Influences of fertilization on Aphis gossypii and insecticide usage

Transcription

1 JEN 129(2) doi: /j Ó 25 Blckwell Verlg, Berlin Influences of fertiliztion on Aphis gossypii nd insecticide usge A. Chu 1, K. M. Heinz 1 nd F. T. Dvies Jr 2 1 Deprtment of Entomology, Texs A&M University, College Sttion, TX, USA; 2 Deprtment of Horticulturl Sciences, Texs A&M University, College Sttion, TX, USA Ms. received: September 16, 24; ccepted: Jnury 2, 25 Abstrct: Fertiliztion levels for ornmentl crops my influence pest popultion dynmics, crop qulity, nd pest mngement strtegy. We exmined the effect of fertiliztion on popultion growth nd within-plnt distribution of melon or cotton phid, Aphis gossypii Glover, on potted chrysnthemum, Dendrnthem grndiflor (Tzvelev). In terms of pest mngement implictions, we lso investigted the effect of fertiliztion on the number of insecticide pplictions needed to control A. gossypii on potted chrysnthemum. Popultion growth rte of A. gossypii incresed with fertiliztion levels from to 38 ppm N nd reched plteu from 38 to 488 ppm N. Incresed fertiliztion beyond 38 ppm N, 1% of the commercil stndrd, did not result in higher phid number. Aphids responded to nutrient vilbility of plnts by distributing themselves in res with higher level of nitrogen. More phids were found in the picl nd middle strt of the plnts thn the bsl strtum, which hd the lowest nitrogen content. Lef nitrogen content incresed with incresed fertiliztion level nd ws consistently higher in the picl nd middle strt thn the bsl strtum. Incresed fertiliztion from to 375 ppm N did not result in higher number of insecticide pplictions. All three insecticides (bifenthrin, kinoprene or pymetrozine) were effective in keeping the phid infesttion below pre-determined level, five phids per plnt, but pymetrozine required the lest number of pplictions. For chrysnthemum, fst-growing crop nd hevy utilizer of nitrogen, incresed fertiliztion shortened the time to flowering, which would llow growers to hrvest their crop sooner nd reduce the time for phid popultion growth. Reduction in time to hrvest could result in significnt reduction of insecticide usge by reducing the time for phid popultion growth. As result, high fertiliztion together with miniml runoff my be useful tctic to n integrted pest mngement (IPM) progrmme for mnging A. gossypii on potted chrysnthemums. Key words: Dendrnthem grndiflor, fertilizer input, insecticide ppliction, melon or cotton phid, popultion growth rte 1 Introduction In greenhouse ornmentl production, fertilizers re being extensively used to produce high-qulity crops. Frequently cited s n unwnted consequence of incresed fertiliztion is n increse in plnt nitrte nd soluble mino cids (Mengel nd Kirkby, 21), which increse plnt s nutritionl qulity nd ttrctiveness to phytophgous insects (vn Emden, 1966; Minkenberg nd Fredrix, 1989; Bentz nd Lrew, 1992; Bentz et l., 1995). Higher levels of lef nitrogen, in turn, enhnce both growth nd reproduction of herbivorous insects (Dixon, 197; Mttson, 198; Lrsson, 1989; Wring nd Cobb, 1992; Dougls, 1993; Slosser et l., 1998) nd reduce their susceptibility to some insecticides (McKenzie et l., 1995). Other studies lso show tht popultion growth rte nd development time of phytophgous insects re influenced not only by plnt nutrient levels but lso nutrient rtios (Busch nd Pheln, 1999; Jnsson nd Ekbom, 22). Even fertilizer source is found to influence ovipositionl choice of femle Bemisi rgentifolii Bellows & Perring on poinsetti by vrying the soluble nitrogen content in the phloem sp (Bentz et l., 1995). Responses by phids to fertiliztion vry gretly. Some studies report tht nitrogen fertiliztion does not ffect either phid fecundity or number. Archer et l. (1995) showed tht the number of Russin whet phid, Diurphis oxi (Mordvilko), is not influenced by nitrogen fertiliztion but is higher on field-grown, nonirrigted whet thn irrigted ones. Bethke et l. (1998) found tht the fecundity of Aphis gossypii Glover differs mong cultivrs of chrysnthemum regrdless of irrigtion or fertilizer levels. However, studies of A. gossypii on cotton show tht phid fecundity increses with incresing nitrogen fertiliztion (Rosenheim et l., 1994; Nevo nd Coll, 21). vn Emden (1966) lso showed tht reproduction of the cbbge phid, Brevicoryne brssice (L.), nd the green pech phid, Myzus persice (Sulz.), on Brussels sprout increse with incresing nitrogen fertiliztion. However, too high fertiliztion level cn be detrimentl to phids (Jnsson nd Smilowitz, 1986; Bethke et l., 1998) s well s the host plnts (Schuch et l., 1998) becuse of high slinity. One reson for the vrible results my well be tht the reltionship between phid growth nd fertiliztion my not be liner. Another

2 9 A. Chu, K. M. Heinz nd F. T. Dvies Jr reson my be tht fertilizer source nd nutrient rtio influence phid development differently. In ddition, ll these studies, with the exception of two (Archer et l., 1995; Nevo nd Coll, 21), evlute the effect of fertiliztion on individul insects within clip cges rther thn free popultions on plnts. The leves tht phids re confined on my differ in their nutrient qulity nd could drmticlly influence phid growth rte. If phids respond to nutrient vilbility within plnts, then one might expect tht the nutrient qulity of the folige would influence how phids distribute themselves within the plnts. Numerous studies hve shown tht developmentl rte nd fecundity of phids re influenced by lef ge (vn Emden nd Bshford, 1969; Wering, 1972; Jnsson nd Smilowitz, 1985). Aphid distribution on plnts lso vries with host plnt nd phid species. For exmple, Jnsson nd Smilowitz (1986) showed tht most M. persice re found on the lower leves of potto nd their popultion growth rte is lso highest on these leves. On sugr beet nd chrysnthemum, Jepson (1983) nd Wytt (1965) found tht M. persice tends to ggregte ner the growth point of the plnts. Aphis gossypii, on the other hnd, tends to remin initilly on the upper leves of chrysnthemum but eventully redistributes to lower leves (Vehrs et l., 1992). In previous study on chrysnthemum, Dvies et l. (24) showed tht lef nitrogen is higher in young nd physiologiclly mture leves thn older, bsl leves. With production griculture, environmentl concerns nd government regultions hve prompted the need to reduce point-source runoff. As result, fertilizer usge for number of ornmentl crops such s roses, poinsettis, nd hydroponiclly grown chrysnthemum hs been modified (Kgeym et l., 1991; Cbrer et l., 1993; Rose nd White, 1994). However, strtegies for judicious use of fertilizers tht mintin plnt mrketbility, minimize phid popultion growth, nd reduce pesticide usge re needed. A better understnding of the influence of fertiliztion not only on pest popultions but lso on pesticide usge my form the foundtion for the development of reduced-input crop mngement prctices. In this study, we used A. gossypii nd chrysnthemum, Dendrnthem grndiflor (Tzvelev) cv. ÔChrmÕ, s our experimentl system. Melon or cotton phid, A. gossypii, is one of the mjor pests of greenhouse-grown chrysnthemum (Furk nd Vedjhi, 199; Vehrs et l., 1992; Guldemond et l., 1994; Storer nd vn Emden, 1995). Our two objectives were: (1) to determine the effects of fertilizer input on both the growth nd withinplnt distribution of A. gossypii on chrysnthemum nd (2) to exmine the combined effects of fertiliztion nd insecticidl input on the control of A. gossypii on potted chrysnthemum. To ddress these objectives, we investigted: (1) the effect of medium to high fertiliztion on A. gossypii bundnce, (2) the effect of low to stndrd fertiliztion on A. gossypii bundnce, (3) the effect of fertiliztion on popultion growth rte nd within-plnt distribution of A. gossypii under greenhouse conditions, nd (4) the effect of fertilizer input on the number of insecticide pplictions needed to control phid popultions on potted chrysnthemum. 2 Mterils nd Methods 2.1 Plnt, fertilizer nd insects To produce potted chrysnthemum for our studies, we followed the culturl prctices recommended to commercil growers (Yoder Brothers Inc., 21). A soilless potting mix (Sunshine Mix no. 1; Sun Gro Horticulture, Cnd Ltd., Bellevue) ws used s growing medi. Rooted chrysnthemum cuttings were trnsplnted into pots (15.5 cm in dimeter, 14.5 cm in depth; ITML Horticulturl Products Inc., Brntford, ON, Cnd), with four cuttings per pot. Chrysnthemum require elevted nd blnced levels of nitrogen nd potssium for proper vegettive growth (Crter, 1992). To mximize pplicbility to chrysnthemum growers, wtersoluble, commercilly vilble nd complete fertilizer [Peters Professionl Pet-lite specil, (15N-6.7P-14.1K); Scotts-Sierr Horticulturl Products Compny, Mrysville, OH, USA] ws used s the source of nutrients. The fertilizer used provides 53% N in nitrte form, 2.4% N in mmonicl form nd 26.1% N in ure form. This formultion is recommended by propgtors to reduce lef yellowing nd increse longevity (Yoder Brothers Inc., 21). The recommended fertilizer rte for pulse or periodic feeding of potted chrysnthemum, bsed on nitrogen, is 35 4 ppm N (Scotts-Sierr Horticulturl Products Compny); therefore, we used 375 ppm N s the stndrd level (1%) for our studies. The mount of phosphorous nd potssium in 375 ppm N fertilizer solution is 175 nd 354 ppm, respectively. Fertiliztion begn right fter trnsplnttion. Plnts were fertilized twice week nd wtered s needed between fertiliztions. Depending on the fertiliztion levels, 2 ml of reverse-osmosis-treted tp wter (for no fertiliztion) or fertilizer solution (for the other fertiliztion levels) ws pplied to ech pot. When there ws cm of new growth on plnts, we pinched ech plnt bck to seven lterls. When nother cm of new growth occurred fter the pinch, we pplied dminozide, plnt growth regultor (B-Nine WSG; Uniroyl Chemicl Compny Inc., Middlebury, CT, USA), to ll pots t the concentrtion of 35 ppm to reduce internode elongtion (Yoder Brothers Inc., 21). Aphids used in the studies were obtined from n A. gossypii colony estblished originlly with individuls collected from chrysnthemum grown in reserch greenhouses t Texs A&M University in College Sttion, Texs. The colony ws mintined in the lbortory t 26 C, 45% reltive humidity (RH), nd under 11 : 13 h (light : drk) (L : D) photoperiod on chrysnthemum nd periodiclly ugmented with individuls collected from nturlly infested chrysnthemum grown in experimentl greenhouses t the university. 2.2 Effect of medium to high fertiliztion levels on A. gossypii We hypothesized tht phid bundnce would increse with incresed host plnt qulity. We mnipulted host plnt qulity by mnipulting fertiliztion cross medium to high fertiliztion rnge ( ppm N) nd determined its influence on phid bundnce. We tested five fertiliztion levels: 75, 188, 281, 375 nd 488 ppm N which is 2, 5, 75, 1 nd 13% of the stndrd level. Two hundred cuttings were trnsplnted into 5 pots. We used complete rndomized design with 1 replictions per tretment with individul pots serving s replictes. The plnts were mintined in growth chmbers t 24 C dy/2 C night, 75% RH. The photoperiod ws 16 : 8 h (L : D) for pproximtely 3 weeks nd then switched to 11 : 13 h (L : D) for the durtion of the experiment to induce flower production. Ó 25 Blckwell Verlg, Berlin, JEN 129(2) doi: /j

3 Fertiliztion nd Insecticide use of A. gossypii 91 On the dy fter dminozide ppliction, when the plnts were pproximtely 4 weeks old, five pterous dults of A. gossypii (6 7 dys old) were trnsferred with cmel s hir brush to the picl region of the plnts in ech pot. We subsequently visully counted ll phids on ech pot t weekly intervls. The experiment ws terminted when pterous phids were found on the bench, wy from the pot. Aphid counts were trnsformed to their nturl logrithms nd nlysed using repeted-mesures two-wy nov tests (SPSS Inc., 2) with fertiliztion level nd growth chmber s the min effects. The Greenhouse Geisser djustment ws used to correct for sphericity (Hnd nd Crowder, 1996). Tukey s honestly significnt difference (Tukey s HSD) test ws used to determine significnce between pirs of men vlues. 2.3 Effect of low to stndrd fertiliztion levels on A. gossypii The previous study ssessed phid responses to fertiliztion level rnging from medium to high. We reduced the rnge of fertiliztion levels in this study in n ttempt to identify response inflection point. Thus, we tested five fertiliztion levels:, 19, 38, 75 nd 375 ppm N which is, 5, 1, 2 nd 1%, respectively, of the stndrd level. We used the sme experimentl protocol nd sttisticl nlyses s our lst experiment, except tht there were only six replictions (pots) per tretment. 2.4 Effect of fertiliztion on A. gossypii under greenhouse conditions We exmined the effect of fertiliztion levels on A. gossypii bundnce nd within-plnt distribution on chrysnthemum under greenhouse conditions tht pproximted commercil production in Texs, USA. We hypothesized tht phid bundnce would increse with incresed fertiliztion nd phid within-plnt distribution would vry mong fertiliztion levels. The experimentl design ws similr to the previous experiments with number of modifictions. We tested five fertiliztion levels:, 19, 38, 75 nd 375 ppm N. The number of replictions (pots) ws 12 per fertiliztion level. We enclosed individul greenhouse benches with 285 cm long 94 cm wide 17 cm high cges constructed with PVC frmes nd covered with Reemy Ò polyester (Reemy, Inc., Old Hickory, TN, USA) to prevent other insects from contminting our experiments. To exmine the within-plnt distribution of A. gossypii, we divided the plnts in ech pot into three strt: picl (picl meristem nd two newly unfurled leves), middle (region between picl nd bsl region where physiologiclly mture leves re) nd bsl (bsl post-physiologiclly mture leves from the oldest remining two to three lterls just bove the soil line). We rndomly selected six pots per fertiliztion level nd inoculted them with phids s described before. We visully counted ll phids in ech strtum on ech pot t 5-dy intervls insted of weekly intervls. To confirm the effect of fertiliztion levels on host plnt qulity, we kept the remining pots (six per fertiliztion level) free of phids for the durtion of the experiment. At the end of the experiment, five leves were rndomly tken from ech plnt strtum in ech pot. We oven-dried the leves t 8 C for 24 h. Nitrogen content in the lef tissue were nlysed using Micro-Dums Combustion Anlysis (Anlyticl Chemistry Lbortory, Institute of Ecology, University of Georgi, Athens, GA, USA). The experiment ws conducted from 23 October to 12 December 21. Temperture nd reltive humidity inside the enclosed benches were monitored for the durtion of the experiment with HOBO Ò H8 Pro Series dt loggers (Onset Computer Corportion, Bourne, MA, USA) recording t 4-h intervls (dily men ± SE; ±.51 C nd 61.9 ± 1.76% RH, n ¼ 52 dys). Dily temperture nd reltive humidity fluctutions were 7.92 ±.6 C nd ± 2.49% RH (men ± SE, n ¼ 52 d). Dy length during this period t College Sttion (TX, USA) (longitude W96.3, ltitude N3.6 ) ws clculted from the dt on sunrise nd sunset provided by the Astronomicl Applictions Deprtment (U.S. Nvl Observtory, Wshington, DC, USA) (dily men ± SE; 1.61 ±.4 h). Aphid counts were trnsformed to their nturl logrithms nd nlysed using repeted-mesures two-wy nov tests with fertiliztion level nd bench s min effects. The Greenhouse Geisser djustment ws used to correct for sphericity. We estimted the popultion growth rte (r) of A. gossypii using the following eqution: r ¼ lnðn xþ1=n x Þ ; ð1þ t where N x is the popultion size t time x, N x+1 the popultion size t time x + 1 nd t the difference in dys between time x + 1 nd x. For exmple, the overll popultion growth rte ws clculted using N x the popultion size t the strt of the experiment, N x+1 the popultion size t the end of the experiment, nd t the durtion of the experiment (2 dys). Popultion growth rte between two consecutive smpling dtes, e.g. between dy 5 nd 1, ws clculted using N x the popultion size t dy 5, N x+1 the popultion size t dy 1, nd t the smpling intervl (5 dys). One-wy nov ws used to nlyse the effect of fertiliztion on the overll popultion growth rte. Tukey s HSD test ws used to determine significnce between pirs. In ddition, repeted-mesures one-wy nov test ws used to nlyse the effect of fertiliztion on popultion growth rtes between smpling dtes. Aphid within-plnt distribution ws first tested with log-liner model test to determine the degree of ssocition between smpling dte, fertiliztion level, nd plnt strt. Becuse of significnt three-wy interction between the three fctors, G-test of independence for multiwy tble, often clled R C test of independence (Sokl nd Rohlf, 1995) were used to test the effect of fertiliztion level on phid within-plnt distribution for ech smpling dte. In ll cses, G-vlues were djusted with Willim s correction. Lef nitrogen content ws nlysed using Scheirer Ry Hre two-wy nov of rnks test with fertiliztion level nd plnt strt s min fctors (Sokl nd Rohlf, 1995). The Gmes nd Howell method ws used to determine significnt differences between pirs. 2.5 Effect of fertiliztion on insecticides usge for controlling A. gossypii We tested whether the number of insecticidl pplictions needed to suppress phid popultions vries with the level of fertiliztion pplied to the host plnts. We predicted tht A. gossypii bundnce would increse with incresed fertiliztion; consequently, greter numbers of insecticidl pplictions would be needed to suppress the infesttions. In this experiment, we exmined the interctive effects of three fertiliztion levels (, 75 nd 375 ppm N) nd three insecticides currently registered for phid control on ornmentls (bifenthrin, kinoprene nd pymetrozine) on popultions of A. gossypii infesting chrysnthemum grown in the greenhouse. The three insecticides were selected for their different modes of ction. Bifenthrin (Tlstr Ò ; FMC Corportion, Ó 25 Blckwell Verlg, Berlin, JEN 129(2) doi: /j

4 92 A. Chu, K. M. Heinz nd F. T. Dvies Jr Phildelphi, PA, USA) is pyrethroid nd contct insecticide. Kinoprene (Enstr II Ò ; Wellmrk Interntionl, Schumberg, IL, USA) is n insect growth regultor tht lso hs systemic properties. Pymetrozine (Endevor Ò ; Syngent Crop Protection, Inc., Greensboro, NC, USA) is systemic insecticide tht cts s feeding inhibitor. We used 3 3 fctoril rndomized design with 1 replictions (pots) per combintion. Three hundred nd sixty rooted chrysnthemum cuttings were trnsplnted into 9 pots. The experiment ws conducted from 9 Jnury to 2 Mrch 23. Temperture nd reltive humidity inside the greenhouse were monitored for the durtion of the experiment with HOBO Ò H8 Pro Series dt logger (Onset Computer Corportion) recording t 4-h intervls (dily men ± SE; ± 2.55 C nd ± 5.88% RH, n ¼ 71 dys). Dily temperture nd reltive humidity fluctutions were 8.7 ±.96 C nd ± 2.53% RH (men ± SE, n ¼ 71 dys). Dy length during this period t College Sttion (longitude W96.3, ltitude N3.6 ) ws clculted from the dt on sunrise nd sunset provided by the Astronomicl Applictions Deprtment (dily men ± SE; ± 1.32 h). Similr to the previous experiments, five pterous dults of A. gossypii (6 7 dys old) were trnsferred to the picl region of the plnts in ech pot on the dy fter dminozide ppliction. We llowed the phids to settle nd reproduce on the plnts for 7 dys to simulte n erly phid infesttion nd visully counted the number of live phids on ech pot t weekly intervls. Tolernce for insect presence nd dmge is extremely low for ornmentl potted plnts. We used 2 phids per pot (five phids per plnt) s our ction threshold to determine if insecticidl pplictions were needed. Aphids were detectble but not conspicuous t this density. Whenever the number of phids of pot exceeded 2, we pplied folir tretment of the ssigned insecticide to the pot. Pots were removed for insecticidl tretment nd returned to their originl loction fter tretment. We followed the recommended rte on the product lbel nd pplied bifenthrin t rte of 1.56 ml/l, kinoprene t rte of 1.29 ml/l, nd pymetrozine t rte of.19 g/l. Tretment sprys were pplied t 414 kp using Solo Ò 15.1-l cpcity bckpck spryer (Model no. 475; Solo Inc., Newport News, VA, USA) equipped with stndrd djustble hollow cone spry hed. Insecticides were pplied to upper nd lower lef surfces until runoff. We terminted the experiment when the flowers of plnts receiving 375 ppm N were fully open. The plnts were 1 weeks old t the time of flower opening. Numbers of insecticidl pplictions ws nlysed using two-wy nov tests nd followed by Tukey s HSD test to determine significnce between pirs of men vlues. 3 Results 3.1 Effect of medium to high fertiliztion levels on A. gossypii The number of phids did not vry with fertiliztion levels rnging from 75 to 488 ppm N (repeted mesures two-wy nov: F 4,34 ¼.73, P ¼.99) (fig. 1). We showed tht incresed fertiliztion did not result in higher phid infesttion. There were neither significnt tretment effect nor significnt interction between smpling dte nd tretment effect (repetedmesures two-wy nov: F 12,12 ¼.415, Greenhouse Geisser djusted P ¼.928). Therefore, the Men number of phids per pot () (b) ppm N 75 ppm N d phid popultion growth rte did not differ significntly mong the fertiliztion levels. Although we detected significnt chmber effect (repeted-mesures two-wy nov: F 2,34 ¼ 16.63, P <.1) nd lso significnt interction between smpling dte nd chmber effects (repeted-mesures two-wy nov: F 6,12 ¼ , Greenhouse Geisser-djusted P <.1), the bsence of significnt interction between smpling dte, chmber, nd fertiliztion suggested tht the overll pttern of influence ws similr (repeted-mesures two-wy nov: F 24,12 ¼.841, Greenhouse Geisser-djusted P ¼.651) cd bc b Dy Dy Fig. 1. Men number of Aphis gossypii per pot t weekly smpling intervls (dy) on chrysnthemum treted with different fertiliztion levels. Grph A represents weekly phid bundnce for the medium to high nitrogen rnge: 75, 188, 281, 375 or 488 ppm N (n ¼ 1, except for 281 ppm N, n ¼ 9). Grph B represents weekly phid bundnce for the low to stndrd nitrogen rnge:, 19, 38, 75 or 375 ppm N (n ¼ 6). Different letter(s) bove the brs indicte significnt differences between fertiliztion levels, pooled cross smpling dtes, t P.5 s determined by repeted mesures two-wy nov (Grph A) or repeted mesures one-wy nov (Grph B), bsed on ln-trnsformed men vlues, nd followed by Tukey s honestly significnt difference test. Untrnsformed men vlues re presented Ó 25 Blckwell Verlg, Berlin, JEN 129(2) doi: /j

5 Fertiliztion nd Insecticide use of A. gossypii Effect of low to stndrd fertiliztion levels on A. gossypii c bc We found neither significnt chmber effect (repetedmesures two-wy nov: F 1,2 ¼.35, P ¼.854) nor significnt interction between chmber nd fertiliztion level (repeted-mesures two-wy nov: F 4,2 ¼ 1.144, P ¼.365). Therefore, we pooled the dt cross the chmbers for further nlyses. The number of phids vried with fertiliztion levels from to 375 ppm N (repeted-mesures one-wy nov: F 4,25 ¼ 12.75, P <.1). Significntly, more phids were found on plnts fertilized with 375 ppm N (men ± SE, 23.5 ± 78.7) thn on plnts fertilized with, 19 or 38 ppm N (men ± SE, 9.54 ± 2.62, 2.8 ± 5.58 nd ± 29.7, respectively) (fig. 1b). The number of phids on plnts fertilized with 75 ppm N ws not significntly different from those fertilized with either 38 or 375 ppm N (men ± SE, ± 62.49, ± 29.7, nd 23.5 ± 78.7, respectively). Furthermore, significnt interction between smpling dte nd fertiliztion level (repeted-mesures one-wy nov: F 12,75 ¼ 4.154, Greenhouse Geisser-djusted P <.1) suggested tht the rte of increse mong the fertiliztion levels ws not prllel; thereby, phid popultion growth rte differed mong fertiliztion levels. 3.3 Effect of fertiliztion on A. gossypii under greenhouse conditions We found neither significnt bench effect (repetedmesures two-wy nov: F 2,15 ¼.785, P ¼.474) nor significnt interction between bench nd fertiliztion level (repeted-mesures two-wy nov: F 8,15 ¼.646, P ¼.729). Therefore, we pooled the dt cross the benches for ll further nlyses. Similr to the previous growth chmber experiment, the number of phids lso vried with fertiliztion levels in the greenhouse (repeted-mesures one-wy nov: F 4,25 ¼ 6.652, P <.1) (fig. 2). There were fewer phids on plnts fertilized with ppm N (men ± SE, ± 24.52) thn on plnts fertilized either with 75 or 375 ppm N (men ± SE, ± nd ± 63.7, respectively). There were no significnt differences in phid number on plnts fertilized either with, 19 or 38 ppm N (men ± SE, ± 24.52, ± nd ± 45.11, respectively). The overll popultion growth rte of A. gossypii on plnts fertilized with ppm N ws lower thn those on plnts fertilized with 38, 75 or 375 ppm N (one-wy nov: F 4,25 ¼ 5.86, P ¼.2). However, the overll popultion growth rte of phids on plnts fertilized with 19 ppm N ws not significntly different from those on plnts fertilized with ppm N nor those fertilized with 38 ppm N or higher (r ¼.2 ±.1 on plnts fertilized with ppm N, r rnged from.22 to.26 on plnts treted with the other levels). We further compred the popultion growth rtes (r) ofaphis gossypii between smpling dtes nd found tht they vried with fertiliztion levels nd time (fig. 3) (repeted-mesures one-wy Men number of phids per pot ppm N 38 nov: F 4,25 ¼ 5.744, P ¼.2, F 3,75 ¼ 12.41, P <.1, respectively). However, there were no significnt interctions between fertiliztion level nd time (repeted-mesures one-wy nov: F 12,75 ¼.513, P ¼.9), which suggested tht the slopes of popultion growth rtes mong the fertiliztion levels were prllel. Our results showed tht there ws significnt threewy interction between smpling dte, fertiliztion level, nd plnt strt (G dj ¼ , d.f. ¼ 24, P <.1). A significnt three-wy interction indicted tht phid within-plnt distribution ws 19 bc b Dy Fig. 2. Men number of Aphis gossypii per pot t 5-dy smpling intervls (dy) on chrysnthemum treted with different fertiliztion levels:, 19, 38, 75 or 375 ppm N (n ¼ 6). Different letter(s) bove the brs indicte significnt differences between fertiliztion levels, pooled cross smpling dtes, t P.5 s determined by repeted-mesures one-wy nov, bsed on ln-trnsformed men vlues, nd followed by Tukey s honestly significnt difference test (repeted-mesures one-wy nov: F 4,25 ¼ 6.652, P <.1). Untrnsformed men vlues re presented Popultion growth rte (r) of Aphis gossypii ppm N 19 ppm N 38 ppm N 75 ppm N 375 ppm N Dys fter phid inocultion Fig. 3. Men popultion growth rte (r) of Aphis gossypii (+SE) on plnts fertilized with, 19, 38, 75 or 375 ppm N t ech smpling intervl: 5, 5 1, 1 15, nd 15 2 d fter phid inocultion Ó 25 Blckwell Verlg, Berlin, JEN 129(2) doi: /j

6 94 A. Chu, K. M. Heinz nd F. T. Dvies Jr influenced by fertiliztion level (G dj vlues rnge from to , d.f. ¼ 8, ll P-vlues were smller thn.1) but the degree of influence differed mong smpling dtes. Mjority of phids (>4%) were found in the bsl region of the plnts when they were fertilized with ppm N (fig. 4). With incresing fertiliztion level, more phids were found in the picl nd the middle regions of the plnts. At the time of hrvest, lef nitrogen content ws significntly different mong fertiliztion levels nd plnt strt (tble 1) (Scheirer Ry Hre test: H ¼ , d.f, ¼ 4, P <.1 nd H ¼ 1.23, d.f. ¼ 2, P ¼.6, respectively). However, there ws no significnt interction between fertiliztion levels nd plnt strt (Scheirer Ry Hre test: H ¼ 1.412, d.f. ¼ 8, P ¼.994). Regrdless of plnt strt, lef nitrogen content ws highest on plnts fertilized with 375 ppm N nd lowest on plnts fertilized either with or 19 ppm N. Plnts fertilized either with 38 or 75 ppm N hd lef nitrogen content in between these two groups (tble 1). Lef nitrogen content ws lso significntly different mong the plnt strt nd consistently higher in the picl thn the bsl region of the plnt. Lef nitrogen content in the middle region ws not significntly different from the picl region when plnts were fertilized with 75 ppm N or higher but ws significntly differed from the picl region when plnts were fertilized with 38 ppm N or lower. Percentge of A. gossypii in ech plnt strtum Dy Dy Fertiliztion tretment (ppm N) Fig. 4. Percentge of Aphis gossypii in ech plnt strtum: picl ( ), middle (h) or bsl ( ) of plnts fertilized with, 19, 38, 75, or 375 ppm N, t dy 5 nd dy 2 fter phid inocultion 3.4 Effect of fertiliztion on insecticides usge for controlling A. gossypii The number of insecticidl pplictions ws minly influenced by the type of insecticide (two-wy nov: F 2,81 ¼ , P <.1) rther thn the fertiliztion level (two-wy nov: F 2,81 ¼.362, P ¼.698), nd no significnt interction ws found between the two fctors (two-wy nov: F 4,81 ¼.658, P ¼.623). Pymetrozine, systemic insecticide, required the fewest pplictions (fig. 5) to keep the phid number below the ction threshold. Bifenthrin required more pplictions compred to pymetrozine. Kinoprene, on the other hnd, required the most pplictions; lmost double the number for pymetrozine. 4 Discussion Our studies demonstrted tht popultion bundnce of A. gossypii ws influenced by fertiliztion levels. The number of phids incresed with fertiliztion levels from to 38 ppm N nd reched plteu from 38 to 488 ppm N. Aphid popultions did not pper to benefit dditionlly from fertiliztion beyond 38 ppm N. Dvies et l. (24) confirmed tht the fertiliztion levels used for our growth chmber experiment lter plnt growth nd qulity. Plnt growth nd lef nitrogen, phosphorous, iron, mngnese, boron, nd molybdenum increses with fertiliztion levels, s do chlorophyll nd photosynthetic rtes. Numerous studies hve investigted the effects of fertiliztion on phid growth nd performnce with vrible results. For exmple, studies of individul A. gossypii on cucumber nd cotton hve shown tht body weight, body size, fecundity, developmentl rte, nd popultion growth rte re enhnced by nitrogen fertiliztion (Petitt et l., 1994; Rosenheim et l., 1994; Nevo nd Coll, 21). In contrst, Bethke et l. (1998) found tht the fecundity of A. gossypii is ffected by chrysnthemum cultivr but not irrigtion or fertilizer level. These studies focus on the effect of fertiliztion on the individul level. Our study, however, exmined the effect of fertiliztion on the popultion level. We found tht the positive response of phid popultions to fertilizer level ws not consistent cross the fertiliztion rnge evluted in this study. The significnt effects of fertiliztion on phids occur only t very low levels in chrysnthemum nd this could prtilly explin the inconsistent detection of fertiliztion effects on phid growth nd development in the literture. Guldemond et l. (1998) showed tht popultion growth rte of A. gossypii on chrysnthemum, estimted t the popultion level, vries with the developmentl stge of chrysnthemum. They found tht popultion growth rte of phids is higher on flowering plnts thn young vegettive plnts (r ¼.32 nd.27, respectively). Resource lloction, nutrition qulity, physiology nd nutrient flow of plnts kept in vegettive growth re very different from plnts tht progress from vegettive to reproductive growth (Reekie nd Bzzz, 1987; Sulnier nd Reekie, 1995). Although the popultion growth rte of A. gossypii Ó 25 Blckwell Verlg, Berlin, JEN 129(2) doi: /j

7 Fertiliztion nd Insecticide use of A. gossypii 95 Tble 1. Nitrogen content (g/kg) in lef tissues tken the picl, middle, nd bsl strt of plnts fertilized with, 19, 38, 75, or 375 ppm N 1 Fertiliztion level 2 Apicl [men (SE)] 4 Plnt strt 3 Middle [men (SE)] 4 Bsl [men (SE)] 4 Fertiliztion effect [men (SE)] (.96),A (1.21),B (.88),B (.87) (3.32) b,a (4.44) b,ab (2.67) b,b (2.21) b (1.2) b,a (1.65) b,b 3.17 (1.47) b,b 34.9 (1.39) b (2.84) b,a 46.2 (3.41) b,a (2.62) b,b 44.3 (2.18) c (.82) c,a (.69) c,a (1.69) c,b (1.69) d Plnt strt 45.2 (2.64) A 39.9 (2.99) AB (2.13) B effect [men (SE)] 6 1 An dequte rnge of nitrogen (g/kg) in lef tissue is considered to be from 45 to 6 nd deficient (severe to moderte) rnge is 15 to 3 (modified from Lunt et l., 1964). 2 Differences between men vlues within column shring the sme letter(s) re not significntly different (P.5) s determined by Scheirer Ry Hre test nd followed by Gmes nd Howell method (Scheirer Ry Hre test for fertiliztion levels: H ¼ , d.f. ¼ 4, P <.1, plnt strt: H ¼ 1.23, d.f. ¼ 2, P ¼.6, nd interctions between fertiliztion levels nd plnt strt: H ¼ 1.412, d.f. ¼ 8, P ¼.994). 3 Differences between men vlues within row shring the sme cpitl letter(s) re not significntly different (P.5) s determined by Scheirer Ry Hre test nd followed by Gmes nd Howell method (Scheirer Ry Hre test for fertiliztion levels: H ¼ , d.f. ¼ 4, P <.1, plnt strt: H ¼ 1.23, d.f. ¼ 2, P ¼.6, nd interctions between fertiliztion levels nd plnt strt: H ¼ 1.412, d.f. ¼ 8, P ¼.994). 4 Ech men nd SE is bsed on smple size of six. 5 The fertiliztion effect men vlues were clculted by pooling cross the plnt strt. Ech men nd SE is bsed on smple size of The plnt strt effect men vlues were clculted by pooling cross the fertiliztion levels. Ech men nd SE is bsed on smple size of 3. Number of insecticidl pplictions Bifenthrin Kinoprene Pymetrozine Fig. 5. Men number of insecticidl pplictions (+SE) of bifenthrin, kinoprene or pymetrozine needed to keep Aphis gossypii below the threshold of 2 phids per pot. Brs shring the sme letter(s) re not significntly different (P.5) s determined by two-wy nov followed by Tukey s honestly significnt difference test (two-wy nov for insecticidl tretments: F 2,81 ¼ , P <.1, fertiliztion levels: F 2,81 ¼.362, P ¼.698, nd interctions between the two fctors: F 4,81 ¼.658, P ¼.623) estimted in our study ws slightly lower (r ¼.26 on plnts fertilized with 375 ppm N), it ws more relistic estimte of phid popultion growth s the plnts progressed from vegettive to reproductive growth during the production cycle. Within-plnt distribution of A. gossypii ws influenced by fertiliztion level. Mjority of phids were found in the picl nd middle region thn the bsl region of most plnts except the ones tht were fertilized with ppm N. On plnts fertilized with b c ppm N, phids distributed mostly in the bsl region, opposite to the distribution pttern found on other fertiliztion levels. The pttern of distribution ws not rndom, since rndom process would yield phid numbers in proportion to lef re. Thus, under rndom null expecttion, we would expect more phids in the middle region thn the other two regions nd more phids to be found in the bsl region thn the picl region. We found higher nitrogen content in leves from both the picl nd the middle region of the plnts thn those from the bsl region. These results suggested tht phids were responding to nutrient vilble in the plnts nd distributed themselves in res with higher nitrogen content. We found tht incresed fertiliztion did not result in higher number of insecticide pplictions. Although the three insecticides were effective in keeping the phid infesttion below the ction threshold, pymetrozine required the lest number of pplictions to do so. Our greenhouse study ws bsed on totl of 9 pots. This smple size is smll reltive to commercil greenhouses tht on verge produce over 15 pots. Post hoc smple-size clcultions bsed upon Person nd HrtleyÕs (1951) power curves nd ssocited equtions (Sokl nd Rohlf, 1995) were pplied to insecticide ppliction dt to determine how mny more replictes might hve been needed to detect significnt differences mong tretments. By setting the power of the F-test t.9 in our clcultions, difference of.7 sprys per pot or greter would be sttisticlly significnt with 5229 replictes per tretment. Likewise, 1914 replictes per tretment would hve been necessry to find differences of.1 sprys per pot or greter with power of only.8. These clcultions suggest tht on lrger scle, such s on n verge production greenhouse, sttisticlly Ó 25 Blckwell Verlg, Berlin, JEN 129(2) doi: /j

8 96 A. Chu, K. M. Heinz nd F. T. Dvies Jr significnt fertiliztion effects on the number of insecticide pplictions would be distinguishble. However, our experiment ended when flowers on plnts fertilized with 375 ppm N were fully open. At tht time, flowers on plnts fertilized with 75 ppm N were just beginning to show colour nd those on plnts fertilized with ppm N were just breking out from the buds. We suspect tht dditionl insecticide pplictions would be needed to control phid infesttion on plnts grown under reduced fertiliztion becuse of longer production time due to dely in flowering. For fst-growing nd nitrogen-demnding crops such s chrysnthemum, incresed fertiliztion shortens the time to flowering. Time to flowering is crucil to growers becuse shorter production time often mens higher profit to cost rtio, fster turn over time, nd possibly fewer pesticide input. As result, incresed fertiliztion together with miniml runoff my help to improve n IPM progrm for mnging A. gossypii on potted chrysnthemum by reducing the time for phid popultion growth, which could possibly result in reduction of insecticide usge. Acknowledgements We would like to thnk Andrew Chow for thorough review of the mnuscript. Thnks lso to Crlee Klttenhof, Pete Kruter, Steve Thompson, nd Chunjiu He for technicl support. We lso thnk Yoder Brother, Inc. for dontion of chrysnthemum cuttings. Finncil support ws provided in prt by the USDA-Ntionl Reserch Inititive for Floriculturl nd Nursery Reserch, grnt nd the Americn Florl Endowment. References Archer, T. L.; Bynum, E. D. Jr.; Onken, A. B.; Wendt, C. W., 1995: Influence of wter nd nitrogen fertilizer on biology of the Russin whet phid (Homopter: Aphidide) on whet. Crop Protect. 14, Bentz, J. A.; Lrew, H. G., 1992: Ovipositionl preference nd nymphl performnce of Trileurodes vporriorum (Homopter: Aleyrodide) on Dendrnthem grndiflor under different fertilizer regimes. J. Econ. Entomol. 85, Bentz, J. A.; Reeves, J. III; Brbos, P.; Frncis, B., 1995: Effect of nitrogen fertilizer source nd level on ovipositionl choice of poinsetti by Bemisi rgentifolii (Homopter: Aleyrodide). J. Econ. Entomol. 88, Bethke, J. A.; Redk, R. A.; Schuch, U. K., 1998: Melon phid performnce on chrysnthemum s medited by cultivr, nd differentil levels of fertiliztion nd irrigtion. Entomol. Exp. Appl. 88, Busch, J. W.; Pheln, P. L., 1999: Mixture models of soyben growth nd herbivore performnce in response to nitrogensulphur-phosphorous nutrient interctions. Ecol. Entomol. 24, Cbrer, R. I.; Evns, R. Y.; Pul, J. L., 1993: Leching losses of N from continer-grown roses. Scienti Hort. 53, Crter, G. D., 1992: Potted chrysnthemums. In: Introduction to Floriculture, 2nd edn. Ed. by Lrson, R. A. Sn Diego, CA: Acdemic Press, Dvies, F. T. Jr.; He, C. J.; Chu, A.; Heinz, K. M.; Crtmill,A. D., 24: Fertility ffects susceptibility of chrysnthemum to cotton phid (Aphis gossypii): influence on plnt growth, photosynthesis, ethylene evolution nd herbivore bundnce. J. Am. Soc. Hort. Sci. 129, Dixon, A. F. G., 197: Qulity nd vilbility of food for sycmore phid popultion. In: Animl Popultions in Reltion to their Food Resources. Ed. by Wtson, A. Symposium British Ecologicl Society no. 1. Oxford: Blckwell Scientific, Dougls, A. E., 1993: The nutritionl qulity of phloem sp utilized by nturl phid popultions. Ecol. Entomol. 18, vn Emden, H. F., 1966: Studies on the reltions of insect nd host plnt III. A comprison of the reproduction of Brevicoryne brssice nd Myzus persice (Hemipter: Aphidide) on Brussels sprout plnts supplied with different rtes of nitrogen nd potssium. Entomol. Exp. Appl. 9, vn Emden, H. F.; Bshford, M. A., 1969: A comprison of the reproduction of Brevicoryne brssice nd Myzus persice in reltion to soluble nitrogen concentrtion nd lef ge (lef position) in the Brussels sprout plnt. Entomol. Exp. Appl. 12, Furk, C.; Vedjhi, S., 199: Orgnophosphorus resistnce in Aphis gossypii (Hemipter, Aphidide) on chrysnthemum in the UK. Ann. Appl. Biol. 116, Guldemond, J. A.; Tigges, W. T.; Devrijer, P. W. F., 1994: Host rces of Aphis gossypii (Homopter, Aphidide) on cucumber nd chrysnthemum. Environ. Entomol. 23, Guldemond, J. A.; vn den Brink, W. J.; den Belder, E., 1998: Methods of ssessing popultion increse in phids nd the effect of growth stge of the host plnt on popultion growth rtes. Entomol. Exp. Appl. 86, Hnd, D.; Crowder, M., 1996: Prcticl Longitudinl Dt Anlysis. London: Chpmn & Hll. Jnsson, J.; Ekbom, B., 22: The effect of different plnt nutrient regimes on the phid Mcrosiphum euphorbie growing on petuni. Entomol. Exp. Appl. 14, Jnsson, R. 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ÔGood NewsÕ. In: Plnt Anlysis nd Fertilizer Problems, vol. IV. Ed. by Bould, C., Prevot, P. nd Mgness, J. R. Humphrey, Est Lnsing, MI: Americn Society for Horticulturl Science, Mttson, W. J. Jr., 198: Herbivory in reltion to plnt nitrogen content. Ann. Rev. Ecol. Syst. 11, McKenzie, C. L.; Slosser, J. E.; Pinchk, W. E.; Crtwright, B., 1995: Effects of nitrogen on cotton phid susceptibility Ó 25 Blckwell Verlg, Berlin, JEN 129(2) doi: /j

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