Effects of coadministration of chemical insecticides with nucleopolyhedrovirus SpltNPV on the dietary intake of the common cutworm <Emphasis Type="Italic">Spodoptera litura</Emphasis> (Lepidoptera: Noctuidae)

Chemical insecticides were administered to larvae of the common cutworm Spodoptera litura (Fabricius) concomitantly with a viral insecticide containing nucleopolyhedrovirus SpltNPV, in order to decrease the level of dietary intake of the virus-infected larvae. Aqueous solutions of imidacloprid (Admire), flubendiamide (Phenix), or cartap (Padan) at non-lethal doses, together with a lethal dose of SpltNPV occlusion bodies (Hasumon-Tenteki), were prepared. The surfaces of small blocks of food were treated with the mixtures and presented to S. litura larvae for 24 h. On the following day, a new diet block was provided which had been treated with one-third or one-fourth of the initial dose of the chemical insecticide. The larvae were reared for 5 days and the level of dietary intake was recorded. The administration of flubendiamide and cartap decreased the dietary intake more strongly in virus-infected larvae than in non-infected larvae.     

Influence of incubation temperature on productivity and quality of Spodoptera litura nucleopolyhedrovirus

Mass production of baculoviruses by in vivo methods is influenced by several factors like larval age at virus treatment, virus concentration and the incubation temperature. The larval age at virus treatment and virus concentration should be synchronized to result in insect death at a fully grown larval stage to maximize the productivity. Since temperature influences both the growth of the larvae and replication of the virus, we evaluated the influence of incubation temperature on mass production of Spodoptera litura nucleopolyhedrovirus (SpltNPV) at four different temperature regimes viz., 25, 30, and 35 °C and room temperature by diet-surface contamination method. Incubation of early fifth instar larvae dosed with 3932.4 polyhedral inclusion bodies (PIB)/mm² at 25 °C enhanced the virus productivity to 6.623 × 10¹¹ PIB yield/100 inoculated larvae, while it was only 1.779 × 10¹¹ at 35 °C. The disease progression in the virus treated larvae was slow with median lethal time (LT₅₀) of 208 h at 25 °C as compared to 136 h at 35 °C. In spite of the slow death which means lower production cycles/year, the productivity/year was higher at 25 °C than at other temperatures. The SpltNPV produced at 25 °C was also found to be of superior quality in terms of low bacterial contaminants than at 35 °C. Neonate larval bioassay conducted with viruses produced at different temperature treatments revealed that they were similar in their activity and virulence. Hence our results indicate that maintenance of the SpltNPV production facility at 25 °C would enhance both the virus productivity and quality.     

Biological activity and identification of nucleopolyhedroviruses isolated from <Emphasis Type="Italic">Mythimna separata</Emphasis> and <Emphasis Type="Italic">Spodoptera litura</Emphasis> in Japan

We compared the infectivity of two nucleopolyhedroviruses (NPVs), MyseNPV G isolated from Mythimna separata (Walker) (Lepidoptera: Noctuidae) and SpltNPV S isolated from Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae). MyseNPV G was more pathogenic against M. separata than against S. litura. Although SpltNPV S was more pathogenic than MyseNPV G against S. litura, it did not infect M. separata. Restriction endonuclease (REN) analysis of viral genomic DNA revealed that the two NPVs have quite different REN profiles. Based on nucleotide sequences of the coding regions of polyhedrin, lef-8 and lef-9, SpltNPV S was closely related to other SpltNPV isolates, whereas MyseNPV G appeared to belong to the Mamestra NPV group, and was distinct from a Chinese isolate of Leucania (=Mythimna) separata NPV. The potential of MyseNPV G and SpltNPV S to control pest insects is discussed.

Effect of plant secondary metabolites on common cutworm,Spodoptera litura (Lepidoptera: Noctuidae)

The effect of various flavonoids, lectins and phenyl β‐_D‐glucoside on larval survival, weights and the activities of digestive (total serine protease and trypsin) and detoxifying (esterase and glutathione‐S‐transferase) enzymes of Spodoptera litura larvae at 7 days after treatment was studied through diet incorporation assay. Flavonoids (rutin, chlorogenic acid, quinic acid, caffeic acid, naringenin, quercitin, kaempferol, myricetin, catechin, and ferulic acid) were incorporated in artificial diet at 100, 500 and 1000 ppm, lectins: groundnut leaf lectin (GLL), concavalin A (ConA) and phenyl β‐_D‐glucoside at 1, 2 and 5 μg/mL. Flavonoids such as rutin, quercitin and kaempferol at 1000 ppm were more toxic to S. litura larvae than quinic acid, caffeic acid, naringenin, myricetin, catechin, and ferulic acid. Larval growth and development were significantly reduced in S. litura larvae fed on a diet with GLL and ConA at 5 μg/mL compared to the larvae fed at 2 and 1 μg/mL concentrations. The larvae fed on flavonoid‐treated diets showed significant reduction in serine protease, trypsin and esterase activities. The flavonoids such as rutin, chlorogenic acid, quinic acid, naringenin, quercitin, kaempferol and myricetin, and lectins, GLL and ConA can be utilized in insect control programs.     

Biological activity of Pakistani isolate SpltNPV-Pak-BNG in second,third and fourth instar larvae of the leafworm Spodoptera litura

Recently, a novel isolate of the baculovirus Spodoptera litura nucleopolyhedrovirus (SpltNPV) has been isolated from Pakistan, which is distinct from the type species SpltNPV-G2 (ICTV). Here, we examined the biological activity of this isolate (SpltNPV-Pak-BNG) in second (L2), third (L3) and fourth instar (L4) larvae of the leafworm S. litura, more specifically to measure biological properties that are relevant for use of this virus for pest control under field conditions. The median lethal dose for L2 and L3 instar larvae was similar, but significantly lower than for L4 larvae. Likewise, the survival time was similar for L2 and L3 larvae (84?h), but was significantly longer for L4 instar larvae (108?h). Thus, in terms of efficacy, S. litura L2 and L3 instar larvae are the preferred targets for S. litura control with SpltNPV-Pak-BNG in field crops in Pakistan. On the basis of our data spray regimes can be designed to control the leafworm in cotton and vegetable crops targeting L2 and L3 larvae.     

Juvenile hormone analogs greatly increase the production of a nucleopolyhedrovirus

The commercial production of baculovirus insecticides is limited by the need to produce the virus in living insects. The influence of juvenile hormone analogs (JHA) on the growth and survival of Spodoptera exigua larvae placed on treated diet in the fifth instar was examined. Weight increases observed in methoprene- and fenoxycarb-treated larvae were over three-fold greater than that of control insects, whereas other compounds resulted in lower weight gains (pyriproxyfen) or highly variable responses (hydroprene). Approximately 90% and 70% of fenoxycarb and methoprene-treated larvae, respectively, molted to a supernumerary sixth instar and attained a final weight at 8–10 days post-treatment that was approximately double the maximum weight observed in control larvae. Inoculation of fenoxycarb and methoprene-treated sixth instars with a nucleopolyhedrovirus (SeMNPV) resulted in 2.4- or 2.9-fold increases in final weights, compared to control larvae inoculated in the fifth instar. The total yield of SeMNPV occlusion bodies (OBs) per larva was 2.7- and 2.9-fold greater in fenoxycarb- and methoprene-treated larvae, respectively, compared to fifth instar controls. A significant but small increase in the yield of OBs/mg larval weight was observed in fenoxycarb-treated insects but not in the methoprene treatment. The LC₅₀ value of OBs harvested from fenoxycarb-treated insects was slightly higher than that of OBs from control insects, whereas no such difference was observed in OBs from methoprene-treated insects. We conclude that appropriate use of JHA technology is likely to provide considerable benefits for the mass production of baculoviruses.     

Cloning and structural characterization of juvenile hormone diol kinase in Spodoptera litura

Juvenile hormone (JH) is one of the key insect hormones that regulate metamorphosis. Juvenile hormone diol kinase (JHDK) is an enzyme involved in JH metabolism and catalyzes JH diol to form a polar end product, JH diol phosphate that has no JH activity. In this study, a JHDK complementary DNA (cDNA) was cloned from Spodoptera litura and the structure and expression of the gene was characterized. The cDNA was 714 base pairs in length and encoded a protein of 183 amino acids with a molecular mass of 21 kDa and an isoelectric point of 4.55. Based on the structure, three putative calcium binding motifs and guanosine triphosphate‐binding motifs were predicted in the protein. Modeling of the 3‐D structure showed that the protein consisted of eight α‐helixes linked with loops, with no β‐sheets. The gene was expressed in the epidermis, fat body and midgut of fifth and sixth instar larvae. The expression level in the epidermis was lower than in the fat body and midgut. The gene was expressed at higher levels at the early stages than in the later stages of fifth and sixth instar midgut and fat body. The results suggest that this gene may be involved in the regulation of the JH titer in larvae of S. litura.     

Hormonal control of diapause and overwintering traits in a leaf beetle, Aulacophora nigripennis

To elucidate whether Juvenile Hormone (JH) regulates physiological status in relation to diapause and cold hardiness, we investigated various physiological and biochemical changes in diapause adults of Aulacophora nigripennis after treatment with exogenous pyriproxyfen, an analogue of JH. Topical application of pyriproxyfen at high dose (≥0.05 μg) caused the diapause adults not only to consume more oxygen and mate earlier, but also to suppress enhancement of chill tolerance at 0°C and accumulation of myo‐inositol. By contrast, a lower dose of pyriproxyfen (0.01 μg) did not, suggesting that the amount of pyriproxyfen between 0.01 and 0.05 μg is a critical dose breaking both diapause and cold hardening. Pyriproxyfen‐treated post‐diapause adults lost triacylglycerols, but not glycogen, more rapidly than the acetone control. It is suggested that triacylglycerols are the main energy resource in both diapause and post‐diapause adults, but are consumed more by the latter because of their higher metabolic rate. Glycogen may be converted mainly into myo‐inositol during diapause, but consumed as an energy fuel for basal metabolism during post‐diapause development. Thus, various physiological and biochemical traits in relation to diapause and cold tolerance in this beetle may be at least in part under the control of JH.     

Chemical and biological stress factors on the activation of nucleopolyhedrovirus infections in covertly infected Spodoptera exigua

Following the consumption of baculovirus occlusion bodies (OBs), insects may succumb to lethal disease, but the survivors can harbour sublethal covert infections and may develop, reproduce and transmit the infection to their offspring. The use of different chemical and biological stressors was examined to determine whether they could be used to activate covert infections in populations of Spodoptera exigua larvae infected by the homologous nucleopolyhedrovirus (SeMNPV). Treatment of covertly infected S. exigua second instars with Tinopal UNPA‐GX, hydroxylamine, paraquat, Bacillus thuringiensis var. kurstaki crystals, spores or mixtures of crystals + spores, or a heterologous nucleopolyhedrovirus (Chrysodeixis chalcites SNPV) did not result in the activation of SeMNPV covert infections. Similarly, virus treatments involving permissive NPVs did not result in greater mortality in covertly infected insects compared with the virus‐free controls. In contrast, 0.1% copper sulphate, 1% iron (II) sulphate and 1 mg/l sodium selenite treatments resulted in 12–41% lethal polyhedrosis disease in covertly infected larvae. A greenhouse trial using copper sulphate and sodium selenite as activation factors applied to covertly infected S. exigua larvae on sweet pepper plants resulted in very low levels of SeMNPV activation (<3%). These results highlight the important roles of copper, iron and selenium in insect immunity and baculovirus‐induced disease. However, these substances seem unlikely to prove useful for the activation of covert SeMNPV infections in S. exigua larvae under greenhouse conditions.     

Biological and genetic characterization of a Pakistani isolate of Spodoptera litura nucleopolyhedrovirus

Spodoptera litura is an emerging insect pest in a wide range of crops worldwide. The insect is difficult to control because of resistance development to synthetic insecticides and emerging resistance to Bacillus thuringiensis toxins. Therefore, there is a need to develop biological control agents, preferably from an indigenous source to avoid risks associated with the importation of exotic natural antagonists. A Pakistani isolate of S. litura nucleopolyhedrovirus (SpltNPV, Baculoviridae), SpltNPV-Pak-BNG, was obtained from the field and characterized biologically and genetically, and compared to a SpltNPV reference isolate, SpltNPV-G1, thought to be of Chinese origin. The dose–mortality response (LD₅₀) of SpltNPV-Pak-BNG was not significantly different from that of the reference isolate SpltNPV-G1, but the time-to-death (LT₅₀) was significantly shorter for SpltNPV-Pak-BNG than for SpltNPV-G1. DNA restriction enzyme profiling indicated that SpltNPV-Pak-BNG and SpltNPV-G1 are different viruses. Sequence analysis of ‘ORF24’, specific for SpltNPV (and S. littoralis NPV as ORF21), and the conserved baculovirus core genes polyhedrin, DNApol, pif-2 and lef-8 confirmed that this was indeed the case and that SpltNPV-Pak-BNG is a genuine SpltNPV variant, whereas the SpltNPV-G1 isolate we used is, in fact, a SpliNPV variant, renamed to SpliNPV-G1. The newly isolated SpltNPV-Pak-BNG has the potential for development as a biocontrol agent of S. litura in Pakistan.     

A new cell line from Spodoptera exigua (Lepidoptera: Noctuidae) and its differentially expressed genes

A new cell line, designated IOZCAS‐Spex XI, was established from the pupal ovaries of Spodoptera exigua (Lepidoptera: Noctuidae) in TNM‐FH medium containing 10% foetal bovine serum. The spherical cells were predominant among the various cell types. The population‐doubling time during the logarithmic phase of growth was 81.7 h. It was confirmed that the cell line originated from S. exigua by DAF‐PCR technique. Analysis of susceptibility to baculovirus showed that the new cell line was susceptible to S. exigua nucleopolyhedrovirus (SeNPV), Autographa californica multiple NPV (AcMNPV) and slightly susceptible to S. litura NPV (SpltNPV), while not permissive to Helicoverpa armigera NPV and Hyphantria cunea NPV (HcNPV). Real‐Time PCR analysis was carried out to compare some differentially expressed genes between the cell line and the primary culture. The result showed that marked significant differences were observed in the expression of the genes of SUMO‐1 activating enzyme, BCCIP‐like protein, 10 kDa HSP, CypA, receptor for activated PKC, PDI‐like protein ERp57, ALDH, DEAD box ATP‐dependent RNA helicase‐like protein (P < 0.01), while a significant difference was obtained in the expression of GST gene between the cell line and the primary culture (P < 0.05).     

Response variability of juvenile hormone and juvenile hormone analogs in workers of the Formosan subterranean termite (Coptotermes formosanus Shiraki)

Juvenile hormone (JH) or juvenile hormone analog (JHA) can induce soldier formation in termites. However, different studies have yielded inconsistent results on the effects of JHA on soldier production in Coptotermes formosanus Shiraki. Using filter paper as the testing substrate, the effects of JH III, pyriproxyfen and methoprene on the intact filter paper left, worker mortality and presoldier formation were tested on six colonies. Our results showed that pyriproxyfen and methoprene were more repellent than JH III. No significant difference in toxicity was observed among methoprene, pyriproxyfen and JH III. JH III and pyriproxyfen did not cause workers to differentiate into presoldiers, but methoprene can induce formation of presoldiers. Colony response variability to methoprene was observed. The confirmation of the effects of JH/JHA on C. formosanus establishes the foundation for molecular studies of soldier differentiation in this species.     

Impact of greenhouse whitefly management on strawberry fruit quality

The greenhouse whitefly, Trialeurodes vaporariorum （Westwood）, is an important pest of strawberries in California, USA. The adults and nymphs feed on phloem sap of leaves to remove the photo-assimilates. The objective of this study is to test the impact of whitefly management with insecticides on strawberry fruit quality. Applications of imidacloprid, thiamethoxam, buprofezin and pyriproxyfen decreased the mean adult whitefly numbers by 2.80-, 2.17-, 1.69- and 1.39-fold, respectively, compared to the untreated control, Similarly, the mean numbers of first and second instar whiteflies were reduced 4.36-, 2.20-, 1.90- and 2.02-fold, respectively, while the mean numbers of third and fourth instars were reduced 5.48-, 2.28-, 2.71- and 1.43-fold, respectively, in plants treated with imidacloprid, thiamethoxam, buprofezin and pyriproxyfen. The mean soluble solids content in imidacloprid, thiamethoxam, buprofezin and pyriproxyfen treatments was 1.04-, 1.06-, 1.03- and 1.04-fold greater, respectively, than that in the control. The whitefly reduction enhanced the mean fruit titratable acidity by 4%-6%. Mean glucose levels in imidacloprid and thiamethoxam treatments were significantly higher than in other treatments. However, the whitefly management did not affect the mean fructose levels, lmidacloprid, thiamethoxam and pyriproxyfen treatments boosted the ascorbic acid levels by up to 4%. The impact of whitefly management on strawberry fruit nutrition and antioxidant capacity is discussed.     

Elevated CO2 and temperature alter development and food utilization of Spodoptera litura fed on resistant soybean

Effects of elevated atmospheric CO₂ (elevated CO₂ vs. ambient CO₂) and temperature (+0.67–0.79°C vs. ambient temperature) on the developmental life cycle of Spodoptera litura and the food utilization of the fourth‐instar larvae fed on soybean (resistant cultivar Lamar vs. susceptible landrace JLNMH) grown in open‐top chambers were studied from 2013 to 2015. The results indicated that: (i) compared with ambient CO₂, elevated CO₂ significantly prolonged the duration of larva and pupa, and adult longevity; significantly decreased the pupation rate, pupal weight, fecundity, the relative growth rate (RGR), efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD); and increased the relative consumption rate (RCR) and approximate digestibility (AD). (ii) Compared with ambient temperature, elevated temperature significantly shortened the duration of larva and pupa; significantly decreased the pupal weight; and increased the RGR, RCR, ECD and ECI. (iii) Compared with the susceptible soybean accession JLNMH, the resistant soybean cultivar Lamar significantly prolonged the duration of larva and pupa; significantly decreased the pupation rate, pupal weight, adult longevity, fecundity and RGR, RCR and AD; and increased the indexes of ECD. (iv) At elevated temperature, S. litura fed on resistant vs. susceptible cultivars showed opposite trends in the RGR, RCR, AD, ECD and ECI. In addition, elevated temperature under elevated CO₂ significantly decreased the RGR (2014), ECD (2013 & 2014) and ECI (2013) and increased the AD (2013 & 2014) compared with other treatment combinations when S. litura fed on Lamar. Future climatic change of temperature and CO₂ concentration would likely affect growth and food utilization of S. litura, with increased food intake, but the reduced fecundity may compensate for the increased food consumption, resulting in no significant reduction in insect‐induced yield loss in soybean production. Nevertheless, use of insect resistant soybean cultivars will aid in ecological management of S. litura and reduce the insecticide load in soybean production.     

Transgenic Rice Plants Expressing a Modified <Emphasis Type="Italic">cry1Ca1</Emphasis> Gene are Resistant to <Emphasis Type="Italic">Spodoptera litura</Emphasis> and <Emphasis Type="Italic">Chilo</Emphasis><Emphasis Type="Italic">suppressalis</Emphasis>

Nucleotide sequence encoding the truncated insecticidal Cry1Ca1 protein from Bacillus thuringiensis was extensively modified based on the codon usage of rice genes. The overall G + C contents of the synthetic cry1Ca1 coding sequence were raised to 65% with an additional bias of enriching for G and C ending codons as preferred by monocots. The synthetic gene was introduced into the Chinese japonica variety, Xiushui 11, by Agrobacterium-mediated transformation. Transgenic rice plants harboring this gene were highly resistant to Chilo suppressalis and Spodoptera litura larvae as revealed by insect bioassays. High levels of Cry1Ca1 protein were obtained in the leaves of transgenic rice, which were effective in achieving 100% mortality of S. litura and C. suppressalis larvae. The levels of Cry1Ca1 expression in the leaves of these transgenic plants were up to 0.34% of the total soluble proteins. The larvae of C. suppressalis and S. litura could consume a maximum of 1.89  and 4.89 mm² of transgenic leaf area whereas the consumption of non-transgenic leaves by these larvae was significantly higher; 58.33 and 61.22 mm², respectively. Analysis of R₁ transgenic plants indicated that the cry1Ca1 was inherited by the progeny plants and provided complete protection against C. suppressalis and S. litura larvae.     

Efficacy of selected adjuvants for protecting Spodoptera litura nucleopolyhedrovirus from sunlight inactivation

Efficacy of selected adjuvants for protecting Spodoptera litura nucleopolyhedrovirus (SpltNPV) from sunlight inactivation was tested in direct sunlight exposure bioassays and in the field on virus-treated Brassica chinensis var parachinensis plants. All adjuvants, except palm oil, gave significant protection to the virus after 16 h of sunlight exposure, as shown by the larval mortalities. Cumulative mortalities after 14 days show that the virus + Tinopal treatment and the virus not to sunlight treatment attained 100% mortality, while the virus in riboflavin treatment and the crude brown sugar treatment caused mortality of less than 30%. However, the LT₅₀ value of virus + Tinopal was 1.2 times lower than the unexposed virus. All virus-treated plants in the field trials had higher yields and lower damage indices than the control plants. Unlike the results from direct sunlight exposure bioassays, adjuvants, including virus + Tinopal LPW, did not significantly enhance efficacy of the virus against early instars of S. litura in the field. The unformulated virus was as effective as virus + Tinopal LPW and Nurelle-D in protecting the plants from infestation. Thus, in a well-planned pest management program, SpltNPV, without any adjuvant, can be used effectively for controlling S. litura on B. chinensis var parachinensis.     

Detoxification of insecticides,allechemicals and heavy metals by glutathione S‐transferase SlGSTE1 in the gut of Spodoptera litura

Insect glutathione S‐transferases (GSTs) play important roles in detoxifying toxic compounds and eliminating oxidative stress caused by these compounds. In this study, detoxification activity of the epsilon GST SlGSTE1 in Spodoptera litura was analyzed for several insecticides and heavy metals. SlGSTE1 was significantly up‐regulated by chlorpyrifos and xanthotoxin in the midgut of S. litura. The recombinant SlGSTE1 had V_max (reaction rate of the enzyme saturated with the substrate) and K_m (michaelis constant and equals to the substrate concentration at half of the maximum reaction rate of the enzyme) values of 27.95 ± 0.88 μmol/min/mg and 0.87 ± 0.028 mmol/L for glutathione, respectively, and V_max and K_m values of 22.96 ± 0.78 μmol/min/mg and 0.83 ± 0.106 mmol/L for 1‐chloro‐2,4‐dinitrobenzene, respectively. In vitro enzyme indirect activity assay showed that the recombinant SlGSTE1 possessed high binding activities to the insecticides chlorpyrifos, deltamethrin, malathion, phoxim and dichloro‐diphenyl‐trichloroethane (DDT). SlGSTE1 showed higher binding activity to toxic heavy metals cadmium, chromium and lead than copper and zinc that are required for insect normal growth. Western blot analysis showed that SlGSTE1 was induced in the gut of larvae fed with chlorpyrifos or cadmium. SlGSTE1 also showed high peroxidase activity. All the results together indicate that SlGSTE1 may play an important role in the gut of S. litura to protect the insect from the toxic effects of these compounds and heavy metals.     

金龟子绿僵菌对斜纹夜蛾幼虫的生防效果、抗氧化酶活性和肠道细菌群落的影响

【目的】测定金龟子绿僵菌(Metarhizium anisopliae)对斜纹夜蛾(Spodoptera litura) 2龄幼虫的毒力,研究金龟子绿僵菌侵染后寄主体内抗氧化酶活性和肠道内细菌群落的变化,探讨斜纹夜蛾对金龟子绿僵菌侵染的防御机制。【方法】采用浸渍法测定不同浓度金龟子绿僵菌对斜纹夜蛾2龄幼虫的毒力;应用IlluminaMiSeq高通量测序技术测定肠道细菌群落。【结果】不同浓度的孢悬液对斜纹夜蛾2龄幼虫均有一定的毒力,处理7 d时半致死浓度(LC₅₀)为3.944 107个孢子/mL;浓度为1.0×10⁹个孢子/mL时,半致死时间最短(LT₅₀)为4.6 d,校正后的死亡率为81.03%。处理后未致死的斜纹夜蛾幼虫体内抗氧化酶活性显著高于对照组。处理后致死的斜纹夜蛾幼虫肠道细菌群落多样性显著高于对照组;且处理后致死的斜纹夜蛾幼虫肠道细菌群落组成与对照组差异显著。【结论】金龟子绿僵菌对斜纹夜蛾幼虫的致死率和致死效率与金龟子绿僵菌的浓度呈正相关;斜纹夜蛾幼虫体内的抗氧化酶可能在抵抗金龟子绿僵菌侵染的过程中起重要作...     

Specificity of herbivore‐induced responses in an invasive species,Alternanthera philoxeroides (alligator weed)

Herbivory‐induced responses in plants can both negatively affect subsequently colonizing herbivores and mitigate the effect of herbivory on the host. However, it is still less known whether plants exhibit specific responses to specialist and generalist herbivores in non‐secondary metabolite traits and how specificity to specialists and generalists differs between invasive and native plant populations. We exposed an invasive plant, Alternanthera philoxeroides, to Agasicles hygrophila (Coleoptera, Chrysomelidae; specialist), Spodoptera litura (Lepidoptera, Noctuidae; generalist), manual clipping, or application of exogenous jasmonic acid and examined both the specificity of elicitation in traits of fitness (e.g., aboveground biomass), morphology (e.g., root:shoot ratio), and chemistry (e.g., C/N ratio and lignin), and specificity of effect on the subsequent performance of A. hygrophila and S. litura. Then, we assessed variation of the specificity between invasive and native populations (USA and Argentina, respectively). The results showed S. litura induced higher branching intensity and specific leaf area but lower C/N ratio than A. hygrophila, whereas A. hygrophila induced higher trichome density than S. litura. The negative effect of induction on subsequent larval growth was greater for S. litura than for A. hygrophila. Invasive populations had a weaker response to S. litura than to A. hygrophila in triterpenoid saponins and C/N ratio, while native populations responded similarly to these two herbivores. The specific effect on the two herbivores feeding on induced plants did not vary between invasive and native populations. Overall, we demonstrate specificity of elicitation to specialist and generalist herbivores in non‐secondary metabolite traits, and that the generalist is more susceptible to induction than the specialist. Furthermore, chemical responses specific to specialist and generalist herbivores only exist in the invasive populations, consistent with an evolutionary change in specificity in the invasive populations.