Influence of precocene II on the sensory system of antennae and mouthparts in larvae of the fruit tree tortricid <Emphasis Type="Italic">Archips podana</Emphasis> Scop. (Lepidoptera: Tortricidae)

The influence of precocene II, an antijuvenile agent, on morphological characters of the chemoreceptor apparatus of antennae and mouthparts was studied in fifth instar A. podana larvae. Treatment with different doses of precocene was performed at the egg stage. It proved to cause changes in the form and number of basiconic sensilla on the maxillary palps and galea and in the size of basiconic sensilla on the second and third antennal segments. The results are discussed with respect to the influence of precocenes on the insect sensory system and the role of the juvenile hormone in regulation of its development.     

Chemical allatectomy of late Locusta embryos by a synthetic precocene and its effect on hopper morphogenesis

The anti-allatin substance, 7-ethoxy-precocene II (= “precocene III”) was topically applied to eggs of Locusta migratoria migratorioides with fully grown embryos in stage XX (about 64 ± 4% of the whole period of egg development). A day after precocene application the eggs were washed for 10–15 s in acetone and then transferred to clean containers for removing precocene residues and for preventing contamination at hatching. The treatment induced prothetelic morphogenetic disturbances which became overt in the subsequent hoppers; the effect was dose dependent and the ED₅₀ (= effective anti-allatin dose 50%) was low, 20.5 μg precocene III per g fresh egg weight (= 0.37 μg per egg). Quite similar results were obtained following application of precocene III to eggs with embryos in stage XXI (73 ± 4% of the egg development). These findings and direct examination of histological sections of the embryonic corpora allata demonstrated that precocene chemically allatectomizes late Locusta embryos. The lethal effect of precocene III was dependent on the washing. When the eggs were washed in acetone a day after application, mortality did not occur in a dose-dependent way; even the highest dose applied, 256 μg precocene III per egg (= 14405 μg per g fresh weight), was less than the LD₅₀ (lethal dose 50%). In contrast, without washing mortality was dose dependent, but it occurred later, at or after hatching; the LD₅₀ was 1334.9 μg per g (= 22.7 μg/egg). The results show that the late embryos are highly susceptible to the anti-allatin effect of the precocene, but are extremely insusceptible to its lethal effect; toward hatching, however, susceptibility to the lethal effect becomes marked.With doses between 45–14405 μg precocene III per g fresh egg weight, the anti-allatin effect became overt by a quite-uniform belated morphogenetic response. All hoppers which hatched from precocenetreated eggs were morphogenetically normal in the 1st instar and in the beginning of the 2nd instar, but the duration of the 2nd instar was almost doubled and at the end of this instar over 96% of the locusts died in the moult, being unable to shed the exuvia. Artificial removal of the apolyzed old cuticle revealed 3rd instar prothetelic adultiforms. These results and some data in the literature indicate that allatectomy of the embryo does not result in prothetelic morphogenetic disturbances in the 1st and early 2nd instar larvae and may impose the question what is the role of the juvenile hormone in late embryos and early larvae.     

Synergistic action of diethyl maleate on the morphogenetic and antigonadotropic activity of precocenes on the seed bug Oxycarenus Iavaterae (F.)

Freshly ecdysed-third instar larvae and adult females of the seed bug Oxycarenus Iavaterae were treated with diethyl maleate (1 or 10 μg/specimen, topically applied), a commonly used depletor of glutathione levels, prior to the application of model precocenes (P1, P2, and EP2; 1–10 μg/specimen, topically applied). The combined treatment resulted in a significant increase of the characteristic antijuvenile hormone effects elicited by the above allatocidins, namely, induction of precocious metamorphosis in larvae and inhibition of ovarian development in adult females. These results, which indicated that diethyl maleate exerted a definite synergistic action, constitute the first example of a synergism strategy to the improvement of precocene activity.     

Disruptive developmental effects of benzyl-1,3-benzodioxole derivatives on unparasitized and parasitized Manduca sexta larvae

Treatment of tobacco hornworm larvae with the benzyl-1,3-benzodioxole derivative J-2710 immediately after ecdysis to the fourth instar disrupted development either during the moult to the fifth instar or shortly thereafter. Larvae given topical applications of 100 μg J-2710 in 1 μl acetone suffered 100% mortality, often after secreting moulting fluid in large pockets between the epidermis and the cuticle later in the fourth instar. Larvae that successfully ecdysed had abnormalities of the mouthparts and cervix that interfered with normal feeding, inhibiting growth in the fifth instar. Larvae of the gregarious endoparasitic wasp Cotesia congregata (=Apanteles congregatus) frequently failed to emerge from host Manduca sexta larvae treated with high doses of J-2710, particularly when the host failed to feed normally. Less potent disruptive effects on Manduca and Cotesia were seen after treatment of larvae with the derivatives J-3370 and J-2581.No anti-juvenile hormone action of J-2710 was observed. J-2710-treated M. sexta larvae showed no precocious metamorphosis and the developmental effects of J-2710 were not prevented by co-application of the juvenile hormone analogue methoprene in doses ranging from 1 to 100 μg/larva. Moreover, J-2710 had no effect on the action of methoprene in the black larval assay for juvenile hormone-like activity, unlike results reported to occur using the Galleria wax wound assay.     

The activity of the corpora allata in the fourth and fifth larval instars of the migratory locust

The presence of juvenile hormone in the haemolymph of larvae of Locusta has been detected by a modified Galleria bioassay and these results are compared with indirect methods of estimating corpus allatum activity. Juvenile hormone is present in the haemolymph during the fourth larval instar except on the last day of the instar, and is absent from the haemolymph of the fifth and final larval instar except on the last day of the instar. Changes in the volumes of the corpora allata simply reflect changes in the growth of the whole insect and are of no value in predicting endocrine activity. Changes in the size of the cells of the corpora allata can be correlated with the presence of juvenile hormone in the haemolymph in the fourth larval instar, but similar changes in cell size occur in the fifth larval instar when no juvenile hormone is present in the haemolymph. The effects of the implantation of corpora allata are unreliable as estimates of corpus allatum activity as isolated corpora allata from fifth instar larvae release juvenile hormone. Indirect methods of measuring corpus allatum activity are thus shown to be unreliable. The R_f value of Locusta juvenile hormone as determined by thin-layer chromatography differs from that of Roeller's juvenile hormone, suggesting that the two hormones might be chemically distinct.     

Juvenile hormone changes associated with diapause induction, maintenance, and termination in the beet webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

At 22°C and under a long-day photoperiod of L:D 16:8, all the last fifth instar Loxostege sticticalis larvae undergo prepupal stage and pupate without diapause. Under a short-day photoperiod of L:D 12:12, in contrast, they all enter diapause with approximately 36 days diapause maintenance and then terminate diapause spontaneously, although only 44% of the larvae terminated diapause successfully. Changes in hemolymph juvenile hormone (JH I) titers of diapause-destined larvae across diapause induction, maintenance and termination were examined using HPLC, and were compared with those of non-diapause-destined larvae from the fifth instar through pupation. JH I titer of the earliest fifth instar diapause-destined larvae remained at a high level with a peak of 220.4 ng/ml, though it decreased continuously to a minimum of 69.0 ng/ml on day 5 in the fifth instar when the larvae stopped feeding to enter diapause. During the diapause maintenance, JH I titer of the mature larvae increased significantly and maintained a high level until day 31 in prepupae. JH I titer declined and fluctuated at low level from 5 days before pupation. In contrast, JH I titer of both the fifth instar non-diapause-destined larvae and prepupae remained and fluctuated at low level consistently, as well as decreased before pupation. These results indicate that diapause induction and maintenance in this species might be a consequence of high JH, whereas diapause termination can be attributed to low JH titer, which was in agreement with the hormonal regulation observed in many other larval-diapausing insects.     

The hormonal regulation of the larval diapause in the codling moth, Laspeyresia pomonella (Lep. Tortricidae)

The hormonal control of the facultative diapause of the codling moth has been investigated. The diapause can be divided into 4 phases or periods: (1) diapause induction by short-day conditions (SD) in young larvae, (2) initiation of the diapause in the early last larval instar by a high titre of juvenile hormone, (3) onset and maintenance of diapause with inactivity of the neuroendocrine system, as evidenced by the results of neck-ligation experiments, (4)termination of diapause by the production of ecdysteroid.Diapause-induced larvae pupated after spinning the cocoon, if the state of induction was changed by injection with the anti-juvenile hormone precocene II at the beginning of the last larval instar and subsequent results of neck-ligation experiments, (4) termination of diapause by the production of ecdysteroid. treated with juvenile hormone during the first 1.5 days after the last larval moult and subsequently reared under SD. Under LD, continuous application of juvenile hormone during the last larval instar and after spinning did not prevent the insects from moulting to either a supernumerary larva, a pupa or a larval-pupal intermediate. Termination of diapause, i.e. pupation, was achieved by injecting diapausing larvae with 20-hydroxyecdysone. Although juvenile hormone was found to have a prothoractropic effect in diapausing larvae, no pupal moult could be induced by the application of the hormone. Contrary to the hormonal situation before pupation of nondiapausing larvae, no juvenile hormone could be detected before or during the pupation of larvae after diapause.     

Morphogenetic effects of precocenes on three aphid species

The disruptive effects of precocenes I, II and III on metamorphosis were assessed in apterous viviparae of Acyrthosiphon pisum, Aphis fabae and Megoura viciae. Prenatally applied precocene I had no effect, precocene II caused supernumerary moulting (metathetely) in M. viciae but precocene III induced both precocious adult development (prothetely) and metathetely in all three species. the latter compound also promoted precocious adult development in alate virginoparae, males and ovipara-producers of M. viciae. However, gynoparae of A. fabae, and oviparae of M. viciae and A. pisum were resistant to this action. When topically applied to young adults of A. fabae or M. viciae none of the precocenes caused alate progeny to be produced but all did so in A. pisum. However, the previous supposition that precocene II promotes wing development because it decreases juvenile hormone titres should be viewed with caution as: (a) Precocene II was more potent than precocenes I and III when inducing wing formation but did not provoke precocious adult development, an overt indication of low juvenile hormone titres. (b) Precocene I and III were equally effective in inducing alate progeny but only the latter provoked precocious adult development. (c) Attempts to prevent or reduce the alata-inducing property of precocene II with juvenile hormone I were unsuccessful.     

Mating behaviour of Plodia interpunctella reared on juvenile hormone-treated diet

Treatment of larval Plodia interpunctella with sublethal doses of juvenile hormone repressed mating of the adults. This repression did not result from a reduced content of sex pheromone of females, but it may have been caused in part by reduced calling behaviour and abnormal antennae. An absence of juvenile hormone at the end of larval life is necessary for the development of normal reproductive behaviour of the adult.     

Treatment of larvae with repeated doses of precocene II induces precocious metamorphic changes in Spodoptera mauritia (Lepidoptera: Noctuidae)

In Spodoptera mauritia repeated daily treatments of larvae with 40 μg of precocene II throughout the fifth and sixth instar larval period had no effect on the larval-larval period but prolonged larval-pupal ecdysis. The resulting pupae showed precocious adult differentiation of mouth parts, wings, eyes, legs, and fat body.     

The Apis mellifera pupal melanization program is affected by treatment with a juvenile hormone analogue

Apis mellifera treated during different developmental phases with pyriproxyfen, a juvenile hormone analogue, show profound alterations in cuticular pigmentation and sclerotization. When the treatment is effected during the feeding phase of the fifth larval instar (LF5), the pupal development is blocked and pigmentation does not occur. Treatment of older larvae, at the spinning phase of the fifth larval instar (LS5), of prepupae (PP) or pupae at the beginning of the pupal period (Pw, white-eyed, unpigmented cuticle pupae) does not impair pigmentation, but, instead, this process is accelerated, intensified and abnormal. Hormonal treatment during these developmental phases (LS5, PP and Pw) induces earlier activity of phenoloxidase, an enzyme of the reaction chain leading to melanin synthesis. Treated pupae have significantly higher enzymatic levels and show a graded response in phenoloxidase activity after treatment with 0.1, 1 or 5&mgr;g pyriproxyfen. Besides pigmentation, other developmental events were also altered in treated bees: pupal development was shortened, and the expression of esterase-6 activity, the onset of which coincides with the beginning of pigmentation, was shifted with the precocious initiation of this process in treated pupae. The significance of these results is discussed in relation to the mode of hormonal action on cuticular pigmentation in insects.     

Evidences for a stage-specific juvenile hormone binding protein in the hemolymph of the silkworm,Bombyx mori L.: Identification and characterization by photoaffinity labeling and immunological analyses

Two molecular forms of juvenile hormone binding proteins were identified in the larval hemolymph of Bombyx mori by photoaffinity labeling. One form having an Mr of 33 kDa was present constantly in the hemolymph of the third to the fifth instar larvae while the other form having an Mr of 35 kDa was detected in the hemolymph until in the early fifth instar larvae but not in the prewandering larvae and prepupae. A 33 kDa binding protein was purified by hydrophobic interaction chromatography, gel filtration, and native PAGE. Antiserum against 33 kDa binding protein cross-reacted with 35 kDa binding protein on Western blots, suggesting that these binding proteins shared the same epitopes. From the results of saturation binding assays, it was inferred that 33 and 35 kDa binding proteins had a similar binding affinity for JH 1. It was revealed that one of these binding proteins, 35 kDa binding protein, was produced in the fat body in a stage-specific manner: fat body of the early fifth instar larvae synthesized both 33 and 35 kDa binding proteins while that of prewandering larvae synthesized only 33 kDa binding protein. © 1996 Wiley-Liss, Inc.     

Behavioral changes and growth inhibition in last instar larvae of Heliothis zea induced by oral and topical application of precocene II

In diet choice tests, newly-ecdysed fifth instar Heliothis zea larvae randomly chose diet containing 4 mM precocene II or diet without precocene II but initially preferred to feed on diet without precocene II. After two days, however, they were found more frequently on diet containing precocene II. Nevertheless, larval growth and development were inhibited when forced to eat diet containing precocene II. Removal of the maxillae, the site of the primary gustatory receptors, did not prevent the growth inhibition caused by larval consumption of diet with precocene II. Topical treatments with precocene II also caused larval growth inhibition, and daily treatments were more detrimental to the larvae than a large single dose. Addition of methylenedioxyprecocene (6,7-methylenedioxy-2,2-dimethylchromene) to the diet did not reverse the observed larval growth inhibition and this compound was itself significantly toxic. These results indicate that larval growth and development are disrupted after precocene II ingestion, but not because of preingestive discrimination by olfaction and gustation.     

Juvenile hormone-dependent vitellogenin synthesis in Locusta migratoria fat body: Inducibility related to sex and stage

Juvenile hormone (JH)-dependent vitellogenin (Vg) synthesis in the fat body of Locusta migratoria is normally limited to sexually mature adult females. As a step toward examining the basis of this limitation, we have tested female and male locusts in a series of stages after the third larval molt for inducibility of Vg synthesis by the synthetic JH analog, methoprene. We find that in the fourth and fifth larval instars fat body of both sexes can be induced to produce Vg, but in the adult stage females respond strongly while no more than trace amounts can be induced in males. Quantitative assays show relative responsiveness in the order: adult female > fifth instar female > fifth instar male ? adult male. During the fifth instar of both sexes, maximal vitellogenic response was obtained in midinstar. After the larval-adult ecdysis, female fat body was unresponsive during the first 4 days, then responsiveness increased and by Day 8 after ecdysis fat bodies were fully as competent to produce Vg as at Day 14, the usual maximum of the first vitellogenic cycle due to endogenous JH. Larval and adult female fat bodies implanted into male larvae are competent for Vg synthesis after metamorphosis, so that the differences between adult male and female cannot be imposed by the male milieu intérieur during the larval-adult molt. In male and female precocious adults, produced by treatment of fourth instars with precocene, fat body responded to methoprene as in normal adults. We conclude that factors intrinsic to the fat body cells, determined early in development, are responsible for differential gene programing in males and females, which is partially expressed by the fifth instar but fully manifest only after a molt in the absence of JH.     

Juvenile hormone coordinates the regulation of the hemolymph ecdysteroid titer during pupal commitment in Manduca sexta

The timing and magnitude of the pupal commitment peak in the hemolymph ecdysteroid titer of fifth instar Manduca sexta larvae are controlled by the combined effects of prothoracicotropic hormone (PTTH), a prothoracic gland-stimulating factor present in the hemolymph, and the biosynthetic competence of the prothoracic glands themselves. The present data indicate those individual effects are coordinated by juvenile hormone (JH): (1) Treatment of larvae with the JH analog (7S)-hydroprene prevents the normal precommitment drop in the titer of the stimulatory factor; (2) treatment of larvae with (7S)-hydroprene suppresses in a dose- and time-dependent manner the biosynthetic competence of the prothoracic glands; and (3) (7S)-hydroprene acts directly on the brain to inhibit the release of PTTH in vitro. Thus, during Manduca development, a drop in the JH titer early in the fifth instar results in a rapid drop in the titer of the stimulatory factor, the gradual acquisition by prothoracic glands of biosynthetic competence, and lastly, the gated release of PTTH into the hemolymph. The resulting increase in ecdysone synthesis by the prothoracic glands gives rise to the small peak in the ecdysteroid titer that drives pupal commitment.     

Juvenile hormone esterase activity during the last larval and pupal stages of Tenebrio molitor

In vitro analysis of juvenile hormone esterase activity of haemolymph of T. molitor was performed during the end of post-embryonic development. Weak activity was found in penultimate stage larvae as in the major part (except the last day) of last-larval instar, while very high activity was monitored in the early pupae (female or male).This pupal peak was the only one detected during development in the insect, coinciding with the pupal juvenile hormone sensitive period. The first juvenile hormone sensitive period, during the lastlarval instar, does not seem to be protected by any juvenile hormone esterase activity in contrast to other species. These results suggest a central control for the drop in juvenile hormone level ceasing synthesis by the corpora allata after integration of external stimuli. This hypothesis could explain the natural occurrence of prothetelic larvae, the absence of pupal adult intermediates and the variable number of instars in Tenebrio.     

The endocrine basis for developmentally stationary prepupae in larvae ofTrichoplusia ni pseudoparasitized byChelonus insularis

Summary Larvae of the cabbage looper,Trichoplusia ni, precociously initiate metamorphosis in the penultimate instar when parasitized byChelonus insularis. Some larvae developing from stung eggs precociously spin cocoons, but upon dissection contain no live or obvious parasites. Such pseudoparasitized larvae greatly slow down in development as prepupae, due to a suppressed ecdysteroid titer which in turn may be caused by a suppressed juvenile hormone titer.Abbreviations JH juvenile hormone - JHA juvenile hormone analog - JHE juvenile hormone esterase     

Role of juvenile hormone in regulating tyrosine glucoside synthesis for pupal tanning in Manduca sexta (L.)

Tyrosine glucoside (α-d-glucopyranosyl-O-l-tyrosine) serves as a reservoir of tyrosine and glucose for pupal and adult cuticle formation, tanning, and pigmentation in several Lepidopteran insects. In the tobacco hornworm, Manduca sexta (L.), detectable quantities appear in the haemolymph 1–2 days after ecdysis of the fifth instar and very high concentrations accumulate between the fourth and eighth days of the stadium. If juvenile hormone II or a mimic (methoprene) is injected into fifth-instar larvae at 24-h intervals after ecdysis, tyrosine glucoside synthesis is almost completely suppressed. Temporary starvation of newly ecdysed larvae that results in the maintenance of a high endogenous juvenile hormone titre, also suppresses and delays the onset of tyrosine glucoside synthesis. The decrease and eventual disappearance of juvenile hormone after ecdysis of the last-larval instar appears to be a necessary prerequisite for the synthesis or activation of tyrosine glucoside synthetase along with the initiation of other metamorphic events.     

Action of two juvenile hormone antagonists on lepidopteran epidermis

The juvenile hormone antagonist ETB (ethyl-4-2(t-butylcarbonyloxy)-butoxybenzoate) caused formation of precocious larval-pupal intermediates after the 4th (penultimate)-larval instar of the tobacco hornworm, Manduca sexta, when 50 μg were applied to any 3rd stage larvae or to 4th stage larvae within 12 hr after ecdysis. This dose was most effective within 12 hr after ecdysis to the 3rd stage. In the black mutant larval assay for juvenile hormone, ETB had activity, 0.75 μg per larva giving half-maximal score. In vitro ETB acted as a juvenile hormone to prevent the ecdysteroid-induced change in commitment at concentrations above 0.1 μg/ml with an ED₅₀ at 2.8 μg/ml and as a partial juvenile hormone antagonist to 0.1 μg/ml juvenile hormone I at concentrations between 10^?3 and 10^?2 μg/ml. By contrast, EMD (ethyl-E-3-methyl-2-dodecenoate) had little juvenile hormone-like activity in vitro up to its limits of solubility (100 μg/ml) and exhibited sporadic partial juvenile hormone antagonistic activity in vitro at concentrations between 1 and 100 μg/ml. Since these concentrations were 10–1000 times that of juvenile hormone I in the medium, EMD apparently is not an efficient competitor.     

Activity of disconnected corpora allata in Locusta migratoria: Juvenile hormone biosynthesis in vitro and physiological effects in vivo

Severance of nervi corporis allati I (NCA I) in day-1 adult female Locusta migratoria resulted in a significant decrease and a loss of the characteristic pattern of juvenile hormone biosynthesis by the corpora allata as determined by radiochemical assay. This decrease in the rate of juvenile hormone biosynthesis was not reflected in basal oöcyte growth. The lengths of the oöcytes were the same in NCA-transectioned and in the sham-operated females. The effect of severance of both NCA I and NCA II on juvenile hormone biosynthesis and ovarian maturation was similar to the effect of NCA I severance only.Rate of juvenile hormone biosynthesis by corpora allata of fourth-instar larvae exhibited a maximum of activity in the middle of the stadium. The severance of NCA I early in the stadium resulted in a very low rate of juvenile hormone biosynthesis and a disappearance of this peak. In NCA I-transectioned larvae, the duration of the stadium was significantly increased although larvae moulted into normal fifth instar.