Insect Mortality Research Articles

Toxicity of Photorhabdus luminescens and Xenorhabdus bovienii bacterial metabolites to pecan aphids (Hemiptera: Aphididae) and the lady beetle Harmonia axyridis (Coleoptera: Coccinellidae)

Toxicity of the metabolites of two bacteria, Photorhabdus luminescens and Xenorhabdus bovienii, symbionts of entomopathogenic nematodes, were tested in the laboratory against the multicolored Asian lady beetle, Harmonia axyridis, the black pecan aphid, Melanocallis caryaefoliae, and the blackmargined aphid, Monellia caryella. Bacterial broth prepared from both P. luminescens and X. bovienii demonstrated high levels of toxicity equivalent to the pyrethroid insecticide bifenthrin and caused higher insect mortality than tryptic soy broth plus yeast extract (TSY) (blank control) against M. caryella; broth culture of P. luminescens was more effective than TSY against M. caryaefoliae. At the levels tested, the metabolites were not toxic to H. axyridis.

Efficacy of entomopathogenic nematode isolates from Turkey against wheat stink bug, Aelia rostrata Boheman (Hemiptera: Pentatomidae) adults under laboratory conditions

BackgroundThe wheat stink bug, Aelia rostrata Boheman (Hemiptera: Pentatomidae), is one of the harmful insects that caused significant product losses in cereals due to outbreaks. Entomopathogenic nematodes (EPNs) are natural enemies of soil insect pests whose effects as a biocontrol agent against many harmful pests have been demonstrated by many laboratories and field/garden studies in the world. The present laboratory studies, using native EPNs [Steinernema carpocapsae (Black sea isolate), S. feltiae (isolate 09-31) (Aydin isolate) and Heterorhabditis bacteriophora (isolate 09-43) (Aydin isolate)] against the wheat stink bug adults, were carried out.ResultsIn the application of EPNs to the soil in plastic cups, the highest mortality rates (75 and 70%) on wheat stink bug occurred at 200 IJs cm−2 concentration of S. carpocapsae isolate at 15 and 12 °C, respectively. In other tested nematode species, the highest insect mortality was observed at 200 IJs cm−2 concentration of S. feltiae and H. bacteriophora isolates, with mortality rates of 65–35% and 55–25%, at 15 and 12 °C, respectively. S. carpocapsae (Black sea isolate) was the most pathogenic among the three nematodes tested.ConclusionsIt was concluded that S. carpocapsae had the potential as a biocontrol agent against the wheat stink bug, A. rostrata. The applications of S. carpocapsae were the great potential for the management of the pest. Effective use of EPNs should be evaluated in integrated pest management strategies between other biological control agents. According to EPNs laboratory experiments results, field trials should be conducted in future studies.

Evaluation of the entomopathogenic nematode, Steinernema asiaticum against the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) under screen house and field conditions

BackgroundThe experiments were conducted at Research Farm, Chaudhary Charan Singh Haryana Agricultural University, Hisar, India. Infectivity and effectiveness of entomopathogenic nematode (EPN), Steinernema asiaticum infective juveniles (IJs) were evaluated against the diamondback moth (DBM), Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) as foliar spray on cabbage plants in screen house with single (30,000 IJs per plant), two (15,000 + 15,000 IJs per plant) or three (10,000 + 10,000 + 10,000 IJs per plant) applications. In the field trial, S. asiaticum (25,000 or 50,000 IJs per plant) and Malathion 50 EC (0.05%) singly or in combination at half the concentrations were used.ResultsIn screen house trial, all the treatments resulted in significantly high larval mortality than untreated plants. Split concentration application (15,000 + 15,000 IJs per plant) gave better DBM larval mortality (48.33%) compared to single application (36.00% at 30,000 IJs per plant). Comparing the two and three split applications, 15,000 IJs was significantly better (23.33% mortality) than 10,000 IJs (13.33%). In the field trial, S. asiaticum alone at 50,000 IJs resulted in 28.8% insect mortality compared to 18.0% in Malathion at 0.05%. Best results (37.5% mortality) were obtained by using nematode IJs at 25,000 per plant in combination with half the recommended concentration of Malathion (0.025%) leading to synergistic effect.ConclusionsThe study revealed that split application (15,000 + 15,000 IJs) of EPN S. asiaticum IJs proved better than single application of IJs at the same concentration (30,000 IJs) in the management of P. xylostella larvae in the screen house conditions. In the field experiment, the best effectiveness was obtained in combination of half the concentrations of EPN and insecticide (S. asiaticum IJs @ 25,000 per plant + Malathion @ 0.025%).

Phytotoxic, cytogenotoxic, and insecticidal activities of compounds from extracts of freshwater Lyngbya sp

ABSTRACT The development of agroecology has promoted the discovery of new bioactive compounds that might act as biocides to control infections and microbial contamination. Algae belonging to Lyngbya genus produce several allelochemicals, which are compounds with crop protection potential. The present study aimed to examine primary and secondary compounds derived from Lyngbya sp. extracts (aqueous and hydroethanolic) on phytotoxic, cytogenotoxic, and insecticidal activities. Determination of compounds indicated the presence predominantly of proteins and flavonoids. The extracts presented physicochemical characteristics that produced (1) 89% germination inhibition using hydroethanolic extract and (2) diminished development of seedlings of L. sativa by hydroethanolic extract as evidenced by reduced radicles length in 83.54%. Aqueous and hydroethanolic Lyngbya sp. extracts significantly interfered with meristematic cells of A. cepa, as evidenced by chromosomal alterations and aberrant mitotic phases in cells. Extracts also exhibited pro-oxidative activity and a potent insecticidal potential on S. zeamais, indicating that the hydroethanolic extract produced 100% insect mortality at 75 mg/ml after 48 hr while the aqueous extract initiated 90% mortality at the same concentration after 82 hr. Therefore, data demonstrate that Lyngbya genus provides basic information for new environmental and ecotoxicological studies to seek a possible source of proteins and flavonoids to be used in agroecological management.

Laboratory evaluation of four types of biochar to manage some stored product insects

Four types of biochars were prepared from rice husk as farm waste, sugarcane bagasse as sugar cane juice store waste, residues of Leucaena leucocephala tree as horticulture waste and chicken manure as chicken farm reduce at 700οC, then evaluated as a alternative to control Tribolium castaneum, Rhyzopertha dominica, Oryzaephlius surinamensis and Sitophilus oryzae. The character of each type has been defined using Scanning Electron Microscopy (SEM) with an Energy Dispersive X-Ray Analysis (EDX) and Fourier transform infrared spectroscopy (FTIR) were used to identify the elemental composition and functional groups distributed on biochars surface. The elemental compositions refer to the chicken manure biochar exhibited a decrease in Carbon concentration and increase Oxygen content; there is a negative correlation between C and O contents. On the other hand, the chicken manure biochar is the only tested biochar that contains Ca, P, and Cl. The chicken manure biochar has the largest number of functional groups on its surface, the mortality of insects was recorded after 10 days which showed that the chicken manure biochar was the most effective which contains more different elements and functional groups on its surface. The most affected insects were O.surinamensis and R. dominica with mortality percentages 86.66 and 73.33. Smaller particles of chicken manure biochar were more effective than larger particles against both R. dominica and O. surinamensis, the smaller particles (1.80—0.94 µm) recorded LC50 1.29 and 0.56 g/kg against R. dominica and O. surinamensis. SEM images for the affected insects showed the adhesion of biochar particles on insect’s body parts, also, the sensilla were disappeared as a result of the friction between biochar particles and insect cuticle. Our results may indicate the promising features of biochar as an alternative method to control some stored product insects with considering the source of biochar which affect its elemental and functional groups contents. Biochar had different efficacy depending upon its moisture contents, with increased moisture the toxicity of biochar decreased.

Fungal consortium of two Beauveria bassiana strains increases their virulence, growth, and resistance to stress: A metabolomic approach.

The use of two or more microorganisms in a microbial consortium has been increasingly applied in the biological control of diseases and pests. Beauveria bassiana is one of the most widely studied fungal species in biological control, yet little is known about its role in fungal consortiums. In a previous study, our group found that a consortium formed by two strains of B. bassiana had significantly greater biocontrol potential against the polyphagous caterpillars Duponchelia fovealis (Lepidoptera: Crambidae) than either strain on its own. In this study, we use GC-MS and LC-MS/MS to evaluate and discuss the metabolomics of the consortium. A total of 21 consortium biomarkers were identified, corresponding to 14 detected by LC-MS/MS and seven by GC-MS. Antioxidant and anti-inflammatory mechanisms are the main properties of the metabolites produced by the consortium. These metabolites can depress the insect’s immune system, increasing its vulnerability and, hence, the fungal virulence of the consortium. In light of these results, we propose an action model of insect mortality due to the metabolites secreted by the consortium. The model includes the inhibition of defense mechanisms such as pro-inflammatory interleukin secretion, cell migration, cell aggregation, Dif, Dorsal and Relish gene transcription, and JAK/STAT and JNK signaling pathways. It also promotes the cleaning of oxidative molecules, like ROS, NOS, and H2O2, and the induction of virulence factors.

Natural association of the entomopathogenic nematode Heterorhabditis indica (Rhabditida: Heterorhabditidae) from the Philippines with the non-symbiotic bacterium Ochrobactrum anthropi (Proteobacteria: Brucellaceae)

BackgroundEntomopathogenic nematodes of the genera Heterorhabditis and Steinernema are widely used as biocontrol agents against diverse insect pests. Their association with symbiont bacteria is found to be the primary cause of insect mortality. The present study reported a comprehensive characterization of a local Philippine EPN isolate using congruent morpho-taxometrical and molecular data and the associated bacterium in the infective dauer juveniles.ResultsUsing an insect-baiting technique, a nematode isolate labeled F2H was recovered from the sandy soils in the coastal area of southern Philippines. Based on morphology and morpho-taxometrics, the F2H isolate collected from Iligan City was identified as Heterorhabditis indica. Analysis of the ITS region of rDNA revealed the highest sequence match to H. indica. The sequences of the bacterial 16S rDNA gene showed that the symbiont of H. indica presented 100% similitude with the sequences of Ochrobactrum anthropi. Further, pairwise alignment and phylogenetic analysis demonstrated that O. anthropi, O. lupini and O. cytisi shared 100% similarity and form a monophyletic clade. These strains have not presented any differences in the phylogenetic and 16S rDNA data, and O. lupini and O. cytisi should be considered a later heterotypic synonym of O. anthropi.ConclusionsThe description of H. indica-O. anthropi association was the first report in the Philippines. This provides additional account and collection of naturally isolated EPN-bacteria, contributing to limited knowledge on its diversity in the Philippines, which can be utilized in the biocontrol of pests after further comprehensive assessments.

Efficacy of binary combinations of powders from selected botanicals against Callosobruchus maculatus Fabricius damage in stored cowpea seeds

The efficacy of powder mixes of two different insecticidal plants against Callosobruchus maculatus Fabricius was determined at the Entomology Research Laboratory, Department of Crop, Soil and Pest Management of the Federal University of Technology, Akure, Ondo State, Nigeria, under ambient laboratory conditions of 26 ± 4° C and 65 ± 10% RH. The powder combinations were made from Azadirachta indica leaf Thaumatococcous daniellii rhizome Eugenia aromatica dry flower buds, seeds of Piper guineense and rhizome of Zingiber officinale in a 1:1 ratio. The binary combinations were assessed at the dosages of 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0 g per 20 g of cowpea seeds in separate 250 ml plastic containers with lids, against five pairs of newly emerged C. maculatus adults. Insect mortality was recorded 24, 48 and 72 hours post treatment and the number of F1 adult emergence was recorded after up to 35 days post treatment. The combination of E. aromatica and T. daniellii, and E. aromatica and Z. officinale produced 60% and 53% mortality respectively, of adults of C. maculatus at the lowest tested dosage (0.2 g/20 g of grain), and 100% and 83% mortality respectively, at the highest tested dosage (2.0 g/20 g of grain). Oviposition and progeny production of C. maculatus were also significantly lower in treatments involving the use of these two combinations; significantly fewer seeds bore beetle eggs and adult exit holes. The combination of E. aromatica and T. daniellii, and E. aromatica and Z. officinale may be included in pest management strategies for mitigating C. maculatus damage to stored cowpea.

Amethyst leaf extract as pest control and fertilizer for soybean plants

Abstract. Rumape O, Kilo A, Ischak NI. 2022. Amethyst leaf extract as pest control and fertilizer for soybean plants. Biodiversitas 23: 3355-3363. Amethyst (Datura metel L.) is a plant that grows and develops in the Gorontalo area, and people use it as traditional medicine. This plant has a natural insecticidal activity that is not yet known by the general public. So far, the results of research on natural insecticides from amethyst have only been tested on a small scale in the laboratory, not yet applied on a large scale in the garden. The purpose of this study was to extract amethyst leaves and apply it as an inhibitor of feeding activity and insect mortality in both the laboratory and soybean gardens. Amethyst leaves were extracted in the laboratory using methanol, n-hexane, and ethyl acetate. The extracts were tested phytochemically to determine the type of secondary metabolite, before applying it. Phytochemical test showed amethyst leaves contain alkaloid, flavonoid, terpenoid, and saponin. The application treatment for the bioactivity used variations in the concentration of amethyst leaf extract of the fractions (methanol, ethyl acetate and n-hexane), namely 1.0, 2.5, 5.0, 7.5, 10%; and 0% as control. In the laboratory, the treatment was applied by contact to 5 insects Spodoptera litura instar III for each concentration treatment with 3 replications. Observation parameters were the percentage decrease in feeding activity and mortality of Spodoptera litura larvae. In the garden, the extracts with varying concentrations of the same as in the laboratory, were applied to soybeans treated with the pest Spodoptera liturain a closed container, and the other was sprayed on plants that were left exposed. The results showed that the three extracts could kill pests, but n-hexane extract was the most effective compared to ethyl acetate and methanol extracts. Amazingly, soybean plants whose yellow leaves turn green after being given the extract. This indicates that the secondary metabolites of amethyst are not only used as insecticides to control pests, but also as plant fertilizers.

Chemical Composition and Insecticidal Properties of Moroccan Lavandula dentata and Lavandula stoechas Essential Oils Against Mediterranean Fruit Fly, Ceratitis capitata.

The current study describes the chemical composition and insecticidal activities of the essential oils (EOs) extracted from Lavandula dentata L. and Lavandula stoechas L. against the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), a worldwide fruit pest. Gas chromatography (GC) and GC-mass spectrophotometry (GC-MS) analyses revealed that L. dentata oil contained camphor (50.8%), 1,8-cineole (6.6%), β-selinene (5%), and borneol (3.2%) as major components. On the other hand, L. stoechas EO was characterized by high contents of camphor (44%), camphene (14.8%), fenchone (9.1%), and 1-10-diepi-cubenol (4.6%). The toxic impact of EOs against C. capitata was evaluated through ingestion and contact methods. All of the EOs were toxic to C. capitata, and insect mortality was dose and time-dependent. In ingestion toxicity assays, L. dentata was the most toxic oil with an LC50 (lethal concentration for 50% mortality) of 6.54% for males and 10.21% for females. Topical applications revealed that all the EOs had a good insecticidal activity at 24h. The results of this study show that L. dentata and L. stoechas EOs may reduce the risks associated with the use of synthetic insecticides and may also be considered as a potent source for the production of botanical insecticides against C. capitata.

Using RNAi to silence heat shock protein has congeneric effects in North America’s Dendroctonus bark beetles

Losses associated with forest pest outbreaks are increasing at an alarming rate, exacerbated by fluctuating climate patterns, and unimpeded by traditional management approaches that fail to keep pace with growing pressures. Future forest pest management strategies demand augmentation with next generation approaches. RNA interference, or RNAi, is a naturally occurring eukaryotic immune response to viral infection that works by disrupting the translation of mRNA into protein and can be manipulated to cause insect mortality through the introduction of carefully designed dsRNAs. The effective induction of the RNAi pathway depends on the exact match of a sequence at least sixteen nucleotides in length, making non-target effects unlikely. Thus, RNAi is increasingly praised as a species-specific pest management approach. The southern pine beetle (SPB), Dendroctonus frontalis, and its congener, the mountain pine beetle (MPB), D. ponderosae, are highly destructive forest pests endemic to North and Central America experiencing unprecedented range expansions, with extensive impacts on affected ecosystems. We have demonstrated that oral ingestion of specific dsRNAs induces gene silencing via RNAi and causes rapid and significant mortality in both SPB and MPB. Here we evaluate the ability of dsRNAs targeting SPB to affect gene expression in MPB, and the ability of dsRNAs targeting MPB to affect gene expression in SPB. We found that species-specific dsRNAs designed for gene silencing in one species can silence genes in the reciprocal species, offering the potential for development of RNAi as a Dendroctonus-specific management tool against rapidly expanding bark beetle populations.

Effectiveness of silicon on immature stages of the fall armyworm [Spodoptera frugiperda (J. E. Smith)

ObjectivesFall armyworm (Spodoptera frugiperda) is a polyphagous pest causing economic losses to various crops. Commonly, chemical pesticides are used to control this pest, but these pesticides have a lot of side effects. Therefore, alternate environment-friendly method are inevitable for the management of S. frugiperda. Silicon (Si) supplementation to crop plants develops induced resistance against pests. MethodsAs the crop damage is done by the larval stage of the Fall armyworm, a laboratory experiment was carried out to investigate the impact of Si on immature stages of S. frugiperda. Treatments consisted of silicon dioxide (SiO2) and potassium silicate (K2SiO3) with two methods of application (foliar spray and soil application). No Si was the control treatment. ResultsThe current results showed that all Si treatments significantly (p ≤ 0.05) affected the immature stages of S. frugiperda. The foliar spray of SiO2 caused the highest larval mortality (40.33 ± 3.45 %) compared to K2SiO3 (29.33 ± 3.26 %) and control (4.67 ± 1.03 %). The greatest effect of Si treatments was observed in the early stages of larvae as insect mortality was significantly higher in 1st (19.67 ± 2.33 %) and 2nd (12.67 ± 1.03 %) instar of larval growth. Similarly, a significantly higher larval mortality was recorded one day (10.67 ± 2.07 %) and two days (19.67 ± 2.33 %) after hatching. Among Si sources, larval mortality was affected more in SiO2 than K2SiO3 and control. Meanwhile, the larval mortality was significantly more affected in Si's foliar spray (26.67 ± 17.26 %) than soil application (22.89 ± 14.46 %). A similar effect was observed in larvae to pupa ratio (59.67 ± 3.45 %), adult fecundity (146.67 ± 18.36 eggs), and neonate emergence (37.83 ± 4.62 %). In the pupa to adult ratio and adult sex ratio, no significant impact of Si sources or application methods was observed. ConclusionsThe current study results showed a significantly negative impact of Si on immature stages of S. frugiperda. Hence, Si application may diminish S. frugiperda colonization and initial damage in maize because it can decrease the fecundity of S. frugiperda and significantly increase the mortality of newly emerging larvae.

Potential of Oscheius tipulae nematodes as biological control agents against Ceratitis capitata.

A survey to collect soil nematodes with potential to control Ceratitis capitata flies was carried out in different locations in Tunisia. Several nematode isolates were recovered, laboratory colonies were established, and their taxonomic identities were determined based on molecular methods. Among all the recovered nematode isolates, two of them, Oscheius tipulae TC2 and OC2, were evaluated for their capacity to control C. capitata flies and for their ability to kill and reproduce on Galleria mellonella larvae. Our results show a great potential of these two isolates as biocontrol agents as they kill C. capitata eggs and pupae and interfere with the metamorphosis of C. capitata larvae. More specifically, TC2 and OC2 nematodes killed 39 and 31% of C. capitata eggs, respectively, impaired the metamorphosis of up to 77% and up to 67% of C. capitata larvae, respectively, and killed up to 66% and up to 58% of C. capitata pupae, respectively. The efficacy of TC2 and OC2 nematodes was particularly high on C. capitata pupae, and significant insect mortalities were observed even at concentrations of 1 and 5 nematodes/pupae, respectively. We also found that TC2 and OC2 nematodes efficiently kill and reproduce in G. mellonella larvae, suggesting that these insects could be used for mass-multiplication of these nematodes. These results reveal the potential of O. tipulae to complement integrated pest management programs against C. capitata flies.

Green synthesis of silver oxide nanoparticles using Panicum miliaceum grains extract for biological applications

In this report, the silver oxide nanoparticles were green synthesized using Panicum miliaceum grains extract and were proposed for the first time. GC–MS analysis explicated 2-Acetylbenzoic acid was the active phytocompound with 97.07% of presence in aqueous grains extract. The synthesized silver oxide nanoparticles were analyzed by several analytical techniques such as UV–visible, XRD, FT-IR, HR-TEM, TG, XPS, EDX and mapping analyses. The results of various analytical techniques confirmed the silver oxide nanoparticles formation. The formed nanoparticles were in 10–25 nm size. The effectual bioactive properties of nanoparticles were revealed through antioxidant, anti-diabetic, anti-inflammatory, larvicidal and insecticidal activities. The high mortality of larvae and insect was observed at 48 h in 100 ppm and 72 h in 100 μg/Kg concentration, respectively. The antibacterial activity explained the bactericidal property of nanoparticles on S. aureus and S. typhi at 150 μg/mL concentration. The effective drug activity of nanoparticles was observed from 98.10 % of toxicity against A549 lung cancer cells at 100 μg/mL concentration. The growth of Vigna unguiculata was efficiently increased by lower concentration (60 ppm) of nanoparticles. According to results, the green synthesized nanoparticles can be applied in pharmaceutical and agricultural sectors as biocompatible, non-toxic and cost-effective material.

Potential of Metarhizium anisopliae and Beauveria bassiana to control Dinoderus porcellus (Coleoptera: Bostrychidae) infesting yam chips

• B. bassiana (Bb115) and M. anisopliae (Met31) isolates are promising biological control agent of D. porcellus . • Bb115 and Met31 isolates at all concentrations caused more than 50% mortality at 7 days post-inoculation. • LT 50 values for Bb115 and Met31 isolates were 2.63 and 3.35 days, respectively. • Bb115 isolate showed the lower LD 90 values and the highest rates of cadaver sporulation. • Bb115 isolate at 10 9 conidia/mL reduced D. porcellus populations and weight loss of stored yam chips. The beetle Dinoderus porcellus Lesne is a serious storage insect pest that causes important losses by destroying stocks of yam chips. In the aim to found an alternative control method to the use of synthetic insecticides for its management, the virulence of the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin (isolate Bb115) and Metarhizium anisopliae (Metschnikoff) Sorokin (isolate Met 31) against adults of D. porcellus was evaluated under laboratory conditions (25 ± 2 °C and 70 ± 5% RH). Then, the effectiveness of the most virulent entomopathogenic fungus as biological agent against D. porcellus was assessed under farmer storage conditions. For each entomopathogenic fungus isolate, four conidial concentration (0, 10 5 , 10 7 , and 10 9 conidia/mL) at the dose of 1 µL were inoculated topically on D. porcellus adults (3–5 days old). Observations focused on insect mortality, cadaver sporulation and weight loss of yam chips. Lethal dose and lethal time values were estimated using probit analysis. Both fungal isolates at all conidial dose caused more than 50% mortality on day 7, with the highest mortality (94.44%) achieved using B. bassiana at the 10 9 conidia/mL. LT 50 values for B. bassiana and M. anisopliae isolates were 2.63 and 3.35 days, respectively, while their LT 90 values were 6.15 and 9.87 days, respectively. Yielding the lower LD 90 values and the highest rates of cadaver sporulation, B. bassiana isolate appeared as the most virulent against D. porcellus . After 3 months of storage, comparatively to the control, the B. bassiana isolate at the highest conidial dose (10 9 conidia/mL) significantly reduced D. porcellus populations, and weight loss of yam chips. This study revealed the potential of B. bassiana and M. anisoplae isolates as biological control agent against D. porcellus for yam chips protection.

Encapsulation of Eucalyptus largiflorens Essential Oil by Mesoporous Silicates for Effective Control of the Cowpea Weevil, Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae)

Although the use of synthetic chemicals is the principal method for insect pest management, their widespread application has led to numerous side effects, including environmental pollution and threats to human and animal health. Plant essential oils have been introduced as promising natural substitutes for synthetic insecticides. However, high volatility and/or low durability are the main limiting factors for essential oil application for control of insect pests. Accordingly, along with an evaluation of the fumigant toxicity of Eucalyptus largiflorens essential oil against the cowpea weevil, Callosobruchus maculatus, essential oil was nanoencapsulated by two mesoporous silicates, MCM-41 and zeolite 3A, to enhance fumigant persistence and toxicity. The chemical profile of essential oil was also analyzed through gas chromatographic-mass spectrometry. E. largiflorens essential oil showed significant concentration-dependent toxicity against insect pests; a concentration of 5.16 μL/L resulted in 100% mortality after 48 h. The toxicity of essential oil could be attributed to the presence of various insecticidal terpenes, such as spathulenol (15.6%), cryptone (7.0%), and 1,8-cineole (5.8%). Fumigant persistence was increased from 6 days to 19 and 17 days for pure and capsulated essential oil with MCM-41 and Zeolite 3A, respectively. The insect mortality also increased from 99 insects in pure essential oil to 178 and 180 insects in MCM-41 and Zeolite 3A encapsulated formulations, respectively. Therefore, the encapsulation of E. largiflorens essential oil by MCM- 41 and Zeolite 3A is a beneficial method for enhancing its persistence and toxicity against C. maculatus.

Characterization and bio-efficacy of entomopathogenic Beauveria associated with cuticle-degrading enzymes to restrain sucking pest Bemisia tabaci.

The entomopathogenic Beauveria spp. were acquired from insect cadavers and soil rhizosphere of cotton, groundnut, and castor. Among Beauveria, five spp. derived from infected insects, eight Beauveria found from soil, and one strain of Beauveria bassiana collected from MTCC 9544. Beauveria were characterized for morphology and cuticle-degrading enzyme activity associated with virulence against Bemisia tabaci. The colony morphology, conidial arrangement, size, and shape confirmed all isolates as Beauveria. The chitinase (EC 3.2.1.14) and lipase (EC 3.1.1.3) activities were observed the highest in Beauveria JAU2, while higher protease (EC 3.4.21.4) activity found in JAU4 followed by JAU2 at 240h. The bio-efficacy of Beauveria (1 × 107 conidia.ml-1) illustrated that potent JAU2 was examined with the highest % mortality and corrected mortality of B. tabaci at 144h followed by JAU1. The LC90 and LC50were determined from potent (JAU1 and JAU2) and weak (JAU6), and it was found the lowest in JAU2. The most potent Beauveria JAU2, isolated from insect cadaver (Harmivora armigera), was illustrated higher virulence than other isolates. The Beauveria JAU2 were recognized as Beauveria bassiana based on the shape of conidia and size (2.00 to 2.09µm dia) as examined in SEM. Study insight into recognition of potent Beauveria bassiana JAU2 was linked with cuticle-degrading enzyme activity for insecticidal action. The JAU2 isolate established the most positive correlation (P0.01: 0.864) between chitinase activity and corrected mortality of insect.

Nucleoprotein of a Rice Rhabdovirus Serves as the Effector to Attenuate Hemolymph Melanization and Facilitate Viral Persistent Propagation in its Leafhopper Vector.

Melanization in the hemolymph of arthropods is a conserved defense strategy against infection by invading pathogens. Numerous plant viruses are persistently transmitted by insect vectors, and must overcome hemolymph melanization. Here, we determine that the plant rhabdovirus rice stripe mosaic virus (RSMV) has evolved to evade the antiviral melanization response in the hemolymph in leafhopepr vectors. After virions enter vector hemolymph cells, viral nucleoprotein N is initially synthesized and directly interacts with prophenoloxidase (PPO), a core component of the melanization pathway and this process strongly activates the expression of PPO. Furthermore, such interaction could effectively inhibit the proteolytic cleavage of the zymogen PPO to active phenoloxidase (PO), finally suppressing hemolymph melanization. The knockdown of PPO expression or treatment with the PO inhibitor also suppresses hemolymph melanization and causes viral excessive accumulation, finally causing a high insect mortality rate. Consistent with this function, microinjection of N into leafhopper vectors attenuates melanization and promotes viral infection. These findings demonstrate that RSMV N serves as the effector to attenuate hemolymph melanization and facilitate viral persistent propagation in its insect vector. Our findings provide the insights in the understanding of ongoing arms race of insect immunity defense and viral counter-defense.

Exposure to clothianidin and predators increases mortality for heptageniidae

Neonicotinoids are a class of insecticide with global impacts on natural environments. Due to their high solubility, they are frequently found in stream ecosystems where they have the potential to impact non-target biota. While environmental concentrations are generally below lethal levels for most organisms, there are concerns that sublethal exposures can impact aquatic insects, particularly mayflies, which are highly sensitive to neonicotinoids. Because sublethal doses of neonicotinoids can reduce mobility in mayflies, exposure could indirectly increase mortality due to predation by impairing their ability to avoid initial detection or escape predators. We examined whether exposure to the neonicotinoid clothianidin at a concentration below the 96-h EC50 (7.5µg/L), would increase the predation risk of Stenacron and Stenonema mayfly nymphs by larval southern two-lined salamanders (Eurycea cirrigera) or eastern dobsonfly nymphs (Corydalus cornutus) using a controlled laboratory experiment. For Stenacron, we found significant interactive effects between pesticide and dobsonfly exposure that increased the hazard ratio (HR). The HR assesses risk relative to a control population, in this case mayflies in similar experimental conditions but without exposure to neonicotinoids or predators. With the addition of clothianidin, the HR of mayflies exposed to a dobsonfly nymph significantly increased from 1.8 to 6.2 while the HR for those exposed to salamanders increased from 7.6 to 12.5. For Stenonema, the HR initially decreased due to dobsonfly exposure (1 to 0.3) but increased when clothianidin and dobsonflies were combined (0.3 to 1.6). Our study shows that aquatic exposure to clothianidin can increase mortality for aquatic insects through predator pressure. Such indirect effects associated with neonicotinoid exposure warrant further investigation to expand our understanding of pesticide impacts to aquatic systems.

Do patterns of insect mortality in temperate and tropical zones have broader implications for insect ecology and pest management?

BackgroundUnderstanding how biotic and abiotic factors affect insect mortality is crucial for both fundamental knowledge of population ecology and for successful pest management. However, because these factors are difficult to quantify and interpret, patterns and dynamics of insect mortality remain unclear, especially comparative mortality across climate zones. Life table analysis provides robust information for quantifying population mortality and population parameters.MethodsIn this study, we estimated cause-of-death probabilities and irreplaceable mortality (the portion of mortality that cannot be replaced by another cause or combination of causes) using a Multiple Decrement Life Table (MDLT) analysis of 268 insect life tables from 107 peer-reviewed journal articles. In particular, we analyzed insect mortality between temperate and tropical climate zones.ResultsSurprisingly, our results suggest that non-natural enemy factors (abiotic) were the major source of insect mortality in both temperate and tropical zones. In addition, we observed that irreplaceable mortality from predators in tropical zones was 3.7-fold greater than in temperate zones. In contrast, irreplaceable mortality from parasitoids and pathogens was low and not different between temperate and tropical zones. Surprisingly, we did not observe differences in natural enemy and non-natural enemy factors based on whether the insect species was native or non-native. We suggest that characterizing predation should be a high priority in tropical conditions. Furthermore, because mortality from parasitoids was low in both tropical and temperate zones, this mortality needs to be better understood, especially as it relates to biological control and integrated pest management.