Insect Control Agents Research Articles

Assessment of Lethal, Sublethal, Transgenerational, and Biochemical Effects of Isaria fumosorosea on Mythimna separata.

Mythimna separata is a destructive polyphagous pest of field crops. Insecticides are generally applied for its control which not only negatively affect natural enemies and the environment and cause resistance in the insect pests. There is a need for the friendly method which is safe for the environment and life. Currently, entomopathogenic fungi are being used as biological control agents for different insects. The influence of Isaria fumosorosea on survival, life table parameters, and enzymatic activities of M. separata were assessed. On the seventh day post-treatment, the highest concentration 3 × 108 spores/mL-1 caused the 92.5% larval mortality. The effect of LC15 and LC50 of I. fumosorosea were recorded on parental generation (F0) and first filial generation (F1) of M. separata. The life table parameters of F1 showed a decreasing trend in the intrinsic rate (r), net reproductive rate (Ro), mean generational time (T), total larval duration, and fecundity ratio in treated groups. In LC15 and LC50, groups the average fecundity ratio was 319.2 and 191.18 eggs/female, respectively. The activities of detoxifying enzymes were concentration-dependent and highest activities were recorded on the third day. I. fumosorosea negatively affected the growth parameters of M. separata and can be included in M. separata management program.

Characterization of the mode of action of eCry1Gb.1Ig, a fall armyworm (Spodoptera frugiperda) active protein, with a novel site of action

Insect pests cause immense agronomic losses worldwide. One of the most destructive of major crops is the Fall Armyworm (Spodoptera frugiperda, FAW). The ability to migrate long distances, a prodigious appetite, and a demonstrated ability to develop resistance to insecticides, make it a difficult target to control. Insecticidal proteins, for example those produced by the bacterium Bacillus thuringiensis, are among the safest and most effective insect control agents. Genetically modified (GM) crops expressing such proteins are a key part of a successful integrated pest management (IPM) program for FAW. However, due to the development of populations resistant to commercialized GM products, new GM traits are desperately needed. Herein, we describe a further characterization of the newly engineered trait protein eCry1Gb.1Ig. Similar to other well characterized Cry proteins, eCry1Gb.1Ig is shown to bind FAW midgut cells and induce cell-death. Binding competition assays using trait proteins from other FAW-active events show a lack of competition when binding FAW brush border membrane vesicles (BBMVs) and when utilizing non-pore-forming versions as competitors in in vivo bioassays. Similarly, insect cell lines expressing SfABCC2 and SfABCC3 (well characterized receptors of existing commercial Cry proteins) are insensitive to eCry1Gb.1Ig. These findings are consistent with results from our previous work showing that eCry1Gb.1Ig is effective in controlling insects with resistance to existing traits. This underscores the value of eCry1Gb.1Ig as a new GM trait protein with a unique site-of-action and its potential positive impact to global food production.

Excito-repellent and Pesticide-Likeness Properties of Essential Oils on Carpophilus dimidiatus (Fabricius) (Nitidulidae) and Oryzaephilus mercator (L.) (Silvanidae).

Carpophilus dimidiatus (Fabricius) (Nitidulidae) and Oryzaephilus mercator (L.) (Silvanidae) are insect pests that cause severe damage in important walnut growing regions in the northwest of Argentina. The current management approaches for these pests involve the use of unsafe phosphorus pesticides whose overuse have led to farmworker poisoning, pest resistance issues, and environmental contamination. Plant extracts, particularly essential oils, are an alternative source of insect control agents. Excito-repellent essential oils can be used to develop ecofriendly tools for managing the pest population without affecting quality and visual appearance of the stored walnuts. Laboratory studies were conducted to assess the excito-repellent effects of C. dimidiatus and O. mercator of 12 essential oils derived from aromatic plants used as food additives and traditional medicine in Argentina: Aloysia citrodora (AC), Aloysia gratissima (AG), Aloysia gratissima var. Gratissima (AGG), Blepharocalyx salicipholius (BS), Hyptis mutabilis (HM), Lippia junelliana (LJ), Lippia turbinata (LT), Mentha x piperita (MP), Minthostachys mollis (MM), Minthostachys verticillata (MV), Origanum vulgare(OV), and Rosmarinus officinalis (RO). The most bioactive EOs (ERijk ≥ 70%) were Aloysia gratissima var. Gratissima (AGG), Minthostachys verticillata, and Lippia junelliana. Their bioactivity profile and chemical space, characterized from GC-MS measures, Generalized Estimating Equations, and Hierarchical Cluster Analysis, revealed that they are mixtures of very functionalized molecules with physicochemical properties similar to those of insecticides with low residual property that enter the insect body through the respiratory system by inhalation. The AGG, MV, and LJ oils are promising as protective agents of walnut products. In our laboratory, studies of their formulations for use in integrated pest management programs are still ongoing.

Insect Mortality Caused by Baculovirus: a Model of Second-Order Phase Transitions

Baculoviruses, especially prevalent in Lepidoptera, have attracted the most attention as biological insect control agents. Infection with baculoviruses is usually fatal and therefore can affect host population density, especially if virus transmission increases with host density. Lepidoptera larvae show a strong dose-dependent response to pathogens such as baculoviruses, so their response to various pathogen exposures was studied in the present work. Models of virus exposure to insect hosts are usually judged by whether or not they generate cyclical population dynamics of multiple host generations. However, the existing theoretical models based on systems of differential equations are of little use for practical application due to the large number of variables and free parameters. In this regard, the possibility of using a mathematical model for describing the epizootic Malacosoma neustria L. and Lymantria dispar L. under the influence of nuclear polyhedrosis virus is considered. To assess the sensitivity of insects to the effects of baculoviruses, laboratory experiments were carried out on the mortality of caterpillars under various infectious loads. In this paper, we consider the possibility of constructing a model for the lifetime of insects after exposure to baculoviruses as an analogue of a second-order phase transition in physical systems and give estimates of the model parameters for two insect species at different titers of baculoviruses and at different ages of caterpillars. The dependence of the parameters of the proposed model on nuclear polyhedrosis virus strains is shown. The importance of the applied parameters for the organization of forest protection measures is substantiated.

Assessment of some physical measures as safe and environmentally friendly alternative control agents for some common coleopteran insects in stored wheat products

Assessment of some physical measures as safe and environmentally friendly alternative control agents for some common coleopteran insects in stored wheat products

Behavioral, Electrophysiological, and Toxicological Responses of Plutella xylostella to Extracts from Angelica pubescens.

Plutella xylostella L. is a destructive pest affecting cruciferous vegetables, causing massive economic losses worldwide. Plant-based insecticides are considered promising insect control agents. The Angelica pubescens extract inhibited female oviposition, with an oviposition deterrence index (ODI) of 61.65% at 12.5 mg/mL. We aimed to identify the bioactive compounds in A. pubescens extract. The compounds from A. pubescens extract were analyzed using LC-MS techniques. The toxicity and behavioral responses of larvae and adults of P. xylostella to ten compounds were investigated. We found that the caryophyllene oxide and 3,4-dimethoxycinnamic acid inhibited female oviposition; the ODIs were 98.31% and 97.59% at 1.25 mg/mL, respectively. The A. pubescens extract, caryophyllene oxide, and 3,4-dimethoxycinnamic acid caused larval mortality, with LC50 values of 21.31, 4.56, and 5.52 mg/mL, respectively. The EAG response of females was higher than that of males under A. pubescens extract conditions, while the EAG response of males was higher than that of females in caryophyllene oxide and 3,4-dimethoxycinnamic acid conditions. The A. pubescens extract and caryophyllene oxide showed repellent activity against both female and male adults, while the 3,4-dimethoxycinnamic acid did not elicit any notable behavioral responses from P. xylostella adults. A. pubescens extract and caryophyllene oxide are potential insecticides, oviposition deterrents, and behavioral regulators against P. xylostella, and they could be potential candidates for the development of biological insecticides to control P. xylostella.

Species and reproductive status influence element concentrations in bat fur

To assess the impact of increasing pollutant levels on wildlife, we measured chemical contaminant loads in bats with different habitat and dietary preferences. Samples were taken from the fur of bats (Eptesicus nilssonii, Myotis brandtii, Myotis mystacinus and Plecotus auritus) to measure concentrations of 55 elements by inductively coupled plasma mass spectrometry (ICP-MS). Variations in element concentrations between different bat groups (species, sex, reproductive status) were analysed with a focus on arsenic (As), mercury (Hg) and lead (Pb) as these are known to cause specific health concerns in wildlife. For M. brandtii we found the highest As concentrations, especially in lactating bats, with a maximum exceeding those from other studies where bats had compromised health. Whereas for M. mystacinus there was a negative correlation between body condition index (BCI) and As concentration, indicating a potential danger for bats in the study area. In M. mystacinus and M. brandtii Hg concentrations were higher for sixteen individuals than in other studies where bats suffered genotoxic effects, although median levels were still below this threshold. Lactating bats from P. auritus and M. brandtii had higher Hg concentrations than bats of other reproductive status, which could endanger offspring as Hg can be transferred through lactation. In females from M. mystacinus Pb concentrations were more than three times higher compared to males. There was also a negative correlation between Pb concentration and BCI, which could mean that Pb has an adverse effect on health. Although many other biotic and abiotic factors should be considered, some of the variations in element concentrations could be due to different behaviours (foraging, roosting, etc.) in the studied species. The high levels of chemical contamination in some of the bats in our study, particularly reproductive individuals, is of conservation concern as bats are important agents for insect control.

Controle biológico do fungus gnats (Bradysia matogrossensis) em mudas de tabaco

ABSTRACT Tobacco production in Brazil is an essential source of income for many families, especially in the southern region. However, it is subject to attack by pests and diseases, such as the fungus gnats insect. To control this pest, the mite Stratiolaelaps scimitus is found in Brazilian soil, which has a predatory potential to fungus gnats. This study aimed to evaluate the use of S. scimitus as an insect control agent, compared to chemical control, in the production of tobacco seedlings in the floating system. The experiment was carried out on a farm in Crissiumal-RS, in a randomized block design, with four replications: T1= control, T2= chemical control based on Imidacloprid and Azadirachtin, and T3= S. scimitus. To analyze the control efficiency, adult insects were captured at different times, and the biological control did not differ from the chemical control. The biological treatment made it possible to reduce the use of chemical products. Concomitantly, questionnaires verified that producers are well accepting the new control model. Therefore, using S. scimitus could reduce the proliferation of fungus gnats in the production of tobacco seedlings in the floating system, but more studies need to be carried out for a better evaluation.

Evaluation of the Efficacy of Commercial Plant Extracts of Palazin and Tondxier Against the Red Flour Beetle Tribolium castaneum (Herbest) Under Laboratory Conditions

Al-Fatlawi, N.C.H. and S. Al-Zurfi. 2023. Evaluation of the Efficacy of Commercial Plant Extracts of Palazin and Tondxier Against the Red Flour Beetle Tribolium castaneum (Herbest) Under Laboratory Conditions. Arab Journal of Plant Protection, 41(1): 54-57. https://doi.org/10.22268/AJPP-41.1.054057 The Effect of Tondxier and Palazin plant extracts on the mortality of the flour beetle T. castaneum (Herb) was investigated. Plant extracts were separately tested under laboratory conditions against the beetles using a topical spray. Beetles were sprayed with plant suspensions at different concentrations (1, 2 and 3 ml/L) for both Tondxier and Palazin. Mortality was recorded daily for 15 days while beetles were kept on wheat flour. Both Tondxier and Palazin had an impact on T. castaneum. Commercial Tondxier was more effective than Palazin at the same concentrations tested. Nevertheless, significant differences in the mortality rate at the end of the experiments between second, and 5 th instar larvae and adults treated with Palazin and Tondxier extracts were observed. Second and 5 th instar larvae were more susceptible, and adults were more resistant to Palazin and Tondxier treatments. This study showed that mortality rate increases with increased concentration and length of exposure times. Results obtained suggested that the two plant extracts of Palazin and Tondxier used in this study can be used as potent insect control agents. Keywords: Palazin, Tondxier, Tribolium castaneum, larvae

Entomopathogenic nematodes isolated from agricultural areas of Thailand and their activity against the larvae of Aedes aegypti, Aedes albopictus and Culex quinquefasciatus (Diptera: Culicidae)

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis have been considered to be effective biological control agents for several insects. In this study, we isolated and identified EPNs from soil samples in agricultural areas of northern Thailand and evaluated their efficacy for controlling larvae of three mosquito vector species, Aedes aegypti, Ae. albopictus and Culex quinquefasciatus. A total of 51 of 1,000 soil samples were positive (5.1% prevalence) for EPNs, which were identified through sequencing of the rDNA and ITS to 37 Steinernema isolates (3.7%) and 14 Heterorhabditis isolates (1.4%). For the bioassay, the larvae of mosquitoes were exposed to Steinernema surkhetense (eALN6.3_TH), Steinernema lamjungense (eALN11.5_TH), Heterorhabditis indica (eACM14.2_TH) and Heterorhabditis bacteriophora (eALN18.2_TH). Heterorhabditis bacteriophora showed the highest efficacy against Ae. aegypti and Cx. quinquefasciatus. At 96 h after exposure, the mortality rates were 60.0 and 91.7%, respectively. The EPNs were observed in the dead mosquito larvae, which were mostly found in the thorax followed by the head and abdomen. Some EPNs were dead with melanization, and some were able to survive in the cavity of mosquito larvae. Our results show the low prevalence of EPN in agricultural areas of Thailand. Moreover, H. bacteriophora may be considered an alternative biocontrol agent for managing and controlling these vector mosquitoes.

Pest management and pesticide used in some Hospitals of Benghazi

Public health pest management involves the control of insects or other vectors that transmit diseases to humans. These pests include mosquitoes, cockroaches, bedbugs and domestic rodents. Chemical pesticides assisted in containing the spread of infection and helped reduce infestations with pests. On the other hand, it may have a high-risk acute toxicity and/or chronic effects, which are dangerous, especially to children. Furthermore, they can cause cancer, neurologic damage, delayed development, reproductive dysfunction, and death in many parts of the world, generally through occupational exposure and accidental poisoning of patients. The current study was based on public hospitals in Benghazi city of Libya using questionnaires to collect data in 2013 and then completed in 2015-2016. The results showed a high level of infestation in the hospitals that were studied. The major insect pest species was the German cockroach (Blattella germanica). Insect control agents containing permethrin, cypermethrin, deltamethrin were used. In addition to different formulations such as baits, traps, gel baits that contain hydramethylnon, imidacloprid, chlorpyriphos. The study acknowledges the benefits those pesticides carried out to hospitals, but also understanding their potential harm and side effects. The most important finding is that pesticides are used extensively in Benghazi’s hospitals. More than 15 different pesticides are presently applied in hospitals, such as fog, spray, and powder pesticides. They are applied in mostly all areas, including areas that contain patients. On the bright side, the study finds that hospitals in Benghazi have started to use less toxic pesticides and try to use other pesticides in safe ways.

Lethal and Sublethal Toxicity Assessment of Cyclosporin C (a Fungal Toxin) against Plutella xylostella (L.).

Secondary metabolites/toxins produced by Purpeocillium lilacinum (Hypocreales; Phiocordycipitaceae), a well-known insect pathogen, can be used for the management of different insect pests. We report the lethal and sublethal effects of cyclosporin C (a toxin produced by P. lilacinum) against a major vegetable pest, Plutella xylostella, at specific organismal (feeding rate, larval growth, adult emergence, fecundity, and adult longevity) and sub-organismal levels (changes in antioxidant and neurophysiological enzyme activities). The toxicity of cyclosporin C against different larval instars of P. xylostella increased with increasing concentrations of the toxin and the maximum percent mortality rates for different P. xylostella larval instars at different times were observed for the 300 µg/mL cyclosporin C treatment, with an average mortality rate of 100% for all larval instars. The median lethal concentrations (LC50) of cyclosporin C against the first, second, third, and fourth larval instars of P. xylostella 72 h post-treatment were 78.05, 60.42, 50.83, and 83.05 μg/mL, respectively. Different concentrations of cyclosporin C caused a reduction in the average leaf consumption and average larval weight. Different life history parameters, such as the pupation rate (%), adult emergence (%), female fecundity, and female longevity were also inhibited when different concentrations of cyclosporin C were applied topically. The cyclosporin C concentrations inhibited the activities of different detoxifying (glutathione S-transferase, carboxylesterase, and acetylcholinesterase) and antioxidant enzyme (superoxide dismutase, catalase, and peroxidase) activities of P. xylostella when compared to the control. These findings can serve as baseline information for the development of cyclosporin C as an insect control agent, although further work on mass production, formulation, and field application is still required.

A novel biofumigant from Tithonia diversifolia (Hemsl.) A. Gray for control of stored grain insect pests

For the well-being of human health as well as ecological concerns and the development of insect resistance to conventional chemical insecticides, efforts have increased worldwide, to find eco-friendly, effective and safer insect control agents which are of natural origin. A bioactive biofumigant molecule named dihydro-p-coumaric acid was isolated and characterized from the leaves of Tithonia diversifolia Hemsl. A. Gray following laboratory bioassays against the rice weevil, Sitophilus oryzae L (Coleoptera: Curculionidae); the lesser grain borer, Rhyzopertha dominica F (Coleoptera: Bostrichidae) and the rust-red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae). The isolated compound acted as a fumigant, toxic to adults of stored grain insect pests with LC50 values of 17.86, and 11.49 μg/L (S. oryzae), 19.80 and 10.29 μg/L (R. dominica) and 24.41 and 17.80 μg/L air (T. casatneum) respectively. Further, in vivo data reveal that the percentage of inhibition of acetyl cholinesterase (AChE) was dose-dependent and in vitro results showed potent AChE inhibitor. The isolated compound acts as an efficient biofumigant against the stored grain insect pests and has no adverse effect on seed germination. From this study, we assume that the isolated biofumigant molecule has the ability for used in IPM programs for stored-grain pests because of its biofumigant activity.

Heavy metal toxicity of drinking water: A silent killer

Heavy metal toxicity has proven to be a major threat and there are several health risks associated with it. The toxic effects of these metals, even though they do not have any biological role, remain present in some or the other form harmful for the human body and its proper functioning. Heavy metals are generally referred to as those metals which possess a specific density of more than 5 g/cm3 and adversely affect the environment and living organisms. These metals are essential to maintain various biochemical and physiological functions in living organisms when in very low concentrations, however they become noxious when they exceed certain threshold concentrations. The most commonly found heavy metals in waste water include arsenic, cadmium, chromium, and copper, lead, nickel, and zinc, all of which cause risks for human health and the environment. Heavy metals enter the surroundings by natural means and through human activities. Various sources of heavy metals include soil erosion, natural weathering of the earth's crust, mining, industrial effluents, urban runoff, sewage discharge, insect or disease control agents applied to crops etc. Some heavy metals, i.e. arsenic, lead, mercury, cadmium, chromium, aluminium causes drastic harmful effect on the environment and living organisms, mainly human beings.

Antennal Sensilla in Vespidae: A Comparison Between a Diurnal and a Nocturnal Polistinae Wasp.

Social wasps have a widespread Neotropical distribution and are important pollinators and biological control agents for pest insects. The foraging activity of wasps is influenced by biotic and abiotic factors that are detected by the antennal sensilla that vary according to species, sex, caste, and environmental conditions. This study compares the types and quantities of antennal sensilla with a scanning electron microscope between the nocturnal Apoica flavissima and the diurnal Polistes simillimus wasps. Six types of sensilla were found in the antennae of both species: placoid, coeloconic, basiconic-type 1, basiconic-type 2, trichoid-type 1, and trichoid-type 2. Sensilla chaetica were found only in the scape and pedicel of A. flavissima. In the nocturnal wasp, there are 19,132.27 ± 1,247.72 sensilla in the left and 17,746.46 ± 1,477.46 in the right antennae, whereas in the diurnal wasp 14,936.72 ± 1,271.69 in the left and 16,090.82 ± 1,345.3 in the right antennae. A. flavissima has a longer antennal length and number of sensilla than P. simillimus. The higher number of antennal sensilla in the nocturnal wasp is not linked with the antennal size. The association of antennal sensilla functions with ecological and behavioral factors of A. flavissima and P. simillimus are discussed.

Functional Coatings by Natural and Synthetic Agents for Insect Control and Their Applications

Insect repellent textiles offer protection against disease-causing vectors such as mosquitoes, flies, and ticks. Protection is based on the incorporation of insect repellent compounds present in plant oil derivatives or synthetic oils. The effectiveness and application of natural insect repellents such as citronella grass, lemongrass, rosemary, peppermint, holy basil, tea tree, neem, lavender, thyme, lemon eucalyptus, clove, and cinnamon oils, as well as synthetic compounds permethrin, allethrin, malathion, DEET, DETA, IR3535, and picaridin, are compared here. The insect repellent and insecticidal effectiveness of natural compounds in their pure form are very low due to their high volatility. The effectiveness has been greatly improved through slow-release systems such as encapsulation of the essential oils and is comparable to synthetic compounds used for insect control purposes. Due to the lasting toxicity of synthetic compounds to humans and the environment, the use of natural compounds should become a more preferred method of insect control.

Behavioral Response, Fumigation Activity, and Contact Activity of Plant Essential Oils Against Tobacco Beetle (Lasioderma serricorne (F.)) Adults.

Tobacco beetle (Lasioderma serricorne (F.)) is one of the main storage pests that harm tobacco leaves. The current control methods mainly include physical control, chemical control, and biological control, but they all have their own disadvantages. In this study, 22 kinds of plant essential oils in grapefruit, peppermint, juniper, eucalyptus, myrrh, lemon grass, geranium, tea tree, cypress, citronella, patchouli, benzoin, rosemary, cinnamon, clary sage, bergamot, mastic, ginger, rose hydrosol, cedar, thyme, and basil, respectively, are selected to explore their behavioral responses against L. serricorne adults using a glass Y-tube olfactometer. The behavioral responses results show that 17 kinds of essential oils in eucalyptus, basil, grapefruit, cypress, mastic, peppermint, patchouli, juniper, geranium, thyme, benzoin, lemon grass, cinnamon, ginger, rosemary, clary sage, and citronella can avoid L. serricorne adults, while five kinds of essential oils in tea tree, rose hydrosol, myrrh, bergamot, and cedar can attract L. serricorne adults. Especially, essential oils in eucalyptus and grapefruit can avoid L. serricorne adults at 1 μl/L with the repellent rates of 94.67 and 94.56%, respectively. Meanwhile, 17 kinds of essential oils which can avoid L. serricorne adults are selected to determine their fumigation activity against L. serricorne adults using the Erlenmeyer flask test method, and bioassay results show that after 72 h of treatment, five kinds of plant essential oils in rosemary, eucalyptus, basil, citronella, and geranium show excellent fumigation activity against L. serricorne adults with the mortality rates of 100.00, 95.29, 95.29, 94.12, and 91.76%, respectively, and their LD50 of the contact activity against L. serricorne adults determined using the leaf-dipping method are 3.60, 3.49, 8.90, 6.70, and 7.80 μl/L, respectively. Our results show that plant essential oils could be developed as environmentally friendly insect control agents.

Predatory Potential of Canthecona furcellata (Pentatomidae: Hemiptera) Against Key Defoliator Pests of Teak in Nursery and Chik Pea under Field Conditions

Canthecona furcellata (Wolff.) (Hemiptera: Pentatomidae) is important biological control agents of many Lepidopteron, Coleopteran and Heteropteran insects. This predatory behavior of the species, this is a promising biological control agent for insect pests of agriculture and forest ecosystem. The nursery and field experiments were conducted to find out the predation potential of E. furcellata. The results revealed that maximum 93.66% predation was recorded on larvae of E. macheralis followed by 89.0 and 84.39% on larvae of H.puera and H. armigera respectively. Therefore, E. furcellata could be utilised effectively against E. machaeralis under field conditions, moreover, H. puera and H. armigera could be employed as laboratory hosts for mass rearing of E. furcellata.

Novel acylpiperidine analogues as potential aphid repellent agents: Rational design, synthesis and repellent activity

Odorant-binding protein (OBP) is a promising potential target and can be used as a template for developing insect control agents due to its ability to bind to and transport semiochemicals to olfactory receptors, thus triggering behavioural responses among insects. In this study, 27 novel acylpiperidine analogues were designed and synthesised by introducing the hydrophobic long chain of the aphid alarm pheromone (E)-β-farnesene (EβF) into the polar acylpiperidine group of the commercial insect repellent icaridine based on the binding cavity characteristics of an OBP of the pea aphid Acyrthosiphon pisum, ApisOBP3. Compound 14c displayed good repellent activity against the pea aphids with a repellence rate of 61.5% at a concentration of 6 μg/μL. The equilibrium dissociation constant (Ki) of compound 14c against ApisOBP3 was 20.92 μM in competitive fluorescence binding assays; this value is similar to the Ki of the commercial insect repellent icaridine (20.56 μM). Molecular dynamics simulation revealed that the EβF long chain of compound 14c showed considerable hydrophobic interactions with the binding domain of ApisOBP3. Moreover, the acylpiperidine moiety of compound 14c formed one hydrogen bond and multiple carbon–hydrogen bonds with the Phe2 and Asn109 residues, respectively. The binding free energy analysis indicated that the contribution of the van der Waals force to the binding affinity was approximately twice as great as that of the electrostatic force. These studies provide significant guidance for the rational designing and efficient identification of novel insect repellent agents.

Identification of entomopathogenic nematodes and their symbiotic bacteria in national parks of Thailand, and mosquitocidal activity of Xenorhabdus griffiniae against Aedes aegypti larvae

Summary Entomopathogenic nematodes (EPN) Steinernema and Heterorhabditis with symbionts with Xenorhabdus and Photorhabdus bacteria, respectively, are reported as biocontrol agents for insect control. The objectives of this study were to identify EPN and their symbiotic bacteria in national parks of Phitsanulok Province, Thailand, and to test how Xenorhabdus isolates attack Aedes aegypti larvae. We collected 810 soil samples from four national parks. The juvenile stage of EPN was isolated from soil samples using a baiting technique with Galleria mellonella followed by a White trap. Partial regions of 28S rDNA and internal transcript spacer were sequenced to identify EPN, and recA sequencing was used to discriminate between Xenorhabdus and Photorhabdus. We found that 74 of the 810 soil samples (9.1%) were positive for the EPN. The EPN were molecularly identified as S. surkhetense, S. longicaudum, H. indica and Heterorhabditis sp. SGmg3, and their symbiotic bacteria were identified as X. stockiae, X. griffiniae, X. indica, X. vietnamensis, P. luminescens subsp. akhurstii, and P. temperata subsp. temperata. Xenorhabdus griffiniae showed potential larvicidal activity against A. aegypti (91% mortality at 72 and 96 h after exposure). This study demonstrates the diversity of EPN and symbiotic bacteria in national parks of Thailand and the potential to use X. griffiniae as a biocontrol agent to kill A. aegypti larvae.