Insect Growth Regulatory Activity Research Articles

Biological activity of coumarins against Spodoptera frugiperda (Lepidoptera: Noctuidae)

In this work, we evaluated the activity of coumarins against larvae Spodoptera frugiperda in a group of compounds (1-7) purchased from SIGMA-ALDRICH (96% purity, as informed by the manufacturer) and a group of coumarin derivatives (compounds 8-15) synthesized according to suitable chemistry procedures. Coumarins were synthesized by the Pechmann method under solvent-free conditions using a bulk Keggin heteropolyacid. The compounds represent a valuable resource for future studies of plant chemical defense. Results indicate that coumarins: (12) 7-methyl-3,4-dimethyl-2H-chromen-2-one, (14) 7-hydroxy-3,4 dimethyl-2H-chromen-2-one, and (15) 4-methyl-2H-benzo[h]-chromen-2-one have highly significant insect growth regulatory activity. Furthermore, sublethal effects were observed such as pupal mortality and adult deformities. Compounds (13) 4,6,7-trimethyl-2H-chromen-2-one and (14) 7-hydroxy-3,4 dimethyl-2H-chromen-2-one caused pupal mortality higher than 40%. The quantitative structure-activity relationships were determined using the available data with the purpose of predicting the toxicity activity of a number of structurally related coumarins. A molecular structure and biological activity relationship is suggested. The observed effects were in part produced by severe alterations of the epithelial cells of the midgut.

Insect growth-regulating activity of 1-benzyl-2-methylbenzimidazole derivatives on silkworms.

Derivatives of 1-benzyl-2-methylbenzimidazoles (BMBIs) were synthesized to evaluate their biological activities against Bombyx mori, a lepidopteran model insect. Synthesized BMBIs exhibited two different biological activities: inhibition of development and acute lethality. From a structural perspective, the activity varied with the position of the substitutions on the 1-benzyl moiety; BMBIs with substitutions on the 2 and/or 4 positions had comparatively high activity in comparison with those with substitutions on the 3-position. There was more activity for the inhibition of development with low doses, and more for acute lethality with high doses. The activity was also affected by the applied stage, that is, application in the 4th instar mostly interfered the larval molting or pupation, whereas that in the 3rd instar caused more acute mortality. Taken together, these results suggest that BMBIs have multiple modes of action.

ENHANCED TOXICITY OF BROWN ALGAL SEAWEED Sargassum wightii GREVILLE WITH ORGANIC INPUTS AGAINST RICE LEAF FOLDER Cnaphalocrocis medinalis GUENEE (LEPIDOPTERA: CRAMBIDAE) UNDER LABORATORY CONDITIONS

Rice leaf folder (Cnaphalocrocis medinalis Guenee) as a key pest have imparted extensive leaf damage during the tillering stage of the crop and has been reported to cause more than 15% damage. The experiment was conducted to evaluate the enhanced insecticidal and IGR activity of solvent extracts (Acetone) of brown algal seaweed Sargassum wightii Greville in combination with organic inputs (Neem Leaf Extracts 3% and 5%) against rice leaf folder C. medinalis in the Seaweed Laboratory, Department of Entomology, Faculty of Agriculture, Annamalai University, Tamil Nadu, India during 2021-2022. The seaweed Extracts @ 6, 7 and 8 per cent alone and in combination of seaweed 6, 7, 8 percent with Neem Leaf Extracts 3 and 5 per cent concentrations were investigated for their enhanced toxicity (larvicidal and Insect Growth Regulator activity) against rice leaf folder compared with standard checks (Neem Leaf Extracts 3% and 5%). The highest mortality (66.66%) was observed in the combination treatment S. wightii seaweed extract 8 per cent + Neem Leaf Extract 5 per cent followed by S. wightii seaweed extract 8% with Neem Leaf Extract 3% which exerted 60.00 per cent mortality. The larva to adult conversion ratio of 1:0.13 in S. wightii seaweed extract 8% with Neem Leaf Extract 5% was the least when compared with other treatments whereas S. wightii seaweed extract 8% with Neem Leaf Extract 3% was the effective treatment in the second experiment with a larval and adult conversion ratio of 1:0.20 meanwhile no mortality was observed in both untreated controls in both the experiments. The combination effect of S. wightii seaweed extract 8% with Neem Leaf Extract 5% was superior than other treatments in reducing the larval vitality, pupation and also influenced insect growth regulator activity in the pupal and adult stages of insect which would be recommended for the future IPM programmes.

Effects of Insect Growth Regulators on Ambrosia Beetles (Coleoptera: Curculionidae)

Abstract Ambrosia beetles, especially the granulate ambrosia beetle, Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae), are serious pests in ornamental nurseries in Georgia during the spring months. Growers spray pyrethroid insecticides to prevent ambrosia beetle attacks on the tree trunk around bud break. Repeated pyrethroid insecticide applications can harm beneficial arthropods and cause a resurgence of minor, secondary pests. Insect growth regulators (IGRs), such as novaluron and azadirachtin, have demonstrated transovarial activity on many insect pests, for which the viability of the eggs was reduced after adult exposure. IGRs, particularly azadirachtin, are also repellent to many insect pests. Thus, the objective of this study was to determine the transovarial and repellent activity of IGRs on ambrosia beetles. Two experiments were conducted in ornamental nurseries in 2019 and 2021. In the first experiment, novaluron, azadirachtin, and permethrin were sprayed as stand-alone and combination treatments with permethrin on maple (Acer) tree bolts. The number of ambrosia beetle attacks was significantly lower in treatments with permethrin in both years. Novaluron and azadirachtin treatments neither reduced ambrosia beetle attacks on the ethanol-infused bolts nor suppressed the recovery of X. crassiusculus from the bolts, suggesting the lack of repellent and transovarial activity, respectively. For the second experiment, novaluron alone and in combination with 1×, 4×, and 8× bark penetrant at the label rate were sprayed on ethanol-infused bolts. None of the novaluron treatments with or without bark penetrant elicited transovarial activity in X. crassiusculus, as the beetle recovery was similar among treatments.

Juvenile hormone antagonistic activity of secondary metabolites from Streptomyces lactacystinicus and their insecticidal activity against Plutella xylostella

• IMBL-1412 isolate showed high JHAN and insecticidal activity against P. xylostella . • IMBL-1823 isolate showed high JHAN and insecticidal activity against P. xylostella . • Both IMBL-1412 and IMBL-1823 were identified as Streptomyces lactacystinicus . • Ethyl acetate fraction of them showed high JHAN and insecticidal activities. Due to their specificity to target insects and low toxicity to non-target organisms, insect growth regulators (IGRs) have been promising alternatives to neurotoxic insecticides. Actinobacteria produce a wide range of secondary metabolites with insecticidal and insect growth regulatory activities. In this study, the culture media of 25 actinobacteria isolates showing high juvenile hormone antagonist (JHAN) activity were assessed for their insecticidal activity to identify novel IGR compounds toxic to Plutella xylostella . Among them, four isolates exhibited high insecticidal activity against 3rd instar larvae of P. xylostella . Two isolates of IMBL-1412 and IMBL-1823 showing relatively high insecticidal activities (greater than90% mortality) were identified as Streptomyces lactacystinicus based on colony color on various International Streptomyces Project (ISP) media and nucleotide sequences of the 16S rRNA gene. The ethyl acetate fractions of both isolates showed high JHAN and insecticidal activities against P. xylostella larvae at a concentration of 100 ppm when the culture media of these two isolates were extracted sequentially using hexane, ethyl acetate, and butyl alcohol. These results suggested that secondary metabolites of these actinobacterial isolates could be efficiently applied to develop novel IGR insecticides for the control of P. xylostella .

Conventional and Organic Wheat Germ Have Distinct Physiological Effects in the Tobacco Hornworm, Manduca Sexta: Use of Black Mutant Assay to Detect Environmental Juvenoid Activity of Insect Growth Regulators.

Stored grains used in artificial diets are often treated with insecticides to control infestation by pests. In recent years, insect growth regulators (IGRs) have become an increasingly popular form of insect pest control in agricultural settings. Most IGRs specifically target insects by either disrupting their endocrine system or their chitin synthesis. One type of IGRs comprises of chemical analogs of juvenile hormone (JH), a major hormone involved in growth and development of insects. Here we demonstrate that conventional wheat germ contains JH activity and impacts growth and development of the tobacco hornworm, Manduca sexta. Feeding diet containing conventional wheat germ delayed the timing of metamorphosis in wildtype larvae by extending the duration of the final instar. Diet with conventional wheat germ also inhibited melanization of the black mutant larvae and induced the expression of the JH response gene, Krüppel homolog 1. We demonstrate that the black mutant bioassay is a sensitive assay that can determine the amount of JH activity in stored grains and suggest that this assay may offer a quick and reliable assay to determine the amount of environmental juvenoids. Researchers are urged to use caution when purchasing stored grains for mass-rearing of research insects.

Juvenile hormone mimics with phenyl ether and amide functionality to be insect growth regulators (IGRs): synthesis, characterization, computational and biological study

A series of substituted phenyl ethers derivatives as juvenile hormone (JH) mimics (V1-V8) have been synthesized. Substituted phenoxyacetic acid and amino acid ethyl ester hydrochloride were prepared using NaOH, SOCl2. DCC method has been used for amide linkage. The structure of prepared compounds has been confirmed by Fourier Transform Infra-Red (FT-IR), Electrospray ionization-Mass spectrometry (ESI-MS), Proton and Carbon-13 nuclear magnetic resonance (1H-NMR, 13C-NMR) spectroscopic techniques. Biological efficacy of synthesized analogs has been carried out under laboratory conditions. Galleria mellonella (honey bee pest) has been chosen as testing insect. Juvenile hormone (JH) activity of synthesized compounds has been tested at different concentrations and compared with the standard juvenile hormone analogs (JHAs) pyriproxyfen (M1) and fenoxycarb (M2) against the fifth larval instar of G. mellonella. Compound ethyl 2-[2-(4-methylphenoxy)aminoacetyl]-3-phenyl-propanoate (V6) exhibited better activity among all the synthesized compounds (V1-V8) with LC50 and LC90 values of 0.11 mg/mL and 0.56 mg/mL respectively. Compounds showed insect growth regulating (IGR) activity at lower concentrations. In silico screening of all synthesized compounds with the W-cavity of juvenile hormone-binding protein (JHBP) of insect G. mellonella has been carried out. Chemical reactivity of synthesized series has been studied using DFT/B3LYP/6-311 + G(d,2p) method. Non-toxic behavior of molecules has also been observed from ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) study using discovery studio client 3.0. Communicated by Ramaswamy H. Sarma

Insecticidal and insect growth regulatory activities of secondary metabolites from entomopathogenic fungi, Lecanicillium attenuatum

AbstractInsect growth regulators (IGRs) are effective alternatives to chemical insecticides because of their specificity and low environmental toxicity. Entomopathogenic fungi are an important natural pathogen of insects and have been developed as biological control agents. They produce a wide range of secondary metabolites such as antibiotics, pesticides, growth‐promoting or inhibiting compounds and insect attracting agents. In this study, to explore novel IGR substances from entomopathogenic fungi, culture extracts of 189 entomopathogenic fungi isolated from Korean soil samples were investigated for their juvenile hormone (JH)‐based IGR activities. Whereas none of the culture extracts exhibited JH agonist (JHA) activity, 14 extracts showed high levels of JH antagonist (JHAN) activity. Among them, culture extract of JEF‐145 strain, which was identified as Lecanicillium attenuatum, showed the highest insecticidal against Aedes albopictus and Plutella xylostella. At liquid culture condition, JHAN activity was observed in culture soup rather than mycelial cake, indicating that substances with JHAN activity are released from the JEF‐145 strain during culture. Furthermore, while extract from solid cultured JEF‐145 strain showed insecticidal activities against both A. albopictus and P. xylostella, that from liquid cultured fungi showed insecticidal activity only against A. albopictus, indicating that L. attenuatum JEF‐145 strain produces different kinds of secondary metabolites with JHAN activity depending on culture conditions. These results suggested that JHAN substances derived from entomopathogenic fungi could be usefully exploited to develop novel eco‐friendly IGR insecticides.

Bioactivity of Plant Essential Oil against Potato Tuber Moth,Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae).

Phthorimaea operculella (Potato tuber moth) is a destructive pest of stored potatoes and potato crops, primarily in subtropical areas of the globe. It is a pest of the field as well as storage, the larvae damage the crop through the foliage, stem, and tubers too. The manifestation of potato tuber moth primes to high economic damages in production worldwide. Post-harvest protection of the potato tubers becomes important and is challenging. A treatment with chemical agents is a possible strategy but cannot be recommended for food items hence alternative methods become important in control of these moths. The present study deals with the assessment of plant oils of Cinnamomum verum, Cupressuss sempervirens and Cymbopogon nardus. These plant oils were used to evaluate the larvicidal, adulticidal, Insect growth regulatory, repellency and oviposition deterrence activities against potato tuber moth. Results of the present work indicated that all the test oils show some promise as pest control agents against P. operculella. Oil of C. verum has exhibited promising toxic action (larvicidal LC50 = 110.10 μg/cm2, adulticidal LC50 = 49.78 μg/cm2). The oil of C. nardus caused promising IGR activity (delay in development = 16.2 days) All three plant oils have shown multifarious activity and can be a part of an eco-friendly and user-friendly method of control.

Toxicity and insect growth regulatory activities of medicinal plant, Withania somnifera, in flesh fly, Sarcophaga ruficornis (Diptera: Sarcophagidae)

BackgroundThe flesh fly Sarcophaga ruficornis is well known for its medical and veterinary importance in causing myiasis in humans and animals. The conventional use of chemical pesticides for controlling insect pests has resulted in environmental pollution besides posing serious hazards to non-target organisms and the development of pest resistance against these compounds. Considering the various harmful and adverse effects of chemical pesticides, an alternative and safe approach for the pest management has to be explored. The plant extracts derived from plants are eco-friendly in nature, easily biodegradable, and can be used as botanical pesticides.ResultsExtracts from root of the medicinal plant Withania somnifera were assessed for their toxicity and insect growth regulatory activity when administered to larvae of S. ruficornis. Topical administration of root extracts of W. somnifera to 0–3-day-old third instar larvae of S. ruficornis resulted into severe disruption of development, moulting, and metamorphosis producing several detrimental effects such as toxicity, prolongation of larval life, ecdysial stasis, abnormal pupariation, reduced normal pupariation and adult emergence, and development of pupal-adult mosaics and adultoids. The LC50 values in topical application of root extracts of W. somnifera were 28.19, 43.49, 47.48, and 48.16 g/μL against S. ruficornis third instar day 0, 1, 2, and 3 larvae, respectively.ConclusionThese effects are similar to those observed as a consequence of the administration of juvenile hormone analogs (juvenoids) and may be due to interference with the normal hormonal mechanism of moulting and metamorphosis. This clearly demonstrates that the root extracts of W. somnifera may be used as an insect growth regulator for the control and management of S. ruficornis along with other bio-rational approaches in integrated pest management programs.

Isolation and characterization of the insect growth regulatory substances from actinomycetes

Insect growth regulators (IGRs) are attractive alternatives to chemical insecticides. Since it has been reported that secondary metabolites from actinomycetes show insecticidal activities against various insect pests, actinomycetes could be a potential source of novel IGR compounds. In the present study, insect juvenile hormone antagonists (JHANs) were identified from actinomycetes and their insect growth regulatory and insecticidal activities were investigated. A total of 363 actinomycetes were screened for their insect growth regulatory and insecticidal activities against Aedes albopictus and Plutella xylostella. Among them, Streptomyces sp. AN120537 showed the highest JHAN and insecticidal activities. Five antimycins were isolated as active compounds by assay-guided fractionation and showed high JHAN activities. These antimycins also exhibited significant insecticidal activities against A. albopictus, P. xylostella, F. occidentalis, and T. urticae. Moreover, dead larvae treated with these antimycins displayed morphological deformities that are similar to those of JH-based IGR-treated insects. This is the first report demonstrating that the insecticidal activities of antimycins resulted from their possible JHAN activity. Based on our results, it is expected that novel JHAN compounds potentially derived from actinomycetes could be efficiently applied as IGR insecticides with a broad insecticidal spectrum.

Influence of Insect Growth Regulators on Stephanitis pyrioides (Hemiptera: Tingidae) Eggs and Nymphs.

The azalea lace bug, Stephanitis pyrioides (Scott) (Hemiptera: Tingidae), is an important insect pest of azaleas (Rhododendron L. spp.) in the USA. Stephanitis pyrioides feeds on azalea foliage and causes extensive chlorosis, which reduces the aesthetic value and marketability of these plants. Because the use of neonicotinoid insecticides has been dramatically reduced or discontinued, growers and landscape managers are seeking alternative tools or strategies to control this insect. Although insect growth regulators (IGRs) are known for their activity against immature insect stages, their activity against egg hatching has not been addressed thoroughly, specifically against S. pyrioides. Thus, a series of experiments was conducted to understand the ovicidal activity of IGRs using novaluron, azadirachtin, pyriproxyfen, and buprofezin against S. pyrioides. The number of newly emerged young instars was significantly lower when leaves implanted with eggs were sprayed on both sides with novaluron, azadirachtin, and buprofezin compared to nontreated and pyriproxyfen treatments. When IGRs plus adjuvant were applied to the adaxial surface of the leaves, the densities of the newly emerged nymphs were significantly lower under the novaluron treatment compared to the nontreated leaves. However, there was no significant difference in the number of nymphs that emerged in the absence of adjuvant. Furthermore, close monitoring revealed reduced levels of egg hatching in the presence of adjuvant with novaluron compared to its absence. The data show that the survival of S. pyrioides first instars was not affected by exposure to dried IGR residues.

Investigations on the Larvicidal Effect of Red Algal Seaweeds of Rameswaram Coast Against Tobacco Caterpillar Spodoptera Litura (Fab.)

Investigations on the insecticidal activity of Red algal seaweeds viz., Gracilaria corticata J. Agardh, Liagora ceranoides J. V. Lamouroux, and Asparagopsis taxiformis (Delile) collected from Rameswaram coastal ecosystem against Leaf eating caterpillar, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) was conducted in the Department of Entomology, Faculty of Agriculture, Annamalai University, India during 2016-2018. Powdered seaweeds at 1, 3, 5, 7, 10 and 20 per cent concentrations were investigated for their toxicity and insect growth regulator activity aganist S.litura under CRD in free choice test with three replications along with control. Observations showed that, larval mortality noticed after 36 hours after treatment in G. corticata treatments and even 100 per cent mortality was achieved at 72 hours of treatment, whereas the other two seaweeds exhibited larval mortality only after 72 hours of treatment and extended further to pupation and adult emergence. Among the concentrations the higher doses (20 and 10%) exhibited the maximum larval mortality (100%) while the maximum doses of other two seaweeds powder treatments did not, exhibited cent per cent larval mortality at any point of time and even pupated and gone for adult emergence also. The results displayed that, all the seaweed had exhibited larval mortality and their inhibiting substance inside needs to be investigated.

Studies on Methanolic Extract of Brown Algal Seaweed Liagora ceranoides J.V. Lamouroux from Southern Coast of Tamilnadu: In vitro Anti-Insect Properties and Phytochemicals

Red algal seaweed Liagora ceranoides collected from Rameswaram coast, Tamilnadu, India was investigated for its repellent, antifeedant, larvicidal, insect growth regulatory activities on Spodoptera litura during 2016-18. Larvicidal action of methanol extract of sea weed was observed from first day of treatment and exhibited gradual increase in mortality up to fifth day. The seaweed’s methanol extracts @200 μl/L concentration resulted 80.00 per cent larval mortality and the survived larvae got pupated. No repellent and antifeedant activity was observed among the treatments. Adult emergence was not observed at 200 μl/L concentration with a pupal: adult conversion ratio of 1:0.00 whereas in control and solvent control the ratio was 1:1.00. Twenty- three phytochemicals were identified in L. ceranoides using GC-MS detection system (Gas Chromatography-Mass Spectrometry) respectively and few of them may be responsible for ant-insect properties.

Insect growth regulatory activity of carvacrol-based 1,3,4-thiadiazoles and 1,3,4-oxadiazoles.

In designing of novel insect growth regulators (IGRs), biologically occurring carvacrol has been structurally modified to thiadiazole and oxadiazole moieties. Two series of carvacrol analogs containing 1,3,4-thiadiazole (VIIIa-e) and 1,3,4-oxadiazole (IXa-e) derivatives are designed and synthesized. Their structures are confirmed by FT-IR, [Formula: see text] NMR, [Formula: see text]C NMR and LC-MS. IGR activity is tested against Spodoptera litura. Several analogs displayed IGR activity against this insect pest. Compounds VIIIe and IXe displayed relatively good IGR activity with [Formula: see text]values 117.43 and 108.83ppm against Spodoptera litura, respectively. Synthesis, characterization and evaluation of carvacrol-based 1,3,4-thiadiazole and 1,3,4-oxadiazole derivatives as potent insect growth regulators (IGRs).

Withania somnifera acts as a potential insect growth regulator in the polyphagous pest, Pericallia ricini

Abstract Both seed and root extracts of the medicinal plant, Ashwagandha, Withania somnifera exhibit insect growth regulatory activity against the polyphagous pest, Pericallia ricini. Topical administration of W. somnifera seed and root extracts to last instar larvae of P. ricini disrupted moulting and metamorphosis, leading to a number of developmental abnormalities such as delay in larval-pupal and pupal-adult ecdysis, formation of larval-pupal, pupal-adult and larval-pupal-adult mosaics/chimeras, ecdysial failure, suppression of pupation and adult emergence and formation of abnormal pupae and adultoids. The treatment with seed extracts was more severe than that of root extracts as it completely suppressed the pupation and adult emergence. The results clearly suggest that the medicinal plant, W. somnifera acts as a potential insect growth regulatory (IGR) disrupting the moulting and metamorphosis as a consequence of interference with the endocrine system.

Insect growth regulatory and larvicidal activity of chalcones against Aedes albopictus

AbstractWidespread use of chemical insecticides has resulted in development of insect resistance and natural products with biological activities could become an attractive alternative to control insect pests. In order to find more effective insecticides for controlling mosquito, various mosquitocidal compounds are studied. Recently, juvenile hormone antagonists (JHANs) have been found to be to safe and effective insecticides for control of mosquito. In order to identify novel insecticidal compounds with JHAN activity, several chalcones were surveyed on their JHAN activities and larvicidal activities against Aedes albopictus larvae. Among them, 2′‐hydroxychalcone and cardamonin showed high levels of JHAN and mosquito larvicidal activities. These results suggested that chalcones with JHAN activity could be useful for control of mosquito larvae.

Larvicidal and Growth-Regulatory Activities of Methanolic and N-hexane Extracts of Leaf of Ficus vallis-choudae Delile (Rosales: Moraceae) against Culex quinquefasciatus (Diptera: Culicidae)

The study aimed at determining the larvicidal and Insect-Growth-Regulating (IGR) potentials of n-hexane and methanolic extracts of Leaf of Ficus vallis-choudae against Culex quinquefasciatus mosquitoes in a bid to develop a cost effective and eco-friendly control lead. Collected leaves of the plants were air-dried, pulverized and sohxlet-extracted. Phytochemical screening of the crude extracts was done following standard protocols. Graded concentrations of 0.00625 to 0.05 mg/L (n-hexane extract) and 0.2 to 0.5 mg/L (methanolic extract) of the crude extract were assayed against fourth larval instar of the mosquito species. The mosquitoes were monitored from zero to 48 hours post-exposure to determine mortality. Sub lethal concentrations of 0.00625 (n-hexane) and 0.2 mg/L (methanol) were assayed for IGR activities. The phytochemical screening of crude extracts of the leaf revealed presence of seven secondary metabolites, whose presence was dependent on extraction solvent. They include flavonoids, tannins, saponins, cardiac glycosides, steroids, anthraquinones and terpenoids. After 48 hours post-exposure, analyses revealed a time and dose-dependent toxicity of the leaf extracts. The LC 50 and LC 90 , respectively, of the n-hexane and methanolic extracts were, 0.022 and 0.042 mg/L, and 0.355 and 0.463 mg/L, respectively. IGR studies revealed significant increase in duration of development by the sub lethal concentrations. This study revealed larvicidal and IGR potential of n-hexane and methanolic extracts of the leaf of Ficus vallis-choudae , and therefore, a promising lead agent for development of larvicides for mosquito vector control .

Secondary Metabolites of Colocasia esculenta Extract as Green Insecticide Against the Cotton Leaf Worm, Spodoptera littoralis (Boisd.)

A petroleum ether extract of Colocasia esculenta leaves yielded two sterols which were identified as; β- sitosterol І, Stigmasterol ІІ, these secondary metabolites showed insecticidal, antifeeding and insect growth regulatory activities against the 4th instar larvae of Spodoptera littoralis. So, the efficacy of this extract and two insect growth regulators belonging to different groups; methoxyfenozide (an ecdysone agonist) and lufenuron (chitin synthesis inhibitor) was assayed against the 4th instar larvae of S. littoralis under laboratory conditions. C. esculenta extract, methoxyfenozide and lufenuron have sub-lethal concentrations LC25 (17.8 gm/liter, 5.07 mg/liter and 0.80 mg/liter), respectively. It was observed that in case of both C. esculenta and methoxyfenozide treatments, the larvae undergo a precocious molting where promoted apolysis process but die due to failure in completing the molting process, at time shorter than the control ones. Ecdysis and sclerotization were incomplete and the pupa that emerged showed many deformities. The joint action of mixing C. esculenta extract at two concentrations (LC10 and LC25) with methoxyfenozide and lufenuron at two concentrations (LC10 and LC25) can be evaluated. All the mixtures of C. esculenta and methoxyfenozide have synergistic activity against treated larvae, while all the mixtures of C. esculenta and lufenuron have antagonistic activity. Biochemical characterization of enzyme activities related to molting process and cuticle synthesis showed that C. esculenta extract treatment caused significant disturbance in enzyme balances either decrease or increase comparing to control ones, the reason behind deformations and mortality may be as a result of change in chitinase, phenoloxidase and protease enzymes. These plant sterols І, ІІ may be considered to be efficient insect growth regulators, as well as having activity similar to phytosteroids, as was evidenced by their significant inhibition of molting processes.

Insecticidal effect of citronella and neem oil Nanoemulsions against Spodoptera litura (Fab)

In order to develop innovative botanical formulations, nanoemulsion formulations of oils (neem oil & citronella oil) mixture were developed and their physiochemical properties were studied. The size of the nanoemulsions was found to be in the range of 11.23 to 17.80 nm using Dynamic Light Scattering analysis and confirmed by Transmission Electron Microscopy. The nanoemulsions were found to be stable as per CIPAC guidelines (MT 36.1). The nanoemulsion formulations were evaluated for their larvicidal and growth regulatory activities against 3rd instars of Spodoptera litura laboratory conditions. Results showed that increased concentration of citronella oil in the nanoemulsion resulted in enhanced larval mortality. The nanoemulsions, NNE-8 with 4.0% citronella oil showed highest larval mortality (80.0%) as compared to only neem oil nanoemulsion. Also, insect growth regulatory activity was found high with increase in concentration of citronella oil till 4.0%, thereafter no significant difference was observed.