Repellency of Plant Extracts against the Legume Flower Thrips Megalurothrips sjostedti (Thysanoptera: Thripidae)

Host selection by thrips is affected by the floral volatile profile of sunflower

Thrips, Frankliniella intonsa, is a highly polyphagous pest with a worldwide distribution. F. intonsa-infested sunflower seeds show marked visual damage. The study findings revealed that significantly more F. intonsa infested confection sunflower compared to oilseed sunflower, via olfactometer bioassay studies, we found that compared with the flower and pollen of oilseed sunflowers, those of confection sunflowers attract F. intonsa. Considering this discrepancy in the preference of F. intonsa on oilseed and confection sunflowers, the volatiles of the flower and pollens of two sunflowers were analysed by gas chromatography-mass spectroscopy. The behavioural responses of F. intonsa were assessed for these compounds using Y-tube bioassays. Geranyl bromide, a unique volatile component of oilseed sunflowers, induced an assertive approach-avoidance behaviour in F. intonsa, whereas the unique component ethyl isovalerate in confection sunflowers attracted F. intonsa. F. intonsa adults demonstrated significant attraction to the blends of confection sunflowers. Furthermore, field verification revealed that intercropping confection and oilseed sunflowers could effectively control F. intonsa. The study provided insights into the chemical cues used by F. intonsa in locating hosts. Therefore, oilseed sunflowers can be used as repellent plants to prevent F. intonsa invasion.

Evaluation of Aphicidal Effect of Essential Oils and Their Synergistic Effect against Myzus persicae (Sulzer) (Hemiptera: Aphididae)

The insecticidal activities of essential oils obtained from black pepper, eucalyptus, rosemary, and tea tree and their binary combinations were investigated against the green peach aphid, Myzus persicae (Aphididae: Hemiptera), under laboratory and glasshouse conditions. All the tested essential oils significantly reduced and controlled the green peach aphid population and caused higher mortality. In this study, black pepper and tea tree pure essential oils were found to be an effective insecticide, with 80% mortality when used through contact application. However, for combinations of essential oils from black pepper + tea tree (BT) and rosemary + tea tree (RT) tested as contact treatment, the mortality was 98.33%. The essential oil combinations exhibited synergistic and additive interactions for insecticidal activities. The combination of black pepper + tea tree, eucalyptus + tea tree (ET), and tea tree + rosemary showed enhanced activity, with synergy rates of 3.24, 2.65, and 2.74, respectively. Essential oils formulation was effective on the mortality of aphids. Fourier Transform Infrared Spectroscopy (FTIR) analysis showed that stability of a mixture of essential oils was not affected by store temperature (15, 25, and 35 °C) and the functional groups were not changed during storage. Based on our results, the essential oils can be used as a commercial insecticide against M. persicae.

Rosmarinus officinialis L. (Lamiales: Lamiaceae), a Promising Repellent Plant for Thrips Management

A number of thrips species are among the most significant agricultural pests globally. Use of repellent intercrop plants is one of the key components in plant-based 'push-pull' strategies to manage pest populations. In this study, the behavioral responses of three thrips species, Frankliniella occidentalis (Pergande), Frankliniella intonsa (Trybom), and Thrips palmi Karny (Thysanoptera: Thripidae) to Rosmarinus officinalis were investigated in Y-tube olfactometer bioassays and cage experiments. In addition, the major volatile compounds from rosemary were identified and the effect of the individual compounds on thrips behavior was evaluated. Females and males of the three thrips species were significantly repelled by the volatiles from cut rosemary leaves. The presence of rosemary plants significantly reduced settlement of females of the three thrips species and eggs laid by F. occidentalis females on target host plants. In total, 47 compounds were identified in the volatiles collected from the cut leaves of rosemary plants. The responses of the three thrips species to 10 major volatile compounds showed significant differences. However, α-pinene, the most abundant volatile, was repellent to F. occidentalis and F. intonsa. Eucalyptol, the second most abundant volatile, showed significant repellent activity to all the three thrips species. Our findings showed that rosemary is a promising repellent plant against the three thrips pests we tested, which could be a good candidate for 'push' plants in plant-based 'push-pull' strategies. The identified volatile compounds that accounted for the repellent activity could be developed as repellents for sustainable thrips management.

Semiochemicals for Thrips and Their Use in Pest Management

Thrips (Thysanoptera) are small insects that can cause huge problems in agriculture, horticulture, and forestry through feeding and the transmission of plant viruses. They produce a rich chemical diversity of pheromones and allomones and also respond to a broad range of semiochemicals from plants. These semiochemicals offer many opportunities to develop new approaches to pest management. Aggregation pheromones and plant-derived semiochemicals are already available in commercial products. We review these semiochemicals and consider how we can move away from using them mainly for monitoring to using them for control. We still know very little about the behavioral responses of thrips to semiochemicals, and we show that research in this area is needed to improve the use of semiochemicals in pest management. We also propose that thrips should be used as a model system for semiochemically mediated behaviors of small insects that have limited ability to fly upwind.

Phytochemical Screening and Bioactivity of Ludwigia spp. in the Control of Plutella xylostella (Lepidoptera: Plutellidae)

Simple Summary

Ludwigia species have several pharmacological applications, but their insecticidal proprieties have not been tested. This research thus aimed to study the effects of aqueous extracts on the biological characteristics of Plutella xylostella. We noted that the L. tomentosa, L. longifolia and L. sericea extracts were active. These species showed the best results regarding their ability to control P. xylostella populations, due to the presence of substances that inhibit food consumption and interfere in the morphological and physiological transformations of the offspring and adult oviposition.

Abstract

We tested the bioactivity of aqueous extracts of Ludwigia spp. (Myrtales: Onagraceae) on the biological cycle of Plutella xylostella. We assessed the duration of and viability during the larval, pupal and adult phases, as well as the influence of the extracts on the fecundity and hatching of P. xylostella eggs. Subsequently, we phytochemically screened the extracts. The extracts of L. tomentosa and L. longifolia reduced the pupal weight instead of prolonging the larval stage of P. xylostella. The L. tomentosa effect caused higher larval mortality and reduced the fecundity and hatching of P. xylostella eggs, and L. sericea reduced the egg survival. The phenolic compounds—flavonoids, condensed tannins and alkaloids—were more abundant in L. nervosa, L. tomentosa, L. sericea and L. longifolia. The L. tomentosa, L. longifolia and L. sericea extracts were bioactive, and these species showed the best results regarding their ability to control P. xylostella populations, because these plants produce substances able to inhibit food consumption and interfere with the morphological and physiological transformations of the offspring and the oviposition of adults.

Methanolic Extract of Winter Cherry Causes Morpho-Histological and Immunological Ailments in Mulberry Pyralid Glyphodes pyloalis

The effect of Withania somnifera a medicinal plant seed extract was tested against lesser mulberry pyralid, a potential pest of mulberry. The mulberry leaves were used for silk production in rural areas of northern Iran. The extract was administered orally by leaf dipping method in two lower (5%W/V) and higher (15%W/V) dosages to third instar larvae (<24 h) for biological assays and to fifth instar larvae (<24 h) for Physiological studies. The results showed formation of larvoids (Ls), larval-pupal intermediates (LPIs), pupoids (Ps) and pupal-adult intermediates (PAIs). The results showed increased larval duration by 1.7 and 2 folds in 5 and 15% treatment, respectively. Fecundity of resultant adults was decreased by 1.2 and 1.3 in 5 and 15% treatment, respectively. Except approximate digestibility (AD) and consumption index (CI) all other feeding indices showed reduction. The feeding deterrence was prominent at 15% (87%) and 5% showing 48% deterrence. Our enzymatic and non-enzymatic assessments upon treatment showed reduction in key components, except detoxifying enzymes. However, the activity of an important enzyme involved in cuticle hardening and immunity called phenoloxidase was reduced. We also investigated the histology of midgut for further analysis and found drastic changes in main cellular elements. Immunological changes following treatment was noticeable in reduced Total Hemocyte Count but surprisingly increased Differential Hemocyte Count. However, the hemocytes structure was extremely damaged. The reduced number of eggs in treated but survived adults indicated reduced ovaries, with vacuolization both in trophocytes and oocytes. The key chemical compounds showed reductions particularly at 15%. The present results are concomitant with few earlier studies on this medicinal plant and deserve further studies particularly in deriving key chemicals that alter metamorphosis similar to insect growth regulators.

TRPA1 modulates noxious odor responses in Lygus hesperus

Lygus hesperus isa key pest of many economically important crops across western North America. Central to many aspects of the lives of these insects is chemical signalling, with identified roles in host plant selection, aggregation and passive mate guarding. The development of novel monitoring and control approaches for this insect will rely on a sound understanding of how these cues are perceived and processed, and their impact on behavior. Towards this end, we investigated allyl isothiocyanate, cinnamaldehyde and citronellal, compounds that are noxious repellents to other insects. We found that L. hesperus avoided areas containing the three compounds and that exposure induced increases in movement velocity and duration in both nymphs and adults. This suggests these compounds may work as repellents. To better understand the underlying physiology of this response, RNA interference by dsRNA injection was used to inhibit the expression of two chemosensory-associated proteins, the odorant receptor co-receptor (Orco) and the transient receptor potential A (TRPA1) channel. While knockdown of Orco did not change the reaction of adult females to citronellal, TRPA1 silencing effectively eliminated the induced increase to movement, suggesting a chemoperceptory role in citronellal detection.

Efficacy of binary combinations between methyl salicylate and carvacrol against thrips Anaphothrips obscurus: laboratory and field trials

BACKGROUND

Thrips Anaphothrips obscurus are one of the cosmopolitan major pests feeding on cereals and other grasses. In order to develop alternatives of chemical insecticides for thrips control, based on fumigant activity screening and evaluation of 22 essential oil (EO) compounds against the thrips, the binary interactions of methyl salicylate and carvacrol (MS-C) with high fumigant toxicity were studied systematically by bioassay and field trials.

RESULTS

The bioassay results showed that six in 22 EO compounds had high fumigant toxicity against both the second-instar nymphs and adults of A. obscurus, including methyl salicylate, carvacrol, thymol, trans-cinnamaldehyde, diallyl trisulfide, and L-perillaldehyde. Furthermore, the combination of methyl salicylate mixed with carvacrol at a volume ratio of 5:5 exhibited the most significant synergism against A. obscurus, with a poison ratio value of 1.32 and a co-toxicity coefficient of 151.15. The optimal formulation of microemulsion (ME) was composed of 5% methyl salicylate, 5% carvacrol, 46% adjuvant and 44% deionized water. The result of dynamic light scattering and stability showed that MS-C 10% ME was a transparent, single-phase and homogeneous liquid system. Field trials indicated that the ME displayed a significant control efficacy of about 89.17% on thrips in peppers, and 82.59% in broad bean on the seventh day post application with a dosage of 600.0 g A.I hm^-2 , respectively.

CONCLUSION

The binary combination of MS-C possesses strikingly synergistic action against thrips A. obscurus, and the MS-C 10% ME has the potential to be developed as a botanical pesticide product for thrips control. © 2019 Society of Chemical Industry.

Oncolytic adenovirus drives specific immune response generated by a poly-epitope pDNA vaccine encoding melanoma neoantigens into the tumor site

Background

DNA vaccines against cancer held great promises due to the generation of a specific and long-lasting immune response. However, when used as a single therapy, they are not able to drive the generated immune response into the tumor, because of the immunosuppressive microenvironment, thus limiting their use in humans. To enhance DNA vaccine efficacy, we combined a new poly-epitope DNA vaccine encoding melanoma tumor associated antigens and B16F1-specific neoantigens with an oncolytic virus administered intratumorally.

Methods

Genomic analysis were performed to find specific mutations in B16F1 melanoma cells. The antigen gene sequences were designed according to these mutations prior to the insertion in the plasmid vector. Mice were injected with B16F1 tumor cells (n = 7–9) and therapeutically vaccinated 2, 9 and 16 days after the tumor injection. The virus was administered intratumorally at day 10, 12 and 14. Immune cell infiltration analysis and cytokine production were performed by flow cytometry, PCR and ELISPOT in the tumor site and in the spleen of animals, 17 days after the tumor injection.

Results

The combination of DNA vaccine and oncolytic virus significantly increased the immune activity into the tumor. In particular, the local intratumoral viral therapy increased the NK infiltration, thus increasing the production of different cytokines, chemokines and enzymes involved in the adaptive immune system recruitment and cytotoxic activity. On the other side, the DNA vaccine generated antigen-specific T cells in the spleen, which migrated into the tumor when recalled by the local viral therapy. The complementarity between these strategies explains the dramatic tumor regression observed only in the combination group compared to all the other control groups.

Conclusions

This study explores the immunological mechanism of the combination between an oncolytic adenovirus and a DNA vaccine against melanoma. It demonstrates that the use of a rational combination therapy involving DNA vaccination could overcome its poor immunogenicity. In this way, it will be possible to exploit the great potential of DNA vaccination, thus allowing a larger use in the clinic.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0644-7) contains supplementary material, which is available to authorized users.

Repellence of Myzus persicae (Sulzer): evidence of two modes of action of volatiles from selected living aromatic plants

BACKGROUND

Intercropping companion plants (CPs) with horticultural crops could be an eco-friendly strategy to optimize pest management. In this research, volatile organic compounds (VOCs) emitted by some CPs were investigated for their repellent properties towards the green peach aphid (Myzus persicae Sulzer). The aim of this study was to understand the modes of action involved: direct effects on the aphid and/or indirect effects via the host plant (pepper, Capsicum annuum L.).

RESULTS

We identified two promising repellent CP species: the volatile blend from basil (Ocimum basilicum, direct repellent effect) and the mixture of (or previously intercropped) C. annuum plants with Tagetes patula cv. Nana (indirect effect). This effect was cultivar-dependent and linked to the volatile bouquet. For the 16 compounds present in the O. basilicum or T. patula bouquets tested individually, (E)-β-farnesene, and eugenol reported good repellent properties against M. persicae. Other compounds were repellent at medium and/or highest concentrations. Thus, the presence of repellent VOCs in a mixture does not mean that it has a repellent propriety.

CONCLUSION

We identified two promising repellent CP species towards M. persicae, with a likely effect of one CP's VOCs on the host plant repellency and highlighted the specific effectiveness of VOC blends. © 2018 Society of Chemical Industry.

Receiver Operating Characteristic curve analysis determines association of individual potato foliage volatiles with onion thrips preference, cultivar and plant age

Tomato spotted wilt virus (TSWV) causes sporadic but serious disease in Australian potato crops. TSWV is naturally spread to potato by thrips of which Thrips tabaci is the most important. Prior studies indicated possible non-preference of potato cultivars to T. tabaci. Select potato cultivars were assessed for non-preference to T. tabaci in paired and group choice trials. Cultivars 'Bismark', 'Tasman' and 'King Edward' were less preferred than 'Atlantic', 'Russet Burbank' and 'Shepody'. Green leaf volatiles were sampled using solid-phase microextraction from the headspace of potato cultivars of two ages that differed in T. tabaci preference. Analysis of headspace volatile data using Receiver Operating Characteristic curves identified individual volatiles associated with T. tabaci preference and non-preference, young and old plants and individual cultivars. These data could be used to inform breeding programs for selection of T. tabaci resistance to assist with TSWV management, and biological testing of novel thrips management compounds.

Primary Screening of Plant Essential Oils as Insecticides, Fumigants, and Repellents Against the Health Pest Paederus fuscipes (Coleoptera: Staphylinidae)

The contact and fumigant toxicity as well as repellent activity of 10 plant essential oils were evaluated against Paederus fuscipes Curtis adults. Essential oils were identified through gas chromatography-mass spectrometry analysis. Results showed that wintergreen oil exhibited optimal contact and fumigant toxicity but had no significant repellent activity against P. fuscipes. The LC50 values of fumigant toxicity of wintergreen oil were 2.680 and 1.591 µL/L air after 1 and 8 h of exposure, respectively. The LC50 values of contact toxicity of wintergreen oil were 0.086 and 0.060 µL/adult after 1 and 8 h of exposure, respectively. Cinnamon oil exhibited the highest repellent activity. In particular, 0.1 µL/cm2 cinnamon oil showed 100% repellency against P. fuscipes even for 6 h. Moreover, 0.01 and 0.005 µL/cm2 cinnamon oil conferred 80% repellency against P. fuscipes for 8 and 4 h, respectively. Overall, wintergreen oil is the best candidate insecticide and fumigant, and cinnamon oil is optimal as a repellent. The low-dose, rapid action of wintergreen oil and the low-dose, persistent repellency of cinnamon oil are important factors that suggest their use as insecticides, fumigants, and repellents against P. fuscipes.