Effects of plant nutrient availability and host plant species on the ...

Biochemical Systematics <strong>and</strong> Ecology 36 (2008) 505–513Contents lists available at ScienceDirectBiochemical Systematics <strong>and</strong> Ecologyjournal homepage: www.elsevier.com/locate/biochemsyseco<strong>Effects</strong> <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> <strong>and</strong> <strong>host</strong> <strong>plant</strong> <strong>species</strong> on theperformance <strong>of</strong> two Pieris butterflies (Lepidoptera: Pieridae)Shaw-Yhi Hwang * , Cheng-Hsiang Liu, Tse-Chi ShenDepartment <strong>of</strong> Entomology, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, TaiwanarticleinfoabstractArticle history:Received 14 August 2007Accepted 1 March 2008Keywords:Pieris rapae crucivoraPieris canidia canidiaHost <strong>plant</strong> <strong>species</strong>Nutrient ecologyNitrogenWaterGlucosinolatesWe assayed the interaction on the <strong>availability</strong> <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>and</strong> <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong> onthe performance <strong>of</strong> two <strong>species</strong> <strong>of</strong> Pieris butterfly. The results indicated that constant application<strong>of</strong> different levels <strong>of</strong> fertilizers to the four different <strong>host</strong> <strong>plant</strong>s resulted to an increasein their content <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s. The chemical analysis showed that the added<strong>nutrient</strong>s increased foliar nitrogen <strong>and</strong> water contents, but there was no effect on the level<strong>of</strong> glucosinolates. Larvae that fed on highly-nutritious foliage increased their growth rates<strong>and</strong> showed a shorter development period. The results <strong>of</strong> feeding trials revealed that the4th-instar larvae, which had fed on <strong>host</strong> <strong>plant</strong>s with higher levels <strong>of</strong> fertilization hada shorter duration <strong>of</strong> development, less consumption rate, higher growth rate <strong>and</strong> foodprocessing efficiency. To summarize, this research revealed that both the <strong>availability</strong> <strong>of</strong><strong>plant</strong> <strong>nutrient</strong> <strong>and</strong> <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong> can strongly influence the physiology <strong>and</strong> foliarchemistry <strong>of</strong> <strong>host</strong> <strong>plant</strong>s. Moreover, the changes <strong>of</strong> phytochemical in the <strong>host</strong> <strong>plant</strong>smay play an important role in affecting the performance (growth <strong>and</strong> food utilizationefficiency) <strong>of</strong> both <strong>species</strong> <strong>of</strong> Pieris butterflies.Ó 2008 Elsevier Ltd. All rights reserved.1. IntroductionMany secondary <strong>plant</strong> metabolites are considered as strong defense <strong>of</strong> <strong>plant</strong>s against herbivores <strong>and</strong> pathogens. The qualitative<strong>and</strong> quantitative difference in secondary metabolites among <strong>plant</strong>s is a confounding argument in the study <strong>of</strong> <strong>plant</strong>insectinteraction. Although the evolution <strong>of</strong> various defense traits is genetically based (Berenbaum et al., 1986; Adler et al.,1995; Hwang <strong>and</strong> Lindroth, 1997), the expression <strong>of</strong> such traits may be modulated by environmental factors (Bryant et al.,1983; Herms <strong>and</strong> Mattson, 1992). Physiological <strong>and</strong> biochemical changes in a <strong>plant</strong>, due to environmental factors, may alterits nutritional value for herbivores. In some cases, these <strong>host</strong> <strong>plant</strong>s’ nutritional <strong>and</strong> allelochemical changes might improvethe quality <strong>of</strong> the <strong>host</strong> <strong>plant</strong> <strong>and</strong>, therefore, can be considered beneficial to herbivores (Mattson <strong>and</strong> Haack, 1987). However,most studies have indicated various responses <strong>of</strong> herbivores against <strong>host</strong> <strong>plant</strong>s, which are environmentally induced withphytochemical changes (Waring <strong>and</strong> Cobb, 1992).Various environmental factors are considered to affect <strong>plant</strong>s’ allocation <strong>of</strong> resources to secondary metabolites (Bryantet al., 1983; Herms <strong>and</strong> Mattson, 1992). The <strong>availability</strong> <strong>of</strong> <strong>nutrient</strong>s has been considered as an important factor that influences<strong>plant</strong> growth <strong>and</strong> the allocation <strong>of</strong> defense compounds (Bryant et al., 1983; Hemming <strong>and</strong> Lindroth, 1999). The application <strong>of</strong>fertilizer is one <strong>of</strong> the primary methods <strong>of</strong> improving the <strong>availability</strong> <strong>of</strong> soil <strong>nutrient</strong>s for <strong>plant</strong>s. Studies have shown that themorphology <strong>and</strong> physiology <strong>of</strong> <strong>plant</strong>s can be influenced by the application <strong>of</strong> fertilizers. Fertilization can change growth rates<strong>of</strong> <strong>plant</strong>s, time <strong>of</strong> maturity, sizes <strong>of</strong> <strong>plant</strong> parts <strong>and</strong> the phytochemical content <strong>of</strong> <strong>plant</strong>s (Myers, 1985; Hemming <strong>and</strong> Lindroth,* Corresponding author. Tel.: þ886 4 2284 0363; fax: þ886 4 2287 5024.E-mail address: ole<strong>and</strong>er@dragon.nchu.edu.tw (S.-Y. Hwang).0305-1978/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.bse.2008.03.001

S.-Y. Hwang et al. / Biochemical Systematics <strong>and</strong> Ecology 36 (2008) 505–513 507had been cultivated in a greenhouse (25 C, 16:8 h light:dark photoperiod) for about 45 days prior to their usages for the bioassays.For the experimental bioassays, the insects were reared in a Percival growth chamber (16:8 h light:dark photoperiod)at a constant temperature <strong>of</strong> 22 C.Long-term developmental trials were conducted to assess the effects <strong>of</strong> phytochemical variations based on the <strong>species</strong> <strong>of</strong><strong>plant</strong>s <strong>and</strong> <strong>availability</strong> <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s on the development <strong>and</strong> growth <strong>of</strong> insects during the entire larval feeding <strong>and</strong> pupalstages. Feeding trials began when the eggs hatched. Every ten newly hatched larvae <strong>of</strong> each <strong>species</strong> <strong>of</strong> insect were weighed<strong>and</strong> reared in a 250 ml plastic rearing cup until they molted to second instars on the leaves from one <strong>of</strong> the 12 treatments(four <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>s three levels <strong>of</strong> fertilization). After molting to second instars, the larva <strong>of</strong> each <strong>species</strong> <strong>of</strong> insectswas individually reared until it pupated in the plastic rearing cups on leaves from one <strong>of</strong> the 12 treatments (four <strong>species</strong> <strong>of</strong><strong>host</strong> <strong>plant</strong>s three levels <strong>of</strong> fertilization). Ten individuals <strong>of</strong> P. rapae crucivora were reared for every treatment (i.e., 10 replicates/treatment 12 treatments ¼ 120 larvae) <strong>and</strong> another 8 individuals <strong>of</strong> P. canidia canidia were also reared per treatment(i.e., 8 replicates/treatment 12 treatments ¼ 96 larvae). Leaf material was changed every day to ensure freshness. Thefollowing traits were measured for each individual insect: development time from hatching to pupation <strong>and</strong> adult eclosion;pupal <strong>and</strong> adult weight; <strong>and</strong> growth rate. Each pupa was weighed one day after pupation <strong>and</strong> was enclosed in a rearing cupuntil an adult emerged. Larval duration was calculated as the time that had elapsed from egg hatching to pupation. Pupal durationwas calculated as the time between pupation <strong>and</strong> adult emergence. The individual growth rate <strong>of</strong> each larva was calculatedaccording to the method used by Gotthard et al. (1994): Growth rate ¼ [ln (pupal weight) ¼ ln (hatching weight)]/larval time; this relative growth rate indicated the mean weight gain per day. Mean <strong>and</strong> st<strong>and</strong>ard errors were calculatedfor larval weights, pupal weights, adult weights, larval duration, pupal duration <strong>and</strong> growth rate for insects, which fed on foliage<strong>of</strong> the 12 different treatments. Additional leaf material from the test <strong>plant</strong>s was also collected during the bioassay todetermine the contents <strong>of</strong> water, nitrogen <strong>and</strong> glucosinolates in the leaf.Fourth instar performance trials were conducted to evaluate the foliar quality effects on growth rates, food consumptionrates, <strong>and</strong> efficiencies <strong>of</strong> food processing on fourth instar larvae <strong>of</strong> both <strong>species</strong> <strong>of</strong> insects. First, about 150 newly hatched larvae,from each <strong>species</strong> <strong>of</strong> insects, were grown on cabbage foliage in a Percival growth chamber (16:8 h light:dark photoperiod)at a constant temperature <strong>of</strong> 22 C until they molted to fourth instars. Each assay consisted <strong>of</strong> a newly molted <strong>and</strong> weighedlarva which was placed into a rearing cup (250 ml) that contains a leaf from a <strong>plant</strong> <strong>of</strong> one <strong>of</strong> the 12 different treatments(n ¼ 12 replicates per treatment for P. rapae crucivora <strong>and</strong> 8 replicates per treatment for P. canidia canidia). Leaves werechanged every 1–2 days, or if necessary during the period <strong>of</strong> bioassay. Upon molting to fifth instars, the larvae were frozen,oven dried for a week at 50 C, <strong>and</strong> reweighed. Nutritional indices were calculated to assess insect growth, consumption, <strong>and</strong>food utilization efficiency (Hare, 1998). These indices were calculated according to the st<strong>and</strong>ard formulae for approximatedigestibility (AD ¼ (Ingestion Feces)/Ingestion), efficiency <strong>of</strong> conversion <strong>of</strong> digested food (ECD ¼ Biomass gained/(IngestionFeces)), <strong>and</strong> efficiency <strong>of</strong> conversion <strong>of</strong> ingested food (ECI ¼ Biomass gained/Ingestion) as described by Waldbauer(1968) <strong>and</strong> Hare (1998). The initial, rather than average weights <strong>of</strong> the larvae, were used to calculate relative growth rate(RGR) <strong>and</strong> relative consumption rate (RCR) (Farrar et al., 1989). The initial dry weight <strong>of</strong> test insects was estimated basedon a wet-to-dry weight conversion factor (¼0.148), determined from 10 newly molted fourth instars for both <strong>species</strong> <strong>of</strong> insect.Likewise, the initial dry weight <strong>of</strong> leaves fed to insects was also estimated by dry weight conversions using the foliagecollected from each <strong>species</strong> <strong>of</strong> <strong>plant</strong> during bioassay. Means <strong>and</strong> st<strong>and</strong>ard errors were calculated for the duration, RGR,RCR, total consumption (TC), AD, ECD, <strong>and</strong> ECI for the insects, which fed on the foliage <strong>of</strong> the 12 different treatments. Aswith the long-term feeding study, the additional leaf material from the test <strong>plant</strong>s was also collected during the bioassayfor the measurement <strong>of</strong> foliar water, nitrogen, <strong>and</strong> glucosinolate content.2.4. Foliar chemistry <strong>of</strong> <strong>plant</strong> materialsConcomitant with the insect feeding studies, extra foliage (similar leaves to those used in the bioassays, 12 samples/treatment)was collected from the <strong>plant</strong>s used in the bioassays <strong>and</strong> flash frozen in liquid nitrogen, freeze-dried, grounded, <strong>and</strong>stored in a freezer at a temperature <strong>of</strong> 20 C. Water, total nitrogen, <strong>and</strong> total content <strong>of</strong> glucosinolates were quantifiedfor each foliar sample. The content <strong>of</strong> water was determined by the difference between the wet <strong>and</strong> dry weights <strong>of</strong> leafsamples. Kjeldahl nitrogen was determined by a micro-Nesslerization technique (Lang, 1958) following acid digestion <strong>of</strong>leaf samples (Parkinson <strong>and</strong> Allen, 1975). Glycine p-toluenesulfonate (5.665%N) was used as the st<strong>and</strong>ard. Total glucosinolateswere quantified based on the determination <strong>of</strong> the glucose released after the digestion <strong>of</strong> myrosinase <strong>and</strong> subsequent deproteinization(Saini <strong>and</strong> Wratten, 1987). A glucose-peroxidase system was used with 4-aminophenazone as the oxygen acceptor.Means <strong>and</strong> st<strong>and</strong>ard errors for foliar water, total nitrogen, <strong>and</strong> total concentration <strong>of</strong> glucosinolates, for each <strong>of</strong> the treatments,were calculated.2.5. Statistical analysisDuring the bioassays, means <strong>and</strong> st<strong>and</strong>ard errors were calculated for the performance parameters (survival, duration, larvalweight, pupal weight, growth rate, consumption rate, <strong>and</strong> food utilization efficiencies) <strong>of</strong> insects <strong>and</strong> for the <strong>plant</strong> chemistry.The data were analyzed using SAS (1988) for Windows V8. Analysis <strong>of</strong> variance (ANOVA) was used to test the effects <strong>of</strong>the <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>s, <strong>availability</strong> <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>and</strong> their interaction on <strong>plant</strong> chemistry <strong>and</strong> on the measured performanceparameters <strong>of</strong> insects.

508S.-Y. Hwang et al. / Biochemical Systematics <strong>and</strong> Ecology 36 (2008) 505–5133. Results3.1. Host-<strong>plant</strong> qualityThe effects <strong>of</strong> <strong>host</strong>-<strong>plant</strong> <strong>species</strong> <strong>and</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> on the concentrations <strong>of</strong> <strong>nutrient</strong>s <strong>and</strong> nitrogen based secondarycompounds varied (Fig. 1). Nitrogen levels generally increased with the elevated concentrations <strong>of</strong> the fertilizer, wherethe level increased more than 100% in two <strong>of</strong> the <strong>plant</strong>-<strong>species</strong> (B. oleracea <strong>and</strong> R. indica), demonstrating that the <strong>availability</strong><strong>of</strong> <strong>nutrient</strong>s, differently influence the contents <strong>of</strong> nitrogen in different <strong>host</strong> <strong>plant</strong>s (a significant <strong>plant</strong> <strong>nutrient</strong> <strong>and</strong> <strong>plant</strong> <strong>species</strong>interaction effect). The water contents <strong>of</strong> two <strong>of</strong> the fertilized <strong>plant</strong> <strong>species</strong> (R. indica <strong>and</strong> C. flexuosa) were slightly higherthan that <strong>of</strong> the unfertilized <strong>plant</strong>s, where the water content also differed significantly among <strong>plant</strong> <strong>species</strong>. This indicatedthat the <strong>availability</strong> <strong>of</strong> <strong>nutrient</strong>s differently influenced the water contents in different <strong>host</strong> <strong>plant</strong>s (Fig. 1). The total level <strong>of</strong>glucosinolates, however, was only affected in the <strong>plant</strong> <strong>species</strong> treatment; total concentration <strong>of</strong> glucosinolates was 3-foldmore in foliage <strong>of</strong> B. oleracea than in the other three <strong>plant</strong> <strong>species</strong>. The effect <strong>of</strong> fertilization on the total content <strong>of</strong>Nitrogen (% dry wt.)8642High NutrModerate NutrNo NutrP valuesNutr

S.-Y. Hwang et al. / Biochemical Systematics <strong>and</strong> Ecology 36 (2008) 505–513 509glucosinolates was not significant. In addition, interactive effect <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>plant</strong> <strong>species</strong> on the total level <strong>of</strong> glucosinolatewas significant: in B. oleracea <strong>and</strong> R. indica treatments with different fertilizers had varied effects. The leaves <strong>of</strong> thefertilized <strong>plant</strong>s appeared to be a darker green in colour.3.2. Larval growth <strong>and</strong> performance trials3.2.1. Long-term developmental trialThe results indicated that the <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>s <strong>and</strong> <strong>availability</strong> <strong>of</strong> <strong>nutrient</strong>s in <strong>plant</strong>s had various effects on the performance<strong>of</strong> these two <strong>species</strong> <strong>of</strong> butterfly (Fig. 2). For P. rapae crucivora, their larval durations, pupal weights, adult weights,<strong>and</strong> larval growth rates, were significantly altered, however, by both <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> <strong>and</strong> <strong>plant</strong> <strong>species</strong> (Fig. 2). Overall,the elevated level <strong>of</strong> <strong>nutrient</strong>s decreased the larval <strong>and</strong> pupal durations. The larval duration also significantly variedamong P. rapae crucivora which was reared on foliage <strong>of</strong> different <strong>species</strong> <strong>of</strong> <strong>plant</strong>s; however, the effects <strong>of</strong> the <strong>availability</strong><strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>s on larval durations were independent <strong>of</strong> each other (no significant interaction).In addition, increased levels <strong>of</strong> <strong>nutrient</strong>s generally increased pupal weights, adult weights, <strong>and</strong> larval growth rates. Moreover,pupal weights, adult weights, <strong>and</strong> larval growth rates also varied significantly among <strong>host</strong> <strong>plant</strong> <strong>species</strong>. P. rapae crucivora thatwere reared on the foliage <strong>of</strong> the two cultivated <strong>host</strong> <strong>plant</strong>s (B. oleracea <strong>and</strong> B. campestris) were heavier (w1.5 fold) <strong>and</strong> grewfaster than those fed on the foliage <strong>of</strong> the two <strong>species</strong> <strong>of</strong> wild <strong>plant</strong>s (R. indica <strong>and</strong> C. flexuosa). However, the effects <strong>of</strong> <strong>availability</strong><strong>of</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>host</strong> <strong>plant</strong> <strong>species</strong> on pupal weights, adult weights, <strong>and</strong> larval growth rates were also independent <strong>of</strong>each other (no significant interaction). Survival rates <strong>of</strong> P. rapae crucivora, however, were not different among <strong>nutrient</strong> <strong>availability</strong>or <strong>plant</strong> <strong>species</strong> treatments.For P. canidia canidia, larval durations, pupal durations, pupal weights, adult weights, <strong>and</strong> larval growth rates, were all significantlyaltered by <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> (Fig. 2). Generally, elevated <strong>nutrient</strong> levels decreased larval durations but theeffect <strong>of</strong> <strong>nutrient</strong> <strong>availability</strong> was influenced by the <strong>host</strong> <strong>plant</strong> <strong>species</strong>. Increased <strong>nutrient</strong> levels generally increased pupalweights, adult weights, <strong>and</strong> larval growth rates. Moreover, pupal weights <strong>and</strong> adult weights also varied significantly among<strong>host</strong> <strong>plant</strong> <strong>species</strong>. The results for P. canidia canidia reared on the foliage <strong>of</strong> the two cultivated <strong>host</strong> <strong>plant</strong>s (B. oleracea <strong>and</strong>B. campestris) were similar to those for P. rapae crucivora which became much heavier (w1.4 fold) than those that fed onthe foliage <strong>of</strong> the two wild <strong>plant</strong> <strong>species</strong> (R. indica <strong>and</strong> C. flexuosa). The <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> also influenced the pupalweights but differed depending on the <strong>host</strong> <strong>plant</strong>. Moreover, the effect <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> on larval growth rateswas influenced by the <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>. Larval survival rate for this <strong>species</strong> varied significantly among <strong>plant</strong> <strong>species</strong>, thosethat fed on the foliage <strong>of</strong> B. oleracea had the lowest survival rate.3.2.2. Fourth instar performance trialResults <strong>of</strong> this performance trial indicated that <strong>host</strong> <strong>plant</strong> <strong>species</strong> <strong>and</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> had more significant effectson performance <strong>of</strong> fourth instar, P. canidia canidia than on those <strong>of</strong> P. rapae crucivora (Fig. 3). For P. rapae crucivora, theduration <strong>of</strong> the fourth instar <strong>and</strong> larval growth rate were significantly altered by <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> (Fig. 3). Overall, theelevated <strong>plant</strong> <strong>nutrient</strong> levels decreased larval duration but increased larval growth rate. Larval consumption (TC <strong>and</strong> RCR)<strong>and</strong> food utilization efficiencies (AD, ECD, <strong>and</strong> ECI) were all significantly altered by both <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> <strong>and</strong> <strong>plant</strong><strong>species</strong>. Increased <strong>host</strong> <strong>plant</strong>’s <strong>nutrient</strong> levels generally decreased fourth instar’s consumption rate <strong>and</strong> increased its food utilizationefficiencies. P. rapae crucivora reared on foliage <strong>of</strong> the two cultivated <strong>host</strong> <strong>plant</strong>s (B. oleracea <strong>and</strong> B. campestris) hadhigher (w1.5 fold) growth efficiency (ECI) than those that fed on the foliage <strong>of</strong> the two wild <strong>plant</strong> <strong>species</strong> (R. indica <strong>and</strong>C. flexuosa). In addition, the effects <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> on larval consumption rate <strong>and</strong> food utilization efficiencies were influencedby the <strong>host</strong> <strong>plant</strong> <strong>species</strong>; the effects varied among <strong>species</strong> (a significantly interactive effect).For P. canidia canidia, the duration <strong>of</strong> the fourth instar, larval growth rate, total consumption, absorption efficiency (AD),<strong>and</strong> growth efficiency (ECI) were all significantly altered by both the <strong>availability</strong> <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>plant</strong> <strong>species</strong> (Fig. 3). Ingeneral, increased levels <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s decreased the fourth instar’s consumption rate, total consumption, <strong>and</strong> increasedits growth rate, absorption efficiency <strong>and</strong> growth efficiency. The results also indicated that the effects <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong>on instar duration, larval growth rate, total consumption, absorption efficiency (AD), <strong>and</strong> growth efficiency (ECI) wereinfluenced by the <strong>host</strong> <strong>plant</strong> <strong>species</strong>; the effects varied among <strong>species</strong> (a significantly interactive effect).4. DiscussionThe results confirm that fertilization can significantly influence the phytochemical contents <strong>of</strong> the <strong>host</strong> <strong>plant</strong>s (Wolfson,1980, 1982; Myers, 1985). Changes in <strong>host</strong> <strong>plant</strong> quality, due to increased levels <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s, can influence the performance<strong>of</strong> both <strong>species</strong> <strong>of</strong> Pieris. The response <strong>of</strong> insect herbivores to phytochemical changes, however, varied among the <strong>species</strong><strong>of</strong> <strong>host</strong> <strong>plant</strong>s.4.1. Foliar chemistryLevels <strong>of</strong> foliar nitrogen typically increased from 50 w 220% under long-term fertilization (Slansky <strong>and</strong> Feeny, 1977; Myers,1985; Estiarte et al., 1994; Chen et al., 2004); thus, the overall increase <strong>of</strong> 1 w 2 folds, observed in this study, is consistent withother studies. The results <strong>of</strong> the contents <strong>of</strong> water in the leaf is also similar with earlier studies showing that soil <strong>nutrient</strong>

510S.-Y. Hwang et al. / Biochemical Systematics <strong>and</strong> Ecology 36 (2008) 505–513P. rapae crucivoraP. canidia canidiaLarval time (days)252015105P valuesNutr

S.-Y. Hwang et al. / Biochemical Systematics <strong>and</strong> Ecology 36 (2008) 505–513 511DUR (days)765432P. rapae crucivorap valuesNutr

512S.-Y. Hwang et al. / Biochemical Systematics <strong>and</strong> Ecology 36 (2008) 505–513The physiological responses <strong>of</strong> the four <strong>species</strong> <strong>of</strong> <strong>plant</strong>s to fertilization were all different from each other. Specifically, theglucosinolate content varied by 8-fold between the foliage <strong>of</strong> B. oleracea compared to those <strong>of</strong> the other three <strong>host</strong> <strong>plant</strong>s.These differences likely reflect the variations in the life history patterns among these four <strong>species</strong> <strong>of</strong> <strong>plant</strong>. The two weed <strong>species</strong>,R. indica <strong>and</strong> C. flexuosa, <strong>and</strong> the cultivated <strong>species</strong>, B. campestris are relatively short-lived <strong>and</strong> fast-growing, compared toB. oleracea. These inherent differences in its life history patterns may allow B. oleracea to have greater plasticity in response tochanges <strong>of</strong> resources such as fertilizers <strong>and</strong> water.4.2. Insect responsesThe experiment on the performance <strong>of</strong> larvae was planned to assess whether the <strong>plant</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>plant</strong> <strong>species</strong> haveinteractive effects on the performance <strong>and</strong> utilization <strong>of</strong> food by these two <strong>species</strong> <strong>of</strong> butterfly. The combined effects <strong>of</strong> the<strong>availability</strong> <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong> on the larval performance, have received relatively little consideration,while <strong>plant</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>plant</strong> <strong>species</strong>, separately, have been shown to influence the performance <strong>of</strong> insects. Variations in thedegree <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>availability</strong> were transformed into significant treatment effects on the larval performance <strong>of</strong> both<strong>species</strong> <strong>of</strong> butterfly. In general, larvae that fed on highly-nutritious foliage had increased growth rates <strong>and</strong> shorter period<strong>of</strong> development compared to those larvae that fed on low-<strong>nutrient</strong> foliage. This result is similar to our previous <strong>and</strong> otherrelated studies which showed that Pieris butterflies grew faster when fed on fertilized <strong>host</strong> <strong>plant</strong>s (Myers, 1985; Chenet al., 2004). Larvae that fed on unfertilized foliage consumed more food (higher consumption rate <strong>and</strong> longer feedingperiod); but the overall performance was poor than larvae that fed on more nutritious foliage (higher growth rate <strong>and</strong>food processing efficiencies). From a <strong>plant</strong> chemistry perspective, highly-fertilized <strong>plant</strong>s have higher nitrogen <strong>and</strong> watercontents, but have similar amount <strong>of</strong> defensive compounds (glucosinolates).The performance, <strong>of</strong> the two <strong>species</strong> <strong>of</strong> Pieris larvae, varied significantly among different <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>s. Except forbody weight, larvae did not perform best, consistently, on the cultivated <strong>host</strong> <strong>plant</strong>s. The larvae <strong>of</strong> both <strong>species</strong> <strong>of</strong> butterflygained more body weights when raised on the foliage <strong>of</strong> cultivated B. oleracea <strong>and</strong> B. campestris, which were the preferred<strong>host</strong> <strong>plant</strong>s for P. rapae crucivora; no significant difference in larval feeding <strong>and</strong> development was found among the cultivated<strong>and</strong> weed <strong>host</strong> <strong>plant</strong>s. Similar observations were found for P. canidia canidia. There is little literature mentioning the performance<strong>of</strong> Pieris butterflies among cultivated <strong>and</strong> wild <strong>host</strong> <strong>plant</strong>s. It was found that P. brassicae larvae that fed on cultivatedB. oleracea var. capitata had the highest food consumption <strong>and</strong> assimilation rates, but lowest for those that fed on the weedNasturtium montanum (Kaushal <strong>and</strong> Vats, 1983). Our current results, however, did not indicate any significant difference in<strong>host</strong>-<strong>plant</strong> suitability among different <strong>host</strong> <strong>plant</strong> <strong>species</strong> for both Pieris butterflies.The interaction between resource <strong>availability</strong> <strong>and</strong> <strong>host</strong> <strong>plant</strong> <strong>species</strong> on insect performance varied between the two Pierisbutterflies. Interaction did not occur for all the performance variables which were tested for P. rapae crucivora. Most variablesfor P. canidia canidia showed some interactions between <strong>plant</strong> <strong>nutrient</strong>s <strong>and</strong> <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>s, suggesting that interactionsbetween resource <strong>availability</strong> in <strong>host</strong> <strong>plant</strong>s <strong>and</strong> <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong>s are common.In conclusion, this research has demonstrated that <strong>availability</strong> <strong>of</strong> <strong>plant</strong> <strong>nutrient</strong> <strong>and</strong> <strong>species</strong> <strong>of</strong> <strong>host</strong> <strong>plant</strong> can strongly influencethe physiology <strong>and</strong> foliar chemistry <strong>of</strong> <strong>host</strong> <strong>plant</strong>s. Moreover, phytochemical changes in <strong>host</strong> <strong>plant</strong>s can affect the performance<strong>of</strong> these <strong>species</strong> <strong>of</strong> Pieris butterfly. More studies involving a variety <strong>of</strong> soil-fertility management methods are inprogress to address the potential <strong>host</strong> <strong>plant</strong> preferences <strong>and</strong> <strong>host</strong> <strong>plant</strong> selections by these two <strong>species</strong> <strong>of</strong> Pieris butterflies.AcknowledgementsWe thank C.M. Cheng, C.W. Tang, for their assistance in conducting bioassays, <strong>and</strong> Mr. R. Haesevoets, for his comments onthe manuscript. Two anonymous reviewers also provided valuable input to improve the manuscript. This research was fundedby a grant, NSC-91-2313-B-005-119, given to S.Y. Hwang.ReferencesAdler, L.S., Schmitt, J., Bowers, M.D., 1995. 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