Rearing the egyptian cotton leafworm,Spodoptera littoralis,on a practical calcium-alginate diet

Larvae ofSpodoptera littoralis (Boisd.) were mass-reared on a calcium-alginate diet consisting of soybeans, alfalfa meal, milk powder, and yeast as the nutrients, with dry citric acid as the gel-setting acid. Larval and pupal survival was 73%; a mean of 2045 eggs per female was oviposited within 4 days. The advantage of using this new technique is discussed.     

Influence of oil droplet size on the toxicity of bifenthrin on cotton to tobacco budworm (Heliothis virescens)

Sprays of bifenthrin and paraffinic oil mixtures were applied to cotton leaves (Gossypium hirsutum L.) to investigate droplet size effects on the mortality of Heliothis virescens (F.). An air-assisted nozzle applied mixtures at 9.4 litre ha ?1 spray rate with volume median diameters (VMD) of 96 and 337 μm, as verified with a Malvern laser diffraction analyzer. An hour after spraying, susceptible 3rd-instars walked for 2-min through wet droplets of spray mixtures applied at bifenthrin rates of 22, 45, 67, 90. and 112 g a.i. ha ?1. Mortality was assessed at 21, 26, 45, 50, 74, and 117h after exposure. Final mean mortality was affected (P =0.01) by bifenthrin rate and droplet size. Bifenthrin applied in 337 μm VMD droplets caused 75.8% mortality, whereas 96-μm VMD droplets resulted in a mortality of 67.9%. Also, the 337 μm VMD droplets killed larvae in 13% less time than the 96μm VMD droplets, based on analysis (P =0.01) using the mean elapsed time till death as the dependent factor.     

Nerve insensitivity resistance to cypermethrin in larvae of the tobacco budworm Heliothis virescens from USA cotton field populations

Spontaneous neuronal activity was recorded from the peripheral nerves of third-instar larvae of strains of Heliothis virescens (F.) obtained directly from cotton fields in the USA. Following a control period the preparations were exposed to increasing concentrations of cis-cypermethrin in a cumulative dose-response assay. A positive response was defined as an increase of at least five-fold in the rate of neuronal activity over that seen during the control period. Up to 35 individuals of each strain were assayed and the responses used to construct a phenotypic profile categorising the individuals from nerve-susceptible to highly nerve-insensitive. An EC₅₀ for the action of cis-cypermethrin was also obtained. There was a positive, significant correlation between non-synergisable resistance to cypermethrin and nerve insensitivity as defined in the neurophysiological assay. It was shown that nerve insensitivity to cypermethrin increased throughout the cotton-growing season.     

Biochemical mechanisms of methoxyfenozide resistance in the cotton leafworm Spodoptera littoralis

BACKGROUND: Methoxyfenozide is a lepidopteran‐specific insecticide that belongs to a new group of insecticides, the non‐steroidal ecdysteroid agonists, also called moulting accelerating compounds (MACs). To investigate the risk of resistance and possible mechanisms conferring resistance to methoxyfenozide, the authors selected in the laboratory for a resistant strain of the cotton leafworm Spodoptera littoralis (Boisd.), which is a representative lepidopteran model and an important pest in cotton and vegetables worldwide, with a high risk for resistance development. RESULTS: After selection with methoxyfenozide during 13 generations, toxicity data showed that the selected strain developed fivefold resistance to methoxyfenozide in comparison with the susceptible strain. Measurement of the detoxification enzymes demonstrated that the monooxygenase (MO) activity was 2.1 times higher in the selected strain, whereas there was no change for esterases and glutathione‐S‐transferases. When the inhibitors piperonyl butoxide (PBO), S,S,S‐tributyl phosphorotrithioate (DEF) and diethyl maleate were tested as synergists, the respective synergistic ratios were 0.97, 0.96 and 1.0 for the susceptible strain, and 2.2, 0.96 and 1.1 for the resistant strain. The significant synergistic effect by PBO concurs with the increased MO activity in the selected strain. CONCLUSION: Taken overall, the present study supports the importance of MO‐mediated metabolism in resistance to methoxyfenozide, directing tactics to fight against resistance development for this novel group of insecticides. Copyright © 2009 Society of Chemical Industry     

Toxicity of pyrethroids to larvae of the egyptian cotton leafworm,Spodoptera littoralis (Boisd.). I. Relative toxicities and knockdown activities of benzyl,and 5-benzyl-3-furylmethyl,cyclopropanecarboxylates

The contact toxicity of ten pyrethroids to larvae of Spodoptera littoralis (Boisd.) was investigated by topical application, and symptoms observed for different combinations of dose and time. Several compounds were sufficiently active to suggest that they may prove useful for the control of populations in the field. Structure and activity are discussed with particular reference to time-dose-response relationships: speed of action is related to both chemical structure and applied dose.     

Multifactorial resistance to transpermethrin in field-collected strains of the tobacco budworm Heliothis virescens F.

The penetration, degradation and excretion of [³H]transpermethrin were examined in susceptible and field-collected pyrethroid-resistant strains of the tobacco budworm Heliothis virescens. No consistent differences in labelled materials excreted or recovered in cuticle rinses were found between the resistant (R) and susceptible (S) larvae. Considerably lower levels of the parent compound were present internally in R compared with S larvae after 24h (P <0.01), clearly identifying a metabolic resistance mechanism in Meloland and Westmorland larvae. Moderate levels of absorbed permethrin accompanied by an absence of poisoning symptoms were observed in certain individuals of both R strains, suggesting a second resistance mechanism. Neurobioassays of R larvae showed a consistently lower sensitivity of the neuromuscular system to pyrethroids when compared with the S larvae, thus confirming the indication from metabolic studies of the additional (site-insensitive) mechanism. Toxicity values suggest a cross-resistance to other pyrethroids.     

Joint action of benzoylphenylureas in binary mixtures against larvae of the cotton leafworm,Spodoptera littoralis

In preliminary laboratory tests, the joint activity of six benzoylphenylureas (BPUs) was studied by investigating the activity of 90 of their binary mixtures against fourth-instar larvae of the cotton leafworm,Spodoptera littoralis (Boisd.), fed for 72 h on 10 ppm BPU-treated castor bean leaves. Experimental mixing ratios were 1:1, 1:4, and 1:9. At 10 ppm, the activity of the six BPUs was divided into two distinct groups. The first included the more active compounds (XRD-473, GR-333, and chlorfluazuron) while the second was composed of the relatively less active ones (diflubenzuron, triflumuron, and Dowco-439). Results of the assays indicated that only 18 of the 90 tested binary mixtures showed potentiation, whereas the majority, 70 mixtures, exhibited additive effects; two interacted antagonistically. Most of the potentiated pairs were at a mixing ratio of 1:9, pairing one strong BPU (at the low ratio) with a weak one (at the high ratio). The mixing ratio of 1:1 resulted in additive effects.     

Toxicity of pyrethroids to larvae of the Egyptian cotton leafworm,Spodoptera littoralis (Boisd.). II. Factors determining the effectiveness of permethrin at ultra-low volume

Factors determining theeffectiveness of permethrinat ultra-low volume against larvae of Spodoptera littoralis (Boisd.) were investigated using a modified Potter tower. Higher mass application rates for 95 % control were necessary when permethrin was used as a residual deposit compared with direct contact plus residual deposit action. Mortality was increased by adjusting droplet density, although the optimum number of drops/ unit area depended on the mass application rate. When mass application rate and droplet density were held constant, mortality increased inversely with the mean droplet diameter. The implications of these results for field applications are discussed.     

Effects of amino acids on the feeding behavior of the larva of the egyptian cotton leafworm,spodoptera littoralis boisd

The effect of 21 amino acids on the feeding response of larvae ofSpodoptera littoralis was investigated using the “Styropor method.” Lamellae of Styropor were treated(a) with different concentrations of amino acids,(b) different concentrations of amino acids mixed with 0.125 M sucrose, and(c) 0.125 M sucrose alone. The weight of Styropor consumed during 48 h served as the criterion of phagostimulation or phagodeterrency. With the sole exception of 0.125 M L-glutamic acid, no phagostimulation occurred in any of the amino acids tested in mixture with 0.125 M sucrose; none was phagostimulant when tested alone. Deterrency was found at 0.125 M in L-alanine, DL-alpha-amino-n-butyric acid, L-serine, L-cystine, L-methionine, L-tyrosine, and L-histidine, when mixed with an equimolar concentration of sucrose. Methionine was highly phagodeterrent also at 0.0625 M and, as was DL-alpha-amino-n-butyric acid, still active even at 0.0125 M. Chemical analysis showed that there was no decomposition of methionine applied on Styropor.     

DPX-MP062—a potent compound for controlling the Egyptian cotton leafworm Spodoptera littoralis (Boisd.)

The effects of DPX-MP062 [methyl 7-chloro-2,3,4a,5-tetrahydro-2-[methoxycarbonyl(4-trifluoromethoxyphenyl)carbamoyl] indeno[1,2-e][1,3,4] oxadiazine-4a-carboxylate] a broad-spectrum insecticide with a novel mode of action, on the Egyptian cotton leafworm, Spodoptera littoralis, were studied in laboratory experiments. Egg hatch was affected by high concentrations (125 mg AI litre^-1) of DPX-MP062. Larvae that hatched from treated eggs were significantly affected at concentrations of 12·5 mg AI litre^-1 and greater. Larvae were fed castor bean leaves treated with DPX-MP062; 1st-instar larvae were the most susceptible development stage. Pupation and adult formation were determined in assays with 5th-instar larvae. There was strong suppression of adult formation; 65 and 91% at 0·5 and 0·75 mg AI litre^-1, respectively. Highly affected larvae died before pupation; slightly affected ones reached pupation 2–4 days later, were smaller than larvae in the untreated control, and were sometimes unable to develop into normal adults. Comparatively high concentrations (50 and 100 mg AI litre^-1) of the test compound were necessary to affect adults by ingestion, but no effects from contact application could be determined at a concentration of 100 mg AI litre^-1. © 1998 Society of Chemical Industry     

Feeding deterrent and growth inhibitory properties of limonoids from Khaya senegalensis against the cotton leafworm, Spodoptera littoralis

Three rearranged phragmalin-type limonoids, khayanolide A, khayanolide B and 1-O-acetylkhayanolide B, and a mexicanolide-type limonoid, khayalactol, have been isolated from the stem bark of Khaya senegalensis (Desr) A Juss (Meliaceae). The antifeedant and growth-inhibitory activities of the isolated compounds were evaluated on Spodoptera littoralis (Boisduval). When added to an artificial diet, khayanolide A, khayanolide B and 1-O-acetylkhayanolide B showed antifeedant activity in a concentration-dependent manner. Khayalactol exhibited strong antifeedant activity without significant differences at all of the tested concentrations (7.5-100 mg kg(-1)). Khayanolide B was the most potent antifeedant with an ECso of 2.19 mg kg(-1). The results also revealed that the isolated compounds caused marked larval growth inhibition on S littoralis after 7 days of feeding on treated diet; this effect was concentration-dependent. Khayanolide B was the most active growth inhibitor among the isolated compounds, with an EC50 of 6.96 mg kg(-1).     

Host plant induction of microsomal monooxygenase activity in relation to diazinon metabolism and toxicity in larvae of the tobacco budworm Heliothis virescens (F.)

The effect of the wild tomato, Lycopersican hirsutam F. glabratam (accession PI 134417), on susceptibility to and metabolism of diazinon, 0,0-diethyl-0-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate, in larvae of the tobacco budworm, Heliothis virescans F., was studied. The larvae were over 4-fold more tolerant to diazinon toxicity when fed on leaves of wild tomato than when fed on an artificial diet. Diazinon injected into fifth instar larvae is converted into two chloroform-soluble and five water-soluble metabolites. Degradation of diazinon was faster in larvae fed tomato leaves (88.1%) than in larvae fed on the artificial diet (68.4%). Some oxon (13.0%) was detected in the latter case but none in larvae fed tomato leaves. The major metabolite was hydroxypyrimidine and its formation was higher (73.2%) in larvae fed tomato leaves than in larvae fed the artificial diet (49.2%). In vitro studies revealed that both diazinon and its oxon were metabolized primarily by the microsomal cytochrome P-450-dependent monooxygenase system which was induced 2.5- to 3.7-fold by feeding on tomato leaves. It was concluded that diazinon was degraded in H. virescens larvae through desulfuration, hydroxylation of the ring-alkyl side chain, and oxidative dearylation reactions, all of which were increased by varying amounts after feeding on tomato leaves. Treatment of the larvae with 2-tridecanone, a naturally occurring toxin in tomato leaves, resulted in increased tolerance to diazinon and increased in vitro degradation of diazinon and its oxon, the induction being dependent on the magnitude of 2-tridecanone treatment. The microsomes of tomato fed larvae had a 1.5- to 2.1-fold higher concentration of cytochrome P-450, accompanied by a 1–2 nm shift in the λmax of the cytochrome P-450 carbon monoxide complex.     

Excretion of unchanged organophosphorus compounds after their consumption by larvae of the Egyptian cotton leafworm,Spodoptera littoralis Boisd

The ingestion and excretion of sublethal doses of phosfolan, monocrotophos, parathion, and leptophos were studied in larvae of the Egyptian cotton leafworm, Spodoptera littoralis Boisd. Styropor (foamed polystyrene) lamellae treated with insecticide-sucrose mixtures were fed to the larvae and recovery of the undecomposed insecticides from the feces could be estimated by gas-liquid chromatography, without any cleanup of the sample. The insecticidal residues on Styropor were found to be stable for 5 days.As regards the percentage of insecticide recovered from the feces, two groups could be distinguished: (a) leptophos, practically complete; parathion, 59–67%; b) phosfolan, 10–23%; monocrotophos, 4–7%. A tentative hypothesis was advanced that both oral toxicity of the four compounds for S. littoralis larvae and their subsequent recovery in the feces were related to water solubility.     

Comparison of insecticide absorption and detoxification in larvae of the bollworm,Heliothis zea,and the tobacco budworm,H. virescens

Rates and nature of metabolism of several insecticides were compared in larvae of the bollworm, Heliothis zea (Boddie), and the tobacco budworm, H virescens (F.). Both species are resistant to organochlorine compounds. In addition, H. virescens is resistant to carbamate and organophosphate insecticides. All test insecticides were metabolized by larvae of both species under in vivo conditions. In most instances, metabolism was more rapid in H. virescens larvae.A series of in vivo and in vitro assays implicated high levels of NADPH-dependent oxidative enzymes as a major metabolic factor in resistance. Other work demonstrated that H. virescens larvae absorbed insecticides at a slower rate than did H. zea larvae. High resistance to organophosphates present in H. virescens may be due to interaction of factors for increased rate of detoxification and decreased rate of absorption.     

Biological effects and metabolism of fenoxycarb after treatment of the fourth and the fifth instars of the tobacco budworm,Heliothis virescens F.

Treatment of 4th and 5th instar larvae of Heliothis virescens with different amounts of fenoxycarb induced an increase in weight of the 5th larval instar, prolongation of the 5th larval instar period, or the formation of dauer larvae. No effects were observed during the 4th instar and the moult to the 5th larval instar. To check whether these effects were due to persistence of fenoxycarb in treated larvae, metabolism of this chemical was analysed. Larvae were fed with radio-labelled fenoxycarb at the first day of the 4th or at the first day of the 5th larval instar. Behaviour of the radio-labelled compounds was followed during each instar. At the time of gut purge, the whole of the radio-labelled material was excreted. The effects observed during the 5th instar of 4th-instar-treated larvae do not appear to be due to the persistence of fenoxycarb. The main metabolites of fenoxycarb were identified using coupled gas chromatography and mass spectrometry.     

Studies of the susceptibility of the cotton leafworm,spodoptera littoralis (boisduval), to various strains ofbacillus thuringiensis

The effect of ten different laboratory strains ofBacillus thuringiensis and of the thermostable exotoxin, was tested on larvae ofSpodoptera littoralis Boisduval. Endotoxin poisoning was not observed and whenever mortality rose substantially above the controls, it seemed due to the thermostable exotoxin and not to the parasporal crystal. Treatment of a commercial preparation with substances dissolving the crystal did not elicit acute toxemia, nor did abrasives administered with this preparation bring about fulminating septicemia.     

Interaction of proteinase inhibitors with Cry1Ac toxicity and the presence of 15 chymotrypsin cDNAs in the midgut of the tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae)

BACKGROUND: The potential development of resistance to Bacillus thuringiensis (Bt) cotton and surging of non‐targeted insects is a major risk in the durability of Bt plant technology. Midgut proteinases are involved in Bt activation and degradation. Proteinase inhibitors may be used to control a wide range of insects and delay Bt resistance development. Proactive action to examine proteinase inhibitors for synergistic interaction with Bt toxin and cloning of proteinase cDNAs for RNAi is necessary to make transgenic cotton more versatile and durable. RESULTS: A sublethal dose (15 ppb) of Cry1Ac, 0.5% benzamidine and 0.02% phenylmethylsulfonyl fluoride significantly suppressed midgut azocaseinase, tryptic and chymotryptic activities, and resulted in reductions in larval and pupal length and mass of Heliothis virescens. The combination of proteinase inhibitor and Bt suppressed 20–37% more larval body mass and 26–80% more enzymatic activities than the inhibitor only or Bt only. To facilitate knockdown‐resistance‐related proteinase genes, 15 midgut chymotrypsin cDNAs were sequenced. Most predicted chymotrypsins contained the conserved N‐termini IVGG, three catalytic center residues (His, Asp and Ser), substrate specificity determinant (Ser or Gly) and cysteines for disulfide bridges. These putative chymotrypsins were separated into three distinct groups, indicating the diverse proteinases evolved in this polyphagous insect. CONCLUSION: H. virescens has evolved diverse midgut proteinase genes. Proteinase inhibitors have potential insecticidal activity, and the interaction of Bt with proteinase inhibitors is desirable for enhancing Bt toxicity and delaying resistance development. Intensive sequencing of chymotrypsin cDNAs will facilitate future functional examinations of individual roles in Bt toxicity and resistance development and facilitate targeted control using RNAi and/or proteinase inhibitors. Copyright © 2012 Society of Chemical Industry     

Comparative toxicity of two ecdysteroid agonists,RH-2485 and RH-5992, on susceptible and pyrethroid-resistant strains of the Egyptian cotton leafworm,Spodoptera littoralis

The comparative toxicity of two non-steroidal ecdysteroid agonists, RH-2485 and RH-5992 (tebufenozide), on development stages, fecundity and egg viability of a susceptible laboratory strain and a pyrethroid-resistant field strain ofSpodoptera littoralis (Boisduval) was evaluated. Taking the LC₅₀s as the criterion, RH-2485 was 3–7-fold more potent than RH-5992 against the susceptible and 7–14-fold more against the field strain. The LC₅₀ of RH-2485 in the 1st and 6th instars of the susceptible strain was 0.32 and 0.57 mg a.i./l, respectively. The field strain showed a mild cross-resistance of about threefold to both compounds in 1st instars and to a lesser extent in 6th instars. A considerable increase in fecundity (~3-fold) and no effect on egg viability was observed when 6th instars were fed on cotton leaves treated with 0.25 mg a.i./l RH-2485 (~LC₄₀). Our results indicate that both compounds are potentially potent insecticides for controllingS. littoralis larvae, being 10-60-fold more potent than a previous ecdysteroid agonist, RH-5849.     

Night observations on the cotton leafworm,Spodoptera littoralis: Reliability of pheromone traps for population assessment and efficacy of widely separated pheromone dispensers for mating disruption

Night observations on the cotton leafworm,Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), were conducted in pheromone-treated and untreated plots in which males, females, mating pairs on plants, and males caught in traps were collected. Results indicated that emergence of a new population was rapid (8-9 days) and that the number of virgin females and of mating pairs on plants reached a peak 5–6 days prior to that of males captured in pheromone traps. Males responded to pheromone traps most actively when the actual virgin female popution had already declined considerably. Dispensers adsorbed with(Z,E)-9,11-tetradecadienyl acetate and located 25 m apart, effectively reduced male captures in traps. However, the number of native mating pairs observed in the treated field during the night was not reduced. Few releasers at wide spacing, even with high amounts of the major pheromonal component, were ineffective in causing mating disruption ofSpodoptera littoralis.     

Toxicity of the chitin synthesis inhibitors,diflubenzuron and its dichloro-analogue,to Spodoptera littoralis larvae

The activities of the chitin synthesis inhibitors, diflubenzuron and PH 60–38, against Spodoptera littoralis larvae were assayed by feeding treated alfalfa or poisoned wheat bran baits, by allowing the larvae to imbibe sucrose-containing aqueous dispersions of the compounds, and by injection into larvae. PH 60–38 was less active than diflubenzuron. On alfalfa, diflubenzuron had to be fed for at least 2 days to prevent formation of normal pupae and emergence of adults. For very big (480–540 mg) larvae, feeding diflubenzuron at concentrations of 50 mg/litre for 2 days or 2.5 mg/litre for 3 days prevented adult emergence. For 200–250 mg larvae, this was achieved by feeding concentrations of 100 mg/litre for 2 days, 5 mg/litre for 3 days or 3.5 mg/litre for 4 days. In all larvae > 150 mg, mortality in feeding experiments occurred in the prepupal or the pupal stage. Only with 30–50 mg and 100–150 mg larvae was there considerable mortality during moults between larval instars, the larvae being unable to liberate themselves from the old larval skins and head capsules. Diflubenzuron incorporated into wheat bran baits at concentrations of from 2.5 to 10 000 μg/g killed approximately 70–90% of the insects. When imbibed, diflubenzuron was much less toxic as a wettable powder than as a liquid formulation but the two formulations were equitoxic when injected into the larvae.