Plutella Xylostella Larvae Research Articles

Short Communication: Larvicidal and antifeedant activities of Kalanchoe daigremontiana against Plutella xylostella larvae

Abstract. Hidayati D, Darmanto Y, Nurhidayati T, Abdulgani N. 2016. Short Communication: Larvicidal and antifeedant activities of Kalanchoe daigremontiana against Plutella xylostella larvae. Nusantara Bioscience 8: 312-315. Larvicidal and antifeedant activities of Kalanchoe daigremontiana polar extract were tested on fourth instar of Plutella xylostella larva using choice test, leaf dipping method and antifeedant capacity test (no choice test). K. daigremontiana polar extract in level of 0.25, 0.5, 0.75, 1, 1.25, and 1.5% were used on choice test to determined the larvae behavior tendencies of an attractant or to be an antifeedant, while on toxicity test were used extract in level of 0.25% and 0.5%, whereas on antifeedant capacity test were in level of 0.75, 1, 1.25, and 1.5%. The Probit analysis resulted that 50% of lethal concentration (LC50) was found at 72 hours exposure of 0,5% polar extract. Effective concentration for antifeedant at 1.25%, while antifeedant capacity percentage was in level of 84.85%.

Insecticidal Constituents from Buddlej aalbiflora Hemsl.

Eleven known compounds, deoxymikanolide (1), 1,3-dihydroxyxanthone (2), kumatakenin (3), apigenin (4), chrysin (5), kaempferol (6), Iso-kaempferol (7), luteolin (8), luteolin-3′,4′-dimethylether-7-O-β-glucoside (9), luteolin-7-O-β-glucoside (10) and quercetin (11) were identified in MeOH extract of Buddleja albiflora Hemsl (Oleaceae). These compounds (each, 1, 0.5 and 0.25 mg mL−1) were tested for insecticidal activity against 3rd and 4th-instar larvae of Plutella xylostella, 3rd-instar larvae of Mythimna separata and 3rd-instar larvae of Macrosiphoniella sanborni. The lowest 50% anti-feedant concentration (AFC50) against P. xylostella and 50% lethal concentration (LC50) against P. xylostella and M. sanborni were observed as 0.0058, 0.0046 and 3.4048 mg L−1, respectively.

Chemical composition, cytotoxicity and insecticidal activities of Acorus calamus accessions from the western Himalayas

Twenty one accessions of Acorus calamus were evaluated for essential oil composition and biological activities during 2009–2014. Essential oil from fresh rhizomes of A. calamus was obtained by hydro–distillation method, and analyzed by GC–FID and GC–MS. The essential oil yield ranged from 1.10±0.28 to 2.50±0.01%. β-asarone, shyobunone and α-asarone were the major constituents in the rhizome oil. Accession IHBT/AC/16 recorded the lowest β-asarone content (31.56%) and IHBT/AC/1 recorded the highest (91.27%). Two accessions, viz., IHBT/AC/7 and IHBT/AC/16, representing triploid and diploid accessions that contain high and low β-asarone content, respectively, were tested for biological activities. The cytotoxicity of these accessions was evaluated against human colorectal adenocarcinoma (HT–29), human epidermoid carcinoma (KB) and human cervical cancer (SiHa) cells at 24, 48 and 72h. Both accessions at 300μg/mL and 72h showed the highest activity against all the tumoral cells. The essential oils of two accessions showed promising larvicidal activities against 2nd instar larvae of Spodoptera litura and Plutella xylostella. However, P. xylostella larvae were more susceptible than the S. litura larvae, and essential oils of accession IHBT/AC/7 were more toxic than accession IHBT/AC/16.

Translational Control of Host Gene Expression by a Cys-Motif Protein Encoded in a Bracovirus.

Translational control is a strategy that various viruses use to manipulate their hosts to suppress acute antiviral response. Polydnaviruses, a group of insect double-stranded DNA viruses symbiotic to some endoparasitoid wasps, are divided into two genera: ichnovirus (IV) and bracovirus (BV). In IV, some Cys-motif genes are known as host translation-inhibitory factors (HTIF). The genome of endoparasitoid wasp Cotesia plutellae contains a Cys-motif gene (Cp-TSP13) homologous to an HTIF known as teratocyte-secretory protein 14 (TSP14) of Microplitis croceipes. Cp-TSP13 consists of 129 amino acid residues with a predicted molecular weight of 13.987 kDa and pI value of 7.928. Genomic DNA region encoding its open reading frame has three introns. Cp-TSP13 possesses six conserved cysteine residues as other Cys-motif genes functioning as HTIF. Cp-TSP13 was expressed in Plutella xylostella larvae parasitized by C. plutellae. C. plutellae bracovirus (CpBV) was purified and injected into non-parasitized P. xylostella that expressed Cp-TSP13. Cp-TSP13 was cloned into a eukaryotic expression vector and used to infect Sf9 cells to transiently express Cp-TSP13. The synthesized Cp-TSP13 protein was detected in culture broth. An overlaying experiment showed that the purified Cp-TSP13 entered hemocytes. It was localized in the cytosol. Recombinant Cp-TSP13 significantly inhibited protein synthesis of secretory proteins when it was added to in vitro cultured fat body. In addition, the recombinant Cp-TSP13 directly inhibited the translation of fat body mRNAs in in vitro translation assay using rabbit reticulocyte lysate. Moreover, the recombinant Cp-TSP13 significantly suppressed cellular immune responses by inhibiting hemocyte-spreading behavior. It also exhibited significant insecticidal activities by both injection and feeding routes. These results indicate that Cp-TSP13 is a viral HTIF.

Insecticidal activity of sesquiterpene lactones and monoterpenoid from the fruits of Carpesium abrotanoides

The isolation of secondary metabolites produced by plants can lead to the discovery of new insecticidal agents. The aim of this study was to identify secondary metabolites from the fruits of Carpesium abrotanoides, a well-known medicinal and poisonous plant belonging to the family Asteraceae, with the potential to act as natural insecticides. Two new sesquiterpene lactones 9β-hydroxy-1βH, 11αH-guaia-4,10(14)-dien-12,8α-olide (1) and 9β-hydroxy-1βH, 11βH-guaia-4,10(14)-dien-12,8α-olide (2) along with four known sesquiterpene lactones (3-6) and one monoterpenoid (7) have been isolated. The structures of these compounds were established on the basis of 1D and 2D NMR data and HRESIMS data interpretation. To characterize their insecticidal activities, bioassays were conducted using two insect pest species of agricultural importance. Compounds 1–7 showed antifeedant effects to 3rd instar larvae of Plutella xylostella (Lepidoptera: Plutellidae) in a concentration-dependant manner with EC50 of 19.84, 42.82, 97.94, 96.90, 39.94, 37.35 and 43.99mg/L, respectively. Moreover, all of these compounds display stomach-contact combination toxicity toward 4rd instar larvae of Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae) (LD50=18.71, 80.29, 230.65, 319.67, 31.18, 40.87 and 68.47mg/L, respectively). In general, this is the first report of insecticidal activities of secondary metabolites isolated from C. abrotanoides. Moreover, compound 1 showed the best insecticidal activity in the test, demonstrating its potential to be used as a natural insecticides.

Genome-Wide Host-Pathogen Interaction Unveiled by Transcriptomic Response of Diamondback Moth to Fungal Infection.

Genome-wide insight into insect pest response to the infection of Beauveria bassiana (fungal insect pathogen) is critical for genetic improvement of fungal insecticides but has been poorly explored. We constructed three pairs of transcriptomes of Plutella xylostella larvae at 24, 36 and 48 hours post treatment of infection (hptI) and of control (hptC) for insight into the host-pathogen interaction at genomic level. There were 2143, 3200 and 2967 host genes differentially expressed at 24, 36 and 48 hptI/hptC respectively. These infection-responsive genes (~15% of the host genome) were enriched in various immune processes, such as complement and coagulation cascades, protein digestion and absorption, and drug metabolism-cytochrome P450. Fungal penetration into cuticle and host defense reaction began at 24 hptI, followed by most intensive host immune response at 36 hptI and attenuated immunity at 48 hptI. Contrastingly, 44% of fungal genes were differentially expressed in the infection course and enriched in several biological processes, such as antioxidant activity, peroxidase activity and proteolysis. There were 1636 fungal genes co-expressed during 24–48 hptI, including 116 encoding putative secretion proteins. Our results provide novel insights into the insect-pathogen interaction and help to probe molecular mechanisms involved in the fungal infection to the global pest.

General odorant-binding proteins and sex pheromone guide larvae of Plutella xylostella to better food

Olfaction of Lepidopteran larvae has received little attention, compared to the damage to crops done by insects at this stage. We report that larvae of the diamondback moth Plutella xylostella are attracted to their natural sex pheromone and to their major component (Z)-11-hexadecenal, but only in a food context. For such task they use two general odorant-binding proteins (GOBPs), abundantly expressed in the three major sensilla basiconica of the larval antenna, as shown by whole-mount immunostaining and immunocytochemistry experiments. None of the three genes encoding pheromone-binding proteins (PBPs) are expressed at this stage. Both recombinant GOBPs bind (Z)-11-hexadecenal and the corresponding alcohol, but not the acetate. Binding experiments performed with five mutants of GOBP2, where aromatic residues in the binding pocket were replaced with leucine showed that only one or two amino acid substitutions can completely abolish binding to the pheromone shifting the affinity to plant-derived compounds. We hypothesise that detection of their species-specific pheromone may direct larvae to the sites of foraging chosen by their mother when laying eggs, to find better food, as well as to reduce competition with individuals of the same or other species sharing the same host plant. We also provide evidence that GOBP2 is a narrowly tuned binding protein, whose affinity can be easily switched from linear pheromones to branched plants terpenoids, representing a tool better suited for the simple olfactory system of larvae, as compared to the more sophisticated organ of adults.

Improved insecticidal activities of Novel Bacillus thuringiensis Cry1-type genes

Recently, Bacillus thuringiensis (Bt) cry genes encoding insecticidal Cry proteins have been widely applied for the construction of transgenic crops resistant to insect pests. This study aimed to construct novel mutant cry1Ac genes for genetically modified crops with enhanced insecticidal activities. Using multi-site directed mutagenesis, 34 mutant cry1Ac genes were synthesized and converted at 24 amino acid residues, located on domain I (8 residues) and domain II (16 residues). These mutant genes were expressed as a fusion protein with polyhedrin using the baculovirus expression system. The expressed proteins were occluded into polyhedra and activated stably to 65kDa by trypsin. Among these, Mut-N04, N06 and N16 showed high levels of insecticidal activities against larvae of Plutella xylostella, Spodoptera exigua, and Ostrinia furnacalis. Mut-N16, which showed the highest insecticidal activity, is expected to be a desirable cry gene for introduction into transgenic crops. This study could provide useful means to construct mutant cry genes with improved insecticidal activities and expand host spectra for transgenic crops.

Baculoviral p94 homologs encoded in Cotesia plutellae bracovirus suppress both immunity and development of the diamondback moth, Plutellae xylostella.

Polydnaviruses (PDVs) are a group of insect DNA viruses, which exhibit a mutual symbiotic relationship with their specific host wasps. Moreover, most encapsidated genes identified so far in PDVs share homologies with insect-originated genes, but not with virus-originated genes. In the meantime, PDVs associated with 2 wasp genera Cotesia and Glytapanteles encode some genes presumably originated from other viruses. Cotesia plutellae bracovirus (CpBV) encodes 4 genes homologous to baculoviral p94: CpBV-E94k1, CpBV-E94k2, CpBV-E94k3, and CpBV-E94k4. This study was conducted to predict the origin of CpBV-E94ks by comparing their sequences with those of baculoviral orthologs and to determine the physiological functions by their transient expressions in nonparasitized larvae and subsequent specific RNA interference. Our phylogenetic analysis indicated that CpBV-E94ks were clustered with other E94ks originated from different PDVs and shared high similarity with betabaculoviral p94s. These 4 CpBV genes were expressed during most developmental stages of the larvae of Plutella xylostella parasitized by C. plutellae. Expression of these 4 E94ks was mainly detected in hemocytes and fat body. Subsequent functional analysis by in vivo transient expression showed that all 4 viral genes significantly inhibited both host immune and developmental processes. These results suggest that CpBV-E94ks share an origin with betabaculoviral p94s and play parasitic roles in suppressing host immune and developmental processes.

농업해충에 대한 친환경유기농자재들의 살충력 및 섭식저해력 평가

Insecticidal and antifeeding activities of 29 commercialized eco-friendly organic products for managing plant diseases and insect pests against Plutella xylostella larvae, Spodoptera exigua larvae, Frankliniella occidentalis adults, and Myzus persicae adults were tested using spraying and leaf dipping bioassays under laboratory conditions. Products containing 60% Sophora extract (EOIS) and mixtures (EOISm) with Sophora extract, Stemona japonica extract, Melia azedarach extract, and Nepeta cataria extract as well as mixtures (EOISc) with Sophora extract, Chenopodium ambrosioides extract, and Melia azedarach extract as active ingredients showed strong insecticidal activity at recommended concentration against P. xylostella larvae. At half concentration, their insecticidal activities were decreased under 50%. The EOIS gave good insecticidal activity against S. exigua larvae and also showed 85% and 95% insecticidal activity at 24 and 48 hours after treatment to F. occidentalis adults, respectively. For M. persicae adults, EOISm and mixtures (EOIR) containing rape seed extract, neem extract, and castar oil produced 93% and 68% insecticidal activity, but their activities did not be increased at double concentration. EOISm only showed 100% contact toxicity against M. persicae adults exposed to dipping leaves. Interestingly, the insecticidal activity of EOIR and EOICi (citronella oil and derris extract) against M. persicae adults was increased with exposed time and concentration. In addition, EOICe (cedar oil), EOIS, EOISm, EOISc, EOIM (microorganism), EOIR, EOIPe (plant extract), and EOIT (tea tree extract) gave strong antifeeding activity against S. exigua and P. xylostella larvae. EOIB, EOIBs, EOIM, EOICi, and EOIMc showed above 70% antifeeding activity to the lepidopteran larvae. These results indicate that mixtures containing 2 to 3 plant extracts with Sophora extract show good activities against insect pests, although the difference of insecticidal and antifeeding activities was produced depending on both a tested insect species and an active ingredient or concentration.

Dynamics of competition and co-infection between Zoophthora radicans and Pandora blunckii in Plutella xylostella larvae

Abstract Co-inoculation of Zoophthora radicans and Pandora blunckii in Plutella xylostella larvae were investigated. Co-inoculations were made simultaneously or within 4, 8 or 12 hr of each other to achieve different prior residency times; order of inoculation was alternated. The most larvae infected by a particular species occurred when that species was inoculated alone. In co-inoculations, the majority of larvae were infected by only one species; both isolates of Z. radicans always infected more larvae than P. blunckii when they were inoculated last, regardless of prior residency time, while this was only the case for one of the P. blunckii isolates. The proportion of co-infected larvae never exceeded 20 %, and only occurred when both species were inoculated simultaneously or when the prior residency time was 8 hr or less, regardless of the order of inoculation. Prior residency time and order of inoculation affect the likelihood of competing species surviving during co-inoculation.

The endoparasitoid, Cotesia vestalis, regulates host physiology by reprogramming the neuropeptide transcriptional network.

Endoparasitoids develop inside another insect by regulating host immunity and development via maternal factors injected into hosts during oviposition. Prior results have provided insights into parasitism-induced immunosuppression, including the neuropeptide accumulation in parasitized insects. Nonetheless, our understanding of neuropeptide influence on host development and behavior is not yet complete. We posed the hypothesis that parasitization alters expression of genes encoding pro-neuropeptides and used larvae of Plutella xylostella and its endoparasitoid, Cotesia vestalis to test our hypothesis. We prepared transcriptomes from the larval P. xylostella brain-CC-CA complex and identified transcripts encoding 19 neuropeptides. All corresponding cDNAs were confirmed by RACE. Our results demonstrate that parasitism significantly down-regulated, or delayed, expression of genes encoding pro-neuropeptides within 48 h post-parasitization. Changing expression of these genes may account for the previously reported decreased feeding behavior, reduced growth rates and aborted development in the host larvae. In effect, parasitization may operate at the molecular level within the CNS to create global changes in larval host biology. The significance of our finding is that, in addition to the known effects on immunity, parasitoids influence host pro-neuropeptide gene transcription. This finding reveals a new mechanism operating in host-parasitoid relationships to the advantage of the parasitoid.

바이러스 유래 시스타틴 재조합 단백질의 곤충 면역 및 발육 억제효과

Cystatins (CSTs) are reversible and competitive inhibitors of C1A cysteine proteases, corresponding to papain-like cathepsins in plants and animals. A viral CST (CpBV-CST1) was identified from a polydnavirus, Cotesia plutellae bracovirus (CpBV). Our previous study indicated that a transient expression of CpBV-CST1 interfered with immune response and development of Plutella xylostella larvae. To directly demonstrate the protein function, this study produced a recombinant CpBV-CST1 protein (rCpBV-CST1) using bacterial expression system to determine its inhibitory activity against cysteine protease and to assess its physiological alteration in insect immune and development. The open reading frame of CpBV-CST1 encodes a polypeptide of 138 amino acids (). rCpBV-cystatin protein in BL21 STAR (DE3) competent cells containing a recombinant pGEX4T-3:CpBV-CST1 was over-expressed by 0.5 mM IPTG for 4 h. In biological activity assay, the purified rCpBV-CST1 showed a significant inhibition against papain activity. It inhibited a cellular immune response of hemocyte nodule formation in the beet armyworm, Spodoptera exigua. Moreover, its oral administration retarded larval development of the diamondback moth, Plutella xylostella in a dose-dependent manner. These results suggest that CpBV-CST1 may be applied to control insect pest populations.

Molecular markers for Diadegma (Hymenoptera: Ichneumonidae) species distinction and their use to study the effects of companion plants on biocontrol of the diamondback moth

Molecular markers facilitate the quantification of parasitization of pest species and the distinction of related parasitoid species. We designed new markers that allow the distinction of often misidentified Diadegma semiclausum and D. fenestrale parasitization in field-collected diamondback moth (Plutella xylostella) larvae. The markers were applied to study if cornflower (Centaurea cyanus) companion plants increase parasitization of the diamondback moth by Diadegma parasitoids in cabbage fields, as they do in the Mamestra brassicae—Microplitis mediator pest-parasitoid pair. Among 1708 P. xylostella larvae analyzed, we found a high parasitization rate (72.2 % total, 41.7 % by D. semiclausum, 24.9 % by D. fenestrale, 5.6 % by both), but no significant effects of cornflower presence. Our results highlight the need for species-specific markers and the specific action of companion plants. To increase natural control in crop fields, habitat management needs to be tailored to—and acts on—specific target species.

Plutella xylostella (L.) infestations at varying temperatures induce the emission of specific volatile blends by Arabidopsis thaliana (L.) Heynh

The effect of combined abiotic and biotic factors on plant volatile organic compound (VOC) emissions is poorly understood. This study evaluated the VOC emissions produced by Arabidopsis thaliana (L.) Col-0 subjected to 3 temperature regimes (17, 22, and 27°C) in the presence and absence of Plutella xylostella larvae over 2 time intervals (0–4 and 4–8 h), in comparison to control plants. The analyses of VOCs emitted by Arabidopsis plants were made by headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). It was found that certain volatile groups (e.g., alcohols, ketones, aldehydes, and terpenes) are induced by both single factors (temperature or larval infestation) and combined factors (temperature and larvae interactions), whereas other volatile groups (e.g., isothiocyanates [ITCs] and nitrile) were specific to the experimental conditions. ITCs (mainly 4-methylpentyl isothiocyanate) were emitted from plants subjected to larval infestation at 17 and 27°C after the 2 time intervals. The proportions of sulfides (mainly dimethyl disulfide) and 4-(methylthio) butanenitrile were significantly higher on herbivore-infested plants at 22°C compared to the other treatments. Overall, our findings indicate that changes in all experimental conditions caused significant changes to the VOC emissions of Arabidopsis plants. Therefore, the interaction between temperature and larval feeding may represent an important factor determining the variability of volatile emissions by plants subjected to multiple simultaneous factors.

English

The crystal (Cry) proteins produced by Bacillus thuringiensis determine a particular strain's toxicity profile. This study was focused on cloning a cry1Ia gene based on amplicon restriction fragment length polymorphism (ARFLP) profile which would be helpful in developing new biopesticides with broader and higher spectrum of toxicity against Lepidoptera and Coleoptera insect pests. The present paper describes cry1Ia gene from a local isolate of Bacillus thuringiensis (B.t) CFE20(3). A PCR-restriction fragment length polymorphism method for identification of cry1I-type genes from Bacillus thuringiensis was established by designing a pair of primers based on the conserved regions of the genes to amplify 2,169 bp cry1I-type gene fragments. Amplification products were digested with the KpnI and XbaI, and new kind of cry1I-type genes was successfully identified. Escherichia coli DH5α was transformed with recombinant DNA comprising pTZ57R/T and Bt cry1I (2169 bp) amplified from a native isolate CFE20(3) for cloning. The cloned 2169 bp was sequenced and then ligated in the expression vector pQE30 for transformation of E. coli M15 and SG13009 for expression analysis. The sequence obtained shows 99% homology with known cry1Ia from B. thuringiensis subsp. Kurstaki. An expected band size of 81 KDa was observed after sodium dodecyl sulphate - polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicating the expression of cry1I. The toxicity of crude recombinant Cry1I proteins was determined against third instar larvae of Diamond back moth, Plutella xylostella and Spodoptera litura. Cry1I protein was found to be effective against Plutella xylostella. Key words: Bacillus thuringiensis, cry1I, SDS-PAGE, Plutella xylostella, Spodoptera litura.

Screening of liquid media and fermentation of an endophytic Beauveria bassiana strain in a bioreactor.

A novel approach for biological control of insect pests could be the use of the endophytic entomopathogenic Beauveria bassiana isolate ATP-02. For the utilization of the endophyte as a commercial biocontrol agent, the fungus has to be mass-produced. B. bassiana was raised in shake flask cultures to produce high concentrations of total spores (TS), which include blastospores (BS) and submerged conidiospores (SCS). The highest concentration of 1.33×109 TS/mL and the highest yield of 5.32×1010 TS/g sucrose was obtained in the TKI broth with 5% sugar beet molasses which consists of 50% sucrose as a carbon source. In spite of the lower sugar concentration (2.5%) the amount of TS could be increased up to 11-times in contrast to the cultivation with 5% sucrose. The scale-up to a 2 L stirred tank reactor was carried out at 25°C, 200–600 rpm and 1 vvm at pH 5.5. A TS yield of 5.2×1010 TS/g sucrose corresponding to a SCS yield of 0.2×1010 SCS/g sucrose was obtained after 216 h. With regards to the culture medium the cost of 1012 TS amounts to 0.24 €. Plutella xylostella larvae, which were fed with oilseed rape leaves treated with spores from fermentation resulted in 77 ± 5% mortality. Moreover, spores from submerged cultivation were able to colonize oilseed rape leaves via leaf application. This is the first report of fermentation of an endophytic B. bassiana strain in a low-cost culture medium to very high yields of TS.

RNAi-Mediated Knockdown of Serine Protease Inhibitor Genes Increases the Mortality of Plutella xylostella Challenged by Destruxin A

Destruxin A is a mycotoxin that is secreted by entomopathogenic fungi which has a broad-spectrum insecticidal effect. Previous transcript and protein profiling analysis showed that destruxin A has significant effects on the expression of serine protease inhibitor genes (serpin-2, 4, 5) in the larvae of Plutella xylostella. In the current study, we aimed to understand the role of serpins under application of destruxin A. We obtained two full-length cDNA sequences of P. xylostella serpins, named serpin-4 and serpin-5, and cloned the serpin-2 gene whose full-length has already been published. Phylogenetic analysis indicated that these two serpin genes were highly clustered with other serpins associated with the immune response in other insects. The temporal and spatial expression of serpin-2, serpin-4 and serpin-5 were determined to be the highest in the fat body and hemolymph of 4th larval stage using qRT-PCR and western blot detection techniques. RNA interference (RNAi) mediated knockdown of P. xylostella serpin genes was carried out by microinjection of double-stranded RNA (dsRNA). The expression levels of serpins decreased significantly after RNAi. Results showed that the depletion of serpins induced cecropins expression, increased phenoloxidase (PO) activity, body melanization and mortality in the larvae of P. xylostella under the same lethal concentration of destruxin A. The superimposed effects of serpins RNAi were similar with the destruxin A treatment upon mortality of P. xylostella larvae. We discovered for the first time that serpins play indispensable role in P. xylostella when challenged by destruxin A and deduced the possible function mechanism of destruxin A. Our findings are conducive to fully understanding the potential insecticidal mechanism of destruxin A and constitute a well-defined potential molecular target for novel insecticides.

Effect of partial plant resistance in brassicas on tolerance of diamondback moth (Plutella xylostella) larvae to cypermethrin

Brassica cultivars with varying degrees of partial plant resistance were fed to larvae (up to 4th instar) of the diamondback moth (DBM), Plutella xylostella, and were bioassayed by topical application of cypermethrin to investigate the interaction of plant resistance with insecticide. Larvae reared on the least preferred brassica, Minicole, showed a significantly higher LD50 value than those on the most preferred brassica, Chinese cabbage. Bioassay of 4th instar DBM larvae fed on artificial diet containing pure compounds of glucosinolates revealed a negative interaction between their susceptibility to cypermethin and certain glucosinolates (in particular sinigrin), suggesting that such compounds induced the production of insecticide-detoxifying enzymes.

Efficacy of entomopathogenic nematode, Steinernema carpocapsae against the diamondback moth, Plutella xylostella (L.) in laboratory condition

In vitro studies were carried out on the diamondback moth, Plutella xylostella larvae using an insect entomopathogenic nematode isolate, Steinernema carpocapsae obtained from the Koppert company, the Netherlands. Larvae of P. xylostella were collected from cabbage farms around Mashhad city of Iran. During the study, the responses of larvae at 25 °C for three periods of 24, 48 and 72 h with different concentrations of 0, 5, 10, 20, 40, 80, 160 and 320 third instar larvae of nematode (infective stage = IJs) per insect into 10 cm Petri dishes containing filter paper soaked with 1 ml of nematodes suspension were compared. Maximum mortality caused by S. carpocapsae nematode was 88% at 24 h, and it was 100% at 48 and 72 h. With increasing nematode population level and exposure time (ET in hour), mortality of P. xylostella larvae was increased. Based on probit analysis, LC50 values of S. carpocapsae nematode in three test periods were 45.61, 12.02 and 40.80 IJs per insect, respectively. Initial ANOVA was performed for S. carpocapsae nematode. The effect of both nematode population levels (IJ) and ET on third instar larvae of the diamondback moth, P. xylostella and interaction between IJ and ET were significant. In general, it is recommended to apply this nematode in suitable condition for controlling diamondback moth.