Larval testes of the tobacco budworm: a new source of insect ecdysteroids

Comparative analysis of testicular fusion in Spodoptera litura (cutworm) and Bombyx mori (silkworm): Histological and transcriptomic insights

Spodoptera litura commonly known as the cutworm, is among the most destructive lepidopteran pests affecting over 120 plants species. The powerful destructive nature of this lepidopteran is attributable to its high reproductive capacity. The testicular fusion that occurs during metamorphosis from larvae to pupa in S.litura positively influences the reproductive success of the offspring. In contrast, Bombyx mori, the silkworm, retains separate testes throughout its life and does not undergo this fusion process. Microscopic examination reveals that during testicular fusion in S.litura, the peritoneal sheath becomes thinner and more translucent, whereas in B.mori, the analogous region thickens. The outer basement membrane in S.litura exhibits fractures, discontinuity, and uneven thickness accompanied by a significant presence of cellular secretions, large cell size, increased vesicles, liquid droplets, and a proliferation of rough endoplasmic reticulum and mitochondria. In contrast, the testicular peritoneal sheath of B.mori at comparable developmental stage exhibits minimal change. Comparative transcriptomic analysis of the testicular peritoneal sheath reveals a substantial difference in gene expression between the two species. The disparity in differential expressed genes (DEGs) is linked to an enrichment of numerous transcription factors, intracellular signaling pathways involving Ca2+ and GTPase, as well as intracellular protein transport and signaling pathways. Meanwhile, structural proteins including actin, chitin-binding proteins, membrane protein fractions, cell adhesion, extracellular matrix proteins are predominantly identified. Moreover, the study highlights the enrichment of endopeptidases, serine proteases, proteolytic enzymes and matrix metalloproteins, which may play a role in the degradation of the outer membrane. Five transcription factors-Slforkhead, Slproline, Slcyclic, Slsilk, and SlD-ETS were identified, and their expression pattern were confirmed by qRT-PCR. they are candidates for participating in the regulation of testicular fusion. Our findings underscore significant morphological and trancriptomic variation in the testicular peritoneal sheath of S.litura compared to the silkworm, with substantial changes at the transcriptomic level coinciding with testicular fusion. The research provides valuable clues for understanding the complex mechanisms underlying this unique phenomenon in insects.

Dichotomous sperm in Lepidopteran insects: a biorational target for pest management

Lepidoptera are unusual in possessing two distinct kinds of sperm, regular nucleated (eupyrene) sperm and anucleate (apyrene) sperm ('parasperm'). Sperm of both types are transferred to the female and are required for male fertility. Apyrene sperm play 'helper' roles, assisting eupyrene sperm to gain access to unfertilized eggs and influencing the reproductive behavior of mated female moths. Sperm development and behavior are promising targets for environmentally safer, target-specific biorational control strategies in lepidopteran pest insects. Sperm dimorphism provides a wide window in which to manipulate sperm functionality and dynamics, thereby impairing the reproductive fitness of pest species. Opportunities to interfere with spermatozoa are available not only while sperm are still in the male (before copulation), but also in the female (after copulation, when sperm are still in the male-provided spermatophore, or during storage in the female's spermatheca). Biomolecular technologies like RNAi, miRNAs and CRISPR-Cas9 are promising strategies to achieve lepidopteran pest control by targeting genes directly or indirectly involved in dichotomous sperm production, function, or persistence.

Diallyl trisulfide reduced the reproductive capacity of male Sitotroga cerealella via the regulation of juvenile and ecdysone hormones

Environmental pollution and resistance in animals are major concerns for the application of synthetic pesticides. Diallyl trisulfide (DAT), an active compound in garlic essential oil, is a novel tool for active and safe control of agricultural insect pests. In this study, we analysed the effects of DAT (0.01 μL/L) on the protein content in male reproductive tissues (accessory glands, ejaculatory ducts, and testis), and juvenile hormone (JH) and ecdysone titres in a highly detrimental pest of stored products, Sitotroga cerealella. Evaluation of the expression profile of JH and ecdysone pathway-related genes in various tissues indicated that the accessory gland protein and ecdysone titres were markedly decreased after DAT fumigation, whereas the testis protein content and JH titre were increased. However, the protein content of the ejaculatory ducts remained unchanged between the treated and control groups. Further investigation revealed that DAT disrupted the mRNA expression of key enzymes involved in JH and ecdysone pathways. While increased mRNA levels of juvenile hormone acid O-methyltransferase (JHMAT) and Kruppel homologue 1 (Kr-h1) were observed after 4 and 7 h of DAT fumigation, the levels of juvenile hormone epoxide hydrolase (JHEH) were substantially reduced 3 h post-fumigation. mRNA levels of the ecdysone-responsive gene, FTZF1, and cytochrome P450 enzyme, CYP315A1, were notably decreased at 7 h and 4 h, respectively, post-fumigation, whereas CYP314A1 and CYP302A1 mRNA levels decreased after 3 h and 4 h, respectively. While DAT fumigation disrupted sperm number in the testis, ejaculatory ducts, and seminal vesicles, topical application of the 20-hydroxyecdysone (20E) analogue also lowered sperm number in the ejaculatory ducts. Topical application of methoprene, a JH analogue, increased the protein content in the testes, but not in the accessory glands or ejaculatory ducts. However, the survival rate was not affected by the topical application of methoprene or 20E. These data suggest that DAT regulates JH and ecdysone via its molecular pathway genes and modulates endocrine secretion during the male reproductive process.

Stem cell autotomy and niche interaction in different systems

The best known cases of cell autotomy are the formation of erythrocytes and thrombocytes (platelets) from progenitor cells that reside in special niches. Recently, autotomy of stem cells and its enigmatic interaction with the niche has been reported from male germline stem cells (GSCs) in several insect species. First described in lepidopterans, the silkmoth, followed by the gipsy moth and consecutively in hemipterans, foremost the milkweed bug. In both, moths and the milkweed bug, GSCs form finger-like projections toward the niche, the apical cells (homologs of the hub cells in Drosophila). Whereas in the milkweed bug the projection terminals remain at the surface of the niche cells, in the gipsy moth they protrude deeply into the singular niche cell. In both cases, the projections undergo serial retrograde fragmentation with progressing signs of autophagy. In the gipsy moth, the autotomized vesicles are phagocytized and digested by the niche cell. In the milkweed bug the autotomized vesicles accumulate at the niche surface and disintegrate. Autotomy and sprouting of new projections appears to occur continuously. The significance of the GSC-niche interactions, however, remains enigmatic. Our concept on the signaling relationship between stem cell-niche in general and GSC and niche (hub cells and cyst stem cells) in particular has been greatly shaped by Drosophila melanogaster. In comparing the interactions of GSCs with their niche in Drosophila with those in species exhibiting GSC autotomy it is obvious that additional or alternative modes of stem cell-niche communication exist. Thus, essential signaling pathways, including niche-stem cell adhesion (E-cadherin) and the direction of asymmetrical GSC division - as they were found in Drosophila - can hardly be translated into the systems where GSC autotomy was reported. It is shown here that the serial autotomy of GSC projections shows remarkable similarities with Wallerian axonal destruction, developmental axon pruning and dying-back degeneration in neurodegenerative diseases. Especially the hypothesis of an existing evolutionary conserved “autodestruction program” in axons that might also be active in GSC projections appears attractive. Investigations on the underlying signaling pathways have to be carried out. There are two other well known cases of programmed cell autotomy: the enucleation of erythroblasts in the process of erythrocyte maturation and the segregation of thousands of thrombocytes (platelets) from one megakaryocyte. Both progenitor cell types - erythroblasts and megakaryocytes - are associated with a niche in the bone marrow, erythroblasts with a macrophage, which they surround, and the megakaryocytes with the endothelial cells of sinusoids and their extracellular matrix. Although the regulatory mechanisms may be specific in each case, there is one aspect that connects all described processes of programmed cell autotomy and neuronal autodestruction: apoptotic pathways play always a prominent role. Studies on the role of male GSC autotomy in stem cell-niche interaction have just started but are expected to reveal hitherto unknown ways of signal exchange. Spermatogenesis in mammals advance our understanding of insect spermatogenesis. Mammal and insect spermatogenesis share some broad principles, but a comparison of the signaling pathways is difficult. We have intimate knowledge from Drosophila, but of almost no other insect, and we have only limited knowledge from mammals. The discovery of stem cell autotomy as part of the interaction with the niche promises new general insights into the complicated stem cell-niche interdependence.

Study on ecdysteroid levels and gene expression of enzymes related to ecdysteroid biosynthesis in the larval testis of Spodoptera littoralis

We investigated here the ecdysteroid titers and the expression of six genes coding for known enzymes of the ecdysteroid biosynthesis in the testes of last instar larvae of the pest cotton leafworm, Spodoptera littoralis. We showed that the timing of the ecdysteroid profile was the same in testes and in hemolymph, with a small peak at day 2 and a large one at day 4 after ecdysis. Ecdysone and 20-hydroxyecdysone (20E) were detected in both tissues. 20E was the major ecdysteroid in testes and in hemolymph from day 4. Interestingly, the gene expression of the steroidogenetic enzymes, Neverland, and the five cytochrome P450 enzymes encoded by the Halloween genes was confirmed in the testes, and varied during the instar. However, from the data obtained so far, we cannot conclude that the measured ecdysteroids in the testes result from the activity of the genes under study. Indeed, it is suggested that the ecdysone produced centrally in the prothoracic glands, could have been transformed into 20E in the testes, where Sl-shade is well expressed.

Structural characterization and primary in vitro cell culture of locust male germline stem cells and their niche

The establishment of in vitro culture systems to expand stem cells and to elucidate the niche/stem cell interaction is among the most sought-after culture systems of our time. To further investigate niche/stem cell interactions, we evaluated in vitro cultures of isolated intact male germline-niche complexes (i.e., apical complexes), complexes with empty niche spaces, and completely empty niches (i.e., isolated apical cells) from the testes of Locusta migratoria and the interaction of these complexes with isolated germline stem cells, spermatogonia (of transit-amplifying stages), cyst progenitor cells, cyst progenitor cell-like cells, cyst cells, and follicle envelope cells. The structural characteristics of these cell types allow the identification of the different cell types in primary cultures, which we studied in detail by light and electron microscopy. In intact testes germline stem cells strongly adhere to their niche (the apical cell), but emigrate from their niche and form filopodia if the apical complex is put into culture with "standard media." The lively movements of the long filopodia of isolated germline stem cells and spermatogonia may be indicative of their search for specific signals to home to their niche. All other incubated cell types (except for follicle envelope cells) expressed rhizopodia and lobopodia. Nevertheless isolated germline stem cells in culture do not migrate to empty niche spaces of nearby apical cells. This could indicate that apical cells lose their germline stem cell attracting ability in vitro, although apical cells devoid of germline stem cells either by emigration of germline stem cells or by mechanical removal of germline stem cells are capable of surviving in vitro up to 56 days, forming many small lobopodia and performing amoeboid movements. We hypothesize that the breakdown of the apical complex in vitro with standard media interrupts the signaling between the germline stem cells and the niche (and conceivably the cyst progenitor cells) which directs the typical behavior of the male regenerative center. Previously we demonstrated the necessity of the apical cell for the survival of the germline stem cell. From these studies we are now able to culture viable isolated germline stem cells and all cells of its niche complex, although DNA synthesis stops after Day 1 in culture. This enables us to examine the effects of supplements to our standard medium on the interaction of the germline stem cell with its niche, the apical cell. The supplements we evaluated included conditioned medium, tissues, organs, and hemolymph of male locusts, insect hormones, mammalian growth factors, Ca(2+) ion, and a Ca(2+) ionophore. Although biological effects on the germline stem cell and apical cell could be detected with the additives, none of these supplements restored the in vivo behavior of the incubated cell types. We conclude that the strong adhesion between germline stem cells and apical cells in vivo is actively maintained by peripheral factors that reach the apical complex via hemolymph, since a hemolymph-testis barrier does not exist. The in vitro culture model introduced in this study provides a platform to scan for possible regulatory factors that play a key role in a feedback loop that keeps germline stem cell division and sperm disposal in equilibrium.

Parasitic castration of Plutella xylostella larvae induced by polydnaviruses and venom of Cotesia vestalis and Diadegma semiclausum

In the present study, we used gamma-ray to irradiate the female parasitoids to make wasp eggs infertile, resulting in pseudoparasitization, which allowed the analysis of maternal secretions such as polydnaviruses (PDVs) and venom in the absence of larval secretions or teratocytes by the growing parasitoids. We then investigated the spermatogenesis and components of testicular proteins of male Plutella xylostella larvae pseudoparasitized by two endoparasitoids (Cotesia vestalis and Diadegma semiclausum). The results showed that pseudoparasitism by the two endoparasitoids at the early third instar host larvae both induced smaller testes in size than those of nonparasitized host larvae. Both of them caused parasitic castration, and the degree of castration is almost as severe as in naturally parasitized hosts. This suggested that PDVs and venom played a major role in the degeneration of host testes. There are significant differences in the degree of castration induced by the two endoparasitoids, with respect to testicular growth, testicular protein concentrations, and histological changes of germ cells. Cotesia vestalis bracovirus always has a significantly stronger effect on host testicular growth and development than D. semiclausum ichnovirus. SDS-PAGE analysis indicated that synthesis of P 65 and P 67 proteins were clearly inhibited in testes of hosts that were pseudoparasitized by C. vestalis while reduction in synthesis of other proteins was not evident.

Gonadal ecdysteroidogenesis in arthropoda: occurrence and regulation

Ecdysteroids are multifunctional hormones in male and female arthropods and are stored in oocytes for use during embryogenesis. Ecdysteroid biosynthesis and its hormonal regulation are demonstrated for insect gonads, but not for the gonads of other arthropods. The Y-organ in the cephalothorax of crustaceans and the integument of ticks are sources of secreted ecdysteroids in adults, as in earlier stages, but the tissue source is not known for adults in many arthropod groups. Ecdysteroid metabolism occurs in several tissues of adult arthropods. This review summarizes the evidence for ecdysteroid biosynthesis by gonads and its metabolism in adult arthropods and considers the apparent uniqueness of ecdysteroid hormones in arthropods, given the predominance of vertebrate-type steroids in sister invertebrate groups and vertebrates.

Anopheles gambiae males produce and transfer the vitellogenic steroid hormone 20-hydroxyecdysone to females during mating

In female insects, the steroid hormone 20-hydroxyecdysone (20E) plays a major role in activating vitellogenesis, a process required for egg development. By contrast with vertebrates, production of large amounts of hormonal steroids has not been reported in adult male insects. In the present study, we analyzed steroidogenesis in both male and female adult of the malaria mosquito Anopheles gambiae and we found that A. gambiae male mosquitoes produce high amounts of the steroid hormone 20E. Importantly, we found that male accessory glands, but not testes, are the source of 20E. Moreover, this steroid hormone is stored in male accessory glands and delivered to females during mating. These findings suggest that male 20E may not act as a true male sex steroid, but more likely as an allohormone. Our results give new insights into species-specific physiological processes that govern the reproductive success of the malaria mosquito. This could thus lead to the identification of new target genes for manipulating male and/or female reproductive success, a promising way to reduce or eliminate mosquito population and therefore to control malaria transmission.

Apoptosis of male germ-line stem cells after laser ablation of their niche

Male germ-line stem cells (GSCs) and their niche-the apical cells or hub cells-display a unique feature at the apices of insect testicular follicles. In the locust, Locusta migratoria, the niche consists of only one large apical cell surrounded by about 60 GSCs. The apical cell can be readily identified in the intact follicle. Using laser ablation it is feasible to destroy the apical cell exclusively without injuring neighboring GSCs or any other cells. The most immediate effect on GSCs is the loss of their structural polarity. Beginning about 3 h after laser treatment chromatin starts to clump and condense in individual GSCs, and some show the first signs of cellular breakdown. These symptoms intensify during the 96-h observation period after laser ablation of the apical cell. TUNEL staining and electron microscopic observations confirm an apoptotic cell death of the GSCs. Laser ablation of individual GSCs had no effect on neighboring GSCs or the apical cell. Destroyed apical cells were not replaced during the observation period. Mitotic divisions of GSCs ceased after about 24 h after apical cell ablation. It is speculated that it might be a general principle in stem cell-niche relationships that stem cells undergo apoptosis when the niche is dysfunctional. This could be a control mechanism to prevent tumor growth of orphaned GSCs.

Ecdysteroids and juvenile hormones of whiteflies, important insect vectors for plant viruses

Ecdysteroids and juvenile hormones (JHs) regulate many physiological events throughout the insect life cycle, including molting, metamorphosis, ecdysis, diapause, reproduction, and behavior. Fluctuation of whitefly ecdysteroid levels and the identity of the whitefly molting hormone (20-hydroxyecdysone) have only been reported within the last few years. An ecdysteroid commitment peak that is associated with the reprogramming of tissues for a metamorphic molt in many holometabolous and some hemimetabolous insect species was not observed in last nymphal instars of either the sweet potato whitefly, Bemisia tabaci (Biotype B), or the greenhouse whitefly, Trialeurodes vaporariorum. Ecdysteroids reach peak levels 1-2 days prior to the initiation of the nymphal-adult metamorphic molt. Adult eye and wing differentiation which signal the onset of this molt begin earlier in 4th instar T. vaporariorum (Stages 4 and 5, respectively) than in B. tabaci (Stage 6), and the premolt peak is 3-4 times greater in B. tabaci ( approximately 400 fg/microg protein) than in T. vaporariorum ( approximately 120 fg/microg protein). The JH of B. tabaci nymphs and eggs was found to be JH III, supporting the view that JHs I and II are, with rare exception, only present in lepidopteran insects. In B. tabaci eggs, JH levels were approximately 10 times greater on day 2/3 (0.44 fg/egg or 0.54 ng/g) than on day 5 (0.04 fg/egg or 0.054 ng/g) post-oviposition. Approximately, 1.4 fg/2nd-3rd instar nymph (0.36 ng/g) was detected. It is probable that the relatively high level of JH in day 2/3 eggs is associated with the differentiation of various whitefly tissues during embryonic development.

Testis ecdysiotropic peptides in Rhodnius prolixus: biological activity and distribution in the nervous system and testis

In Rhodnius prolixus, testes from both pharate adult and adult males are shown to produce and release ecdysteroids in vitro. Proteinaceous brain extracts from these stages caused stimulation of ecdysteroid production by testes of unfed adults. Therefore, the brain of Rhodnius contains peptides with testis ecdysiotropic activity. The Lymantria testis ecdysiotropin (LTE) also stimulated the in vitro production of ecdysteroids by unfed adult testis but had no stimulatory effect on prothoracic glands. Western blot analysis of brain peptides using anti-LTE revealed the presence of several medium to small size immunoreactive peptides. Two of these peptides with sizes of 16.8 and 11.0 kDa were present only during pharate adult development and the adult stage. Immunohistochemical analysis using confocal laser scanning microscopy revealed abundant LTE-immunoreactive material in cytoplasmic granules of specific neurosecretory cells in the brain and suboesophageal ganglion and the epithelium of the testis sheath. Clusters of two cytologically distinct cell types were seen within the medial neurosecretory cells (MNC) and also a pair of neurons in the posterior protocerebrum. Feeding in both larvae and adult males resulted in massive release of LTE-immunoreactive material from the MNC cells, suggesting a role of LTE-related peptides in both larval-adult development and in male reproductive development. Release from the MNC cells of LTE-immunoreactive material exhibited a clear daily cycling during larval-adult development, which was synchronous with the rhythms of release of prothoracicotropic hormone and bombyxin reported previously. The testis sheath exhibited intense immunofluorescence in pharate adults and unfed adults, which disappeared following a blood meal. It is concluded that LTE-related peptides are developmentally regulated in several locations and may act as ecdysiotropins in Rhodnius. Those in the MNC cells are very probably classical hormones, i.e. are transported to their target sites via the insect haemolymph.

No evidence of androgenic hormone from the testes of the glowworm, Lampyris noctiluca

The widely accepted concept, stating that insects have no true sex hormones, and that primary as well as secondary sex characteristics are controlled by the genetic inventory of each single cell, is challenged by the report of Naisse, J. [1966a. Contrôle endocrinien de la différenciation sexuelle chez l'Insecte Lampyris noctiluca (Coléoptère Malacoderme Lampyride). I. Rôle androgène des testicules, Arch. Biol. Liège, 77, 139-201] on the discovery of an androgenic hormone in the glowworm, Lampyris noctiluca. This case is of special interest, since it may point to an ancestral mode of sex differentiation in arthropods, considering that androgenic hormones have been discovered and characterized in crustaceans. With the intention to further characterize the androgenic hormone in the glowworm, and to establish a bioassay, we tried to repeat Naisses's transplantation experiments, according to which, androgen producing testes implanted into female larvae should masculinize the female's gonads and all other female features of the sexually strongly dimorphic pupae and beetles. We found, however, that larval development of the glowworm proceeded differently than reported by Naisse, and that sexing of larvae was not possible. Therefore, "blind" transplantations had to be performed. The results of our experiments showed, however, unequivocally, that an androgenic hormone, allegedly synthesized by the apical tissue of larval testes, was not involved in sex differentiation. We found, that in transplants, where testes and ovaries were even located closely to each other, both matured and formed spermatozoa in the testes and vitellogenic oocytes in the ovaries. Masculinization of ovaries was never observed, and the sex of the recipient was always in accordance with the sex of its own gonads. We therefore conclude that Lampyris noctiluca does not synthesize an androgenic hormone in the larval testes, and that sex differentiation is probably regulated as in other insect species. (The apical testis tissue of the glowworm was previously shown to represent progenitors of spermatogonial cyst cells [Balles, S., Maas, U., Sehn, E., Dorn, A., 2002. Testis differentiation in the glowworm, Lampyris noctiluca, with special reference to the apical tissue. J. Morphol. 251, 22-37].).

Testis differentiation in the glowworm, Lampyris noctiluca, with special reference to the apical tissue

The gonads of Lampyris noctiluca are sexually undifferentiated during the first larval instars. They consist of many gonadal follicles that include the germ stem cells enclosed by the somatic cells of the follicle wall. Follicle wall cells are more numerous at the follicle apices than at the distal parts, but different cell types cannot be distinguished. In male larvae, the appearance of apical follicle tissue, derived from follicle wall cells, marks the onset of testis differentiation. When maximally expressed, the apical tissue occupies about the upper half of the testis follicles and can be observed in larvae of the fifth and sixth instar. The apical tissue is characterized by its "light" appearance (due to poor stainability) caused by the small number cellular organelles, especially a paucity of free ribosomes. Maximal expression of the apical tissue must be very brief, since in most examined fifth and sixth instar larvae the apical tissue is partly or mostly translocated into the center of the upper half of the follicles and spermatogonia then occupy the apical follicle tips. During and after translocation apical cells form projections that grow around clusters of spermatogonia (spermatocysts). Thus, the apical cells transform into spermatocyst envelope cells. They retain their "light" appearance but undergo dramatic subcellular differentiation: smooth ER becomes extremely prominent, forming stacks and whorls of parallel cisternae. Golgi complexes are also conspicuous. The cellular organization suggests secretory activity. The possibility of ecdysteroid production and its function is discussed. The spermatocyst envelope cells persist into the pupal stage. When spermiohistogenesis takes place in cysts, cyst envelope cells show signs of regression. At all stages of testis development apical cells and their derivatives, the spermatocyst envelope cells, phagocytize degenerating spermatogonia. Although this is an important task of these cells, the impressive formation of sER in the cyst envelope cells is indicative of an additional, as yet unknown, function.

Testis ecdysiotropin, an insect gonadotropin that induces synthesis of ecdysteroid

Testes of lepidoptera synthesized ecdysteroid in a somewhat different temporal pattern than the prothoracic glands that release ecdysteroid to the hemolymph. Brain extracts from Heliothis virescens and Lymantria dispar induced testes to synthesize ecdysteroid, but did not affect prothoracic glands. The testis ecdysiotropin (LTE) was isolated from L. dispar pupal brains by a series of high-pressure chromatography steps. Its sequence was Ile-Ser-Asp-Phe-Asp-Glu-Tyr-Glu-Pro-Leu-Asn-Asp-Ala-Asp-Asn-Asn-Glu-Val-Leu-Asp-Phe-OH, of molecular mass 2,473 Daltons. The predominant signaling pathway for LTE was via G(i) protein, IP3, diacylglycerol and PKC; a modulating pathway, apparently mediated by an angiotensin II-like peptide, was controlled via G(s) protein, cAMP, and PKA. Testis ecdysteroid caused isolated testis sheaths to also synthesize a growth factor that induced development of the male genital tract. The growth factor appeared to be a glycoprotein similar to vertebrate alpha-1-glycoprotein. A polyclonal antibody to LTE indicated LTE-like peptide in L. dispar brain medial neurosecretory cells, the suboesophageal, and other ganglia, and also in its target organ, the testis sheath. LTE immunoreactivity was also seen in testis sheaths of Rhodnius prolixus. LTE-like immunoactivity was also detected in developing optic lobes, antennae, frontal ganglia, and elongating spermatids of developing L. dispar pupae. This may indicate that LTE has a role in development as well as stimulation of testis ecdysteroid synthesis. Published 2001 Wiley-Liss, Inc.

Cyclic AMP-dependent and independent stimulations of ovarian steroidogenesis by brain factors in the blowfly, Phormia regina

The involvement of cyclic-AMP (cAMP) as a potential second messenger in the neurohormonal control of ovarian steroidogenesis was investigated in the adult female blowfly Phormia regina. Individual measurements of ovarian cAMP concentrations and of ovarian biosynthesis of ecdysteroids, stimulated after a protein meal, demonstrated that steroidogenesis is preceded by a peak of cAMP in the ovaries. In vitro, ovarian steroidogenesis was stimulated by cell-permeable analogues of cAMP and by forskolin. Crude brain extracts were also able to elicit a rise of cAMP in the ovaries in vitro and the secretion of ecdysteroids into the medium: such extracts were more active before than after the protein meal, suggesting a rapid release of neuroendocrine material after feeding. Extracts were then prepared from the dorso-medial part of the brain, containing the neurosecretory cells of the pars intercerebralis (PI): these extracts were again found to stimulate the ovarian ecdysteroid secretion, but surprisingly, they failed to trigger a rise of cAMP in the ovaries in vitro. However, extracts from the rest of the cephalic nervous mass, deprived of PI, were also steroidogenic and they increased ovarian cAMP. Experiments with Rp-cAMPS, a cAMP antagonist, were not able to prevent the ecdysteroid stimulation by PI extracts, but did so partly for the extracts deprived of PI. This study thus indicates that at least two different cephalic factors are able to stimulate ovarian steroidogenesis in the blowfly, one elaborated by PI and acting via a cAMP-independent mechanism, and the other elaborated outside PI and using cAMP as a second messenger.

Action and pharmacokinetics of a novel insect growth regulator, halofenozide, in adult beetles of aubeonymus mariaefranciscae and leptinotarsa decemlineata

Topical application of halofenozide on adults of the Colorado potato beetle (CPB), Leptinotarsa decemlineata, and Aubeonymus mariaefranciscae (AMF) exhibited its effects in a different way in the two coleopterans. In CPB, the fecundity was strongly affected, whereas the main effect in AMF was a drastic decrease of the progeny survival. The rate of penetration of labeled halofenozide through the cuticle followed a similar pattern in CPB and AMF, whereas the rate of excretion was much more rapid in AMF. The extremely slow excretion of the product in CPB suggested that this fact must contribute to the prolonged action of halofenozide on fecundity at its highest dose of 20 &mgr;g per adult. Retention of halofenozide in the reproductive system of males of AMF and CPB was low, whereas high levels of radioactivity were recovered in females (ovaries + eggs). Comparing females of both coleopterans, CBP retained a higher amount than AMF. Moreover, treated CPB adults showed a rapid cessation of oviposition due to distorted ovaries, detrimental oocyte growth, and loss of oviposition due to the fact that yolk protein synthesis and/or incorporation into eggs was reduced. In AMF, the development of the progeny was strongly affected, and more than 80% of first-instar larvae died after egg hatching in the first 25 days after the treatment, due to premature molting and inhibition of ecdysis. Cross sections of intoxicated first larval instars of AMF originating from adults that were topically treated with halofenozide showed the presence of a double cuticle and these larvae could not shed the old cuticle. Arch. Copyright 1999 Wiley-Liss, Inc.

Angiotensin II and angiotensin-converting enzyme as candidate compounds modulating the effects of testis ecdysiotropin in testes of the gypsy moth, Lymantria dispar1

Lymantria dispar testes synthesize immunodetectable ecdysteroid in vitro in response to the brain peptide, testis ecdysiotropin (TE), acting primarily via a cascade involving Gi protein, diacyl glycerol, and phosphokinase C. However, a component of TE activation also involves the opposite cascade, Gs protein, cAMP, and phosphokinase A. Excess cAMP inhibits the action of TE, acting as a feedback modulator. Here, we show that bovine angiotensin II (AII) and bovine angiotensin converting enzyme (ACE) act like cAMP, inducing synthesis of immunodetectable ecdysteroid by pupal testes in vitro, but are antagonistic to coincubated TE. In addition, an insect ACE antibody clearly stains the spermatogenic cells through all stages of development, as well as testis sheath tissue where ecdysteroid is synthesized. AII induces synthesis of cAMP by pupal testes in vitro. Therefore, insect homologs of mammalian AII and ACE are good candidates for the peptides responsible for the cAMP cascade and as modulators of TE action in lepidopteran testes. Saralasin, an analog of AII that blocks angiotensin receptors in mammals, behaved like AII in inducing ecdysteroid secretion with ecdysteroidogenic effects additive to either angiotensin or ACE. Therefore, the receptors for the insect form of angiotensin on lepidopteran testis cells are probably different from those in mammals. Saralasin also inhibited ecdysteroid synthesis when combined with TE, as did AII.

Immunocytochemical localization of testis ecdysiotropin in the pupa of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae)

Antiserum against testis ecdysiotropin isolated from the gypsy moth, Lymantria dispar, reacted with neurons in the protocerebrum, optic and antennal lobes, subesophageal, thoracic and abdominal ganglia, as well as in nerve tracts extending through the optic lobes, tritocerebrum, and interganglionic connectives of the pupal stage of these insects. Testis ecdysiotropin is a peptide required by immature moths to initiate production of testes ecdysteroid, which is necessary for the development of the male reproductive system and initiation of spermatogenesis. Antiserum against testis ecdysiotropin also detected an accumulation of testis ecdysiotripic-like material between the inner and outer testis sheaths of pupae. The localization of this peptide in the imaginal disks of the last larval stage, cells and nerve fibers in the optic and antennal lobes of the pupa of both sexes, as well as in the testes during development of the adult reproductive system indicates that testis ecdysiotropin has a much larger impact on adult metamorphosis than development of the reproductive system and initiation of gametogenesis. Although this peptide may have a modulatory role in the central nervous system (CNS), it may also initiate a cascade of activity required for the development of the adult nervous system, in addition to its role in reproduction.

Pheromonotropic and pheromonostatic activity in moths

Pheromone biosynthesis in many species of moths requires a pheromonotropic neurosecretion, the pheromone biosynthesis activating neuropeptide (PBAN), from the brain-subesophageal ganglion-corpora cardiaca complex. Some investigations suggest that PBAN is released into the hemolymph and acts directly on sex pheromone glands (SPG) via a Ca++/calmodulin-dependent adenylate cyclase. Others suggest, however, that PBAN acts via octopamine that is released by nerves from the terminal abdominal ganglion innervating the SPG. These findings suggest that there are controversies on the mode of action of PBAN and other pheromonotropic factors, sometimes even within the same species. Mating in many insects results in temporary or permanent suppression of pheromone production and/or receptivity. Such a suppression may result from physical blockage of the gonopore or deposition of pheromonostatic factor(s) by the male during copulation that result in suppressed pheromone production and/or receptivity in females either directly or by a primer effect. In several species of insects, including moths, a pheromonostatic factor is transferred in the seminal fluid of males. Similar to the controversies associated with the pheromonotropic activity of PBAN, sometimes even within the same species, there appear to be controversies in pheromonostasis in heliothines as well. This paper reviews these conflicting findings and presents some data on pheromonostatic and pheromonotropic activity in Heliothis virescens that support and conflict with current information, raising further questions. Answers to some of the questions are partly available; however, they remain to be answered unequivocally.

Hormonal regulation of ovarian ecdysteroid production in the autogenous mosquito, Aedes atropalpus

The effects of juvenile hormone (JH) and egg development neurosecretory hormone (EDNH) on ovarian ecdysteroid production during vitellogenesis in the autogenous mosquito, Aedes atropalpus, were investigated using in vitro techniques coupled with radioimmunoassay (RIA) and high-pressure liquid chromatography (HPLC). Normal females were characterized by quantitative, qualitative, and temporal patterns of in vitro ovarian ecdysteroid production. Females decapitated at emergence showed little ovarian ecdysteroid production and did not undergo vitellogenesis. A 500-ng dose of JH-I applied topically to decapitated females restored normal patterns of ecdysteroid production. In both normal and experimental females, ecdysone constituted the major portion of the ecdysteroids secreted by the ovaries in vitro. However, significant amounts of other RIA-active materials were detected, one of which was probably 20-OH-ecdysone. Fat body incubations indicated that these tissues produce little RIA-active material during the peak of vitellogenesis. During that period, the ovaries were the major source of ecdysteroid. Various doses of JH-I, applied to abdomens isolated at emergence, enhanced ovarian responsiveness to subsequent applications of head extracts containing EDNH both in vivo and in vitro. A 500-ng dose of JH-I, applied topically to blood-fed, decapitated Aedes aegypti, stimulated a significant increase in in vitro ovarian ecdysteroid production. Similarities between these data and those demonstrating prothoracicotropic effects of JH in the Lepidoptera are discussed.