Conventional Chemical Insecticides Research Articles

ANTIBIOSIS AND ANTIXENOSIS IN TOMATO GENOTYPES AGAINST Helicoverpa armigera HUBNER

<p><strong>Background</strong>. Farmers rely on the use of synthetic insecticides in managing <em>Helicoverpa</em> <em>armigera</em>, hole-boring insect pest on tomato, but they are detrimental to human health. Therefore a more reliable and ecofriendly control measure is needed such as host plant resistance<strong>. Objective</strong>. To assess the mechanisms of resistance in tomato varieties: NGB00724, NGB00724, Anaya, Kelvin, Mona, Roma VF (susceptible varieties), Tropimech and UC82B in laboratory and screen house. <strong>Methodology</strong>. Second larval instars were fed with leaves of the different tomato varieties and their development was observed till adult stage. Study was done in the screen house where number of larvae and eggs were also observed. Larval period and weight, and percentage adult emergence were assessed in tomato varieties. Metabolites (phenol, flavonoids, terpenoids, protein, reducing sugars and total sugars) in tomato leaves were determined following standard procedures. <strong>Results</strong>. <em>Helicoverpa</em> <em>armigera</em> fed with tomato leaves, Anaya recorded the lowest larval period (9.67 days). Also, larvae fed on Anaya and Mona had the lowest larval weight (0.19 g and 0.25 g). Also significantly lower percentage of adult emergence was observed on Anaya and Mona (16.7%) Mona, NGB00725 and Anaya significantly harbored the lower number of <em>Helicoverpa</em> <em>armigera</em> adult (0.1, 0.4, 0.4). The lowest number of eggs (0.5) was recorded from adults placed on Anaya variety. There was high and negative significant correlation of r = -0.865 between phenols and adult emergence. Phenols and oviposition were significantly negatively correlated (r = -0.816). <strong>Implication. </strong>Anaya and Mona hinder the development of <em>Helicoverpa</em> <em>armigera</em> larvae when fed on it. Phenol has negative impact on the development and oviposition of <em>Helicoverpa</em> <em>armigera</em>. <strong>Conclusion</strong>. It was revealed through this study that availability of promising resistant varieties can effectively combat the damage caused by <em>Helicoverpa</em> <em>armigera</em> and lessen the shortcomings related with the application of conventional chemical insecticides in tomato production.</p>

Biological control potential of two Beauveria bassiana isolates against the stink bugs Nezara viridula L. and Piezodorus guildinii Westwood (Hemiptera: Pentatomidae) in common bean

BackgroundThe stink bugs, Nezara viridula L. and Piezodorus guildinii Westwood (Hemiptera: Pentatomidae) are the most important and widespread species of polyphagous stink bugs in the tropical and subtropical regions of Latin America, which affect the quality and yield of the common bean (Phaseolus vulgaris L.). The use of synthetic chemical insecticides is the major control strategy to manage stink bugs in common beans and alternatives are needed. In this study, mortality and median Lethal Time (LT50) of two Cuban isolates of the entomopathogenic fungus Beauveria bassiana (18 S-O-R and 96 P-O-E), as well as one commercial Cuban isolate (Bb-18), at a concentration of 1 × 108 conidia/ml were evaluated. These evaluations were conducted against both stink bug species using Petri dish bioassays and a semi-field experiment in common beans.ResultsIn Petri dish bioassays, the isolates 18 S-O-R and 96 P-O-E caused 100% mortality of both N. viridula and P. guildinii. This was significantly higher than for isolate Bb-18, which caused 86.3% N. viridula and 81.3% P. guildinii mortality. In the semi-field experiment, when pooling both stink bug species, total mortality after 14 days was 91.3% for 18 S-O-R, 80.0% for 96 P-O-E and 73.8% for Bb-18 isolates. LT50 value for isolate 18 S-O-R tested under laboratory conditions was 6.04 ± 0.18 days for N. viridula and 5.32 ± 0.14 days for P. guildinii at the same concentration of 1 × 108 conidia/ml. LT50 value for isolate 18 S-O-R in semi field was 6.79 ± 0.37 days for N. viridula and 7.71 ± 0.32 days for P. guildinii at 1 × 108 conidia/ml.ConclusionThe study highlights the potential of B. bassiana 18 S-O-R as a promising candidate for control of stink bugs in common bean under tropical conditions as an alternative to conventional chemical insecticides in integrated pest management (IPM) programs. Moving forward, further research should focus on validating the efficacy under diverse field conditions and integrating application methods into practical IPM approaches. Future use of B. bassiana will enhance sustainability and reduce environmental impacts associated with pesticide use.

Neem's promise: The way to a sustainable future and eco-friendly biopesticides

Modern agriculture must include pest management since pests can seriously harm crops and lower yields, resulting in considerable financial losses. Conventional chemical insecticides have been used as the main method of pest management, but their detrimental effects on the environment and human health have inspired the quest for new environmentally friendly options. In this situation, Azadirachta indica showed promise as a sustainable and eco-friendly biopesticide. This research shows many aspects for Azadirachta indica as an environment friendly biopesticide. Neem is well known for having antiviral, antiseptic, and antifungal characteristics, which make it a crucial component in remedies for many illnesses, skin disorders, and mouth care. It is also beneficial to the environment. When added to the soil, its seeds and leaves help increase the fertility of the soil and structure. Additionally, the tree's large root system helps stop soil erosion. Azadirachta indica, is a great asset in the field of pest control and agricultural sustainability due to its repellent and antifeedant qualities. These characteristics are a result of neem's bioactive substances, known as Azadirachtin which has been the subject of in-depth study and use because of its function as a natural repellent and antifeedant Azadirachtin is a potent natural insect growth regulator because it interferes with beetle feeding, molting, and reproduction. Furthermore, the eco-friendliness of azadirachtin and its safety for people and non-target animals highlight its essential function in sustainable pest management techniques, aiding in the advancement of environmentally friendly and healthier agricultural systems. The neem plant is a unique botanical gem that has enormous medicinal, farming, and cultural significance. Its adaptability and environmental friendliness make it an important resource for sustainable agriculture and human well-being. Three commercialized neem-based formulations were tested aphid, Myzus persicae, including Azatrol, Triple Action Neem Oil (70% neem oil), and Pure Neem Oil (100% neem oil) in greenhouse and laboratory settings. A bioassay using a leaf disc choice test indicated that of the established neem-based insecticides tested were effective against the aphid at the recommended concentrations. However, a doubling in the quantity of Azatrol and Triple Action Neem Oil resulted in a 50% decrease in the number of aphids landing on handled leaf tissue compared to untreated leaf tissue.

Synthesis, toxicological and in silico evaluation of novel spiro pyrimidines against Culex pipiens L. referring to chitinase enzyme

The exponential development of resistance to conventional chemical insecticides adds another important motive for the creation of novel insecticidal active agents. One of the keys to meeting this challenge is the exploration of novel classes of insecticidal molecules with different modes of action. Herein, a novel series of spiro pyrimidine derivatives was prepared using some green synthetic methodologies such as microwave irradiation, and sonication under ultrasound waves. Spiro pyrimidine aminonitrile 1 is a key starting material for the synthesis of targets 2–9 by reaction with different carbon electrophiles and nitrogen nucleophiles. The structures of all the newly synthesized compounds were approved using spectral data. The toxicological efficiency and biological impacts of the synthesized spiro pyrimidine derivatives were assessed against Culex pipiens L. larvae. The toxicity of synthesized compounds showed remarkable variations against the C. pipiens larvae. Where, 3, 4 and 2 were the most efficient compounds with LC50 values of 12.43, 16.29 and 21.73 µg/mL, respectively. While 1 was the least potent compound with an LC50 value of 95.18 µg/mL. As well, other compounds were arranged according to LC50 values as follows 5 > 7 > 6 > 9 > 8. In addition, 3 and 4 exhibited significant prolongation of the developmental duration and greatly inhibited adult emergence. Moreover, many morphological deformities were observed in all developmental stages. Furthermore, cytotoxicity of the most effective compounds was assessed against the normal human cells (WI-38) as non-target organisms, where compounds 2, 4 and 3 showed weak to non-toxic effects. The study of binding affinity and correlation between chemical structure and reactivity was carried out using molecular docking study and DFT calculations to investigate their mode of action. This study shed light on promising compounds with larvicidal activity and biological impacts on the C. pipiens life cycle.

Efficacy of plant products in controlling disease vector mosquitoes, a review

AbstractMosquitoes pose a severe threat to the environment as vectors of numerous harmful diseases affecting humans and animals. Mosquitoes transmit pathogens that cause dengue, chikungunya, malaria, zika, yellow fever, Japanese encephalitis, and filariasis. Today's mosquito control strategies heavily rely on the use of chemical insecticides such as N,N‐diethyl‐meta‐toluamide (DEET), N,N‐diethyl mandelic acid amide (DEM), and dimethyl phthalate (DMP). However, the widespread use of chemical insecticides has resulted in pollution, bio‐magnification, and other health and environmental issues. It has also become ineffective because of the mosquitoes' aptitude to develop resistance, emphasizing the urgent need for safe, effective, and long‐lasting strategies. An alternative and promising approach to circumventing these obstacles involves the implementation of insecticides made from natural compounds found in plants. Therefore, the scientific community has shifted its focus towards plant‐based phytochemicals, oils, and extracts, as these are eco‐friendly, safe, and cost‐effective alternatives to conventional chemical insecticides. This review aims to provide details on current advances in plant‐based products (plant compounds, extracts, and essential oils), which are used to control all the life cycle stages (egg, larva, pupa, and adult) of the mosquito genera Aedes, Anopheles, and Culex. Hopefully, this review will pave the way to devise control strategies against these challenging pests.

Pathogenicity of Heterorhabditis bacteriophora in Ultraviolet Light–Irradiated Agar Suspension on Spodoptera frugiperda (Lepidoptera: Noctuidae) Larvae

Abstract Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is an economically important pest of variety of crops, including maize (Zea mays L.), rice (Oryza sativa L.), and cotton (Gossypium spp.). Conventional chemical insecticides are usually used for management of this pest; however, a viable alternative is the use of microbial agents or their biological products, such as entomopathogenic nematodes. Their efficacy, however, is affected by abiotic conditions including ultraviolet (UV) light and desiccation. It is therefore necessary to develop formulations that preserve or extend the viability of the agent or product while facilitating ease of application. This laboratory study was conducted to determine the pathogenicity of the nematode Heterorhabditis bacteriophora (Poinar) against S. frugiperda third-instar larvae. Infective juveniles (IJs) of the nematode were tested at a concentration of 350 IJs/ml in two substrates (water and 0.1% [w/v] agar suspension) with four periods of exposure (0, 5, 10 and 15 min) to UV radiation at 253.7 nm. Each of the eight treatments included 40 larvae, with each treatment replicated three times in a completely randomized design (two factors of type of medium and UV exposure time). We determined that the 0.1% (w/v) agar suspension, compared with the water substrate, protected the IJs from harmful UV light and thus improved the survival and pathogenicity of the IJs against third-instar S. frugiperda.

EFFICIENCY OF BIOLOGICAL CONTROL OF FALL ARMYWORM IN SWEET CORN

The cultivation of sweet corn has great importance in Brazil due to its nutritional quality and several possibilities for use. It is a crop that attracts a large number of pests, especially the carcass caterpillar, which can generate great qualitative and quantitative losses. Because it is mainly used in natura the application of agrochemicals to the control of these pests can cause risk to human health. Thus, the experiment was carried out with the objective of testing the efficiency of the use of biological insecticides in comparison to conventional chemical insecticides in the control of the military caterpillar. The biological insecticides Bio BB, Bio MB, Bio Bt Premium Akb, Agree and Bac-Control WP and the chemical insecticides Dimax 480 SC and Incrível, were applied in the maize crop at 3 different times at 28, 43 and 50 days after seeding. In all applications, the biological products proved to be as efficient in controlling the caterpillar carcass as the chemical insecticides. The products based on Beauveria bassiana and Metharrizium anisopliae showed greater efficiency in pest control proving that the biological insecticides are efficient in pest control in sweet corn contributing to a sustainable management of the crop.

Insecticidal Properties of Erythritol on Four Tropical Tephritid Fruit Flies, Zeugodacus cucurbitae, Ceratitis capitata, Bactrocera dorsalis, and B. latifrons (Diptera: Tephritidae)

Tephritid fruit flies are among the most destructive agricultural pests of fruits and vegetables worldwide and can impose trade barriers against the movement of fresh tropical commodities. Primary pre-harvest control methods for these flies rely on the spraying of conventional chemical insecticides or bait sprays. However, resistance to these control methods has been reported in fruit flies. Erythritol is a non-nutritive sugar alternative for human consumption, which has been tested and confirmed for its insecticidal properties against various insect pest species. In this study, using laboratory bioassays, we evaluated the insecticidal effect of erythritol alone or various erythritol formulations containing sucrose and/or protein on four tropical fruit fly species established in Hawaii (e.g., melon fly, Mediterranean fruit fly, oriental fruit fly, and Malaysian fruit fly). In addition, the effects of other non-nutritive hexose and pentose sugar alcohols, such as sorbitol, mannitol, and xylitol, were tested. Among the different standalone and combinatory treatments tested, 1M erythritol and a combinatory formulation of 2M erythritol + 0.5M sucrose appeared to be the most detrimental to the survival of all four species of tested flies, suggesting the potential of using erythritol as a non-toxic management tool for the control of tropical tephritid fruit flies.

Optimum Flight Height for the Control of Desert Locusts Using Unmanned Aerial Vehicles (UAV)

Desert locust is one of the most destructive migratory pest in the world. Current methods of control rely on conventional chemical insecticides during invasion. Some environmentally friendly biopesticides based on Metarhizium acridum and insect growth regulators have also been deployed in preventive control operations. They have been tested in sprayers mounted on commonly used platforms such as vehicles, aircraft, and human. However, despite being used successfully, these tools present many challenges, hence the need to supplement them with suitable alternatives. The successful use of drones to control pests such as fall armyworm, planthoppers, aphids, among others, makes it an attractive technology that has the potential to improve locust management, especially in inaccessible areas. However, key parameters for the safe and optimal use of drones in desert locust control are not documented. This study established the key parameters for spraying desert locusts with a drone. To test the optimum height for spraying Metarhizium acridum on the locusts, the drone was flown at five different heights: 2.5, 5, 7.5, 10, and 12.5 m. At each height, the drone sprayed the ink mixture on spray cards pinned to the ground to approximate the droplet density and compare it to the standard droplet density recommended for desert locust control. To assess the efficacy of M. acridum and the effectiveness of drones in its application, 50 g of spores were mixed in 1 L of diesel and sprayed on caged live locusts of different stages (3rd and 4th instars, as well as the adults); they were monitored for twenty-one days in a controlled room, and their mortality was determined. Variation in droplet density between the tested heights was significant. A height of 10 m agrees with the recommended standard droplet density within the 45 droplets/cm2 range. Mortality varied among the locusts’ developmental stages within and between heights. Survival probability varied between heights for 3rd instar, 4th instar, and adults. All the developmental stages of the desert locust were susceptible to Novacrid and the recommended target stage is the 3rd instar. Management of desert locusts by the use of drone technology appears promising when the pesticides are applied at an optimum height and standard operating procedures are followed. Further research could explore the gap in the effects of environmental parameters on flight application efficiency.

Bioinsecticidal activity of actinomycete secondary metabolites against the acetylcholinesterase of the legume’s insect pest Acyrthosiphon pisum: a computational study

BackgroundAcyrthosiphon pisum or pea aphid is an insect of the Aphididae family, which attacks various species of legumes such as beans and peas. This pest causes economically heavy crop losses around the world. The use of conventional chemical insecticides is the only way to control its development. However, the harmful consequences of these chemicals are well known. They pollute various compartments of the environment, thus constituting a major risk for human and environmental health. The search for a more ecological alternative, respectful of the environment is, therefore, a necessity. Actinomycetes represent a source of biologically active secondary metabolites, such as antibiotics and biopesticidal agents. In this study, 150 secondary metabolites of actinomycetes have made the objective of an in silico research by molecular docking, by screening their potential inhibitors against the enzyme acetylcholinesterase (AChE) of A. pisum. ResultsThe 3D structure of AChE, unavailable in the PDB database, was first modeled using the Modeller program, then the stereochemical quality of the model was validated. The molecular docking performed by the Autodock Vina algorithm allowed the selection of two metabolites giving binding energy equal to or lower than that of the co-crystallized inhibitor tetrahydro-acridine (−10.3Kcal/mol). The top-two metabolites are diazepinomicine (−10.9 Kcal/mol), and hygromycin (−10.3 Kcal/mol). These components have shown numerous interactions with the key residues of the catalytic site of the AChE enzyme, indicating their potential to inhibit its biological activity. The environmental and health safety of these components, as well as their bioavailability, were also studied by the verification of several pharmacokinetic and ADMET criteria. Diazepinomicine has shown excellent results verifying most of the criteria studied. A 50-ns MD simulation was also performed in order to test the stability of the complexes formed. ConclusionsIn addition to its favorable pharmacokinetic properties, the special chemical structure of diazepinomicin allows this molecule to interact intensely with AChE notably through the involvement of its two groups farnesyl diphosphate and dibenzodiazepinone which ensure several hydrogen and hydrophobic interactions, that offers very high stability to the complex AChE diazepinomicin. In conclusion, diazepinomicin can be suggested as a potential bioinsecticidal agent against the pest A. pisum.

Regional selection of insecticides and fungal biopesticides to control aphids and thrips and improve the forage quality of alfalfa crops

The efficacies of biological and conventional chemical insecticides against two major insect pests of alfalfa (aphids and thrips) were compared in three sites across China’s alfalfa belt. In addition, the persistence of the residues of chemical insecticides in alfalfa and their influence on the quality of alfalfa hay were examined. Efficacy varied among the different biological and chemical insecticides. The chemical insecticides were significantly more effective than biopesticides in a short time-frame. The efficacy period of biopesticides was significantly longer than that of chemical insecticides, and the corrected mortality rate of aphids in all regions was above 50% at 14 days after application. The analysis of pesticide residues showed that the residual doses of all the pesticides were within the allowed ranges after the safe period. The acid detergent fiber and neutral detergent fiber contents in alfalfa hay were higher and the protein content was lower in chemical insecticide treatments than in biopesticide treatments in Hebei. The relative feeding value of alfalfa hay treated with Metarhizium anisopliae IPP330189 was the highest among the treatments. Compared with chemical insecticides, the yield of alfalfa hay was higher in the biopesticides treatments. Biopesticides show a stronger control effect on insect populations and also a better improvement in the quality of alfalfa hay than chemical insecticides. This study provides a basis for exploring and developing a comprehensive control regime for alfalfa insect pests in the different alfalfa-growing regions in China, and for reducing chemical insecticide usage and improving forage quality.

CONTACT EFFECT OF Jatropha curcas L. EXTRACTS FOR THE CONTROL OF Callosobruchus subinnotatus (Pic) ON STORED BAMBARA NUT, Vigna subterranea (L.) VERDCOURT

The research was conducted in the year 2017 at the Entomology Laboratory of the Department of Crop Protection, Bayero University Kano to assess insecticidal properties of Jatropha curcas L. leaf and seed powders on Callosobruchus subinnotatus (Pic) infesting stored bambara nut, Vigna subterranea (L.) Verdcourt. The study aimed at comparing the effectiveness of the product with conventional chemical insecticide (pirimiphos-methyl 2%). Factorial experiment of 2×2×2 levels (leaf and seed powders at the rates of 0.0 and 0.5 g, with and without addition of the synthetic chemical at 0.01 g/20 g bambara nut seed) were laid out in a completely randomized design and replicated three times. Results obtained indicated positive contact effect of Jatropha leaf/seed extracts on adult bruchids. The results also showed strong repellent both singly and combined treatments although better results were obtained on leaf and seed combination with increase with the time of exposure. In conclusion, appreciable level of protection on bambara nut seeds was achieved using seed powder of J. curcas. Therefore, it is recommended that for effective management of C. Subinnotatus infesting bambara nut, farmers could use 1.0 g seed powder on 20 g bambara nut seeds.

EFFECT OF FUMIGATION OF POWDER LEAF AND SEED EXTRACTS OF JATROPHA CURCAS L. ON CALLOSOBRUCHUS SUBINNOTATUS (PIC) ON STORED BAMBARA (VIGNA SUBTERRANEA (L.) VERDCOURT) NUTS

The research was conducted in the year 2017 at the Entomology Laboratory of the Department of Crop Protection, Bayero University, Kano to assess fumigation properties of Jatropha curcas L. leaf and seed powders on Callosobruchus subinnotatus (Pic) infesting stored bambara nut, Vigna subterranea (L.) Verdcourt. The study aimed at comparing the effectiveness of the products with conventional chemical insecticide (pirimiphos-methyl 2%). Factorial experiment of 2×2×2 levels (leaf and seed powders at the rates of 0.0, 0.5. 1.0 and 1.5 g, with and without addition of the synthetic chemical at 0.01 g/20 g bambara nut seed) were laid out in a completely randomized design and replicated three times. Fumigant toxicity effect was observed on the emerged insects, though the result was significantly (P< 0.001) lower. In conclusion, appreciable level of protection on bambara nut seeds was achieved using seed powder of J. curcas. Therefore, it is recommended that for effective management of C. subinnotatus infesting bambara nut, farmers could use 1.0 g seed powder on 20 g bambara nut seeds.

SUSTAINABLE CONTROL OF CODLING MOTH, CYDIA POMONELLA L. IN SOME APPLE ORCHARDS OF BULGARIA

The codling moth (CM), Cydia pomonella L., is the key pest of pome fruits in Bulgaria. Reduction of pesticide use is an important consideration for human health as well as for conservation of biodiversity. Environmentally friendly methods such as semiochemicals are among the most promising. These trials were carried out during the years 2020 and 2021 in southeast Bulgaria to test the effectiveness of microencapsulated sprayable pheromones in apple orchards using CIDETRAK® CM MEC (pheromone) liquid formulations as well as the effectiveness of mating disruption (MD) using CIDETRAK® CMDA COMBO™ MESO™ -A dispensers at rate of 80 dispensers per ha. Monitoring of CM flights was implemented using pheromone or pheromone and kairomone lures with traps during the years of the study. The traps baited with standard PHEROCON® CM L2 lures were changed at 4-week intervals. We also used PHEROCON® CMDA COMBO™ - P + AA lures, which is a new product developed by Trécé Inc., USA for use in orchards with MD. The traps baited with PHEROCON® CM DA COMBO - P + AA lures were changed at 8-week intervals. The damage in the treatment plot increased slowly over time and even in late cultivars, fruit damage by CM was below the economical threshold from 0.1 to 0.2% in both years of the study. Comparatively, ten insecticide treatments were applied to the reference orchard located in the region during the season, targeting CM and other pests. Correspondingly, fruit damage at harvest in the reference orchard by CM was from 2.2 to 2.5%. The significance of differences in the damage rate between the trial and the reference orchard was estimated by Chi-square tests. These new products developed by Trécé Inc., USA can be used in organic farming and fits perfectly into any IPM system. The use of CIDETRAK® CM MEC and CIDETRAK® CMDA COMBO™ MESO™ - A dispensers will help growers to decrease the number of chemical treatments in the field. Introduction of these products for pest management should result in reduction of the use of conventional chemical insecticide treatments, thus resulting in less environmental pollution and improved food quality.

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.

Larvicidal potential of cell wall degrading enzymes from Trichoderma asperellum against Aedes aegypti (Diptera: Culicidae).

Aedes aegypti is a mosquito vector of arboviruses such as dengue, chikungunya, zika and yellow fever that cause important public health diseases. The incidence and gravity of these diseases justifies the search for effective measures to reduce the presence of this vector in the environment. Bioinsecticides are an effective alternative method for insect control, with added ecological benefits such as biodegradability. The current study demonstrates that a chitinolytic enzyme complex produced by the fungus Trichoderma asperellum can disrupt cuticle formation in the L3 larvae phase of A. aegypti, suggesting such biolarvicidal action could be used for mosquito control. T. asperellum was exposed to chitin from different sources. This induction of cell wall degrading enzymes, including chitinase, N-acetylglucosaminidase and β-1,3-glucanase. Groups of 20 L3 larvae of A. aegypti were exposed to varying concentrations of chitinolytic enzymes induced with commercial chitin (CWDE) and larvae cell wall degrading enzymes (L-CWDE). After 72 h of exposure to the CWDE, 100% of larvae were killed. The same percent mortality was observed after 48 h of exposure to L-CWDE at half the CWDE enzyme mixture concentration. Exoskeleton deterioration was further observed by scanning and electron microscopy. Our findings indicate that L-CWDE produced by T. asperellum reflect chitinolytic enzymes with greater specificity for L3 larval biomolecules. This specificity is characterized by the high percentage of mortality compared with CWDE treatments and also by abrupt changes in patterns of the cellular structures visualized by scanning and transmission electron microscopy. These mixtures of chitinolytic enzymes could be candidates, as adjuvant or synergistic molecules, to replace conventional chemical insecticides currently in use.

Bio-efficacy of novel chemicals and tribal pesticide-based integrated modules against brown planthopper in rice

Rice brown planthopper (BPH), Nilaparvata lugens (Stal.) is a major menace and cause of significant damage to rice throughout Asian countries. Farmers mostly rely on conventional chemical insecticides to control this pest, however injudicious application of chemicals lead to the problem of insecticide resistance and environmental pollution. Considering the economic importance of BPH a research was conducted during kharif season 2018–2019 to investigate the field-efficacy vis.-a-vis. non-target toxicity and economics of some bio-rational pest management schedules at a BPH biotype 4 endemic location (Burdwan district) of West Bengal, India. Among various treatment schedules, triflumezopyrim (30 g a.i. ha−1), pymetrozine (175 g a.i. ha−1) and sulfoxaflor (30 g a.i. ha−1) in a rotational application with aqueous extract of Jatropha gossypiifolia + cow urine @ 1:1 ratio (3.5%) and aqueous extract of Argemone maxicana + ‘toddy’ @ 1:2 ratio (3.0%) significantly reduced the nymphs and adult populations of BPH. The aforesaid insecticides and indigenous components were also found to be safe to prevailing predatory fauna including Cyrtorhinus lividipennis, Ophionea spp. and spider complex in the field. Though there was a short-term decline in predatory populations after application of insecticides, it started increasing gradually within a week after treatment. Yield of rice significantly increased over control in those treatment schedules during both the years with an incremental cost: benefit ratio of 1:2.62 to 1:3.99. These superior semi-organic modules, as an approach towards “eco-friendly agriculture”, can be an excellent alternative of truly chemical schedules in controlling rice BPH in coming years.

Additive interactions of some reduced-risk biocides and two entomopathogenic nematodes suggest implications for integrated control of Spodoptera litura (Lepidoptera: Noctuidae)

Higher volumes of conventional and novel chemical insecticides are applied by farmers to control resistant strains of armyworm (Spodoperta litura) in Pakistan without knowing their risks to the environment and to public health. Ten reduced-risk insecticides were tested for their compatibility with two entomopathogenic nematodes (EPNs); Heterorhabditis indica and Steinernema carpocapsae against S. litura. The insecticide emamectin benzoate was highly toxic (LC50 = 2.97 mg/l) against 3rd instar S. litura larvae when applied alone whereas, novaluron and methoxyfenozide were the least toxic (LC50 = 29.56 mg/l and 21.06 mg/l), respectively. All the insecticides proved harmless against the two EPNs even 96 h after treatment. Indoxacarb, flubendiamide and spinetoram produced the greatest mortalities (72–76%) of S. litura larvae after 72 h when applied in mixtures with H. indica. Lowest mortalities (44.00 ± 3.74% and 48.00 ± 2.89) were observed for mixtures of H. indica with methoxyfenozide and chlorfenapyr, respectively. The positive control treatments with both EPNs (S. carpocapsae and H. indica) produced > 50% mortality 96 h after treatment. For insecticide mixtures with S. carpocapsae, only indoxacarb produced 90% mortality of larvae, whereas, indoxacarb, flubendiamide, emamectin benzoate, and spinetoram produced 90–92% mortality of larvae when applied in mixtures with H. indica. Additive interactions (Chi-square < 3.84) of EPN mixtures with reduced volumes of reduced-risk insecticides suggest opportunities to develop more environmentally favorable pest management programs for S. litura.

English

Cabbage aphid, Brevicoryne brassicae is among the notorious insect pests of Canola (Brassica napus) and other Brassica spp., with a reported loss of up to 75%. It has gained resistance against conventional chemical insecticides. So, to activate inducer mediated plant resistance is among the workable solutions against this pest. Henceforth, inducer-mediated resistance based on categorizes of induced-resistance (IR), nutrient-deterrence (ND) and sulphur-integration (SI), was applied in 18 treatments. Their responses against aphid development period, reproduction time, progeny production, immature becoming adults, percent survival and mortalities, were noted-down. In the IR category, all the biological parameters were affected significantly by 1 mM (1 and mM should be in the same line) mM salicylic acid-T4 treatment, whereas in ND, silicon 50 kg ha-1-T10 was more effective. Likewise, during SI studies, bio-sulphur-T15 remained an efficient one. Overall, the developmental period of B. brassicae nymphs was delayed by T10 (Si 50 kg ha-1), followed by T4 (1 mM SA), while Compost-T16 expedited their development. Besides these, reproduction time was reduced at the most by T4, followed by T15. Aphid progeny production was again decreased significantly by T4 and T10, while T16 (Compost) presented the maximum progenies. Associatively, the least number of nymphs becoming adults were shown in T4, T10 followed by T7 (1 mM CA). The highest percent nymph survival was shown in T1 (control) and T16 (compost) with the highest nymph percent mortality in T4 and T7. Hence, salicylic acid, silicon, and bio-sulphur showed maximum effective resistance responses but in concentration-dependent manner. These findings can be used in future integrated pest management programs of aphids and other specialists on related hosts. © 2021 Friends Science Publishers

Thermophilic Chitinases: Structural, Functional and Engineering Attributes for Industrial Applications.

Chitin is the second most widely found natural polymer next to cellulose. Chitinases degrade the insoluble chitin to bioactive chitooligomers and monomers for various industrial applications. Based on their function, these enzymes act as biocontrol agents against pathogenic fungi and invasive pests compared with conventional chemical fungicides and insecticides. They have other functional roles in shellfish waste management, fungal protoplast generation, and Single-Cell Protein production. Among the chitinases, thermophilic and thermostable chitinases are gaining popularity in recent years, as they can withstand high temperatures and maintain the enzyme stability for longer periods. Not all chitinases are thermostable; hence, tailor-made thermophilic chitinases are designed to enhance their thermostability by direct evolution, genetic engineering involving mutagenesis, and proteomics approach. Although research has been done extensively on cloning and expression of thermophilic chitinase genes, there are only few papers discussing on the mechanism of chitin degradation using thermophiles. The current review discusses the sources of thermophilic chitinases, improvement of protein stability by gene manipulation, metagenomics approaches, chitin degradation mechanism in thermophiles, and their prospective applications for industrial, agricultural, and pharmaceutical purposes.