Contact activity of diflubenzuron against Spodoptera littoralis larvae

The effect of diflubenzuron as a residue on glass or applied topically to Spodoptera littoralis larvae was investigated. Diflubenzuron was active as a residue on glass against 100 and 200 mg larvae; the toxicity of residues was identical whether a dispersable formulation or a wettable powder or the technical substance were used. By topical application, diflubenzuron had an ED₅₀ for cumulative percentage mortality up to the adult stage of 004 and 0066 μg/larva for 100 and 200mg larvae respectively. Neither the site of the topical application nor whether the larvae were kept singly or in groups of ten after the treatment had an influence on toxicity. The data indicate that diflubenzuron has contact toxicity to at least one insect species as well as the known stomach poison action.     

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.     

The effect of BAY SIR 8514 onspodoptera littoralis (Boisduval) eggs and larvae

The chitin biosynthesis inhibitor diflubenzuron and its analog BAY SIR 8514 are equitoxic for eggs ofSpodoptera littoralis. BAY SIR 8514 residues on alfalfa fed toSpodoptera larvae were more toxic than diflubenzuron residues, whereas BAY SIR 8514 topically applied to these larvae was consistently twice as toxic as diflubenzuron, according to different criteria.     

Rearing the honeydew moth,Cryptoblabes gnidiella,and the effect of diflubenzuron on its eggs

The rearing of the honeydew moth,Cryptoblabes gnidiella Mill., is described. The toxicity at 27° and 22° C of diflubenzuron against eggs ofC. gnidiella was assayed by dipping in aqueous dilutions of a 5% liquid experimental formulation and of a 25% wettable powder (w.p.). The w.p. was more active than the liquid formulation, and toxicity at 27° was higher than at 22°C, for both formulations. The LC-50s of the w.p. were 0.00025 and 0.006%, and of the liquid formulation 0.009 and 0.095 a.i., at 27° and 22°C, respectively; the LC-90s of the w.p. were 0.0033 and 0.037%, and of the liquid formulation 0.36 and 2.5% a.i., at 27° and 22° C, respectively.     

The inhibition of chitin synthesis in spodoptera littoralis larvae by flufenoxuron,teflubenzuron and diflubenzuron

The chitin precursor [¹⁴C] N-acetylglucosamine injected into the haemolymph of Spodoptera littoralis (Boisduval) larva was incorporated into the chitin exponentially with time. When caterpillars were injected with precursor at the commencement of feeding on acylurea-treated leaf discs, flufenoxuron, teflubenzuron and diflubenzuron were found to be equally effective inhibitors of chitin synthesis, measured after 21 h. The dose response curves by feeding are not parallel, indicating that the relative potency of the compounds will vary across the dose range. When chitin precursor was injected simultaneously with topically applied diflubenzuron, flufenoxuron or teflubenzuron, all three acylureas were found to be equally effective as inhibitors of chitin synthesis when measured after five hours. The I₅₀values (50% inhibition of chitin synthesis) were not significantly different; average 600 ng, compared with LD₅₀values (50% lethal dose) of ～ 13 ng for flufenoxuron and teflubenzuron but 130 ng for diflubenzuron (topical application). Injection of precursor 24 h after topical application of insecticide gave an I₅₀value which had dropped 670- and 150-fold for flufenoxuron and teflubenzuron respectively but only 20-fold for diflubenzuron. It is postulated that the reason for the low increase in diflubenzuron effectiveness with time was due either to less diflubenzuron than flufenoxuron reaching the site of action, or more probably, a faster rate of metabolism and excretion for diflubenzuron. The lower toxicity of diflubenzuron compared with flufenoxuron and teflubenzuron may not be due to any inherent differences in biochemical effectiveness, but rather to different penetration/metabolism properties.     

The ovicidal action of insecticides and insect growth regulator/insecticide mixtures on the eggs of various ages of susceptible and diflubenzuron-resistant strains of Spodoptera littoralis boisd

The ovicidal action of four insecticides and three insect growth regulators, on eggs of various ages of the susceptible (S) strain of Spodoptera littoralis, was investigated. The results revealed that diflubenzuron was the most toxic compound tested on 0-1-day-old eggs, followed by triprene and then methoprene; chlorpyrifos came next in its toxicity, followed by cypermethrin then fenvalerate; methomyl was the least effective. With the progress of embryonic development, 1-2-day-old eggs showed slight tolerance to the action of the pesticides and juvenoids, but apparently resisted the action of diflubenzuron. Eggs 2-3 days old showed increased tolerance to the insecticides and diflubenzuron and, to a lesser extent, to the action of the two juvenoids. A total of 21 insecticide or insect growth regulator-insecticide mixtures, based on their toxicity equivalents (LD₂₅ + LD₂₅), were applied jointly on 0-1-day-old eggs of the S strain. The mixtures which produced high synergism on this stage could be arranged, according to their decreasing order of potentiation, as follows: fenvalerate/diflubenzuron, cypermethrin/triprene, methomyl/methoprene, cypermethrin/methoprene, fenvalerate/ methoprene, cypermethrin/methomyl, cypermethrin/diflubenzuron, fenvalerate/triprene, diflubenzuron/methoprene and methomyl/triprene. The mixtures that produced synergistic effects on 0-1-day-old eggs were also tested against the 1-2 and 2-3-day-oldeggs of the S strain. Theresults indicated that themixtures fenvalerate/diflubenzuron, and cypermethrin with either triprene or diflubenzuron, when tested on 1-2-day-old eggs, produced levels of synergism nearly similar to those achieved on newly deposited eggs. On the other hand, the mixtures cypermethrin/methomyl, and fenvalerate with methoprene or triprene, showed comparatively lower levels of synergism. However, the synergistic action of the mixture cypermethrin/methoprene, previously detected on newly deposited eggs, became an additive effect on 1-2-day-old eggs. Only the mixtures fenvalerate/diflubenzuron, cypermethrin/triprene and fenvalerate/methoprene showed synergism on 2-3-day-old eggs. The mixtures which showed synergistic effects on 0-1-day-old eggs of the S strain were further tested on eggs of various ages of the diflubenzuron-resistant (R_d) strain. As regards 0-1-day-old eggs, only the combinations cypermethrin/triprene, methomyl/methoprene and fenvalerate/methoprene produced additive effects. The mixture cypermethrin/diflubenzuron was still synergistic against newly deposited eggs of the R_d strain, in a manner similar to that indicated with the S strain. Apparent levels of antagonism were shown to the other insecticide-juvenoid mixtures as well as to the diflubenzuron/methoprene combination. The combinations cypermethrin/methomyl and fenvalerate/diflubenzuron had some effect on the freshly deposited eggs of the R_d strain but produced lower levels of potentiation. With the increase in age of the eggs, the mixture cypermethrin/diflubenzuron showed a lower level of synergism on the 1-2 day-old eggs than was observed in younger eggs. The additive effects, previously detected with some of the mixtures on newly deposited eggs became an antagonistic effect for the 1-2-day-old eggs. The eggs at this stage were more able to resist thejoint action of the other mixtures tested. Moreover, with further increase in the age of the eggs, the combination cypermethrin/diflubenzuron produced a lower level of potentiation on 2-3 day-old eggs, followed by fenvalerate/diflubenzuron at an even lower level, while the other mixtures showed various levels of antagonism.     

Comparative toxicity of several insecticides to eggs,larvae and adults of the Egyptian cottonworm,Spodoptera littoralis,in laboratory trials

Insecticides commonly used in cotton fields in Israel against lepidopterous pests were tested against eggs, as well as against 2nd-instar larvae and adults raised from eggs ofSpodoptera littoralis (Boisduval) collected in cotton fields in the Bet She’an Valley. Methomyl, chlorpyrifos, methidathion, monocrotophos, ethyl parathion, and methyl parathion were effective against eggs even at low doses, profenofos and phosfolan were less active, and azinphos-methyl was ineffective. The doses needed for 90% kill (LD ₉₀ ) of the 2nd-instar larvae were 8.5, 35, 280, 1300 and 3400 g a.i./1000 m ² for chlorpyrifos, methomyl, profenofos, methyl parathion and ethyl parathion, respectively; monocrotophos was inactive against 2nd-instar larvae even at relatively high doses. The LD ₉₀ of adults was reached with 16, 32, 1700 and 6100 ga.i./l000 m² of chlorpyrifos, methomyl, ethyl parathion and profenofos, respectively. Only chlorpyrifos and methomyl gave successful control of all three stages of the insect tested, at doses close to those generally used with aerial applications.     

The effect of diflubenzuron feeding on glycosaminoglycan and sulfhemoglobin biosynthesis in mice

Diflubenzuron (Dimilin), an inhibitor of insect chitin synthesis, was fed to mice in concentrations of 50 to 2000 ppm in the diet. The activity of the mammalian hexosamine transferases responsible for glycosaminoglycan (mucopolysaccharide) formation was monitored by measuring the in vivo rate of incorporation of a labeled precursor into hyaluronic acid and chondroitin sulfate of skin. No inhibition of biosynthesis was noted at any concentration; indeed the insecticide appeared to stimulate the production of these compounds. After 3 weeks on the diet, mice eating 1000 and 2000 ppm diflubenzuron showed obvious signs of cyanosis, and sulfhemoglobin was demonstrated in the blood of mice eating more than 200 ppm. The amount of sulfhemoglobin appeared to be related to the dietary insecticide content and the highest level seen was 13% of total hemoglobin in the 2000-ppm group after 31 days. These values returned to normal within 3 weeks when diflubenzuron was removed from the diet.     

The effect of diflubenzuron on Eggs and larvae ofEarias Insulana (Boisd.)

Diflubenzuron was tested for its efficacy against the eggs and larvae ofEarias insulana Boisd. in laboratory experiments. The toxicity obtained on dipping the eggs was only moderate and, moreover, the results were highly inconsistent. The mortality of larvae on an artificial diet into which the wettable powder had been incorporated, was relatively high.     

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     

The Use of Sex Pheromones in the Control of Spodoptera littoralis Boisd.1)

An even network of pheromone traps baited with virgin females of Spodoptera littoralis Boisd. was established in Cyprus. By relating trap catches with meteorology it was shown that no major immigration of S. littoralis to Cyprus from surrounding land-masses had occurred. Direct control of S. littoralis by the synthetic pheromones recently synthesized or the sterile male technique may therefore be possible in such an area of ecological isolation.     

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.     

Antifeeding and protease- and amylase-inhibiting activity of fentin acetate in Spodoptera littoralis larvae

Fentin acetate (FA) at effective antifeedant concentrations does not have a high, immediate toxicity for 170–190 mg larvae of the Egyptian cotton leafworm (Spodoptera littoralis); the mortality of such larvae exposed to FA residues on leaves is not appreciably higher than that of larvae being starved. The antifeedant effect of FA is also not due to an influence on sensory receptors on the mouth parts. Protease and amylase are inhibited in vivo in larvae feeding on FA-treated leaves; the enzyme inhibition increases with the concentrations of the leaf-dipping suspensions. At 0.05% FA, protease and amylase activity was only about 20 and 30%, respectively, of that of the control larvae and was lower than in starved larvae.Antifeeding and enzymatic inhibition are also obtained by injecting FA into the haemocoel, results which indicate that FA does not inhibit the digestive enzymes directly, but seems to affect the enzyme production in the gut. This interpretation is strengthened by the finding that the addition of massive amounts of FA to the enzyme reaction mixture does not affect the enzyme activity.     

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.     

基于优化的MaxEnt模型预测海灰翅夜蛾潜在地理分布区

海灰翅夜蛾Spodoptera littoralis是全球范围内热带和亚热带地区的重大农业入侵害虫,也是我国进境检疫性有害生物,其对欧洲、非洲和亚洲地区的农作物产生严重危害,并造成大量的经济损失。本研究基于海灰翅夜蛾的世界617个分布记录和8个生物气候因子,利用优化的MaxEnt模型预测其在全球和我国的潜在地理分布区,并进一步分析其在我国的传入、定殖和扩散风险。结果表明:气温是影响海灰翅夜蛾潜在地理分布的主导生物气候因子。其在全球的潜在地理分布区主要位于北美洲南部、南美洲、非洲、亚洲西部和东部、欧洲南部和大洋洲,在我国主要位于东部和南部地区。在我国,其潜在地理分布区范围内有着较多的贸易口岸和广泛的寄主分布,增大了其传入我国的风险,并为其定殖和扩散提供了有利的条件。建议海关口岸、农林行业部门加强对海灰翅夜蛾的检疫、调查和监测工作,严防海灰翅夜蛾传入。     

A Stable Synthetic Pyrethroid,NRDC 147, and the Control of Spodoptera littoralis

Abstract

Pyrethrins, the botanical insecticides and their synthetic analogues are well known for their power of producing very rapid paralysis (knockdown) in treated insects. The use of pyrethrins or synthetic analogues in agriculture to combat insect pests on field crops has been rather limited. The main reason for this is their non-persistence in field conditions. A recently developed synthetic pyrethroid NRDC 147, which is 10–100 times more stable in light than previous pyrethroids was tested in the laboratory and field against the Egyptian cotton leafworm Spodoptera littoralis (Boisd). Results indicate higher efficiency (LC₅₀ 320 ppm), compared with 460, 422, 1250, 180, 2150 and 265 ppm for cyolane, chlorpyrifos, leptophos, methomyl, monocrotophos and methamidophos respectively. The residual effect (LT₅₀) is more than 7 days in the field for NRDC 147, while it was 5.8, 6.8 and 4.2 for cyolane, leptophos and methamidophos.     

The toxicity of diflubenzuron to Oxya japonica (Willemse) and its effect on moulting

A laboratory evaluation of the acute toxicity of diflubenzuron against the final stage of Oxya japonica nymphs showed that it was more effective in preventing the development of the nymphs into the adults when applied topically, than when injected. Histological studies revealed that treated nymphs that subsequently died, before or during ecdysis, suffered from severe endocuticular lesions. Comparable abnormalities and disruption of endocuticular deposition and growth were also seen in nymphs that were treated topically with diflubenzuron at 50 or 200 μg a.i. per insect, although these nymphs appeared normal externally.     

The use of Bacillus thuringiensis to control two lepidopterous insect pests (Agrotis ypsilon and Spodoptera littoralis)

An area of 50 feddans cultivated with soybeans was treated withBacillus thuringiensis (B.t.) baits againstAgrotis ypsilon and 60 feddans were sprayed withB.t. spray againstSpodoptera littoralis. WhenB.t. baits were used, the percentage of kill ofA. ypsilon reached 96.1–96.4% compared to 97.4–98% kill on using hostathion baits. WhenB.t. was sprayed againstS. littoralis, a percentage of larval kill 88.3% was obtained. This increased to 97.3% after the second application. On the other hand, the precentage of kill reached 96.8% when lannate was sprayed once. The average yield was 1.54 tons/fed. whenB.t. was sprayed twice againstS. littoralis and 1.42 tons/fed. when sprayed once. Areas, treated with lannate gave 1.44 tons/fed., while in the untreated area the yield was comparatively low being 0.83 tons/fed.Mith 4 tables     

Effect of Clerodane-Type Diterpenoids Isolated from Salvia spp. on the Feeding Behaviour of Spodoptera littoralis

Twenty-nine clerodane-type diterpenoids isolated from species of Salvia growing in Mexico, or analogues of them, were tested for antifeedant activity against Spodoptera littoralis larvae using behavioural and electrophysiological bioassays. Eight of the compounds showed potent antifeedant activity in choice and no-choice bioassays and these compounds also stimulated dose-dependent responses from neurones in the lateral styloconic sensilla of S. littoralis.