Xylostella Larvae Research Articles

Tritrophic metabolism of plant chemical defenses and its effects on herbivore and predator performance.

Insect herbivores are frequently reported to metabolize plant defense compounds, but the physiological and ecological consequences are not fully understood. It has rarely been studied whether such metabolism is genuinely beneficial to the insect, and whether there are any effects on higher trophic levels. Here, we manipulated the detoxification of plant defenses in the herbivorous pest diamondback moth (Plutella xylostella) to evaluate changes in fitness, and additionally examined the effects on a predatory lacewing (Chrysoperla carnea). Silencing glucosinolate sulfatase genes resulted in the systemic accumulation of toxic isothiocyanates in P. xylostella larvae, impairing larval development and adult reproduction. The predatory lacewing C. carnea, however, efficiently degraded ingested isothiocyanates via a general conjugation pathway, with no negative effects on survival, reproduction, or even prey preference. These results illustrate how plant defenses and their detoxification strongly influence herbivore fitness but might only subtly affect a third trophic level.

Effectiveness of Flame for Preplant Pest Management in Leaf Vegetable Fields

Widespread herbicide-resistant weeds and severe insect pest infestations pose a challenge to the preplant pest management (PPPM) strategy currently in use in leaf vegetable fields in southern China. The aim of this study was to develop a new weed and insect control method for use before planting leaf vegetables in southern China. Two flaming machines (a tractor mounted and a trolley flaming machine) were designed, and their efficacies for the control of insect and weed pests were evaluated and compared in two field trials. With liquefied petroleum gas (LPG) at 101 kg·ha−1, flaming machines reduced plant numbers by 86.7% to 98.8% 2 days after treatment (DAT), which was equal to or higher than the reduction after application of paraquat at 900 g·ha−1. Some weed species, especially awnless barnyard grass (Echinochloa colona) and goosegrass (Eleusine indica), regrew at 7 DAT, resulting in a decrease in control efficacy. Flaming machines also reduced the number of diamondback moth (Plutella xylostella) larvae by 83.0% to 88.2% and the number of adult striped flea beetles (Phyllotreta striolata) by 64.9% to 80.9%. This is the first report on flaming treatment in China to show that this method is a promising alternative to chemical pesticides for PPPM in leaf vegetable fields.

Application of Solid Dispersion Technique to Improve Solubility and Sustain Release of Emamectin Benzoate.

The solid dispersion technique, which is widely used in the medical field, was applied to prepare a pesticide dosage form of emamectin benzoate (EM). The preparation, physicochemical characterization, aqueous solubility, release dynamics, photolytic degradation, bioactivity, and sustained-release effects of the prepared EM solid dispersions were studied by a solvent method, using polymer materials as the carriers. Water-soluble polyvinyl pyrrolidone (PVP) K30 and water-insoluble polyacrylic resin (PR)III were used as the carriers. The influence of various parameters, such as different EM:PVP-K30 and EM:PRIII feed ratios, solvent and container choices, rotational speed and mixing time effects on pesticide loading, and the entrapment rate of the solid dispersions were investigated. The optimal conditions for the preparation of EM-PVP-K30 solid dispersions required the use of methanol and a feed ratio between 1:1 and 1:50, along with a rotational speed and mixing time of 600 rpm and 60 min, respectively. For the preparation of EM-PRIII solid dispersions, the use of methanol and a feed ratio between 1:4 and 1:50 were required, in addition to the use of a porcelain mortar for carrying out the process. Under optimized conditions, the prepared EM-PVP-K30 solid dispersions resembled potato-like, round, and irregular structures with a jagged surface. In contrast, the EM-PRIII solid dispersions were irregular solids with a microporous surface structure. The results of X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), ultraviolet (UV) spectrometry, and infrared (IR) spectrometry showed that the solid dispersions were formed by intermolecular hydrogen bonding. The solid dispersion preparation in PVP-K30 significantly improved the solubility and dissolution rate of EM, particularly the aqueous solubility, which reached a maximum of 37.5-times the EM technical solubility, when the feed ratio of 1:10 was employed to prepare the dispersion. Importantly, the wettable powder of EM-PVP-K30 solid dispersion enhanced the insecticidal activity of EM against the Plutella xylostella larvae. Furthermore, the solid dispersion preparation in PRIII afforded a significant advantage by prolonging the EM technical release in water at a pH below 7.0, especially when the PRIII content in solid dispersions was high. While the amplified toxicity of the wettable powder of EM-PRIII solid dispersions against the P. xylostella larvae showed no significant differences from that of the EM technical, the long-term toxicity under the field condition was much better than that of the commercially available EM 1.5% emulsifiable concentrate. Notably, solid dispersions with both the PVP-K30 and PRIII carriers reduced the effect of UV photolysis.

MicroRNA-998–3p contributes to Cry1Ac-resistance by targeting ABCC2 in lepidopteran insects

Cry protein toxins produced by Bacillus thuringiensis (Bt) are now widely used in sprays and transgenic crops to control insect pests. Most recently, ATP-binding cassette transporter proteins (ABC transporter), including ABCC2, ABCC3, ABCG1, ABCA2 and ABCB1, were reported as putative receptors for different Cry toxins. However, little is known about the regulatory mechanism involved in the expression of these ABC transporter genes. In the present study, a conserved target site of miR-998–3p was identified from the coding sequence (CDS) of ABCC2 in diverse lepidopteran insects. Luciferase reporter assays demonstrated that miR-998–3p could bind to the CDS of ABCC2 and down-regulate its expression through a conserved site and several non-conserved sites in three representative lepidopteran pests, including Helicoverpa armigera, Spodoptera exigua and Plutella xylostella. Injection of miR-998–3p agomir significantly reduced the abundance of ABCC2, accompanied by increased tolerance to Cry1Ac toxin in H. armigera, S. exigua and P. xylostella (Cry-S) larvae, while injection of miR-998–3p antagomir increased the abundance of ABCC2 dramatically, and thereby reduced the Cry1Ac resistance in a Cry1Ac resistant population of P. xylostella (GX-R). These results give a better understanding of the mechanisms of post-transcriptional regulation of ABCC2, and will be helpful for further studies on the role of miRNAs in the regulation of Cry1Ac resistance in lepidopteran pests.

C-terminal conserved motifs of Neprilysin1 in Cotesia plutellae are not required for immune suppression of the Diamondback moth, Plutella xylostella (L.)

Abstract Cotesia plutellae, an endoparasitoid wasp, parasitizes Plutella xylostella larvae and disrupts host immune responses through parasitic factors. These immune disruptive factors are known as maternal factors (venom proteins, polydnavirus, and ovary proteins) and an embryonic factor (teratocytes). In this study, we identified neprilysin-1 (Cp-NEP1) known as a potential immunosuppressive gene from the transcriptome of venom glands in C. plutellae. Cp-NEP1 encoding 451 amino acids belonged to the hymenopteran NEP1 family through phylogenetic analysis. Based on the structural comparison, Cp-NEP1 has lacked in conserved motifs such as a substrate binding (NAYY/F), zinc-binding (HExxH and ExxxD), and protein folding and maturation (CxxW). In order to investigate the function of Cp-NEP1 in host immune response, we constructed a recombinant Cp-NEP1 (rCp-NEP1) harboring N-terminally fused 6X His-tag. rCp-NEP1 was successfully expressed in Escherichia coli and purified. Pre-heated E. coli induced the spike of nodule formation whereas co-injection of rCp-NEP1 with pre-heated E. coli exhibited suppression of nodule formation. Quantitative real-time PCR showed that expression of phenoloxidase related to nodule formation was also suppressed when rCp-NEP1 was co-injected with preheated E. coli. These results suggest that Cp-NEP1 contributes to immunosuppression and that conserved motifs lacking in Cp-NEP1 are not necessary for immune suppression in the host.

Roles of Midgut Cadherin from Two Moths in Different Bacillus thuringiensis Action Mechanisms: Correlation among Toxin Binding, Cellular Toxicity, and Synergism.

The midgut cadherin has been described as one of the main functional receptors for Bacillus thuringiensis (Bt) toxins. Plutella xylostella (P. xylostella) and Helicoverpa armigera (H. armigera) are two major target pests of Bt toxins in China, and the roles of their cadherins in the action of Bt toxins have been only partially studied. Here, we expressed the two cadherins in Sf9 cells and their partial extracellular domains in Escherichia coli and tested them for Bt toxin binding, cellular toxicity, and synergism with toxins. Our results suggested that PxCad might function as a Cry1Ac receptor, although it showed lower binding levels to Cry1Ac and reduced cytotoxicity compared with HaCad. PxCad and HaCad are not receptors for Cry2A, Cry1B, Cry1C, and Cry1F toxins, although some of them can bind to the cadherins. The PxCad-TBR exhibits higher enhancement of Cry1Ac and weak enhancement of Cry1F toxicity in P. xylostella larvae, although it is not the receptor of Cry1F.

Effects of Aqueous Extracts from Amazon Plants on Plutella xylostella (Lepidoptera: Plutellidae) and Brevicoryne brassicae (Homoptera: Aphididae) in Laboratory, Semifield, and field trials.

We evaluated the insecticide activities of aqueous extracts of five species of plants from the Ecuadorian Amazon (Deguelia utilis (ACSm.) AMGAZEVEDO (Leguminosae: Papilionoideae), Xanthosoma purpuratum K. Krause (Alismatales: Araceae), Clibadium sp. (Asteracea: Asterales), Witheringia solanacea L'Hér (Solanales: Solanaceae), and Dieffenbachia costata H. Karst. ex Schott (Alismatales: Araceae)) plus Cymbopogon citratus Stapf. (Poales: Poaceae) under laboratory, open-field conditions in Plutella xylostella L. (diamondback moth), and semifield conditions in Brevicoryne brassicae L. Tap water was used as a negative control, and synthetic insecticides were used as positive controls. In a laboratory bioassay, aqueous extracts of D. utilis resulted in P. xylostella larval mortality. In contrast to chlorpyrifos, all botanicals were oviposition deterrents. All extracts except Clibadium sp. decreased leaf consumption by P. xylostella larvae. In semifield experiments, D. utilis, Clibadium sp., D. costata, and X. purpuratum initially controlled the population of B. brassicae, but 7 d after application, all botanicals except the D. utilis lost their ability to control the pest. In field experiments on broccoli crops in both dry and rainy seasons, the extracts did not control the abundance of P. xylostella, where as a mixture of two insecticides (chlorpyrifos + lambda cyhalothrin) did. These results show some incongruences from laboratory to semifield and field conditions, indicating that more studies, including the identification of the chemicals responsible for the biological activity, its stability, and the effects of chemotypes on insecticidal activity, are needed to understand the potential of these plant species as botanical insecticides.

Polyhydroxy cucurbitane triterpenes from Hemsleya penxianensis tubers

Ten new cucurbitane triterpenoids, hemsleyacins A–J (1–10), together with three known cucurbitane triterpenoids, dihydrocucurbitacin F (11), scandenogenin D (12), and jinfushanencin F (13), were separated from ethanolic tuber extracts of Hemsleya penxianensis. The absolute configurations of the new compounds were established based on NMR, HRESIMS, and CD spectra. Compounds 7 and 10–12 were evaluated in terms of their antifeedant activity against Plutella xylostella larvae. The result showed that compound 10 exhibited potent antifeedant activity against P. xylostella larvae after 48 h of treatment. Furthermore, the MTT test showed that compound 11 exhibited potent inhibition toward the UMUC-3 and T24 cell lines with IC50 values of 29.12 and 35.62 μM, respectively, compared to the positive control cisplatin IC50 values of 8.27 and 13.72 μM. Western blot analysis revealed that compound 11 treatments substantially inhibited the phosphorylation of IκBα.

Effects of floral resources on the longevity and parasitism of Cotesia vestalis Haliday (Hymenoptera: Braconidae) on Plutella xylostella (L.) (Lepidoptera: Plutellidae) in Vietnam

Parasitoids are important biological control of crop pests. In Vietnam, Cotesia vestalis is a native wasp species that has demonstrated its applicability as a natural insect pest enemy. Many adult parasitoids require food resources such as nectar and pollen to optimize their life cycles. Potential effects of yellow cosmos (Cosmos sulphureus), shrub verbena flower (Lantana camara), common zinnia (Zinnia elegans), and coriander flower (Coriandrum sativum L.) on the longevity and parasitism of C. vestalis were investigated. Results showed that nutrition resources from yellow cosmos (C. sulphureus) and shrub verbena flower (Lantana camara) significantly increased the longevity of C. vestalis in comparison with water (P < 0.001). Kaplan-Meier estimates of survival functions of female Cotesia vestalis exposed to different food sources indicated a significant difference in the treatments (P < 0.01). Male and female wasps feeding on Cosmos sulphureus, Lantana camara, and Coriandrum sativum survived significantly longer than wasps fed on water or Zinnia elegans. Parasitism efficiency of C. vestalis was tested on diamondback moth Plutella xylostella (L.) larvae for different food resources. Cosmos sulphureus, Lantana camara, Coriandrum sativum treatments gave the different mean number of emergence parasitoids per day compared to water treatment. Results implied that food resources from flowers benefitted the longevity of C. vestalis.

Parasitism of diamondback moth Plutella xylostella by the solitary parasitoid wasp Cotesia vestalis in Samoa

Plutella xylostella is a major pest of crucifier crops in Samoa and other Pacific islands. This pest has developed resistance to most insecticides available in the island nations so the objective of this study was to examine potential biological control options for P. xylostella in Samoa. Existing parasitism of P. xylostella on Chinese cabbage (Brassica rapa subspp.) was investigated at a farm in Alesia and at the USP farm in Alafua, and established populations of Cotesia vestalis were found at both locations. Plutella xylostella larvae turn light yellow and show sluggish behaviour after parasitism, and they could be easily differentiated from unparasitised ones. Developing C. vestalis larvae emerge from their hosts and spin white cocoon around their body. After 5–6 days, a single adult emerges from the C. vestalis cocoon. The average parasitism rate between April 2015 and March 2016 was 10–18% but was significantly higher at the USP farm than the Alesia farm. This result could be because no insecticides were applied to the crops at USP. Parasitism was highest between June and August when the lowest average daily temperatures occur.

Effect of WAM‐1 transgenic Arabidopsis thaliana on the development and gut microbial composition of diamondback moth (Plutella xylostella) larvae (Lepidoptera: Plutellidae)

AbstractWAM‐1 is a cathelicidin antimicrobial peptide found on the Macropus eugenii (Tammar wallaby) genome. It possesses antibiotic activity against a broad spectrum of bacteria and fungi. In order to investigate the impact of this WAM‐1 antimicrobial peptide on development and midgut microbial composition of Plutella xylostella (DBM) larvae, the WAM‐1 was introduced into Arabidopsis thaliana using the Agrobacterium‐mediated floral‐dip transformation method. WAM‐1 expression was confirmed by reverse transcriptase PCR analysis. The larval growth and developmental variations and midgut microbial compositions were analysed after DBM larvae had fed on transgenic plants. Transgenic plant‐fed DBM larvae showed significantly higher mortality, a prolonged developmental period and less weight gain. Enterobacteriaceae was the highest dominating family in all samples including transgenic and non‐transgenic plants fed larvae. However, its abundance was substantially lower in the WAM‐1 Arabidopsis‐fed larvae. Furthermore, Moraxellaceae and Bacillaceae were the next dominating families in the WAM‐1 transgenic Arabidopsis‐fed larvae whereas Enterococcaceae and Xanthomonadaceae were dominant in the non‐transgenic Arabidopsis‐fed larvae. Abundance of Pseudomonadaceae was also relatively higher in WAM‐1 transgenic‐fed larvae whereas it was much lower in other samples. Therefore, our findings suggest that WAM‐1 has an impact on gut microbial composition but a minor effect on larval development.

The effect of host plant on the development and larval midgut protease activity of Plutella xylostella (Lepidoptera: Plutellidae)

Plutella xylostella L. (diamondback moth) is a pest of cruciferous plants and has devastating effects on the yield and quality of cruciferous vegetables. Insect midgut protease plays an important role in the digestion of host plant nutrients and the detoxification of defensive compounds. The effects of host plants on the larval midgut protease activity and the performance of P. xylostella larvae were examined on six different host plants, including qingan 70, lvqiu 66, qingan 80, Brassica chinensis, broccoli and oilseed rape The results showed that P. xylostella larvae ingested all hosts, and the protease activities were significantly different at different instars. In the 3rd instar and early 4th instar, which were the important periods for digestion, 4 proteases activities of P. xylostella were greater than activity in other instars. Meanwhile, the activities of the high-alkaline trypsin and low-alkaline trypsin (important proteases in the insect midgut) were greatest when P. xylostella larvae ingested qingan 80. The relative host suitability, ranked from highest to lowest was: broccoli > oilseed rape = Brassica chinensis > qingan 70 > qingan 80 > lvqiu66. The intrinsic rate of increase indicated that P. xylostella had the best adaptability and food receptivity to the oilseed rape, whereas when P. xylostella larvae ingested Brassica chinensis, the activities of the trypsin were highest. This suggests Brassica chinensis in an appropriate host for P. xylostella that highly elevates the activities of trypsin that subsequently helps the insect to digest nutrients obtained from host plants. In practical application, we can reduce the harm to target plants by adjusting the plantation structure by optimally planting different hosts limit growth and reproduction to minimize pest outbreaks.

Aktivitas Sinergistik Campuran Ekstrak Buah Piper aduncum dan Tiga Jenis Insektisida terhadap Ulat Plutella xylostella

Synergistic Activity of Mixtures of Piper aduncum Fruit Extract and Three Commercial Insecticides against the Diamond Back Moth, Plutella xylostellaPlutella xylostella is an important pest of Brassicaceae vegetable crops. Frequent use of insecticides containing single active ingredients can cause resistance in P. xylostella. This work was done to evaluate the synergism between Piper aduncum fruit extract and three commercial insecticides, i.e. abamectin, chlorfenapyr, and spinetoram, against P. xylostella from Pacet District, Cianjur Regency. Results of leaf-residue feeding bioassays with 48-h feeding treatment showed that LC95 of abamectin, chlorfenapyr, and spinetoram at 96 h after treatment (HAT) was about 5.8, 7.0, and 1.9-fold higher than their respective field rates. Thus, P. xylostella larvae from Pacet-Cianjur were not susceptible to abamectin and chlorfenapyr, but were still fairly susceptible to spinetoram. LC95 of P. aduncum extract at 96 HAT was 0.68% (w/v). Based on combination index at the LC95 level - 96 HAT, mixtures of P. aduncum extract with all three test insecticides were synergistic. Thus, P. aduncum extract is potential to be used as an alternative ingredient to increase the effectiveness of the three test insecticides against P. xylostella.

Integrating biocontrol agents with farmer\u2019s practice: impact on diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) and cabbage yield

A field trial was conducted in a farmer’s field by integrating biocontrol agents, a multiple insecticide tolerant strain (MITs), Trichogramma chilonis and formulation of Bacillus thuringiensis (NBAIR BtG4) with reduced insecticidal spray as a biocontrol-based IPM compared to insecticidal application as a farmer’s practice, for the management of the diamondback moth (DBM), Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) infesting cabbage. Six T. chilonis releases of 100,000 parasitized eggs ha− 1 were applied. Along with parasitoid release, a liquid formulation of B. thuringiensis (2%) was applied after third and fifth releases of T. chilonis. The number of P. xylostella larvae were significantly reduced in the field treated with biocontrol-based IPM as compared to farmer’s practice after 30 and 45 days after treatment. After the 45 days, the holes on cabbage leaves were 2.2/plant in the field treated with biocontrol, opposed to 8.0 holes per plant were recorded in the farmer’s practice filed. Only 7% of cabbage head damage was recorded in the field treated with biocontrol, whereas, in farmer’s practice field, those were 32.2%. The cost-benefit analysis showed that integrating these biological control agents along with a reduced number of insecticidal sprays could reduce DBM population and percent head damage with an eventual increase in the yield.

Effects of Cantharidin and Norcantharidin on Larval Feeding and Adult Oviposition Preferences of the Diamondback Moth (Lepidoptera: Plutellidae).

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a destructive insect pest of cruciferous plants that has developed resistance to almost every listed commercial insecticide. Cantharidin as an animal-derived biopesticide is a natural defensive compound produced by Meloidae insects with toxicity to many insects including P. xylostella. Norcantharidin is an important substitute of cantharidin and has similar insecticidal activities to cantharidin. Although the toxicity of cantharidin and norcantharidin to P. xylostella has been reported, little research has focused on the effects of cantharidin or norcantharidin on the behavior of P. xylostella. In this study, we investigated the feeding behavior of third-instar larvae and the oviposition preference of adult P. xylostella in order to explore the effects of different concentrations of cantharidin and norcantharidin. Results show that cantharidin and norcantharidin have antifeedant effect on P. xylostella larvae. The values for AFC50 were 13.0228 and 149.4210 mg/ml, respectively. Furthermore, the oviposition deterrence rate of cantharidin on P. xylostella ranged from 49.37 to 58.24% and that of norcantharidin was from 20.88 to 33.33%. These results suggest cantharidin and norcantharidin may have repellent and antifeedant effect on P. xylostella, which could contribute toward using biopesticides to manage P. xylostella and may provide a new strategy for integrated pest management.

The conserved cysteine residues in Bacillus thuringiensis Cry1Ac protoxin are not essential for the bipyramidal crystal formation.

To evaluate the function of conserved cysteine residues in Cry1Ac protoxin, we constructed a series of Cry1Ac mutants in which single or multiple cysteine residues were replaced with serine. It was found that cysteine substitution had little effect on the protoxin expression and bipyramidal crystal formation. Bioassays using Plutella xylostella larvae showed that two mutants with fourteen cysteine residues in the C-terminal half and all sixteen residues replaced had similar toxicity as wildtype Cry1Ac protoxin. Our study suggests that the conserved cysteine resudues in the Cry1Ac protoxin are not essential for deposition into a bipyramidal crystal even though the C-terminal half was directly involved in crystal formation.

Assessment of Yersinia entomophaga as a control agent of the diamondback moth Plutella xylostella.

The application of the biocontrol bacterium Yersinia entomophaga as a foliar spray was assessed for its efficacy against larvae of the diamondback moth, Plutella xylostella. The bacterium was applied as either a broth suspension, or as a biopolymer-based gel foliar spray and compared with commercial insecticides Dipel (Bacillus thuringiensis) and Spinosad. The performance of Y. entomophaga was comparable with that of Dipel. The gel-based formulation extended leaf persistence over that of the basic broth culture spray, while also providing higher initial foliar deposition rates. The bacterium was found to multiply within the P. xylostella larvae to 5.8 × 105 cells per larva, while the median lethal dose (LD50) was determined to be 2.69 × 103 cells per larva. Importantly, B. thuringiensis Cry1A-resistant, Cry1C-resistant, indoxacarb/pyrethroid-resistant, and Spinosad-resistant P. xylostella larvae were susceptible to Y. entomophaga.

Inhibitory Effect of Protease Inhibitors on Larval Midgut Protease Activities and the Performance of Plutella xylostella (Lepidoptera: Plutellidae).

Plutella xylostella L. (diamondback moth) is a pest of cruciferous plants. To understand the relationship among protease inhibitors, protease activities and the growth and development of this insect, the activities of midgut proteases of P. xylostella larvae were determined in this study. Protease samples were extracted from the midguts of P. xylostella larvae, and the protease activities were determined using enzyme specific substrates. The results showed that CaCl2, EDTA, and EGTA inhibited only the trypsin. Among the common protease inhibitors, phenylmethyl sulfonyl fluorine (PMSF), Nα-p-methyl sulfonyl-L-lysine chloromethylketone (TLCK), Nα-methyl sulfonyl-L- phenylalanine chloromethyl ketone (TPCK), soybean trypsin inhibitor (STI), and PMSF inhibited the total protease, high-alkaline trypsin (a trypsin subtype with highly alkaline pH optimum), low-alkaline trypsin (another trypsin subtype with slightly alkaline pH optimum), and chymotrypsin; TLCK inhibited the total protease and high-alkaline trypsin, whereas TPCK only activated the high-alkaline trypsin activities. STI had an inhibitory effect on all the proteases. These results showed that protease inhibitors had a certain extent inhibition to protease activities in the larval midgut of P. xylostella and that STI can potentially be used for effective pest control. The development of P. xylostella was delayed in the presence of different inhibitors. These effects were also related to the concentration of the inhibitor. A higher STI concentration showed a longer lasting effect but lower effect in this study compared to that of TLCK. The protease inhibitors had some inhibitory effect on the synthesis and secretion of proteases, and interfered with the protease activity, thereby inhibiting the absorption of nutrients and delaying the growth and development of P. xylostella and reducing their ability to reproduce. These findings should provide the baseline information about using for effective pest management in the future.

Impact of insecticides on the efficacy of entomopathogenic nematodes against the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) on cabbage in northern Benin

Description of the subject. The article deals with the study of compatibility of entomopathogenic nematode (EPN) species with insecticides currently used against diamondback moth (DBM) Plutella xylostella (L.) in northern Benin Objectives. The aim of this work was to determine the impact of five insecticides on the efficacy of entomopathogenic nematodes against DBM larvae. Method. Infective juveniles (IJs) of two EPN species (Steinernema sp. 83a and Heterorhabditis sonorensis KF723827) were exposed to five insecticides used against P. xylostella larvae in Djougou for 48 h. The number of surviving nematodes was used to infest DBM larvae. The experiment was carried out under laboratory and semi-field conditions. Results. The bioassays carried out in laboratory showed that the survival rate of nematodes exposed to KARATE 2.5 WG, LAMBDA SUPER 2.5EC or neem oil ranges between 95% and 98%. In the treated plots, Steinernema sp. 83a was the most virulent with the highest P. xylostella mortality (87% at 50 IJs·cm-2 after 24 h) while only 35% larval mortality was recorded for H. sonorensis applied at the same dose. Population density of nematodes which penetrated DBM larvae reached 9 ± 3I IJs·larva-1 for H. sonorensis KF723827 and 6 ± 2 IJs·larva-1 for Steinernema sp. 83a. In cadaver of DBM, nematode reproduction did not appear to be affected by the contact with insecticides. Conclusions. Based on our research, we conclude that the three insecticides did not affect EPNs efficiency and could be used in combination against DBM.

Two arrays of defense strategies of Brassicaceae plants that eavesdrop on mint volatiles

ABSTRACT Brassica rapa can eavesdrop on volatile compounds emitted from peppermint and consequently boost its defense responses against Plutella xylostella. In the current study, to assess how B. rapa receiver plants cultivated near peppermint plants resist P. xylostella, two biological assays were conducted. The data showed that the receiver plants cultivated with peppermint exhibited lower weight gain of P. xylostella larvae, compared to that exhibited by non-receiver plants. Moreover, a lower rate of oviposition of adult female P. xylostella was observed on B. rapa plants cultivated with peppermint plants compared to the rate on B. rapa plants cultivated with glass-enclosed peppermint plants, although receiver B. rapa plants that had been previously incubated with peppermint for 7 days and non-receiver B. rapa plants exhibited similar rates of oviposition. Taking all these findings together, we conclude that cultivation of B. rapa receiver plants with peppermint results in two arrays of defense strategies.