Xylostella Larvae Research Articles

Screening insectary refugia plants that increase the performance of Diadegma semiclausum Hellen (Hymenoptera: Ichneumonidae) against diamondback moth larvae

Abstract. Asmoro PP, Dadang, Pudjianto, Winasa IW. 2021. Screening insectary refugia plants that increase the performance of Diadegma semiclausum Hellen (Hymenoptera: Ichneumonidae) against diamondback moth larvae. Biodiversitas 22: 4254-4260. Habitat manipulation through the planting of insectary refugia plants is one way of controlling pests. These refugia plants serve as the source of nutrients that improve the fitness of parasitoid against insect pests. In the cabbage agroecosystem, the presence of refugia plants is expected to benefit the parasitoid D. semiclausum. This study aimed to select insectary refugia plants beneficial for the D. semiclausum in term of attracting and increasing their longevity, and parasitization ability against P. xylostella larvae. Ten species of refugia plants were used in this study, i.e., Ageratum conyzoides, Galinsoga parviflora, Sphagneticola trilobata, Synedrella nodiflora, Portulaca oleracea, Rorippa indica, Brassica rapa, Apium graveolens, Ocimum basilicum, and Arachis pintoi. The methods used in this study included testing the response of the imago olfactory to refugia plants and its effect on the longevity and parasitization level. The results showed that of the ten species of investigated, R. indica and A. graveolens were the most attractive for the presence of parasitoids. The two refugia plants could also increase the longevity and parasitization rate compared to the water treatment. R. indica and A. graveolens are recommended as refuge plants in the cabbage agroecosystems to control P. xylostella.

Double-Stranded RNA-Degrading Enzymes Reduce the Efficiency of RNA Interference in Plutella xylostella.

Simple SummaryThe efficiency of Lepidoptera RNA interference (RNAi) is highly varied among different species, different periods, and different genes. The stability of dsRNA is one of the important factors. DsRNA-degrading enzymes (dsRNases) are the key factors affecting the stability of dsRNA in insects. The efficiency of RNAi in diamondback moths was low and unstable. Furthermore, in vitro experiments, we found that dsRNA was completely degraded when incubated with the hemolymph or gut fluid of diamondback moths. Therefore, we hypothesized that the efficiency of RNAi in diamondback moths was decreased predominantly due to degradation of dsRNA by dsRNase. In this study, we identified four dsRNases in diamondback moths: PxdsRNase1 was mainly expressed in the hemolymph; and PxdsRNase2 and PxdsRNase3 were mainly expressed in the intestinal tract. PxdsRNase1, PxdsRNase2, and PxdsRNase3 were verified to be involved in the RNAi process in diamondback moths. In vitro, the recombinant protein of PxdsRNase1 degraded dsRNA completely and PxdsRNase3 cleaved dsRNA without complete degradation. Overall, our findings provided a fundamental basis for understanding the mechanism of dsRNase involvement in the RNAi process and using RNAi to control diamondback moths in the future.DsRNA-degrading enzymes (dsRNases) have been recognized as important factors in reducing RNA interference (RNAi) efficiency in different insect species. However, dsRNases in Plutella xylostella are still unknown. We identified the full-length cDNAs of PxdsRNase1, PxdsRNase2, PxdsRNase3, and PxdsRNase4. Gene expression profile showed that PxdsRNase1 was mainly expressed in the hemolymph; and that PxdsRNase2 and PxdsRNase3 were mainly expressed in the intestinal tract. The expression of PxCht (Chitinase of P. xylostella) in P. xylostella larvae injected with the mixture of dsPxCht (dsRNA of PxCht) and dsPxdsRNase1 (dsRNA of PxdsRNase1), dsPxdsRNase2 (dsRNA of PxdsRNase2), or dsPxdsRNase3 (dsRNA of PxdsRNase3) was significantly higher than that in the larvae injected with the mixture of dsGFP (dsRNA of green fluorescent protein gene, GFP) and dsPxCht; the transcription level of PxCht in the larvae feeding on the mixture of dsPxCht and dsPxdsRNase1, dsPxdsRNase2, or dsPxdsRNase3 was significantly higher than that in the larvae feeding on the mixture of dsPxCht and dsGFP. The recombinant protein of PxdsRNase1 degraded dsRNA rapidly, PxdsRNase3 cleaved dsRNA without complete degradation, and PxdsRNase2 could not degrade dsRNA in vitro. These results suggested that PxdsRNases1, PxdsRNases2, and PxdsRNases3 were involved in the dsRNA degradation to reduce RNAi efficiency with different mechanisms.

Antifeedant properties and contact toxicities of the trichocellins A-I and B-II from a Trichoderma reesei against Plutella xylostella larvae

Antifeedant properties and contact toxicities of the trichocellins A-I and B-II from a Trichoderma reesei against Plutella xylostella larvae

Exposure to (Z)-11-hexadecenal [(Z)-11-16:Ald] increases Brassica nigra susceptibility to subsequent herbivory

It is well established that plants emit, detect and respond to volatile organic compounds; however, knowledge on the ability of plants to detect and respond to volatiles emitted by non-plant organisms is limited. Recent studies indicated that plants detect insect-emitted volatiles that induce defence responses; however, the mechanisms underlying this detection and defence priming is unknown. Therefore, we explored if exposure to a main component of Plutella xylostella female sex pheromone namely (Z)-11-hexadecenal [(Z)-11-16:Ald] induced detectable early and late stage defence-related plant responses in Brassica nigra. Exposure to biologically relevant levels of vapourised (Z)-11-16:Ald released from a loaded septum induced a change in volatile emissions of receiver plants after herbivore attack and increased the leaf area consumed by P. xylostella larvae. Further experiments examining the effects of the (Z)-11-16:Ald on several stages of plant defence-related responses showed that exposure to 100 ppm of (Z)-11-16:Ald in liquid state induced depolarisation of the transmembrane potential (Vm), an increase in cytosolic calcium concentration [Ca2+]cyt, production of H2O2 and an increase in expression of reactive oxygen species (ROS)-mediated genes and ROS-scavenging enzyme activity. The results suggest that exposure to volatile (Z)-11-16:Ald increases the susceptibility of B. nigra to subsequent herbivory. This unexpected finding, suggest alternative ecological effects of detecting insect pheromone to those reported earlier. Experiments conducted in vitro showed that high doses of (Z)-11-16:Ald induced defence-related responses, but further experiments should assess how specific the response is to this particular aldehyde.

Docking-based generation of antibodies mimicking Cry1A/1B protein binding sites as potential insecticidal agents against diamondback moth (Plutella xylostella).

Broad use of insecticidal Cry proteins from Bacillus thuringiensis in biopesticides and transgenic crops has resulted in cases of practical field resistance, highlighting the need for novel approaches to insect control. Previously we described an anti-Cry1Ab idiotypic-antibody (B12-scFv) displaying toxicity against rice leafroller (Cnaphalocrocis medinalis) larvae, supporting the potential of antibodies for pest control. The goal of the present study was to generate insecticidal antibodies against diamondback moth (Plutella xylostella) larvae. Four genetically engineered antibodies (GEAbs) were designed in silico from B12-scFv using three-dimensional (3D) structure and docking predictions to alkaline phosphatase (ALP) as a Cry1Ac receptor in P. xylostella. Among these GEAbs, the GEAb-dVL antibody consisting of two light chains had overlapping binding sites with Cry1A and Cry1B proteins and displayed high binding affinity to P. xylostella midgut brush border membrane (BBM) proteins. Proteins in BBM identified by pull-down assays as binding to GEAb-dVL included an ABC transporter and V-ATPase subunit A protein. Despite lacking the α-helical structures in Cry1A that are responsible for pore formation, ingestion of GEAb-dVL disrupted the P. xylostella larval midgut epithelium and resulted in toxicity. Apoptotic genes were activated in gut cells upon treatment with GEAb-dVL . This study describes the first insecticidal GEAb targeting P. xylostella by mimicking Cry proteins. Data support that GEAb-dVL toxicity is associated to activation of intracellular cell death pathways, in contrast to pore-formation associated toxicity of Cry proteins. This work provides a foundation for the design of novel insecticidal antibodies for insect control. © 2021 Society of Chemical Industry.

Characterization of a new strain of Metarhizium novozealandicum with potential to be developed as a biopesticide

ABSTRACT The fungal species Metarhizium novozealandicum, that occurs only in New Zealand and Australia has been poorly studied. In this work, a new strain of M. novozealandicum isolated from a larva of Wiseana sp. is described based on morphology, genomic multilocus (ITS, EF-1α and β-tubulin) phylogeny, growth in different culture media and insecticidal activity. The isolate AgR-F177 was clustered in the same clade with M. novozealandicum. AgR-F177 colonies developed faster on Sabouraud Dextrose Agar (SDA) than on Potato Dextrose Agar (PDA) when incubated at 25°C, with no growth observed at 30°C on either media. Conidia yield on an oat-based medium in semisolid fermentation was 7.41 x 108conidia/g of substrate and a higher yield of 1.68 x 109conidia/g of substrate was obtained using solid fermentation on cooked rice. AgR-F177 formed microsclerotia (MS) in liquid fermentation after 7 days reaching the maximum yield of 3.3 × 103 MS/mL after 10 days. AgR-F177 caused mortality in Wiseana copularis, Costelytra giveni and Plutella xylostella larvae with efficacies up to 100%, 69.2%, and 45.7%, respectively. The ease of production of AgR-F177 with different fermentation systems and its pathogenicity against different insect pests reveal its potential as a new biopesticide.

Adaptations of Plutella xylostella adult females and larvae to waxy host plants

The diamondback moth (DBM), Plutella xylostella, is an oligophagous pest of cruciferous crops worldwide. Host plants of the DBM possess epicuticular wax, but thick wax is unfavorable to the selection of oviposition sites for female DBMs. How the DBM responds to host plant wax regarding oviposition site selection is largely unknown. The glucosinolates and wax levels in the cotyledons and true leaves of Chinese kale are different, which makes this plant an ideal host for exploring the oviposition behavior of the DBM. We found that although the true leaves contained more glucosinolates and waxy powder than cotyledons of healthy Chinese kale, DBM females preferred to lay eggs on the cotyledons over true leaves. However, the number of eggs laid on true leaves increased significantly when the waxy powder was artificially removed. Furthermore, the hatched larvae greatly preferred to feed and performed better on true leaves. In light of the current results, we propose that DBM females are hindered from laying eggs on the true leaves of Chinese kale by the outer layer of leaf wax powder. However, DBM females and larvae can adapt to the waxy host plant through adaptations: i.e., DBM females first lay eggs on the cotyledons where less wax exists, the hatched larvae then crawl to and spin silk nets on true leaves; the silk nets help subsequent DBM females overcome the obstacle of the wax and oviposit successfully on true leaves. These findings highlight new insights into plant–insect interactions.

Metal-organic framework nanohybrid carrier for precise pesticide delivery and pest management

Smart core–shell nanocarriers can release pesticides in response to stimuli from the microenvironment associated with pests and the physiological behaviors of protected crops. In this work, a smart nanocarrier (MIL-101(Fe)@silica) with dual functions of site-specific delivery and plant nutrition was fabricated to deliver chlorantraniliprole (CAP) for sustainable pest management. The results showed that the developed CAP@MIL-101(Fe)@silica with a size of approximately 270 nm had a stable core–shell nanostructure with a highly crystallized regular octahedron. The photostability of the drug loaded in the carrier under UV-light irradiation was 16.5 times higher than that of technical CAP. The introduction of the silica shell prevented the premature escape of CAP from the MIL-101(Fe) core in the environment and endowed the developed nanohybrid carrier with base-triggered release properties. In a laboratory bioassay, CAP@MIL-101(Fe)@silica had favorable insecticidal activity (LC50 = 0.389 mg/L) in controlling Plutella xylostella larvae. After fourteen days of spraying in the greenhouse experiment, the mortality of the CAP@MIL-101(Fe)@silica treatment (86%) against P. xylostella larvae was significantly higher than that of the CAP suspension concentration treatment (36.7%). In addition, MIL-101(Fe)@silica was safe for crops and could enhance the crop fresh weight and dry weight by 18.6–19.6% and 4.8–17.7%, respectively. Therefore, MIL-101(Fe)@silica could be used as a biocompatible carrier for site-specific pesticide delivery and simultaneously as a fertilizer for crop growth, which would be a novel route for the development of a precise pesticide delivery nanoplatform.

Anti-idiotypic single-chain variable fragment antibody partially mimic the functionally spatial structure of Cry2Aa toxin

The anti-idiotypic antibody is widely used in the field of immunology to simulate structural features or even induce the biological activity of antigens. In this study, we obtained seven anti-idiotypic single-chain variable fragments (scFv) antibodies of Cry2Aa toxin from a phage-displayed mutant library constructed using error-prone PCR technique. A mutant designated 2–12B showed the best binding ability amongst all anti-idiotypic scFv isolates to Plutella xylostella brush border membrane vesicles (BBMVs). 2–12B and Cry2Aa toxin shared a potential receptor of polycalin in P. xylostella BBMVs. Homology modeling and molecular docking demonstrated that 2–12B and Cry2Aa toxin have seven common binding amino acid residues in polycalin. Insect bioassay results suggested that 2–12 had insecticidal efficacy against P. xylostella larvae. These results indicated that the Cry2Aa anti-idiotypic scFv antibody 2–12B partially mimicked the structure and function of Cry2Aa toxin. The anti-idiotypic scFv antibody provides the basic material for the future study of surrogate molecules or new insecticidal materials.

Comparative study of the ditrophic interaction between Beauveria bassiana and Plutella xylostella

In the present investigation, hyperparasitic interaction between B. bassiana, TM (MH590235) and P. xylostella was studied through scanning electron microscopy and chromatographic techniques. Dose-mortality responses showed an increase in mortality of larva with an increase in spore concentration. The LC50 value for B. bassiana isolate TM (MH590235) was 2.4 × 107 spores mL-1. The ditrophic interaction between B. bassiana and P. xylostella after 24h revealed the adherence of conidia on stemmata, sensory setae, maxillary palpi and legs. After 48h post-infection (hpi), germination of the conidia and appressorium formation was observed. Formation of hyphae and initiation of fungal networking was observed at 72 hpi. Complete ramification by mycelia and conidiogenesis of B. bassiana was observed over the mycosed cadaver after 168 hpi. Subsequently, typical sympodial conidiophores of B. bassiana bearing secondary spores were also observed. The metabolome profile of healthy larvae of P. xylostella revealed the presence of non-volatile organic compounds (NVOCs) like docosene, nonadecene, palmitic acid and heneicosane. However, the NVOC profile was different in the P. xylostella larvae hyperparasitized by B. bassiana. The metabolites present in the infected cadaver were phthalate esters, hydroxyquebrachamine and lactones.

Effects of cabbage cultivars on the food consumption and utilization parameters of diamondback moth, Plutella xylostella (L.)

Food consumption and utilization parameters of Plutella xylostella (L.) were studied on the leaves of eight cabbage cultivars under laboratory conditions (27 ± 2 °C, 70 ± 5 % RH, 16 L: 8D photoperiod). The present study evaluated the effect of different biochemical factors of cabbage cultivars on the food consumption and utilization parameters of P. xylostella. All the food consumption and utilization parameters differed significantly among the cabbage cultivars. The highest values of relative consumption rate (RCR) and relative growth rate (RGR) were observed on the cabbage cultivars ‘NS 183’, ‘DEB 806’, ‘Green Express’ and ‘Mohor’. The highest values of the efficiency of conversion of ingested (3.94 %) and digested (4.95 %) food was observed on the cabbage cultivar ‘DEB 806’. In contrast, the 4th instar P. xylostella larvae fed on the cabbage cultivar ‘Lucky Ball’ exhibited the lowest values of RCR (1.31 mg food consumed/mg body weight/ day), RGR (0.33 mg weight gain/mg body weight/ day), ECI (2.47 %) and ECD (2.95 %). The food consumption and utilization parameters of P. xylostella were positively correlated with the protein: carbohydrate (P:C) ratio of cabbage cultivars. The food consumption and utilization parameters of P. xylostella showed a non-significant correlation with the total glucosinolate content and total phenolic content of cabbage cultivars. The present study will help to identify effective resistant or tolerant cabbage cultivars for the development of Integrated Pest Management strategies against P. xylostella.

Biological Activity of Ethanol Extracts and Essential Oils from Curcuma longa (Zingiberaceae), Cymbopogon nardus (Gramineae), and Acorus calamus (Acoraceae) against Plutella xylostella (Lepidoptera: Plutellidae)

Abstract The diamondback moth, Plutella xylostella (L.), is a major pest that has developed resistance to many groups of synthetic insecticides. Natural plant products present reliable alternatives for its management. In this study, the activities of essential oils and ethanol extracts from three medicinal plants, i.e., Curcuma longa L. (Zingiberaceae), Cymbopogon nardus (L.) Rendle (Gramineae), and Acorus calamus L. (Acoraceae), from Thailand against P. xylostella were evaluated. Four concentrations of the extracts (i.e., 0.625, 1.25, 2.5, and 5%) were tested. The essential oils and ethanol extracts of Cu. longa, Cy. nardus, and A. calamus exhibited different degrees of activity against P. xylostella. Of these, both the essential oil and ethanol extract of A. calamus at 5% (v/v) concentration exhibited feeding toxicity for P. xylostella larvae, resulting in 100% mortality 1 d after treatment, with a median lethal concentration of 0.528% for the essential oil and 1.074% for the ethanol extract. Furthermore, all concentrations of A. calamus ethanol extract exhibited contact toxicity to the larvae, resulting in >75% mortality 3 d after treatment. All tested extracts, except A. calamus ethanol extract at the 0.625% concentration, exhibited high repellent activity against P. xylostella larvae, while Cu. longa and Cy. nardus ethanol extracts at 5% (w/v) concentration and A. calamus essential oil at 2.5% (v/v) concentration deterred oviposition by P. xylostella adults with an effective repellency >70%. These results indicate that both essential oils and ethanol extracts of these plants have the potential to be developed as insecticides for use in integrated pest management of P. xylostella.

Performance of the aphidophagous coccinellid Eriopis connexa fed on single species and mixed-species prey

ABSTRACT Biological control in the open field often involves simultaneous infestations of different pest species. In brassica crops, aphids and diamondback moth are major pest species worldwide. The aphidophagous Coccinellinae Eriopis connexa (Germar) is a common predator in crop ecosystems including brassicas. We hypothesised that the performance of E. connexa would be improved if it were fed a mixed diet of prey available in the brassica ecosystem compared with the standard rearing prey; eggs of Anagasta kuehniella (Zeller). We evaluated diamondback moth, Plutella xylostella (L.) larvae, the brassica aphid, Lipaphis pseudobrassicae (Davis) when provided as single species, as mixtures of two species, or as all three species alternated over time. Developmental time and survival of E. connexa larvae fed diets of mixed prey and alternated available prey were superior to individuals that fed only P. xylostella larvae. Only 33% of E. connexa larvae that fed on P. xylostella alone survived and their development was delayed by 6 days. However, mean daily predation of P. xylostella larvae as single, mixed or alternated prey was 9.1 ± 0.2, 3.1 ± 0.1 and 9.4 ± 0.5 individuals, respectively, showing that this species was consumed even in the presence of preferred prey. Adult female E. connexa that consumed only P. xylostella did not lay eggs indicating that this prey could sustain the development and maintenance of E. connexa, but they are not essential prey. Predation of P. xylostella did not enhance or negatively affect E. connexa performance.

Symbiotic bracovirus of a parasite manipulates host lipid metabolism via tachykinin signaling.

Parasites alter host energy homeostasis for their own development, but the mechanisms underlying this phenomenon remain largely unknown. Here, we show that Cotesia vestalis, an endoparasitic wasp of Plutella xylostella larvae, stimulates a reduction of host lipid levels. This process requires excess secretion of P. xylostella tachykinin (PxTK) peptides from enteroendocrine cells (EEs) in the midgut of the parasitized host larvae. We found that parasitization upregulates PxTK signaling to suppress lipogenesis in midgut enterocytes (ECs) in a non-cell-autonomous manner, and the reduced host lipid level benefits the development of wasp offspring and their subsequent parasitic ability. We further found that a C. vestalis bracovirus (CvBV) gene, CvBV 9–2, is responsible for PxTK induction, which in turn reduces the systemic lipid level of the host. Taken together, these findings illustrate a novel mechanism for parasite manipulation of host energy homeostasis by a symbiotic bracovirus gene to promote the development and increase the parasitic efficiency of an agriculturally important wasp species.

Microwave-assisted regioselective reaction of furanone derivative supported by DFT stimulation and molecular docking to afford controlling insecticidal agents

The furanone 1 was allowed to react with different nitrogen nucleophiles such as hydrazine hydrate, hydroxyl amine, anisidine, anthranilic acid, glycine, ethylglycinate and isatin and some carbon nicleophiles under Michael reaction conditions assisted by microwave irradiation. They afforded new synthesized some important heterocyclic compounds 2–16. The structures of the synthesized new compounds were characterized by spectral data and elemental analysis. DFT calculation is serving to clarify not only the active electrophilic sites attacked by suitable nucleophiles in the organic reaction but also the bioactivity of the larvicidal compounds. The larvicidal activities of the synthesized compounds were tested against Plutella xylostella and Helicoverpa armigera larvae in vitro. The results revealed that the synthesized compounds 4, 13 and 14 showed good insecticidal activity against Plutella xylostella larvae with 100%, 87.2% and 91.4% activities, respectively, while 13 and 14 displayed 92% and %, 94.8 activities, respectively, against Helicoverpa armigera larvae. Therefore, they exhibited good larvicidal activity. The executed molecular docking simulations evinced the selective binding of the novel synthesized compounds toward acetylcholinesterase (AchE) of Drosophila Melanogaster, which signifies their role as a prominent larvicides. Compound 4, 13 and 14 showed clear docking affinity and to the assumed binding sites in terms of both calculated binding energies and the types of interactions, which provided a solid rationalization for the conducted experimental results.

Unraveling the Mode of Action of Cordyceps fumosorosea: Potential Biocontrol Agent against Plutella xylostella (Lepidoptera: Plutellidae)

Simple SummaryThe diamondback moth is a major destructive pest of cruciferous plants with a worldwide global distribution. Biological control, especially the use of insect pathogenic fungi as a novel control measure, remains the subject of intensive experimentation. The goal is to develop an efficient and eco-friendly alternative to chemical insecticides. The current study successfully explored and compared in-depth infection events between highly pathogenic and less pathogenic fungal strains. Our study for the first time provides new insights into the mechanisms by which fungal conidia parasitize diamondback moth larvae and ultimately aid in the development of the highly pathogenic strain into an effective biopesticide for the eco-friendly management of the diamondback moth.The entomopathogenic fungus, Cordyceps fumosorosea is a potential eco-friendly biocontrol agent. The present study revealed the entire course of infection of P. xylostella by C. fumosorosea with particular reference to cuticular penetration. Comparative studies on the infection of Plutella xylostella larvae by two strains of C. fumosorosea with different pathogenicity were carried out using light, scanning, and transmission electron microscopy. We found that C. fumosorosea tended to adhere to the cuticle surfaces containing protrusions. Although conidia of the lower pathogenic strain IFCF-D58 germinated, they failed to penetrate and complete the development cycle. In contrast, the higher pathogenic strain IFCF01 began to germinate within 4 h and attached to the cuticle by a thin mucilaginous matrix within 8 h post-inoculation. After 24 h post-inoculation, germ tubes and penetrating hyphae reached the cuticular epidermis and began to enter the haemocoel. Within 36 h post-inoculation, the hyphal bodies colonized the body cavity. Hyphae penetrated from inside to outside of the body after 48 h and sporulated the cadavers. After 72 h post-inoculation, numerous conidia emerged and the mycelial covered the entire cuticular surface. The two strains showed similarities in terms of conidial size and germination rate. However, IFCF-D58 exhibited significantly fewer appressoria and longer penetrating hyphae compared to the more infective IFCF01 on all surface topographies. The current pathogen invasion sequence of events suggested that the aggressive growth and propagation along with rapid and massive in vivo production of blastospores facilitate the conidia of IFCF01 to quickly overcome the diamondback moth’s defense mechanism.

Occurrence of arthropod pests associated with Brassica carinata and impact of defoliation on yield

AbstractBrassica carinata has the potential to become an economical biofuel winter crop in the Southeast U.S. An IPM program is needed to provide management recommendations for B. carinata in the region. This study serves as the first steps in the developing IPM tactics documenting pest occurrence, pest position within the canopy, and the impact of defoliation on B. carinata yield. The study was performed in Jay, FL, during the 2017–2018 and 2018–2019 winter/spring crop seasons. Pest species in B. carinata were documented by plant inspection within 16 genotypes of B. carinata, and the presence of insect pests in three canopy zones (upper, medium, and lower canopy) was documented. The defoliation impact on B. carinata was evaluated by artificial defoliation. Five levels of defoliation (2017–2018 crop season: 0%, 5%, 25%, 50%, and 100%; 2018–2019 crop season: 0%, 50%, 75%, 90%, and 100%) were artificially applied during vegetative, flowering, and pod formation stages of the commercial cultivar “Avanza64.” During the 2018–2019 crop season, two experiments were performed, a one‐time defoliation event and continuous defoliation. The plants were hand harvested and the average number of pods per plants, seeds per pod, thousand seed weight, and yield were estimated and correlated with defoliation levels. Results indicated the following species of pests associated with B. carinata: Microtheca ochroloma Stål (Coleoptera: Chrysomelidae), Plutela xylostella larvae, Pieris rapae L. (Lepidoptera: Pieridae), Diabrotica undecimpunctata Barber (Coleoptera: Chrysomelidae), Lipaphis pseudobrassicae Davis (Hemiptera: Aphididae), Leptoglossus phyllopus L. (Hemiptera: Coreidae), and Chloridea virescens F. (Lepidoptera: Noctuidae). The insect distribution within the plant canopy was not uniform. Different levels of artificial B. carinata defoliation did not affect seed weight, the number of seeds per pod, or the oil content of the seeds. The number of pods per plants and estimated yield were negatively impacted by defoliation during the vegetative and flowering stages.

Functional analysis of a carboxylesterase gene involved in beta-cypermethrin and phoxim resistance in Plutella xylostella (L.).

Carboxylesterases (CarEs) are associated with detoxification of xenobiotics, including insecticides, in organism bodies. Overexpression of CarE genes is considered to have an important role in insecticide resistance in insects, however its involvement in multi-insecticide resistance has rarely been reported. This study aimed to assess the function of a CarE gene (PxαE8) in resistance to five insecticides in Plutella xylostella. Relative expression of PxαE8 in three multi-insecticide-resistant Plutella xylostella populations, GD-2017, GD-2019 and HN, was14.8-, 19.5- and 28.0-fold higher than that in the susceptible population. Exposure to lethal concentrations associated with 25% mortality (LC25 ) of beta-cypermethrin, chlorantraniliprole, metaflumizone, phoxim and tebufenozide could induce the specific activity of CarEs and increase the relative expression of PxαE8. By contrast, knockdown of PxαE8 expression dramatically reduced the activity of CarEs and increased the resistance of P. xylostella (GD-2019) larvae to beta-cypermethrin and phoxim by 47.4% and 45.5%, respectively. Further, a transgenic line of Drosophila melanogaster overexpressing PxαE8 was constructed and the bioassay results showed that the tolerance of transgenic Drosophila to beta-cypermethrin and phoxim was 3.93- and 3.98-fold higher than that of the untransgenic line. These results provide evidence that overexpression of PxαE8 is involved in resistance, at least to beta-cypermethrin and phoxim, in multi-insecticide-resistant P. xylostella populations, which could help in further understanding the molecular mechanisms of multi-insecticide resistance in this pest. © 2020 Society of Chemical Industry.

The role of bacterial symbionts in the biodegradation of chlorpyrifos in the digestive tract of Plutella xylostella larvae

Abstract. Hadi MS, Abadi AL, Himawan T, MAsruri, Lestari SR, Rahardjo BT, Aini LQ, Setiawan Y, Tarno H. 2021. The role of bacterial symbionts in the biodegradation of chlorpyrifos in the digestive tract of Plutella xylostella larvae. Biodiversitas 22: 702-712. Several species in the order Lepidoptera act as plant pests, one of which is Plutella xylostella. Plutella xylostella is one of the most destructive pests of cabbage and other horticultural crops. The use of chemical insecticides as pest control for P. xylostella causes many problems, such as the increased pest resistance to pesticides. The objectives of this study are: (i) to obtain and characterize symbiont bacteria in the digestive tract of P. xylostella collected from organic and conventional agriculture soils; (ii) to evaluate the potential of bacterial symbionts in the digestive tract of P. xylostella from organic and conventional soils in degrading the active ingredient of chlorpyrifos insecticide; (iii) To determine the biodegradation process of chlorpyrifos insecticide by symbiont bacteria in the digestive tract of P. xylostella; and (iv) to identify the derivative compounds from the biodegradation of chlorpyrifos insecticide. The results showed 30 symbiont bacteria isolated from the digestive tract of P. xylostella collected from organic soil and 36 symbiont bacteria isolated from the digestive tract of P. xylostella from conventional farming soil. There are 15 species of symbiont bacteria in 5 genera from the digestive tract of P. xylostella from organic and conventional farming capable of degrading the chlorpyrifos insecticide. They are identified as Providencia sp., Pseudomonas sp., Serratia sp., Proteus sp., and Aeromonas sp. Chlorpyrifos-derived compounds from the biodegradation of symbiont bacteria are less toxic than chlorpyrifos compounds.

Insecticidal Efficacy of Syzygium aromaticum, Tephrosia vogelii and Croton dichogamus Extracts against Plutella xylostella and Trichoplusia ni on Brassica oleracea crop in Northern Tanzania.

The insecticidal efficacy of 10%, 5% and 1% w/v of Tephrosia vogelii, Croton dichogamus and Syzygium aromaticum aqueous plant extracts were assessed against larvae of Plutella xylostella and Trichoplusia ni on Brassica oleracea var. capitata crop field. Synthetic organophosphate pesticide (Chlorpyrifos) was used as a positive control and the negative controls were water and water plus soap. It was revealed that, aqueous plant extracts significantly (P ≤ 0.05) controlled the number of P. xylostella and T. ni larvae compared to negative controls. The 10% concentration of aqueous plant extracts showed significant higher efficacy in terms of reducing the insect population and their damage than 1% and 5 % concentration. The population of P. xylostella larvae per B. oleracea in five weeks of treatment applications at 10% w/v of T. vogelii, C. dichogamus and S. aromaticum aqueous plant extracts were 0.08, 0.15, 0.13, 0.05 and 0.08; 0.08, 0.20, 0.15, 0.13 and 0.18; 0.03, 0.05, 0.15, 0.18 and 0.13, respectively which was significantly (P ≤ 0.05) lower than in water (1.13, 1.68, 2.28, 2.20 and 3.28) and water plus soap (0.75, 1.60, 2.58, 1.83 and 3.30) negative controls respectively. The number of T. ni larvae per B. oleracea in five weeks of treatment applications at 10% w/v of T. vogelii, C. dichogamus and S. aromaticum of aqueous plant extracts were 0.00, 0.03, 0.05, 0.03 and 0.00; 0.03, 0.08, 0.05, 0.08 and 0.08; 0.05, 0.03, 0.00, 0.05 and 0.03, respectively which was significantly (P ≤ 0.05) lower than in water (0.50, 0.63, 0.60, 0.48 and 0.78) and water plus soap (0.30, 0.48, 68, 0.65 and 0.80) negative controls. The percentage damage of B. oleracea in five weeks of treatment applications at 10% w/v of T. vogelii, C. dichogamus and S. aromaticum aqueous plant extracts were 10.0, 6.3, 7.5, 7.5 and 5.6; 11.3, 11.3, 11.3, 11.3 and 12.5; 8.8, 8.1, 6.9, 8.1 and 9.4, respectively compared with water (33.8, 33.1, 38.8, 45.0 and 70.6) and water plus soap (30.0, 31.9, 41.3, 41.3 and 56.3). These pesticidal plants can be recommended for smallholder farmers to significantly control P. xylostella and T. ni larvae in B. oleracea crop.