I. Ishaaya

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.

The effect of IKI-7899, a new chitin synthesis inhibitor, on larvae ofTribolium castaneum andSpodoptera littoralis

The effect of IKI-7899 and diflubenzuron on larval development and emergence ofTribolium castaneum and ofSpodoptera littoralis was determined. The LC50 of IKI-7899 at adult emergence ofT. castaneum larvae fed the compound in their diet and the ED50 of S.littoralis larvae treated topically were approximately one-sixth those of diflubenzuron.

Evaluation of benzoylphenyl ureas for controlling the spiny bollworm, Earias insulana (Boisd.), in cotton

Abstract Three benzoylphenyl ureas (BPUs) were compared for their relative toxicity against different life stages of the spiny bollworm (SBW), Earias insulana (Boisd.). Results showed that the LC50 values of chlorfluazuron, teflubenzuron and hexaflumuron ingested by neonate larvae of the spiny bollworm, were 0.01, 0.05 and 0.25 p.p.m. (a.i.), respectively. A dipping concentration of 50 p.p.m. (a.i.) hexaflumuron and teflubenzuron resulted in suppression of ∼ 80% and 50% egg hatch, respectively, whereas chlorfluazuron showed no effect. Egg hatch inhibition of 65% and 42% was obtained after 7–10 days exposure to hexaflumuron and teflubenzuron, respectively. No significant response was found with chlorfluazuron. In addition, a gradual decline in egg viability was observed with the increase of adult exposure to treated cotton plants. Treatments of 50 p.p.m. (a.i.) chlorfluazuron, teflubenzuron and hexaflumuron under experimental field conditions, gave satisfactory control of SBW larvae that had been introduced as neonates on to the treated young cotton bolls. The level of damaged bolls after treatment with the benzoylphenyl ureas ranged from 10% to 12%, compared with 77% in the untreated control. Our results indicate that chlorfluazuron and teflubenzuron, and possibly other BPUs, have potential for controlling SBW larvae under field conditions.

Induction of prolonged larval feeding stage by juvenile hormone analogues inTribolium Castaneum

Dietary ZR-512 and ZR-619 at concentrations of 10 — 1000 ppm induced prolongation of the larval feeding period up to tenfold, increasing larval weight up to double that of untreated larvae.A comparison study of four juvenoids, using 200 ppm of ZR-512, ZR-515, ZR-619 or ZR-777, showed that ZR-515 elicits the highest larval weight (6.2 mg) and ZR-777 the lowest (3.6 mg). In all cases a pronounced enhancement of larval weight — of 50 — 250% relative to untreated larvae (2.4 mg) — was obtained.Tr. castaneum larvae reared up to their 3rd instars on a diet containing 100 ppm of ZR-512, ZR-515, ZR-619 or ZR-777 and then transferred to a juvenile hormone-free diet, were not affected. The period between 4th instar larva and pupation should therefore be considered as critical for juvenile hormone effect.The induced prolongation of the larval stage after juvenile hormone treatment was followed by a pronounced enhancement of cuticle phenoloxidase activity, indicating an alteration of the larval biochemical processes.Although juvenile hormone treatment inhibitsTr. castaneum pupation and emergence, it markedly prolongs larval feeding stage and weight and thus accelerates damage.

Phenoloxidase activity at various stages of development in the egyptian cotton worm Spodoptera littoralis

Abstract The phenoloxidase activity in Spodoptera littoralis was determined at various stages of development. During an instar period the activity of this enzyme was at its lowest after ecdysis, which then increased sharply and reached its maximum at the pharate stage. During larval-pupal development the highest activity occurred at the pharate pupal stage, reaching about fifteen and ten times that of the postecdysed larvae when it was expressed in terms of fresh larval weight and dried cuticle respectively. This activity was far stronger than that obtained in the pharate larvae (peak of activity) of the 4th and 5th instars. After larval-pupal ecdysis the activity dropped sharply and reached in untanned pupae about 40 per cent of that of the pharate pupa. During egg development the phenoloxidase system was at its highest activity compared with other stages of development, i.e., larval or pupal. In fertilized eggs the activity increased with age and reached in 3-day-old eggs, about 130 per cent that of the newly laid eggs. Striking results pointing to a strong phenoloxidase activity in the female genital organs indicate the presence of this enzyme in the early stage of egg development. These findings are strengthened by the fact that unfertilized eggs laid by virgin females exhibit a relatively high activity, albeit lower than in fertilized eggs. The general pattern of the phenoloxidase activity during the different stages of insect development (i.e., egg, larva and pupa) points to the possibility of a hormonal mechanism directing this system.

Synthesis and Insecticidal Activity of Heptafluoroisopropyl-Containing Benzoylphenylurea Structures†

Fourteen novel heptafluoroisopropyl-containing benzoylphenylureas were designed and synthesized. Their insecticidal activities against armyworm ( Pseudaletia separata Walker) were examined and compared with the commercial product diflubenzuron. Three compounds (IIi, IIj, and IIk) showed excellent insecticidal effect, and their activity resembled that of diflubenzuron. Compound IIi also showed nearly the same insecticidal activity as novaluron on African cotton leafworm ( Spodoptera littoralis ). Furthermore, results from a field trial indicated that 5% EC IIi exhibited similar efficacy in comparison with chlorfluazuron and hexaflumuron against imported cabbage worm ( Pieris rapae L.) and diamondback moth ( Plutella xylostella ), respectively.

Comparative toxicity of chlorfluazuron (IKI-7899) and cypermethrin to Spodoptera littoralis, Lobesia botrana and Drosophila melanogaster

Abstract Chlorfluazuron sprayed on cotton seedlings was more efficient than cypermethrin against third-instar larvae of the Egyptian cotton leafworm, Spodoptera littoralis . At a concentration of 3·2 x 10 −5 % a.i., chlorfluazuron caused 98 ± 2% larval mortality and cypermethrin 35 ± 9%. All larvae in chlorfluazuron assays died during moulting; hence the leaf area consumed during the test instar was not appreciably affected. On the other hand, in cypermethrin assays, larvae died during the intermoult stage. Chlorfluazuron exhibited potency similar to that of cypermethrin on third-instar larvae of the grape berry moth Lobesia botrana , resulting in 90–95% and 33–34% mortality in treatment concentrations of 5 x 10 −3 % and 2 x 10 −4 % a.i., respectively. In another grapevine pest, Drosophila melanogaster , cypermethrin suppressed larval and adult formation to a greater extent than chlorfluazuron. The high potency of chlorfluazuron on various insects, together with its low toxicity to man and the environment, renders this compound a potential agent for controlling important agricultural pests.

The effect of BAY SIR 8514, diflubenzuron, and Hercules 24108 on growth and development ofTribolium confusum

The effect of BAY SIR 8514, diflubenzuron and Hercules 24108 on larval growth, pupation and emergence ofTribolium confusum was determined. BAY SIR 8514 was about twice as active as diflubenzuron, whereas Hercules 24108 was much less active. BAY SIR 8514 is suggested, in addition to diflubenzuron, as a potential insecticide against stored-product insects.

Activity of soluble and membrane-bound threhalase in apterous and alate morphs of Aphis citricola☆

1. n1. The optimum conditions for trehalase activity of either soluble or membrane-bound trehalase of both apterous and alate morphs of Aphis citricola were determined. n n2. n2. Sodium deoxycholate (DOC) act as a solubilizing agent for membrane-bound trehalase, with no appreciable effect on its activity. n n3. n3. Alates exhibit about a 50% higher level of soluble protein compared with that of apterase. Trehalase activity of this fraction in alates is 70–85% higher than that in apterase, as determined per mg protein or per aphid. The activity of the membrane-bound trehalase was on the same level in both morphs when determined relative to mg protein. n n4. n4. The relative high activity of the soluble trehalase in alates may reflect an increased energy supply needed for sustaining physical activity involved in aphid flight.

Studies of the trehalase activity in eggs of the egyptian cotton worm, Spodoptera littoralis☆

Abstract In eggs of Spodoptera littoralis , the optimum conditions for trehalase activity involve a reaction mixture of 0.05 M acetate buffer (pH 3.5) and 1.5% trehalose at 37°C for 60 min. A catalytic period of up to 90 min was found to be linear, the K m value was 0.03 M, and the enzyme activity reached its maximum at 55°C. In the presence of sodium deoxycholate, the trehalase activity was strongly enhanced, indicating the presence of an active system of membrane-bound trehalase. A decrease of about 20% in the activity of the membrane enzyme was observed in the first instar larvae shortly before hatching, with no appreciable change in the activity of the soluble enzyme. Urea and divalent cations were found to suppress considerably the enzyme activity, HgCl 2 being the most effective compound.