulfs Alfisol (USDA-NRCS, 23). The Choee soil consisted of deep, poorly drined, slowly permele soil, nd ws lck sndy lom on the surfce over sndy cly susurfce. The Choee lom ws clssified s Fine-Lomy, Siliceous, Superctive, Hyperthermic Typic Argiquolls Mollisol (USDA-NRCS, 23). Due to low elevtion in the depression, the Boc

3 2438 ARTICLE IN PRESS H. Li et l. / Soil Biology & Biochemistry 39 (27) Adult weevil nd soil ssessments Fig. 1. Soil type oundry, soil units (Boc snd, Alfisol; Choee fine sndy lom, Mollisol) nd Diprepes trps (n ¼ 1) under Swingle rootstock tree cnopy. snd nd Choee lom were poorly drined nd the Boc snd hd very low wter holding cpcity (USDA-NRCS, 23). The citrus trees, plnted in 1992, were in two-row eds with 3 8 m tree spcing. A dringe furrow for evcuting surfce wter ws necessry for every four rows of trees. The trees hd een infested y Diprepes root weevils during the 6 yers prior to the eginning of the study. During the study period, the trees received regulr grove cre including irrigtion, fertiliztion nd pest control. Typiclly, tree irrigtion ws sed on rin ptterns, nd the irrigtion rte ws usully 87 L tree 1 h 1 using microsprinklers. Fertiliztion ws typiclly t the rtes of 22 N, 44 P nd 22 K kg h 1 with four equl pplictions ech yer using stndrd mixture of (N P K). No lime ws pplied. The pest tretment involved sprys of Sevin 8S (Byer Crop Science, Reserch Tringle Prk, NC) with four uniform pplictions per yer (ech ppliction per seson) sed on the regionl recommendtion. The fruit yield in the grove ws etween 36 nd 5 Mg h 1. Wether dt t the site were otined from Florid Automted Wether Network (FAWN, University of Florid). The.6-m nnul ir temperture (ir temperture sensor instlled t.6 m ove the ground) during the study period verged C, close to the 3-yer verge, 22. 1C. The.1-m nnul soil temperture (soil temperture sensor instlled t.1 m soil depth) verged C, which ws 2.4 1C higher thn the ir temperture. The 2-m totl rinfll (rin guge instlled t 2 m ove the ground) vried etween 1137 nd 129 mm, lso close to the 3-yer verge, 1216 mm. Ech yer 3% of rinfll occurred in the spring, nd 6% of the rinfll ws from July to Septemer. There ws no significnt difference in nnul ir temperture or totl rinfll during the 3 yers. The Diprepes dult popultion ws monitored weekly using 1 modified pyrmidl Tedders trps s descried in McCoy et l. (23). Trps were plced ner tree trunks, 12 m prt, long the tree ed in 3 12 m grid pttern (Fig. 1). The weevil monitoring re ws 2 7 m in the northern lock nd 1 m 7 m in the southern lock. The weevils were monitored weekly from April to Decemer (39 weeks) in 21, Jnury to Decemer (52 weeks) in 22, nd Jnury to Septemer (36 weeks) in 23. Trp geo-positions were determined using Grmin GPS12 system (Grmin Interntionl, Olthe, KS). Soil t ech trp ws smpled in Octoer 23. A composite soil smple ws tken t the.3 m depth. Soil smples were ir-dried. Volumetric SWC t the.15 m depth ws mesured using Scout TDR proe (Spectrum, Plinfield, IL). Grvimetric SWC ws determined using soil dried t 1 1C in the oven using the method descried in Li et l. (22). The use of two methods in the SWC mesurements ws to test if the TDR quick mesurements were relile compred to the grvimetric SWC mesurements, time consuming method. Soil texturl clss ws nlyzed using the hydrometer method, nd soil chemicl chrcteristics were determined for ph-h 2 O (m/v, 1:1), SMP-uffer ph, soil orgnic mtter (SOM) y comustion, nd the Mehlich-I extrcted mjor nd minor ctions (P, K, Mg, C, Mn nd Fe) y inductively coupled rgon plsm emission spectrophotometer (Horwitz, 2). Ction exchnge cpcity (CEC) ws determined using the eqution CEC ¼ (K/78+C/4+Mg/24)+Fctor, where Fctor ¼ (8 ph uffer ) 8(Horwitz, 2) Dt nlysis, mpping nd forecsting We exmined the temporl nd sptil vriility of Diprepes root weevil popultion nd their correltions with environmentl soil chrcteristics using their monthly men nd weekly men dt cross the 3 yers. Descriptive sttistics nd correltion were done using PROC UNIVARIATE nd PROC CORR procedures (SAS Institute, 199). Homogeneity of vrince of dtsets ws verified using the Brtlett test, nd normlity nd residul distriution of dt sets were confirmed using PROC UNIVARIATE (SAS Institute, 199). The ANOVA for monthly mens of Diprepes root weevil ws done using PROC GLM. Multiple comprisons of mens were done using LSMEANS sttement for post hoc Tukey test to otin honestly significnt differences (SAS Institute, 199). For semivriogrm nlysis we used PROC VARIOGRAM (SAS Institute., 1996). Soils, trees nd weevils were mpped using ArcMp 9.1 (Environmentl Systems Reserch Institute Inc, Redlnds, CA). Bsed on the constnt nd liner reltionships etween Diprepes weevil popultion nd soil chrcteristics cross the 3 yers, simple nd multivrite liner models were determined using PROC GLM (SAS Institute, 199) for

4 H. Li et l. / Soil Biology & Biochemistry 39 (27) estimting future dynmicl ptterns of Diprepes weevil popultion relted to soil chrcteristics. Using the moving verge forecst model (SAS Institute, 1993), we estimted the future Diprepes popultion pttern ginst time (t) s the verge of the lst N monitoring of the underlying time series, which were the 3-yer mens of the weekly Diprepes field monitoring dt. The simple unweighted moving verge model ws descried y the eqution s follows: Di tþ1 ¼ Di t þ Di t 1 þ Di t 2 þþdi t j, (1) N where Di t+1 is the forecst for the Diprepes root weevil for future period (week), Di the 3-yer men of weekly monitoring dt of Diprepes root weevil popultion, t the numer of weeks, j the totl of consecutive numer of weeks of monitoring, nd N is the moving verge intervl of the period (week). We used N ¼ 2 in the moving verge forecst estimtions. We used PROC EXPAND (SAS Institute, 1993) to generte new time series of weekly Diprepes weevil popultion y computtion of the moving verge of the originl series (3-yer men of weekly Diprepes weevil monitoring dt in 21, 22 nd 23). The stndrd errors (S.E.) of the unweighted moving verge forecst dt were lso estimted. 3. Results 3.1. Three-yer sptil nd temporl ptterns of Diprepes root weevil A totl of 962, 945 nd 549 Diprepes dult weevils were trpped in 21 (April Decemer), 22 (Jnury Decemer) nd 23 (Jnury Septemer), respectively. The men nd stndrd devition (S.D.) of dults per 3 12 m 2 (per trp monitoring re), were similr in the first 2 yers (Tle 1). The smple vrince ws 8, 73 nd 31, which ws proportionl to dult weevil density cross the 3 yers. The 3-yer men weevil density ws dults per 3 12 m 2 (or weevils m 2 ). The highest density ws 38 dults per 3 12 m 2 (or weevils m 2 ) in 21. Monthly men root weevil popultion showed trend to decrese cross the 3 yers (24.6, 18.2 nd 15.3 dult weevils per trp in 21, 22 nd 23, respectively). Differences in monthly men Diprepes popultion were significnt in 21 (ANOVA; F ¼ 12.63; d.f. ¼ 8, 3; Po.1), in 22 (ANOVA; F ¼ 4.17; d.f. ¼ 11, 4; Po.4), nd in 23 (ANOVA; F ¼ 2.43; d.f. ¼ 8, 27; Po.43). The post hoc Tukey test showed tht the honestly significnt difference (HSD) ws 25.8 weevils per month in 21, 35.8 weevils per month in 22 nd 18.6 weevils per month in 23. The weekly weevil popultion peked in the second week of My in 21 (13 dults) nd in the lst week of April in 22 (112 dults), s shown the timing nd vritions of weevil density per trp (Fig. 2). Tle 1 Descriptive sttistics of weekly Diprepes root weevil popultion monitored in 21, 22 nd 23, grvimetricl soil wter content (SWC), time-domin-reflectory volumetric wter content (TDR), cly, snd, silt, soil orgnic mtter content (SOM), nd Mehlich-I extrctle nutrient vriles determined in 23 (n ¼ 1) Vrile Men S.D. Min. Mx. Kurtosis Skewness CV Di Di Di SWC TDR Snd Cly Silt SOM CEC ph P K Mg C Mn Fe CV: coefficient of vrition in %. Weekly Diprepes dult popultions in 21, 22 nd in 23, respectively. SWC, grvimetric soil wter content (kg kg 1 ); TDR, volumetric soil wter content (m 3 m 3 ); snd, cly, silt (g kg 1 ); orgnic mtter content (g kg 1 ); CEC (Cmol kg 1 ); nd P, K, Mg, C, Mn nd Fe (mg kg 1 ). Weekly density of Diprepes root weevil (dults trp -1 ) Week of yer Fig. 2. Temporl ptterns of weekly density (men nd S.E., n ¼ 1) of Diprepes root weevil dult popultion in 21 (A), 22 (B), nd 23 (C). Diprepes root weevil density ppered prolonged, grdul decrese trend from June to Decemer in 21 (Fig. 2A). However, it showed quick decrese pttern

5 244 ARTICLE IN PRESS H. Li et l. / Soil Biology & Biochemistry 39 (27) from lte summer in 22 (Fig. 2B). The outreks of dult weevils in the spring were likely relted to the increse of ir nd soil temperture. The.6-m ir temperture incresed y C to rech C, nd soil temperture incresed y C to rech C from Jnury to April, which my hve contriuted to the outrek of the dult weevil. Peks of the weevil density in the spring were not relted to rinfll. Only the weekly peks of weevil popultion in lte summer (August nd Septemer) occurred with high weekly rinfll ( mm), nd the weekly weevil popultion ws strongly correlted with the weekly rinfll during this period (r ¼.91). Sptilly, weevil popultion ws more undnt in the est nd south thn other res cross the field ech yer (Fig. 3). The higher weevil density ws found in the Mollisol soil, nd the interpolted res of high weevil density were limited to the Mollisol (Choee lom) nd some trnsition res cross the Alfisol (Boc snd) during the 3 yers (Fig. 3). Although high weevil density res chnged loctions ech yer, the weevil distriution ws not skewed, s shown y the very smll kurtosis vlues ( ) in Tle 1 (kurtosiso3, the threshold of skew distriution). The weevil density ws significntly different etween soil types (Fig. 4A). Per 3 12 m 2 (per trp re) the weevil density ws 14.5, 15.6 nd 9.9 weevils (n ¼ 57) in the Mollisol ginst 6.1, 5. nd 2.3 weevils (n ¼ 43) in the Alfisol in 21, 22 nd 23, respectively. The Mollisol (Choee lom) hd significntly higher weevil density thn in the Alfisol (Boc snd) in 21 (Po.1, HSD ¼ 2.41 weevils), in 22 (Po.4, HSD ¼ 2.43 weevils) nd in 23 (Po.65, HSD ¼ 1.77 weevils) Sptil ptterns of soil chrcteristics Among the soil vriles, the distriution of silt content, nd C nd K concentrtions were positively skewed (kurtosis , Tle 1) The Alfisol (n ¼ 43) nd Mollisol (n ¼ 57) contined little cly nd silt (Fig. 4B). Both soils contined significntly higher snd content with 92 g kg 1 in the Alfisol nd 888 g kg 1 in the Mollisol (Po.192), close to the verge snd content in Florid citrus soil (94 g kg 1 ). The soils were slightly cidic (6.37.7, Tle 1) ut the vlue ws in the rnge of optimum soil ph for citrus production (ph ). There ws no ph difference for the two soils (Fig. 4C). Both soils were very poor in SOM, ut the SOM vlue ws more thn two times higher in the lomy Mollisol (14.5 mg g 1 ) thn the sndy Alfisol (Po.1, Fig. 4C). Grvimetricl SWC nd volumetric TDR wter content were higher in the Mollisol (Po.15, Fig. 4D). Both soils were poor in P, K, Mg nd Mn ut not in Fe. As lom, the Mollisol hd significntly higher concentrtion for ll the Mehlich-I extrctle nutrients thn the sndy Alfisol (Fig. 4E nd F). The C concentrtion hd the highest S.D. nd the highest rnge mong ll the soil vriles (Tle 1) nd C level ws three times higher in the Mollisol (1766 mg kg 1 ) thn in the Alfisol (52 mg kg 1 ). The Mg concentrtions were low ut different (44 mg kg 1 in Alfisol nd 122 mg kg 1 in Mollisol, Po.1). As result, the C/Mg rtios in these soils were very high (12/1 14/1). The interpolted sptil ptterns of soil physicl nd chemicl vriles mtched soil-type oundries. Higher grvimetricl SWC nd volumetric TDR wter content, SOM, Mg, K nd P were distriuted within the lomy Mollisol (Fig. 5), which were comprle to the Diprepes weevil distriution ptterns cross the 3 yers (Fig. 3) Correltions etween Diprepes root weevil nd soil vriles Monthly density of Diprepes dult weevil ws correlted t the 1 monitoring trps ech yer (.47oro.63, Tle 2). The weevil density ws correlted with grvimetric SWC, volumetric TDR, snd, cly, SOM, CEC, P, K, Mg nd C cross the 3 yers (Tle 2). For other soil vriles, the weevil ws ssocited with soil ph in 21, soil Fe in 22, nd soil Mn in 23. The monthly mens of Diprepes root weevil popultion ws ssocited with ll mesured soil physicl nd chemicl vriles except soil ph nd silt content (Tle 2). Soil vriles were correlted with ech other except for silt nd ph (.28oro.98, Tle 3). As the most dynmic vrile in the soil, wter content (oth grvimetric SWC nd volumetric TDR) were significntly correlted to snd, cly, SOM, CEC, P, K, Mg, C nd Fe (Tle 3). The Fig. 3. Interpolted sptil ptterns of Diprepes dult root weevil density (dults per 3 12 m 2 ) in 21 (A), in 22 (B), nd in 23 (C).

6 H. Li et l. / Soil Biology & Biochemistry 39 (27) Diprepes dults SOM (g kg -1 ) or CEC (Cmol kg -1 ) P,K or Mg (g kg -1 ) A Aflisol (Boc snd) c c d Mollisol (Choee lom) Di 1 Di 2 Di 3 Cly Silt D C E ph SOM CEC SWC TDR P K Mg Mn Fe B F Clyor silt (g kg -1 ) Mn or Fe (mg kg -1 ) SWC (kg kg -1 ) or TDR (m 3 m -3 ) Fig. 4. Men nd S.E. of Diprepes weevil density in 21 (Di1), 22 (Di2) nd 23 (Di3) (A); texture (B); ph, soil orgnic mtter (SOM) nd ction exchnge cpcity (CEC) (C); soil wter content (SWC) nd (TDR) (D); soil P, K nd Mg (E); nd soil Mn nd Fe (F) in Alfisol nd Mollisol. Ech r, n ¼ 57 for Boc snd (Alfisol) nd n ¼ 43 for Choee lom (Mollisol). Post hoc Tukey test honestly significnt differences (HSD, ¼.5) re: Di1 ¼ 2.41 dults, Di1 ¼ 2.43 dults, Di1 ¼ 1.77 dults, cly ¼ 7.87 g kg 1, silt ¼ 7.87 g kg 1,pH¼.33, SOM ¼ 1.38 g kg 1, CEC ¼ 1.97 Cmol kg 1,SWC¼.12 kg kg 1, TDR ¼.23 m 3 m 3,P¼ 5.83 mg kg 1,K¼ 9.38 mg kg 1,Mg¼ mg kg 1,Mn¼.54 mg kg 1 nd Fe ¼ 2.51 mg kg 1. Fig. 5. Interpolted sptil ptterns of grvimetric soil wter content (kg kg 1 ) (A), cly content (g kg 1 ) (B), soil orgnic mtter content (g kg 1 ) (C), Melich-I extrctle soil Mg (mg kg 1 ) (D), K (mg kg 1 ) (E) nd P concentrtion (mg kg 1 ) (F).

7 2442 ARTICLE IN PRESS H. Li et l. / Soil Biology & Biochemistry 39 (27) correltions of SOM nd Mg with ll soil vriles were strong except with soil ph nd silt. The correltion etween soil C nd CEC (r ¼.98, Tle 3) reveled the importnce of C concentrtions mong the nutrients in these slightly cidic Alfisol nd Mollisol. Correltion coefficients of soil vriles y soil type (Mollisol or Alfisol) were similr to these for the whole site s shown in Tle 2. By importnce of the regression Tle 2 Correltion etween weekly men Diprepes root weevil density in 21, 22, 23, nd 3-yer weekly men Diprepes root weevil density relted to grvimetricl soil wter content (SWC); time-domin-reflectory volumetric soil wter content (TDR); soil texture (snd, cly nd silt); orgnic mtter content (SOM); ph, ction exchnge cpcity (CEC); nd mcro nd minor soil nutrients (P, K, Mg, C, Mn nd Fe) Vriles Di1 Di2 Di3 3-yer Di Person correltion coefficient (r) Di2.63 ** 1 Di3.47 **.56 ** 1 3-yer Di.88 **.86 **.77 ** 1 SWC.37 **.52 **.42 **.51 ** TDR.36 **.47 **.39 **.48 ** Snd.34 **.34 **.33 **.4 ** Cly.38 **.52 **.55 **.56 ** Silt.11ns.1ns.3ns.5ns SOM.44 **.55 **.55 **.6 ** PH.23 *.4ns.11ns.17ns CEC.38 **.57 **.54 **.57 ** P.23 **.35 **.29 **.34 ** K.42 **.53 **.55 **.58 ** Mg.49 **.65 **.53 **.65 ** C.32 **.52 **.48 **.5 ** Mn.28 **.26 **.14ns.28 ** Fe.14ns.32 **.19ns.24 * Diprepes root weevil popultion in 21, 22, 23, nd 3-yer totl popultion (3-yer Di). n ¼ 1. ns, * nd ** : non-significnt nd significnt t proilities Po.5 nd Po.1, respectively. reltionships (highest R 2 vlues) mong the soil vriles, SOM (g kg 1 ) nd Mg concentrtion (mg kg 1 ) would e estimted using SWC (kg kg 1 ) or TDR (m 3 m 3 ), descried s follows: SOM ¼ 4974:8SWCþ 1242:8 ðr 2 ¼ :56; Po:1; n ¼ 1Þ, SOM ¼ 7438:4TDR 4377:9 ðr 2 ¼ :43; Po:1; n ¼ 1Þ, Mg ¼ 965:2SWCþ ðr 2 ¼ :48; Po:1; n ¼ 1Þ, Mg ¼ 546:7TDRþ 3871 ðr 2 ¼ :43; Po:1; n ¼ 1Þ. The semivrigrm for the Diprepes weevil vried etween 4.8 nd 17.1 in 21, in 22 nd in 23, which ws proportionl to the weevil density cross these yers. The semivriogrm for the weevil tended to increse from est to west cross the grove, nd the utocorreltion rnge for the weevil (6 m) ws within the interpolted distriution pttern of the weevil shown in Fig. 3. The semivriogrms for SWC, TDR, cly, SOM, Mg, C nd K lso incresed from est to west nd their utocorreltion distnce ws etween 6 nd 9 m with specific ptterns (semivriogrm grph not shown) Exponentil growth model nd moving verge model From the strt of the yer to the popultion pek in the spring, the cptured dult Diprepes weevils showed n exponentil pttern ech yer. Incresing until the popultion pek (within the first weeks), the growth of the weevil popultion (Di) with time (t, week) ws descried ð2þ ð3þ ð4þ ð5þ Tle 3 Liner correltions of grvimetricl soil wter content (SWC); time-domin-reflectory volumetric soil wter content (TDR); snd, cly, silt, orgnic mtter content (SOM); ph; ction exchnge cpcity (CEC); nd mcro nd microsoil nutrients (P, K, Mg, C, Mn nd Fe) SWC TDR Snd Cly Silt SOM ph CEC P K Mg C Mn Fe Person correltion coefficient (r) SWC 1 TDR.86 ** 1 Snd.34 **.38 ** 1 Cly.67 **.67 **.48 ** 1 Silt.9ns.6ns.78 **.17ns 1 SOM.75 **.66 **.42 **.73 **.4ns 1 ph.11ns.3ns.2ns.2ns.4ns.22ns 1 CEC.72 **.7 **.48 **.72 **.3ns.81 **.19ns 1 P.39 **.33 **.26 **.39 **.2ns.4 **.17ns.3 ** 1 K.63 **.6 **.43 **.62 **.5ns.72 **.34**.61 **.52 ** 1 Mg.68 **.66 **.48 **.77 **.1ns.84 **.16ns.76 **.41 **.76 ** 1 C.64 **.64 **.45 **.63 **.6ns.71 **.34 **.98 **.21ns.49 **.64 ** 1 Mn.9ns.8ns.1ns.17ns.2ns.28 *.54 **.8ns.19ns.35 **.5 **.21ns 1 Fe.28 **.34 **.32 **.3 **.14ns.28 **.67 **.57 **.5ns.8ns.28 *.69 **.22ns 1 n ¼ 1. ns, * nd ** : non-significnt nd significnt t proilities Po.5 nd Po.1, respectively.

8 H. Li et l. / Soil Biology & Biochemistry 39 (27) y the exponentil equtions s follows: 21 : Di ¼ 7:747 e :1333t ðr 2 ¼ :72; Po:1; n ¼ 6Þ, 22 : Di ¼ 8:2465 e :1461t ðr 2 ¼ :7; Po:1; n ¼ 17Þ, 23 : Di ¼ 3:259 e :1557t ðr 2 ¼ :54; Po:5; n ¼ 14Þ. The exponentil growth of the Diprepes weevil popultion showed the est fit y the 3-yer men popultion (R 2 ¼.81, Po.1, n ¼ 17, Fig. 6). The moving verge model forecst using Eq. (1) demonstrtes tht the future temporl ptterns of the Diprepes weevil popultion would e highly vrile with time, comprle to the field oservtion ptterns shown y the 3-yer men weekly Diprepes dt (Fig. 7A). Ech point in the 3-yer field time series dtset is the men of monitoring dt from 39 weeks 1 trps in 21, 52 weeks 1 trps in 22, nd 36 weeks 1 trps in 23. The field weekly men is from n ¼ 2 1 for Jnury Mrch, n ¼ 3 1 for Mrch Septemer, nd n ¼ 2 1 for Septemer Decemer. The moving verge forecst vries etween (rnge ) weevils, which is very close to the men nd S.D. ( weevils) of the 3-yer field dtset. The forecsted pek, with lg time step of 1 week compred to the fieldmonitored pek, exhiited smoother chnge with time steps thn the 3-yer field dtset (Fig. 7A). The other smller forecsted peks lso show the weevil undnce vritions in lte summer. The S.E. of the moving verge forecst dt vried etween.3 nd 17 weevils, nd the highest S.E. follows the yerly pek in erly spring (Fig. 7A). When plotted ginst the 3-yer men field dt, the regression shows tht the forecst dt re strongly relted to the multi-yer field monitoring dt (R 2 ¼.88, Fig. 7B). Diprepes dults Di = e t R 2 =.81 P < Week of yer Fig. 6. Exponentil growth pttern of Diprepes root weevil popultion from the strt of the seson to the yerly pek in the spring. t: time in weeks. ð6þ ð7þ ð8þ Diprepes weekly dults Forecst weekly Diprepes (Di) dults Week of yer Di Forecst =.873 Di Monitored R 2 =.88 3-yr men Forecst SE of forecst yr weekly men of field monitored Diprepes (Di) dults Fig. 7. Moving verge model forecst of development ptterns of Diprepes dult weevil popultion nd the 3-yer men Diprepes dult popultion monitored in the grove (A) nd regression reltionship of the forecst dt nd the field monitoring dt (B) Soil chrcteristics-sed simple nd multivrite liner soil-diprepes models Using the 3-yer men of weekly Diprepes root weevil popultion cptured in the 1 trps, the prmeters of the est-fit models (highest R 2 ) for the Diprepes vrile were SWC, cly, SOM nd Mg concentrtion (Fig. 8). All the regression lines showed trend to increse with incresing SWC, cly, SOM nd Mg concentrtions. There ws more pronounced increse of weevil numer with higher SOM nd Mg concentrtion (.36oR 2 o.44) with smller root men squre errors (RMSE, Fig. 8). The simple or polynomil regression showed significnt reltionship etween the TDR nd weevil cross the 3 yers (.17oR 2 o.32, Po.1, equtions not shown). By including ll significnt physicl prmeters (SWC, cly nd snd) or significnt chemicl prmeters (SOM, K nd Mg) into stepwise multivrite liner models to estimte the size of the Diprepes weevil popultion, the model coefficient of determintion incresed (R 2 ¼.37 nd R 2 ¼.46), long with smller RMSE (Tle 4). All the estimte prmeters nd intercepts were significnt (Po.1).

9 2444 ARTICLE IN PRESS H. Li et l. / Soil Biology & Biochemistry 39 (27) yr men Di prepes dults 6 Di=88.335SWC R 2 =.29 A 4 P<.1 RMSE =5.47 weevils Grvimetric soil wter content (SWC, kg kg -1 ) Di=.1296Cly R 2 =.32 P<.1 RMSE = 5.23weevils B Cly content (Cly, g kg -1 ) yr men Di prepes dults 3-yr men Di prepes dults Di=.6845SOM R 2 =.36 P<.1 RMSE = 5.6 weevils C Di=.795Mg R 2 =.44 P<.1 RMSE = 4.89 weevils Soilorgnic mtter content (SOM, g kg -1 ) Soil Mg concentrtion (Mg, mg kg -1 ) D yr men Di prepes dults Fig. 8. Regression reltionship of 3-yer men weekly Diprepes dult weevil (Di), grvimetric soil wter content (SWC) (A), cly content (B), soil orgnic mtter content (SOM) (C), nd soil Mg concentrtion (D). RMSE: model root men squre error. Tle 4 Soil physicl nd chemicl chrcteristics-sed multivrite liner models for estimting Diprepes root weevil density popultion Multivrite liner models R 2 RMSE F P Soil physicl chrcteristics-sed model eqution Di ¼ SWC Cly o.1 Di ¼ SWC.3646 Snd o.1 Di ¼ SWC Cly.2329 Snd o.1 Soil chemicl chrcteristics-sed eqution Di ¼ SOM ph o.1 Di ¼ SOM+.672 K o.1 Di ¼ SOM Mg K o.1 Soil physico-chemicl chrcteristics-sed eqution Di ¼ SWC Cly SOM Mg K Di ¼ TDR+.198 Cly SOM Mg K o o.1 Di: 3-yer men Diprepes weevil dt (n ¼ 3 1, yer trp); SWC: grvimetricl soil wter content; TDR: time-domin-reflectory volumetric soil wter content nd SOM: soil orgnic mtter content Soil grvimetricl wter content, SWC (kg kg 1 ); cly (g kg 1 ); snd (g kg 1 ); soil orgnic mtter, SOM (g kg 1 ); ph, K nd Mg concentrtions (mg kg 1 ); RMSE: Root Men Squre Error. 4. Discussion 4.1. Soil wter content, cly, snd, SOM, Mg nd Diprepes weevil reltions The significnt correltions etween the 3-yer weekly men of Diprepes root weevil, SWC, TDR, cly, snd, SOM, Mg, C nd K vriles in the slightly cidic Alfisol nd Mollisol (Tle 2) suggested tht the correltions etween the dult weevil nd soil vriles were constnt from yer to yer, nd tht their correltions were not due to chnce. One of the explntions for the influence of environmentl soil chrcteristics on dult weevil popultions would e tht SWC nd texture would ffect survivl of Diprepes lrve (Li et l., 26, 27, ) nd thus, dult weevil popultions. In citrus grove with strongly cidic Mollisol (ph 4.8), 1 yer of Diprepes dult weevil ws relted to soil Mg nd C (Li et l., 24). In nother citrus grove with ner neutrl Spodosol (ph 6.6), 2 of 3 yers of Diprepes dult weevil ws ssocited with snd, SWC, ph nd Mg (Li et l., 27). The results of this study further support the ide tht weevil ptterns would

10 H. Li et l. / Soil Biology & Biochemistry 39 (27) e ssocited with prticulr soil chrcteristics where re the citrus trees on which the weevils feed (Li et l., 24, 26, 27). Differences in cly, snd nd SOM would cuse vriility in soil ertion, nd wter nd nutrient vilility (Li et l., 22, 25, 26) to influence citrus tree sttus, nd therefore these vriles were mong the most importnt soil prmeters ssocited with Diprepes weevil ptterns (Tle 2). Better ertion in sndy soil would fvor lrvl survivl (survivl of Diprepes lrve ws 76 85% in sndy soil ginst only 58 64% in lomy soil, Li et l., 26) nd thus, dult density should e higher in the sndy soil. However, our results showed the opposite with lower weevil density in the sndy Alfisol thn in the lomy Mollisol (Fig. 2). An expliction would e the poor wter holding Alfisol ws too dry (SWCo.4 kg kg 1, Fig. 4D), nd there ws no enough moisture for lrvl survivl. In other studies, cteri, fungi, nemtodes, ph, moisture nd SOM, ech hd unique distriution pttern (Klironomos et l., 1999) ut lrvl pupl weight ws not influenced y soil wter vilility (Lower et l., 23). Also, nemtode numers were greter in the surfce lyer of plots with 35% susurfce cly thn in plots with 3% susurfce cly (McSorley nd Frederick, 22). The strong influence of soil moisture on the dult popultion in these slightly cidic Alfisol nd Mollisol ws shown y the significnt regression reltionship of Diprepes vs. SWC nd TDR (Fig. 8). Soil wter nd Diprepes weevil were highly vrile (CV %, Tle 1), therefore, these two vriles were correlted with ech other. The higher SWC nd TDR in the lomy Mollisol thn in the sndy Alfisol (Fig. 4D) ws ecuse of its higher cly content (Fig. 4B) nd higher SOM (Fig. 4C). Soil orgnic mtter holds wter nd contins nutrients nd thus, SWC nd Mg nd C concentrtions were high in the Mollisol. The reltionship of SWC nd SOM in this slightly cidic (ph 6.3, Tle 1) Mollisol ws comprle to the results found in strongly cidic (ph 4.8) Mollisol in nother citrus grove, reported in Li et l. (24). Soil ph hs een mong the most importnt vriles relted to the emergence of Diprepes weevils from strongly cidic Mollisol (Li et l., 25) nd to the density of Diprepes dults in ner-neutrl Spodosol in citrus groves (Li et l., 27). However, soil ph ws correlted with the weevil in only 1 yer (21) in these slightly cidic Mollisol nd Alfisol (Tle 2). The lck of correltion etween ph nd the multi-yer Diprepes dult popultion could e ecuse soil ph hd little vrition s shown y the smll S.D. (.7 units) nd smll CV (11.8%) in these slightly cidic Alfisol nd Mollisol (Tle 1). Also, the other difference ws tht the Mg concentrtion in the slightly cidic Alfisol nd Mollisol were only 2 4% of the Mg level in the strongly cidic Mollisol nd the ner neutrl Spodosol (Li et l., 27). The resons of the low Mg concentrtion in these slightly cidic Alfisol nd Mollisol deserve more future study Impliction of the models for controlling Diprepes root weevil The outrek of Diprepes dult weevils from the strt of the yer (mid-ferury) to the pek in the spring (April My) exhiited n exponentil trend of insect growth (Fig. 6). The growth of popultion ws exponentil in theory when popultions were in the initil growth phses t the strt of the seson when competition nd dmge-induced plnt stress should hve less influence (Byers nd Cstle, 25). Our dt showed tht the outreks of soil-inhiting Diprepes root weevil could occur etween April nd My when soil tempertures incresed from C in Ferury to C in April. Insect growth nd plnt functions re regulted y temperture. Ech species, whether plnt, lrv, or n dult weevil is dpted to grow est over certin minimum tempertures nd essentilly ceses growth t its mximum temperture (Mttson nd Hck, 1987; Li et l., 27c). The exponentil eqution (R 2 ¼.81, Fig. 6), otined with the 3-yer men of weevil monitoring dt, suggested the est timing of insecticide ppliction ws when the weevil numers re t their highest in the spring (lte April). Models proly would e dequte for specific sitution in predicting popultions, their dmge nd control costs (Byers nd Cstle, 25). For prcticl mngement, our moving verge forecst model (Fig. 7), estlished using the 3-yer weekly men of field monitoring dt, would e useful for predicting future development of the weevil popultion cross period of yer. The model hs generted the new series y computing moving verges of the originl series monitored cross the 3 yers. The moving verge model removed sesonl nd irregulr vrition to show the smoothed trend ptterns (Fig. 7), which quntified the vriility (growth, pek nd decrese) of weevil development for mking mngement decisions. For exmple, historiclly this grove hs een spryed with four pplictions of insecticides ech yer with one ppliction in ech seson. However, such equl timing of insecticide pplictions would not e efficient sed on the weevil temporl pttern (Fig. 2). The forecst trend (Fig. 7) suggests tht insecticides should e pplied in the spring, in the summer, nd erly in the fll. Also, higher rtes of insecticides should e pplied in the spring, nd lower rtes should e pplied in the summer nd in the fll. Such rtes need to e further determined in future study. The sptil pttern of weevils with soil units (Fig. 2) lso suggests tht insecticide pplictions should e vrile not only in time ut lso in spce. The weevil density ws high in the lomy Mollisol (Fig. 2) nd therefore higher rte of insecticides should e pplied in the Mollisol re. The sndy Alfisol would require smller concentrtion of insecticides ecuse of the lower weevil popultion density (Fig. 2). A site-specific rte of insecticide pplictions should e more logicl nd pproprite thn n uniform rte for the whole grove. In ddition, the Mollisol

11 2446 ARTICLE IN PRESS H. Li et l. / Soil Biology & Biochemistry 39 (27) oundry is likely suitle reference for delineting mngement zones. As shown in Fox et l. (24), soil line technique defining reltionships of soil chrcteristics nd vegettion indices would provide mens for directing systems mngement. Also, interfcil oundries of soil properties nd soil units identified using interpoltion techniques were suitle entities for mngement in production systems (Alphen Vn nd Stoovogel, 2; Li et l., 25). Controlling the root weevil using the interpolted ptterns (Fig. 3) should e more prcticl nd less costly. Becuse of the correltion etween root weevil, soil wter, texture nd nutrients for the whole grove (Tle 2), it ws not necessry to estlish soil vrile-sed models for ech soil type. The SWC, TDR, cly, SOM, Mg nd K concentrtions were high in the lomy Mollisol, thus the estimtions of weevil numers y the simple or multivrite liner equtions (Tle 4) should e high for the lomy Mollisol. The multiple liner models hve incresed the model predictive power (R 2 ) compred to the simple liner models (Tle 4). More sptil vriles were included nd thus, more vritions in the dt were explined in the multiple liner models. However, from prcticl point of view, simple liner models re more comprehensive in showing the reltionship etween two vriles. These simple liner models re esier to understnd, more prcticl, nd less costly to put into prctice in predicting nd controlling the outcome of pest popultion in the future (Li et l., 27). Also, there will e need of further exmintion of correltion etween Diprepes root weevil, soil N, microil iomss C nd nemtode levels in the soil. These vriles re importnt to tree root sttus nd lrvl survivl. Future study will lso include the development of independent dtsets from similr sites for vlidtions of our Diprepes root weevil time series forecst model nd SWC nd SOM-sed simple nd multivrite liner models. Models re often incorported in decisionmking frmework (Worner, 1991; Toin et l., 21; Li et l., 26, 27). Model predictions of fungi infesttions y finding the est-fitting prmeters (plots of soil moisture nd reltive humidity), were close to the 3-yer field oservtions (Weseloh, 22). The development nd resistnce to crop rottion of western corn rootworm popultion were lso dequtely predicted using prmeters of popultion density nd initil llele frequency in time-step model (Crowder nd Onstd, 25). Since citrus growers need regulr soil testing to determine soil physicl nd chemicl conditions for tree fertiliztion purposes, soil chrcteristics-sed models would e useful for forecsting future Diprepes weevil ptterns in ny specific site for reducing lor cost for weevil control. Our exponentil growth model (Fig. 6), moving verge forecst (Fig. 7) nd soil chrcteristics-sed simple nd multivrite models (Tle 4), hve the implictions for vrile rte nd less frequent sprys to contriute to pesticide risk reduction. 5. Conclusions The reltionships etween time, soil physicl nd chemicl vriles nd multi-yer Diprepes root weevil dynmic ptterns in the sndy Alfisol nd lomy Mollisol, yielded insights for development of time series model nd soil chrcteristics-sed models for future mngement of citrus root weevil. The correltions of multi-yer Diprepes root weevil nd soil vriles were the sis for estlishing the process model nd the regression models. Soil wter could e criticl to sustining productivity of ecosystems in res with high rinfll nd low elevtion. As result, SWC ecme n importnt component relted to Diprepes weevil popultion in these slightly cidic Alfisol nd Mollisol. The Diprepes root weevil time series model nd soil chrcteristics-sed simple nd multivrite liner models hve the impliction in timing of efficient tretment pplictions efore the outreks of soilinhiting insect pest. The model predictions hve the potentil for less frequency of sprying from excess use of costly pesticides tht cn hrm the environment, nd for reducing field insect monitoring tht is time consuming. With site-specific mngement sed on soil nd lndscpe chrcteristics, these simple nd multivrite liner models could e pprecited to put into prctice for pest control in the future. It ws suggested tht using field pest monitoring dt nd esily mesured soil chrcteristics such s TDR to crete site-specific mthemticl models could e useful for pest mngement through estimtes of pest dynmicl ptterns in spce nd time. Comining time series nd environmentl soil vriility sed models to predict temporl nd sptil pest ptterns would e useful for reducing the cost of field monitoring nd for site-specific mngement of the pest. These models hve implictions for site-specific vrile rtes nd less frequent sprys to lower environmentl pressure nd costs from insecticides y conventionl pplictions. Acknowledgments We thnk Florid Citrus Production Reserch Advisory Council for finncil support nd In Jckson for technicl ssistnce. References Alphen Vn, B.J., Stoovogel, J.J., 2. A function pproch to soil chrcteriztion in support of precision griculture. Soil Science Society of Americ Journl 64, Byers, J.A., Cstle, S.J., 25. Arewide models compring synchronous versus synchronous tretments for control of dispersing insect pests. Journl of Economic Entomology 98, Crowder, D.W., Onstd, D.W., 25. 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