Triphenyl derivatives of group IV elements as inhibitors of growth and digestive enzymes of Tribolium castaneum larvae

The potency of triphenyl derivatives of group IV elements in inhibiting the growth of first and fourth instar Tribolium castaneum larvae is much greater for Ph₃SnCl and Ph₃PbCl than for Ph₃GeCl, Ph₃SiOH, and Ph₃CCl. Pupated larvae emerge normally, showing that the pupal stage is not affected. The larval growth retardation may result from an antifeeding effect involving digestive enzyme inhibition. Ph₃SnCl and Ph₃PbCl at 500 μmol/kg of diet completely inhibit larval growth (fourth instar larvae) and provide a reduction of 56–59, 29–33, and 2–15% in the in vivo activity of invertase, amylase, and protease, respectively. Under these conditions Ph₃GeCl, Ph₃SiOH, and Ph₃CCl are essentially inactive. High concentrations (5 × 10^?4 and 2 × 10^?3M) of Ph₃SnCl and Ph₃GeCl acting in vitro strongly inhibit invertase, amylase, and protease activities, whereas Ph₃PbCl is moderately inhibitory and Ph₃SiOH and Ph₃CCl are inactive. When both in vivo and in vitro findings are considered, Ph₃SnCl is the most potent inhibitor of larval digestive enzymes.     

Pyrethroid synergism and prevention of emergence inTribolium castaneum andMusca domestica vicina by the insect growth regulator RO 13-5223

Ethyl [2-(4-phenoxyphenoxy)ethyl] carbamate (RO 13-5223) at a dietary concentration of 100 mg kg^-1 synergized the toxicity of thetrans- andcis-isomers of permethrin and cypermethrin in inhibiting the growth (measured as gain in larval weight) ofTribolium castaneum andMusca domestica vicina. With both species the synergism factor forcis-cypermethrin with 100 mg kg^-1 synergist was 1.5- to twofold for RO 13-5223 and about fourfold for piperonyl butoxide. Synergism was more pronounced with first instar than with fourth instarT. castaneum larvae. Methoprene was not a pyrethroid synergist withT. castaneum larvae, so the synergistic effect of RO 13-5223 appears to depend on its structural features and not its insect-growth-regulator activity. Joint application of RO 13-5223 and pyrethroids resulted in a dual effect on bothT. castaneum andM. domestica: increased inhibition of larval growth due to pyrethroid synergism, and progeny suppression — expressed by larval and pupal mortality — due to RO 13-5223 juvenilizing activity.     

Effect of avermectin B1 on the development and fecundity of the california red scale,Aonidiella auranth,and on two of its natural enemies:Chilocorus bipustulatus andAphytis holoxanthus

Various immature stages of male and female California red scale,Aonidiella aurantii (Maskell) (Homoptera: Diaspididae), were treated with avermectin B₁ (MK-936) at concentrations ranging from 10 to 100 ppm. Treatments at 10 ppm completely arrested crawler development and 20 and 100 ppm caused 100% mortality of 48-h and 7-day-old male and female 1st instar nymphs, respectively. The development of the 2nd instar was slightly affected by MK-936 at up to 40 ppm. Sublethal doses of the chemical applied to immature stages caused no dramatic reduction in the fecundity of the subsequent, mature females. MK-936 applied to male prepupal and pupal stages and mated females did not prevent male emergence, nor did it affect the ability of males to copulate and inseminate female scales, or the female fecundity. The development and adult emergence of treatedAphytis holoxanthus DeBach (Hymenoptera: Aphelinidae) larvae and pupae parasitizingChrysomphalus aonidum L. scales were not influenced by a 9 ppm MK-936 treatment; leaves sprayed with this concentration had residual toxicity onA. holoxanthus adults for only 24 h post-treatment. Feeding byChilocorus bipustulatus L. (Coleoptera: Coc-cinellidae) on 0.9 ppm MK-936-treated Florida red scales resulted in 100% mortality of 2nd instars and induced sterility in the females.     

Phenyltin compounds inhibit digestive enzymes of Tribolium confusum larvae

The potency of dietary phenyltin compounds in inhibiting the growth of first and fourth instar Tribolium confusum L. larvae and the gut proteolytic activity of fourth instar larvae decreases in the order of triphenyltin chloride (Ph₃SnCl) ? diphenyltin dichloride (Ph₂SnCl₂) ? phenyltin trichloride or tetraphenyltin. The growth retardation, which prolongs the larval stage without affecting pupation or emergence, may result from an antifeeding effect involving gut protease inhibition by Ph₃Sn⁺ and Ph₂Sn²⁺. Gut amylase and invertase activities are less sensitive than the protease activity to in vivo inhibition. Under in vitro conditions, relatively high concentrations of Ph₃SnCl and Ph₂SnCl₂ are required for inhibition, the order of enzyme sensitivity is protease > amylase > invertase, and Ph₂SnCl₂ is more potent than Ph₃SnCl. Proteins such as casein, albumin and hemoglobin, but not carbohydrates such as starch and sucrose bind Ph₃Sn⁺ so it is inaccessible for inhibition of digestive enzymes. The level of Ph₃Sn⁺ inhibiting gut protease in vivo is far below that necessary for in vitro inhibition of this enzyme activity. It is speculated that the in vivo inhibitory effects of Ph₃Sn⁺ and Ph₂Sn²⁺ on digestive enzymes may result from binding to the enzyme protein, its zymogen or to other proteins involved in production of the digestive enzymes.     

The effect of some benzoyl phenylureas on the larvae of earias insulana

Diflubenzuron, PH 60-38, PH 6043, penfluron (PH 60-44), PH 6045, triflumuron, chlorfuazuron (IKI-7899), teflubenzuron (CME 134), XRD473 and Dowco 439 were tested for their efficacy against the larvae of the spiny bollworm,Earias insulana (Boisd.), in laboratory experiments. The compounds were incorporated at different concentrations in an artificial diet and 5-day-old larvae were introduced and grown on the treated diets until pupation and adult emergence. Teflubenzuron was active at 0.1 ppm, chlorfuazuron at 0.75 ppm and PH 60-38 at 10 ppm; triflumuron and diflubenzuron were active only at 50 ppm; all the rest of the compounds were even less active. When cotton bolls were dipped in teflubenzuron and offered to 6-day-old larvae in the laboratory, only 4% and 10% of the larvae penetrated inside the bolls treated with 50 and 25 ppm a.i., respectively, whereas 68% penetrated inside untreated bolls.     

Feeding deterrents forphilosamia ricini (samia cynthia subsp.Ricini) fromtithonia diversifolia

Tagitinin A and C and hispidulin isolated fromTithonia diversifolia (Hemsl.) Gray, were potent feeding deterrents, when evaluated against 4th instar caterpillars of the Eri-silkworm(Philosamia ricini Hutt.) (Lepidoptera: Saturniidae); tagitinin F was not.     

Mechanisms of resistance to diflubenzuron in the house fly, Musca domestica (L.)

The mechanisms of resistance to the chitin synthesis inhibitor diflubenzuron were investigated in a diflubenzuron-selected strain of the house fly (Musca domestica L.) with > 1000 × resistance, and in an OMS-12-selected strain [O-ethyl O-(2,4-dichlorophenyl)phosphoramidothioate] with 380 × resistance to diflubenzuron. In agreement with the accepted mode of action of diflubenzuron, chitin synthesis was reduced less in larvae of the resistant (R) than of a susceptible (S) strain. Cuticular penetration of diflubenzuron into larvae of the R strains was about half that of the S. Both piperonyl butoxide and sesamex synergized diflubenzuron markedly in the R strains, indicating that mixed-function oxidase enzymes play a major role in resistance. Limited synergism by DEF (S,S,S-tributyl phosphorotrithioate) and diethylmaleate indicated that esterases and glutathione-dependent transferases play a relatively small role in resistance. Larvae of the S and R strains exhibited a similar pattern of in vivo cleavage of ³H- and ¹⁴C-labeled diflubenzuron at N₁C₂ and N₁C₁ bonds. However, there were marked differences in the amounts of major metabolites produced: R larvae metabolized diflubenzuron at considerably higher rates, resulting in 18-fold lower accumulation of unmetabolized diflubenzuron by comparison with S larvae. Polar metabolites were excreted at a 2-fold higher rate by R larvae. The high levels of resistance to diflubenzuron in R-Diflubenzuron and R-OMS-12 larvae are due to the combined effect of reduced cuticular penetration, increased metabolism, and rapid excretion of the chemical.     

Response ofSpodoptera littoralis (Boisd.) andEarias insulana (Boisd.) larvae to azadirachtin and salannin

The effect of azadirachtin and salannin, two triterpenoids isolated from seeds of neem (Azadirachta indica A. Juss), on the feeding response ofSpodoptera littoralis (Boisd.) andEarias insulana (Boisd.) larvae, was investigated. Styropor (foamed polystyrene) lamellae were painted on both sides with a mixture of 5% sucrose with different concentrations of either azadirachtin or salannin dissoled in methanol-water (3∶7). Azadirachtin strongly suppressed feeding inS. littoralis larvae even at 0.001%, whereas salannin showed some antifeedant activity at 0.005% and above. Larvae ofE. insulana were deterred from feeding on azadirachtin-treated lamellae even at 0.005%, whereas salannin was effective only at 0.01% and above. Azadirachtin applied on cotton leaves deterred larvae ofS. littoralis from feeding at all concentrations ranging between 0.001 and 0.02%.     

Noxious effects of neem extracts onCrocidolomia binotalis

The potential of neem extracts to control the cabbage webworm,Crocidolomia binotalis Zell. (Lepidoptera: Pyralidae), was investigated in the laboratory. Neem, besides being an antifeedant at as low as 0.001% of the methanolic extract, was shown to be very toxic, as evidenced by high larval mortality and poor emergence. It also caused disruption of normal development: significant delays in larval moults, appearance of permanent larvae in the 3rd and 6th instars, and abnormal pupation. A possible interference with hormonal activity is discussed.     

Inhibition of chitin synthesis by two 1-(2,6-disubstituted benzoyl)-3-phenylurea insecticides. II

The knowledge of the biochemical mode of action of 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea (diflubenzuron) is presented, explaining the insecticidal effect. Like its structural analog, 1-(2,6-dichlorobenzyl)-3-(3,4-dichlorophenyl)urea (Du 19111), it inhibits chitin synthesis in the cuticle of larvae. Virtually complete inhibition was demonstrable 15 min after the application of diflubenzuron. Neither diflubenzuron nor Du 19111 has any effect upon chitinase activity either in vivo or in vitro. The insecticidal effect upon the cuticle, therefore, must be explained as an inhibition of chitin synthesis and not as an activation of chitin degradation. In contrast to the action of Du 19111, no accumulation of N-acetylglucosamine occurs upon treatment of larvae with diflubenzuron. Similarities and differences in the mode of action of both compounds are discussed, together with other effects reported in the literature.     

Susceptibility of the carob moth,Ectomyelois ceratoniae,toBacillus thuringiensis

A 1% concentration ofBacillus thuringiensis wettable power (containing 16,000 IU/mg), applied at a rate of 48,000 IU/cm², killed 95% of 4th-instar larvae of the carob moth,Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae), after 66 h and 100% after 85 h of exposure in laboratory tests. The mortality caused by a 0.5% concentration (24,000 IU/cm²) was significantly lower and presumably inadequate for practical application against this pest.     

Synthesis and insecticidal activities of novel derivatives of podophyllotoxin: Part XII

In order to find the biorational pesticides, eight novel 4β-substituted phenoxyaniline derivatives of podophyllotoxin have been synthesized with significant stereoselectivity and improved yields by employing the BF₃·Et₂O/NaI reagent system and evaluated for their antifeedant effect against 5th instar larvae of Pieris rapae and effect on the development of 5th instar larvae of P. rapae as well as for insecticidal activity against P. rapae. The antifeedant activities showed that these compounds exhibited less potent than podophyllotoxin. Though these derivatives showed less potent antifeedant activities than podophyllotoxin, they acted as growth development inhibitor to 5th instar larvae of P. rapae, which were found that the animals treated with podophyllotoxin and its derivatives showed moulting disturbances and/or deformities. Also, the insecticidal activity results show that all of these derivatives of PPT showed delayed insecticidal activity, which differs from traditional neurotoxic insecticides. Among them, compounds possessing a 4β-phenoxyaniline moiety substituted (CO₂C₂H₅, Cl and OH) at para position exhibited greater insecticidal activity against P. rapae than podophyllotoxin.     

Functional response of <Emphasis Type="Italic">Geocoris ochropterus</Emphasis> Fieber (Hemiptera: Geocoridae) to different egg densities of <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> (Hübner) (Lepidoptera: Noctuidae)

The biology and predatory efficiency of Geocoris ochropterus Fieber (Hemiptera: Geocoridae) has been studied extensively against many insect pests, but information on functional response of different stages of G. ochropterus to Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is lacking so far. The functional response of different stages of G. ochropterus to varying densities of eggs of H. armigera was investigated in the laboratory at 26?±?2°C, 65?±?2% RH and 12 L: 12D. Immature stages i.e. 3rd, 4th, 5th instar and adult predator exhibited type II functional response. Handling time decreased with increasing predator’s developmental stage. Adult G. ochropterus followed by fifth instar exhibited highest egg consumption and attack rate compared to other stages. Functional response parameters indicate that the adult and fifth instar of G. ochropterus were more voracious and efficient than other juveniles and might be useful as promising biocontrol agent against H. armigera.     

Carboxylamidases inSpodoptera exigua: properties and distribution in the larval body

Resistance to many insecticides demonstrated by the beet armyworm,Spodoptera exigua (Hübner), can be caused by the action of carboxylamidases. A colorimetric method, based on the hydrolysis of 4-nitroacetanilide to 4-nitroaniline by carboxylamidases, was used for evaluating biochemical properties of these detoxifying enzymes in beet armyworm. The optimum pH and temperature were 7.5 and 38°C, respectively. K_m (Michaelis constant) and V_max (maximal velocity) at 28°C were 2.3 X 10^-4 M and 2.06 nmol min^-1 mg protein^-1, respectively. The enzyme activity was evaluated in several body parts and located mostly (66.2%) in the midgut. The soluble fraction (supernatant of 105,000g) contained the highest enzyme activity relative to the total (69.3%), and exhibited the highest specific activity. Carboxylamidase activity was totally inhibitedin vitro at a concentration of 10^-6 M methomyl. The analysis of thein vitro inhibition kinetics indicated the ability of methomyl and diflubenzuron to inhibit carboxylamidases noncompetitively. Over 95% inhibitionin vivo was obtained when the larvae were fed with castor bean leaves dipped in 250 mgl ^-1 of methomyl. Thein vivo enzyme activity could be reduced to half with a pretreatment of 15 mgl ^-1 diflubenzuron.     

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.     

Effect of some benzoylphenyl ureas onearias insulana eggs of different age

Diflubenzuron, PH 60–43, PH 60–45, penfluron(PH 60–44) and triflumuron were assayed by a dipping technique for their toxicity toEarias insulana (Boisd ) eggs of different age Testing at a screening concentration of 0 1% a 1 showed that diflubenzuron, triflumuron and PH 60–43 were highly active, whereas PH 60–44 and PH 60–45 were nearly inactive With triflumuron the mortality of 0-1-day-old eggs was >90% even at 0 005%, at 0 001% it was 50% In 1-2-day-old eggs, a >90% kill was obtained even at 0 0005%, whereas at 0 00025% it was 86% PH 60–43 was also highly active, at 0 01% the kill of 0-1-day-old eggs was >90% Again, this rate of kill was obtained with 1-2-day-old eggs at a still lower concentration, 0 005% Both compounds were inactive against 2-3-day-old eggs, even at 0 1%     

Inhibitory effect of the antifeeding compound AC-24,055 [4′-(3,3-dimethyl-1-triazeno) acetanilide] on digestive enzymes of Spodoptera littoralis larvae

The effect of the antifeeding compound AC-24,055 on the main digestive enzymes of Spodoptera littoralis was determined. The inhibitory effect of AC-24,055 on the amylolytic and proteolytic activity increased with concentration and was well correlated with the antifeedant activity. After 3-day feeding on sugar beet leaves treated with 0.1% AC-24,055, more than 90% suppression of both amylase and protease activity was obtained, whereas at some lower concentrations a slight increase in invertase activity, especially after prolonged feeding, was observed. At 0.1% AC-24,055 the inhibition of the proteolytic activity was considerably stronger than it was in starved larvae. These results suggest that the inhibitory effect on the digestive enzymes is due not only to starvation but also to the effect of the antifeedant. Protease and amylase inhibition was obtained also by injecting AC-24,055 into the larval hemolymph. Maximum inhibition of both amylase and protease, about 50% and 25%, respectively, was reached 2 days after an injection of 5 μg AC-24,055; it then decreased gradually and was abolished 4 days after injection.Adding massive doses of AC-24,055 to the enzyme reaction mixture did not affect the in vitro activity of protease, amylase, or invertase. This indicates that AC-24,055 affects the digestive enzymes indirectly, probably by inhibiting a physiological system affecting the production of these enzymes.     

Insecticidal toxicity of thirteen commercial plant essential oils against <Emphasis Type="Italic">Spodoptera exigua</Emphasis> (Lepidoptera: Noctuidae)

We evaluated the chemical composition of thirteen commercially available plant essential oils and their insecticidal activity against the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Gas chromatography-mass spectrometry was used to characterize the chemical components of the essential oils. A total of 113 compounds were identified, with terpenes (>80%) and aromatic compounds as primary constituents. The toxicity of each pure essential oil was tested separately on third instar larvae and adult beet armyworms by topical application of 0.5 μl oil/ insect. All plant essential oils were found to be harmful to S. exigua, with third instar larvae showing significantly more susceptibility than adults. Essential oils of Cinnamomum zeylanicum and Juniperus virginiana showed the highest toxicity (mortality above 90%) to larvae, while C. zeylanicum and Pogostemon cablin oils were the most harmful compounds (95% mortality) to adults. Cymbopogon winterianus oil caused delayed mortality (similar to the effects of insect growth regulators) as well as malformations in pupae. C. winterianus, Ocimum basilicum and Rosmarinus officinalis oils significantly reduced fecundity, whereas no significant effects were observed on fertility.     

诱集植物香根草对大螟幼虫营养作用及消化酶的影响

香根草能够有效诱集水稻害虫大螟Sesamia inferens(Walker)在其上产卵,但孵化出的幼虫在香根草上不能完成生活史,香根草对大螟幼虫表现出致死作用。为明确香根草对大螟幼虫致死的作用机制,本研究分析测定了取食香根草后大螟幼虫的营养指标及体内消化酶的变化。结果表明,取食香根草能显著影响幼虫的生长效率及体内消化酶活性。与取食水稻的幼虫相比,取食香根草的幼虫粗生长效率ECI和净生长效率ECD显著降低;除蔗糖酶外,其他消化酶的活性在特定龄期呈显著下降的趋势,具体表现为4龄幼虫蛋白酶比活力、2~4龄幼虫淀粉酶比活力和1~4龄幼虫海藻糖酶比活力显著降低,而1~3龄幼虫蔗糖酶比活力显著提高。本文为进一步阐明香根草对大螟的致死作用机制奠定了基础,为开发以香根草为基础的稻螟绿色防控新技术提供了理论依据。     

Behavioral studies of the mobile forms ofsynclera univocalis on jujube,zizyphus mauritiana

One- or two-day-old larvae ofSynclera univocalis Wlk. (Pyralidae: Lepidoptera) were found mostly (83%) on young leaves of jujube (Zizyphus mauritiana Lamk. var.Umran) trees; in 67% of the cases the interveinal area of the tender leaves was folded. As the larvae grew older, the sides of the leaf were folded and the larvae fed within them. The leaf was turned inward by 71% of the larvae, while the rest turned the leaf outward. In 99% of the cases only one larva was found per leaf; very rarely were larvae of two different species of webbers found on the same leaf. The occurrence of the larvae was greatest at a tree height of 1.5-2 m. The distribution of the pest in the orchard was random. The percentage of adults on leaves was significantly higher than on webs, branches, the ground, or hovering. The maximum number of adults counted was at 13.00 hours.