Action of juvenoids on the metamorphosis of cyclorrhaphous Diptera

Administrations of high doses of juvenoids to the last instar larvae of cyclorrhaphous flies cause occasionally lethal defects in puparium formation but mostly affect only the pupal-adult transformation. In pupae, juvenoids impede proliferation and differentiation of the imaginal disks and of abdominal histoblasts: at low doses they cause incomplete rotation of male genitalia and deformations of the ovipositor, at higher doses their effects gradually spread from the tip of abdomen towards the middle of the body. The highest amounts influence the entire abdomen, size and pigmentation of the eyes, and development of hairs and sclerotization of the integument on the head and thorax. Various species slightly differ in the pattern of morphological effects produced, in the ability of affected insects to leave the puparium, and in the sensitivity to juvenoids of different types. A uniform scale for classification of morphological effects in the species examined is described in this paper. The most potent juvenoids are effective at doses around one nanogramme per specimen. Out of 29 selected compounds tested, isopropyl 11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate is the most active juvenoid for Drosophila, Musca, and Sarcophaga; methyl 10,11-epoxy-3,7,11-trimethyl-2,6-tridecadienoate is the most active juvenoid for Ceratilis; and isopropyl 11-chloro-3,7,11-trimethyl-2-dodecenoate possesses the highest activity for Calliphora.     

Morphogenetic and physiological effects of a juvenile hormone analogue on the light brown apple moth,Epiphyas postvittana (Lepidoptera: Tortricidae)

Abstract

The juvenile hormone analogue ZR-619—ethyl 11-methoxy-3,7,11-trimethyl-(2E,4E-dodecadienethiolate) —produced morphological and physiological effects when fed via artificial diet to larvae of Epiphyas postvittana (Walker). Morphological effects included changes in larval head and antennal structures after instar V (supernumerary instars); deformation of pupal and adult structures, particularly in genitalia and wings; and development of individuals with varying mixtures of larval and pupal structures. Physiological effects included prolongation of larval life, increase in larval weight, increase in larval instars, and decrease in fecundity. Effects were directly related to dosage concentrations.     

Ethyl (E)-3,5-ethano-7,11-dimethyl-2,4-dodecadienoate,A new insect growth regulator with potent juvenile hormone activity

A number of analogs of ethyl (2E,4E)-3,7,11-trimethyl-2,4-dodecadienoate were prepared and bioassayed for juvenile hormone activity on the yellow-fever mosquito (Aedes aegypti), the greater wax moth (Galleria mellonella), the yellow mealworm (Tenebrio molitor), the house fly (Musca domestica), and the tobacco budworm (Heliothis virescens). The analog ethyl (E)-3,5-ethanol-7,11-dimethyl-2,4-dodecadienoate (VI), containing a cyclopentene ring, showed remarkable potency on the above insect species. Since this compound possesses a fixed 3-s-trans-diene conformation it may provide some insight into the active conformation of bound 2,4-dienoate analogs.     

Aporphinoid alkaloids and other constituents from Lettowianthus stellatus

Two new aporphinoid alkaloids, f1ttowianthine and 11-methoxylettowianthine were isolated from the root bark of Lettowianthus stellatus, together with the new sesquiterpene 11-hydroxyguaia-4,6-diene and the known compounds liriodenine, (Z)-7-octadecen-9-ynoic acid, methyl (2E,6E,10R)-10,11-epoxy-3,7,11-trimethyl-2,6-dodecadienoate, methyl (2E,6E,10R)-10,11-dihydroxy-3,7,11-trimethyl-2,6-dodecadienoate , and 3,4,5-trimethoxyphenol. The structure elucidation was achieved by spectroscopic methods.     

Action of ecdysoids,juvenoids, and non-hormonal agents on termination of pupal diapause in the flesh fly

Pupal diapause in Sarcophaga crassipalpis can be immediately terminated with high doses of ecdysterone or 5,β-hydroxyecdysterone. Within a range of lower doses diapause is not immediately terminated, but the duration of diapause is shortened. Injection of small doses at 3-day intervals is more effective than a single application of the same total amount. 5,β-hydroxy-ecdysterone is more effective than ecdysterone. The juvenoid isopropyl (2E,4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate does not cause immediate termination of diapause but diapause is shortened. Simultaneous application of ecdysterone and the juvenoid synergistically produce a shorter duration of diapause than either hormone applied separately. Topical application of acetone and several other organic compounds can cause an immediate break of diapause. Neckligated pupae, however, do not respond to acetone treatment. Temperature shocks caused by brief exposure to high or low temperatures are ineffective.Although high doses of ecdysoids cause immediate termination of diapause, subsequent adult morphogenesis is protracted in direct proportion to the dose of ecdysoid. With the highest doses many flies fail to complete adult morphogenesis. Flies receiving high doses of ecdysoid are characterized by developmental abnormalities such as underdeveloped antennae, compound eyes, and mouthparts. By contrast, adultoids produced with juvenoids are characterized by abdominal abnormalities.     

The ovicidal effects of a juvenile hormone and a juvenile hormone analogue on the fleshfly, Sarcophaga bullata

Egg fertility was reduced in adult females of Sarcophaga bullata treated topically with a juvenile hormone (Cecropia JH-1) or a juvenile hormone analogue, ZR-515 (isopropyl-11-methoxy-3,7,11-trimethyl-dodeca-2,4-dienoate), the effect was most noticeable when the flies were treated on the day of ovulation. Depending on the time of treatment, JH and JHA affected different stages of development. Treatment on the day before ovulation produced a high percentage of embryonic arrest; when the flies were treated on the day of ovulation a major proportion of fully developed embryos failed to hatch. Treatment at the early stages of embryogenesis caused mortality of larvae before molting to third instar. There was no delayed mortality after the third instar.

---

Résumé Les effets ovicides d'une hormone juvénile (Cecropia JH-1) et d'un analogue d'hormone juvénile (ZR-515) ont été examinés par application locale sur des femelles adultes de Sarcophaga bullata à différents stades du dévelopement des ufs.Le traitement des mouches le jour de l'ovulation est très efficace et empèche les embryons totalement développés d'éclore et de donner des larves de premier stade.L'application de ces produits un jour avant l'ovulation provoque l'arrêt de l'embryogenèse; quand les mouches sont traitées un jour après l'ovulation, la mortalité est plus tardive et une proportion importante de larves meurt avant la mue donnant le troisième stade.

     

Development of superfluous soldiers induced by juvenile hormone analogues in the termite,Reticulitermes lucifugus santonensis

Summary The synthetic juvenile hormone (JH): 17% alltrans+83%trans, trans, cis-methyl 10-epoxy-3,7,11-trimethyl-2,6 tridecadienoate and juvenile hormone analogues (JHA): methyl 10-chloro-3,7,11-trimethyl-2 dodecenoate and ethyl 10-epoxy-3,7,11-trimethyl-2,6-dodecadienoate administered on filter paper to small groups of the European subterranean termiteReticulitermes lucifugus santonensis Feyt. caused differentiation of larvae and pseudergates into pre-soldiers and/or pseudergate-soldier intercastes. In contrast to the proportion of one soldier to 100–300 other individuals in normal colonies, the effect of the compounds tested that showed JH activity was to induce the development of a large number of superfluous soldiers in quantities that even exceeded the number of other kinds of individuals. Such a disturbance in the caste ratio leads to increased mortality.

---

Zusammenfassung Das synthetische Juvenilhormon (JH): 17% alltrans+83%trans, trans, cis-Methyl 10-epoxy-3,7,11-trimethyl-2,6 tridecadienoate und die Juvenilhormonanaloge (JHA): Methyl 10-chloro-3,7,11-trimethyl-2 dodecenoate und Ethyl 10-epoxy-3,7,11-trimethyl-2,6-dodecadienoate, die auf Filterpapier kleinen Termitengruppen der europäischen ErdtermitenartReticulitermes lucifugus santonensis Feyt. zugeführt wurden, verursachten eine Differenzierung von Larven und Pseudergaten in Vorsoldaten und/oder Interkasten Pseudergate-Soldat. Zum Unterschied vom Verhältnis ein Soldat zu 100 bis 300 anderen Individuen in normalen Kolonien erscheint unter der Einwirkung der getesteten juvenilhormonwirksamen Stoffe eine grosse Menge überzähliger Soldaten, deren Anzahl jene der übrigen Individuen sogar übersteigen kann. Die Gleichgewichtstörung zwischen den Kasten hat eine höhere Absterberate der Termiten zur Folge.

---

Résumé L'hormone juvénile synthétique: 17% alltrans+83%trans, trans, cis-méthyle 10-epoxy-3,7,11-triméthyle-2,6 tridecadienoate et l'analogue de l'hormone juvénile: méthyle 10-chloro-3,7,11-triméthyle-2 dodecenoate et éthyle 10-epoxy-3,7,11-triméthyle-2,6-dodecadienoate, qui ont été administrés amenés sur papier filtre à de petits groupes de termitesReticulitermes lucifugus santonensis Feyt., ont causé une différenciation de larves et de pseudergates en présoldats et/ou intermédiaires pseudergate-soldat. A la différence du rapport de 1 soldat à 100–300 autres individus dans des colonies normales, on assiste sous l'effet de la substance testée avec effet d'hormone juvénile à l'apparition d'un grand nombre de soldats en surplus, dont le nombre peut même dépasser celui des autres individus. Le trouble de l'équilibre entre les castes conduit à un taux de mortalité supérieur des termites.

---

---

Dedicated to Prof.K. Gösswald at the occasion of his 65th birthday.     

Emergence ofKeiferia lycopersicella [Lepidoptera: Gelechiidae], andApanteles sp. [Hymenoptera: Braconidae] from pupae and soil treated with insect growth regulators

Two insect growth regulators (IGR's), ZR-619 (ethylin-methoxy-3,7,11-trimethyl-(2E, 4E)-2,4-dodecadienethiolate), and ZR-777 (Prop-2 ynyl 3,7,11-trimethyl-(2E, 4E)-dodecadienoate) were tested for potential use against the tomato pinworm,Keiferia lycopersicella (Walsh.) The IGR's were applied to cocoons and to soil where cocoons were formed. Both IGR's, alone and in combination, suppressed pinworn adult emergence from 23 to 7% when applied direct but were ineffective when applied to the soil. All treatments of IGR's in both methods of application reduced emergence of the parasitoApanteles sp. to 0% from levels as high as 61%. Use of the IGR's in this situation resulted in greater harm to potential biological control agents than in benefit to pest control.

---

Résumé Deux régulateurs de croissance des insectes: le ZR-619 (éthyl n-méthoxy-3, 7, 11-triméthyl-(2E, 4E)-2, 4-dodecadienethiolate) et le ZR 777 (Prop-2 ynyl-3, 7, 11-triméthyl-(2E, 4E)-dodecadienoate) ont été expérimentés pour lutter contre le ver de la tomateKeiferia lycopersicella (Walsh.). Le traitement a été réalisé dans le sol où s'effectue la nymphose de ce ravageur. Les deux produits, isolément ou en mélange, ont réduit la sortie des adultes de 23 à 7% lorsqu'its, sont appliqués directement sur les nymphes, ils sont inefficaces quand ils sont introduits dans le sol. Les deux méthodes d'emploi ont supprimé les sorties d'Apanteles sp. jusqu'à 0%, à partir d'un taux de parasitisme allant jusqu'à 61%. L'utilisation de ces régulateurs de croissance dans de telles conditions est donc plus dommageable aux antagonistes naturels qu'elle n'est profitable contre le ravageur.

---

---

Florida Agricultural Experiment Stations Journal Series No. 5093.     

Susceptibility of malathion-resistant strains of Tribolium castaneum and T. confusum to the insect growth regulators methoprene and hydroprene

A comparison was made of the effects of methoprene (isopropyl 11-methoxy-3, 7, 11-trimethyl-2, 4-dodecadienoate) and hydroprene (ethyl 3, 7, 11-trimethyl dodeca-2, 4 dienoate) on the developmental survival of three malathion-resistant strains of Tribolium castaneum (Herbst) and one of T. confusum J. du Val, with a malathion-susceptible strain of each species. No cross-resistance to either IGR in any of the malathion-resistant strains was detected.

---

Résumé On a fait une comparaison des effets de methoprene (isopropyl 11-methoxy-3, 7, 11-trimethyl-2, 4-dodecadienoate) et hydroprene (ethyl 3, 7, 11-trimethyldodeca-2, 4 dienoate) sur le développement de trois races de Tribolium castaneum résistantes au malathion, et une race de T. confusum résistante au malathion, avec une race de chaque espèce prédisposée au malathion. Aucune résistance croisée a l'un ou l'autre IGR ne fut découverte dans les races résistantes au malathion.

     

Morphological effects of insect growth regulating compounds on Aedes aegypti (Diptera: Culicidae) larvae.

Cuticular development of $\text{Aedes aegypti}$ larvae was examined by electron microscopy and comparisons were made between larvae exposed to methoprene, isopropyl (E, E)-11-methoxy-3, 7, 11-trimethyl-2, 4-dodecadienoate, those treated with the fluorescent insect growth regulator, 5-[[[5-(dimethylamino)-1-naphthalenyl]-sulfonyl]amino]-1, 3-benzodioxole (DNSAB), and untreated larvae. Larvae of all three groups were routinely fixed at 24, 48, and 72 hr posttreatment. Thin sections of the sixth-abdominal segment, anal papillae, midgut tissue, and Malpighian tubules were examined for morphological variations from controls.     

Haemolymph ecdysteroid titre and epidermal cell commitment of the female southwestern corn borer larvae

The epidermal cell commitment (to pupation or formation of immaculate larvae) and related haemolymph ecdysteroid titres of the southwestern corn borer, Diatraea grandiosella were studied in both nondiapause-bound and diapause-bound last-instar female larvae. Cell commitment was estimated by examining the characteristics of new cuticle secreted in response to an injection of 20-hydroxyecdysone. Haemolymph ecdysteroid titres were determined by radioimmunoassay. Juvenile hormone effect on epidermal cell commitment was studied by applying a juvenile hormone mimic (ZR-515) to last-instar non-diapause-bound larvae and examining the resulting cuticle.In non-diapause-bound larvae, the epidermis of different body regions was committed to pupal development at different times. When pupal cuticular characteristics were evaluated by a scoring system, it appeared that the development of normal pupal cuticle is discontinuous. Three sudden increases in pupal characteristics were observed at 1.67, 2.67 and 3.67 days into the last-larval instar. Haemolymph ecdysteroid titre changes were correlated with the sudden increases in pupal characteristics. Peak ecdysteroid titres were found at 1.67, 2.33, and 3.33 days into the final instar. A fourth ecdysteroid peak (138.8 ng/ml of haemolymph) occurred in pharate pupae. In contrast, the commitment of diapause-bound larvae to produce immaculate integument was made in a fast and continuous fashion. Full commitment was made by 50% of the individuals 4 days (ca. first quarter) into the stadium. Haemolymph ecdysteroid titres fluctuated during the first 2 weeks of the stadium but no significant peaks were observed prior to pharate stage. An ecdysteroid peak (29.8 ng/ml of haemolymph) was identified in pharate immaculate larvae.Pupal development could be completely prevented in 26.7% of nondiapause-bound larvae as late as 4 days into the last instar by topical application of ZR-515. This indicates that the commitment to pupation as revealed by 20-hydroxyecdysone injection is reversible.     

The rôle of juvenile hormone in housefly ovarian follicle morphogenesis

Oögenesis in the housefly, Musca domestica, was divided into a series of 10 stages where stage 1 was the germarium, stage 4 was the beginning of yolk deposition, stage 7 was characterized by maximal nurse cell development, stage 9 by the degeneration of the nurse cells and chorion formation, and stage 10 was the mature egg. It required 69 hr from eclosion at 27°C to develop mature eggs. This represented an oöcyte volume increase of 3700-fold, a seventeenfold increase in follicle length, and a sevenfold increase in weight. The application of 2 μg of isopropyl (E,E)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate (ZR-515) to allatectomized (-CA) flies stimulated egg development, which progressed at the same rate as the controls. The -CA flies did not develop eggs past stage 4, which represented a cessation of development at a volume of 1·4 per cent that of a mature egg and an ovarian dry weight of 11 per cent that of a mature ovary. The follicle cells from -CA flies did not differentiate into the squamous condition over the nurse chamber, did not become columnar over the oöcyte, did not produce the chorion or vitelline membrane, and did not decrease in number as they did on the stage 10 follicles. Endomitosis in the nurse cell nuclei of -CA flies stopped development at 290 c, but maximum development of 2400 c occurred in stage 7 follicles from controls, and then the nurse cells began to disintegrate.     

Activation of the prothoracic gland by juvenile hormone and prothoracicotropic hormone in Mamestra brassicae

The effects of JHA (ZR-515) application or brain implantation on metamorphosis and adult development were examined in the last instar larvae and pupae of Mamestra brassicae. When JHA was applied to neck-ligated 4- or 5-day-old larvae or to the isolated abdomens of 5-day-old larvae containing implanted prothoracic glands taken from 5-day-old larvae, the insects pupated. Dauer pupae and diapausing pupae treated with JHA showed adult development. By contrast, pupation could not be induced by the application of JHA to 2- or 3-day-old neck-ligated larvae or to the isolated abdomens of 5-day-old larvae containing implanted prothoracic glands from 0-day-old larvae. Implantation of a brain into neck-ligated 3- or 5-day-old larvae (at the beginning of gut emptying and wandering) caused pupation of the host. A similar result was obtained when both a brain and the prothoracic glands from 0- or 5-day-old larvae were implanted into the isolated abdomens of 5-day-old larvae. These results indicate that activation of the prothoracic glands by application of JHA is temporally restricted to the last part of the last larval instar and to the pupal stage, while the activation by prothoracicotropic hormone (PTTH) can occur throughout the last larval instar and the pupal stage. In addition, the implantation of brains or application of JHA to neck-ligated 5-day-old larvae 25 days after ligation seldom induced pupation of the hosts, a result which suggests that larval prothoracic glands maintained under juvenile hormone (JH) or PTTH-free conditions for long periods of time may become insensitive to reactivation by both hormones.     

Synthesis of the Thiirane Analogs of Juvenile Hormone III and Other Juvenile Hormone Mimics

Methyl (2E,6E)-10,11-epithio-3,7,11-trimethyl-2,6-dodecadienoate (the thiirane analog of JH III), 6,7-epithiogeranyl 4-methylphenyl ether and 6,7-epithiogeranyl 3,4-methylenedioxyphenyl ether were synthesized. An infrared absorption band at ~1090 cm^?1 was attributable to the thiirane group. The biological activity of these three sulfur-containing JH mimics was tested on Culex pipiens, Aedes aegypti and Spodoptera litura to reveal weak or no JH-like activity.     

Induction of perfect superlarvae by the application of juvenile hormone analogue to starved larvae of the silkworm,Bombyx mori

Topical application of juvenile hormone analogue, methoprene, induced a supernumerary larval moult in the silkworm, Bombyx mori. The incidence changed greatly depending on developmental stages and physiological states of the methoprene-treated larvae. When methoprene was applied to feeding larvae, only those treatments from the middle of the 2nd instar until the middle of the 4th instar were effective. An 18-h starvation period from the beginning of the 4th instar and a dose of 1 μg of methoprene per larva were required for 100% incidence of the perfect superlarvae. Allatectomy had no effects on the induction of superlarvae by methoprene. The treated 4th-instar larvae ecdysed to the 5th instar without any delay compared to the controls, and underwent an additional larval ecdysis 4.5 days later. The induced 6th-instar larvae took 8.5 days until the onset of cocoon spinning. The induced superlarvae showed reduced growth rates but an increase of final mass due to prolonged feeding period. A sharp but reduced peak in ecdysteroid titre in the haemolymph appeared one and a half days prior to each larval ecdysis in the treated larvae, suggesting that methoprene provokes the extra larval moult through an additional release of ecdysteroids.     

Activities of 2,4-dihydroxy-6-n-pentylbenzoic acid derivatives

Esters of 2-hydroxy-4-methoxy-6-n-pentylbenzoic acid (2-8) (methyl, ethyl, butyl, pentyl, isopropyl, sec-butyl and benzyl), olivetol (9), methyl, ethyl, butyl perlatolates (10-12), 2,4-dihydroxy-6-n-pentylbenzoic acid (15), and methyl and ethyl esters of (15) were prepared through structural modifications of perlatolic acid (1) with the aim to detect new antifungal and antibacterial substances and also to evaluate the toxicity by the brine shrimp lethality assay against Artemia salina. The antifungal assays were carried out against the fungus Cladosporium sphaerospermum through the bioautography method, and methyl 2,4-dihydroxy-6-n-pentylbenzoate (13) showed the highest antifungal activity (2.5 yg). Olivetol (9) and 2,4-dihydroxy-6-n-pentylbenzoic acid (15) are also potent inhibitors of the growth of the fungus (5.0 microg). Except for methyl (10), the ethyl (11) and butyl (12) perlatolates were less active than perlatolic acid (1). The activities presented by methyl (2) and ethyl (3) 2-hydroxy-4-methoxy-6-n-pentylbenzoates and methyl (13) and ethyl (14) 2,4-dihydroxy-6-n-pentylbenzo-ates suggest that compounds with a free hydroxy group in the aromatic ring (C-4) have a more pronounced effect against C. sphaerospermum. Antibacterial activities were tested by the disc diffusion method using pathogenic strains of S. aureus and E. coli. The compounds were weakly active with inhibition zones between 9-15 mm. The 2-hydroxy-4-methoxy-6-n-pentylbenzoic esters 2-8 and alkyl perlatolates 10-12 were selective against E. coli. Perlatolic acid (1) and methyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (2) were the most active with LD50 values of 24.1 microM and 27.2 microM, respectively. The other compounds were not toxic to Artemia salina larvae.     

Brain-independent development in the moth Sesamia nonagrioides

The caterpillars of Sesamia nonagrioides developing under long-day (LD) photoperiod pupate in the 5th or 6th instar whereas under short day (SD) conditions they enter diapause and undergo several extra larval molts. The diapause is terminated within 1-3 instars upon transfer of SD larvae to the LD conditions. Brain removal from the 6th instar larvae promotes pupation followed by imaginal development; however, one third of the SD larvae and 12% of the LD larvae debrained at the start of the instar first undergo 1-2 larval molts. The incidence of larval molts is enhanced by the brain implants. Exclusively pupal molts occur in the LD larvae debrained late in the 6th instar. Decapitation elicits pupation in both LD and SD larvae, except for some of the 4th and 5th and rarely 6th instar that are induced to a fast larval molt. The pupation of decapitated larvae is reverted to a larval molt by application of a juvenile hormone (JH) agonist. No molts occur in abdomens isolated from the head and thorax prior to the wandering stage. Abdomens isolated later undergo a larval (SD insects) or a pupal (LD insects) molt. Taken together the data reveal that in S. nonagrioides (1) several larval molts followed by a pupal and imaginal molt can occur without brain; (2) an unknown head factor outside the brain is needed for the pupal-adult molt; (3) brain exerts both stimulatory and inhibitory effect on the corpora allata (CA); (4) larval molts induced in CA absence suggest considerable JH persistence.     

Effects of a synthetic juvenile hormone and some analogues on Ephestia spp. (Lepidoptera: Phycitidae)

Depending on their stage of development, treatment of mature larvae of Ephestia kühniella with a synthetic juvenile hormone resulted in the production of super larvae (which invariably prolonged larval life) and larval-pupal intermediates. When migrating last-instar larvae were treated with the juvenile hormone analogues (JHA) ethyl-3,7, n-trimethyldodeca-2,4-dienoate (ZR512) and isopropyl ii-methoxy-3,7, ii-trimethyldodeca-2,4-dienoate (ZR515), larval-pupal intermediates and pupal mortality were induced. However, when applied topically, ZR515 appeared more effective than ZR512. Both analogues prevented adult emergence when topically applied to the migrating larvae at doses between 28–52 ng. One-day-old pupae were most susceptible while older individuals became less sensitive with age. When larvae pupated in corrugated cardboard rolls were treated with ZR512 those of both E. cautella and E. kiihniella failed to emerge. At an estimated dose of 179 ng cm^-2, ZR515 prevented 77^-6%E. cautella and 100%E. kühniella larvae from emerging as adults. The control of Ephestia by JHA treatment of the pupation sites is discussed.     

Larval esterases of the southwestern corn borer, Diatraea grandiosella: Temporal changes and specificity

Disc electrophoresis was used to examine and characterize the esterases present in the fat body, haemolymph, and midgut of last stage larvae of the southwestern corn borer, Diatraea grandiosella. Significant temporal changes were observed in the pattern of the 4 major esterases of the fat body and 3 major esterases of the haemolymph. These changing profiles presumably relate, in part, to a requirement for the degradation of juvenile hormone (JH) in preparation for metamorphosis.The binding capacity of esterases present in the larval midgut towards JH I and three JH mimics (alkyl-3,7,11-trimethyl-2,4-dodecadienoates) was also examined. The midgut of last stage nondiapausing larvae was shown to contain a carboxylesterase which bound all three JH mimics. Another esterase which bound JH I, but not the mimics, was also present. An esterase with a similar electrophoretic mobility was detected in the haemolymph and integument. Since the JH I binding esterase did not bind the JH mimics, the mimics do not appear to synergize JH by inhibiting its ester hydrolysis.     

Relationship between starvation and supernumerary ecdysis and recognition of the penultimate-larval instar in the common cutworm, Spodoptera litura

Supernumerary ecdysis of the common cutworm, Spodoptera litura was induced by crowded rearing and starvation. Long periods of starvation in the 3rd- and 4th-larval instars induced higher proportions of extra ecdyses, up to 100%. The pupal weights were essentially similar in spite of different instar numbers. However, starvation in the 5th (penultimate) and 6th instars hardly induced supernumerary ecdysis. Starvation caused a fluctuation in the head-capsule sizes of the larvae, but those larvae with head capsules wider than 1.65 mm were destined to become last instar at the next ecdysis. The significance of a threshold for the penultimate instar is discussed in relation to phase polymorphism.Crowded rearing also caused an increase in the proportion of extra ecdyses in the following generation, whereas isolation decreased it. It is concluded that supernumerary ecdysis is not a phase character, but is for recovery from reduced size due to food shortage.