Sensory organs of the thoracic legs of the moth Manduca sexta

Summary The thoracic legs of the moth Manduca sexta acquire a new form and develop a new complement of sensory organs and muscles during metamorphosis from larva to adult. Because of our interest in the reorganization of neural circuitry and the acquisition of new behaviors during metamorphosis, we are characterizing sensory elements of larval and adult legs so that we may determine the contribution of new sensory inputs to the changes in behaviors. Here we describe the sensory structures of adult legs using scanning electron microscopy to view the external sensilla and cobalt staining to examine innervation by underlying sensory neurons. We find that, in contrast to larval legs, the adult legs are covered with a diverse array of sensilla. All three pairs of thoracic legs contain scattered, singly innervated scalelike sensilla. Campaniform sensilla occur singly or in clusters near joints. Hair plates, consisting of numerous singly innervated hairs, are also present near joints. Other more specialized sensilla occur on distal leg segments. These include singly innervated spines, two additional classes of singly innervated hairs, and three classes of multiply innervated sensilla. Internal sensory organs include chordotonal organs, subgenual organs, and multipolar joint receptors.     

Spatio-temporal distribution patterns of two tachinid flies,Epicampocera succincta andCompsilura concinnata parasitizingPieris

Larvae of genus Pieris in the northern part of Kyoto City are parasitized by two tachinid flies:Epicampocera succincta, a specialist on genus Pieris, and Compsilura concinnata, a generalist with very wide host-range. We surveyed the parasitism rates of Pieris by both flies for two years at six study areas. In these study areas, there lived three host species in the genus Pieris: P. rapae, P. melete, and P. napi, but neither tachinid parasitized P. napi to any significant extent. In the mountainous district, P. rapae and P. melete coexisted and their populations were relatively continuous, while in the lowland, only P. rapae larvae were abundant in spring and autumn, but even they disappeared in summer. Parasitisms by E. succincta occurred mainly in mountainous district and never in the lowland. C. concinnata parasitized Pieris in all the areas, but its parasitisms occurred mainly in autumn. We analyzed the factors affecting the spatial and temporal patterns of parasitism rates and presumed that the temporal discontinuity of host population restricted the distribution of the specialist parasitoid.     

Eclosion hormone-stimulated cGMP levels in the central nervous system of Manduca sexta: inhibition by lipid metabolism blockers,increase in inositol(1,4,5)trisphosphate and further evidence against the involvement of nitric oxide

Previous studies have shown that the neuropeptide, eclosion hormone, stimulates a nitric oxide-independent increase in the levels of cGMP in the nervous system of Manduca sexta. By contrast, recent results in Bombyx mori suggest that eclosion hormone increases cGMP via the production of nitric oxide. In view of these conflicting results we have carried out additional studies to test whether nitric oxide is involved in this process in Manduca. Evidence presented here supports our earlier observations that in Manduca the eclosion hormone-stimulated increase in cGMP is nitric oxide-and carbon monoxide-independent. In addition, we show that a wide variety of inhibitors of lipid metabolism block the eclosion hormone-stimulated cGMP increase. This supports the hypothesis that the activation of the guanylate cyclase is mediated by a lipid messenger. We also show that eclosion hormone stimulates an increase in the levels of inositol(1,4,5)trisphosphate. The time-course of this increase is consistent with the hypothesis that eclosion hormone stimulation of a phospholipase C is an early event in the cascade that results in an increase in cGMP. Receptor-mediated lipid hydrolysis is often mediated by G protein-coupled receptors. Experiments using pertussis toxin show that the eclosion hormone-stimulated increase in cGMP is not mediated by a pertussis toxin-sensitive G protein.Abbreviations AACOCF ₃ arachidonyl trifluoromethyl ketone - 4-BPB 4-bromophenacyl bromide - cGMP guanosine 3,5 cyclic monophosphate - D609 tricyclodecan-9-yl-xanthogenate - DEDA 7,7 dimethyleicosadienoic acid - DAG diacylglycerol - EH eclosion hormone - ET-18-OCH ₃ 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphorylcholine - ETYA 5,8,11,14-eicosatetraynoic acid - InsP ₃ inositol(1,4,5)trisphosphate - LO lipoxygenase - Lyso-PA lysophosphatidic acid - HPLC highpressure liquid chromatography - NDGA nordihydroguaiaretic acid - NOS nitric oxide synthase - OEPC oleoxyethyl phosphorylylcholine - ONO-RS-082 2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid - oxo-M oxotremorine-M - PAF platelet-activating factor - PKC protein kinase C - PLA ₂ phospholipase A₂ - PLC phospholipase C - PLD phospholipase D - PPH phosphatidate phosphohydrolase - PtdIns(4,5)P ₂ phosphatidylinositol bisphosphate - PTX pertussis toxin - TEA triethylamine - TFA trifluoroacetic acid - U-73122 1-(6-((17-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione     

Identity and expression pattern of chemosensory proteins in Heliothis virescens (Lepidoptera, Noctuidae)

Analyzing the chemosensory organs of the moth Heliothis virescens, three proteins belonging to the family of insect chemosensory proteins (CSPs) have been cloned; they are called HvirCSP1, HvirCSP2 and HvirCSP3. The HvirCSPs show about 50% identity between each other and 30–76% identity to CSPs from other species. Overall, they are rather hydrophilic proteins but include a conserved hydrophobic motif. Tissue distribution and temporal expression pattern during the last pupal stages were assessed by Northern blots. HvirCSP mRNAs were detected in various parts of the adult body with a particular high expression level in legs. The expression of HvirCSP1 in legs started early during adult development, in parallel with the appearance of the cuticle. HvirCSP1 mRNA was detectable five days before eclosion (day E-5), increased dramatically on day E-3 and remained at high level into adult life. The tissue distribution and the time course of appearance of HvirCSPs are in agreement with a possible role in contact chemosensation.     

Night and day service: Distyly and mixed pollination system in Faramea cyanea (Rubiaceae)

Currently, pollination is seen as involving more generalist interactions than specialized ones. Supporting this trend, some nocturnal distylous flowers may also receive floral visitors during the day, and since the latter contribute to fruit set, the pollination system is mixed and less specialized. Common among the Rubiaceae, distyly has been regarded as a reproductive strategy which requires a precise and specialized pollination system, and in this important tropical family, environmental disturbance and pollination failure have been used to explain anomalies in distylous features. Faramea cyanea Müll. Arg. is a common tree species in forest formations in the increasingly threatened Cerrado biome, the Neotropical savannas in Central Brazil. We evaluated the floral morphology, pollination biology and breeding system of a population of F. cyanea. Despite their moth pollination features, flowers were visited by diurnal (bees) as well as nocturnal (moths) pollinators. Experimental results showed that both pollinator groups contributed equally to pollen flow and legitimate pollination. The population presented distyly, isoplethy and heteromorphic self-incompatibility. Although F. cyanea did not present exact reciprocal herkogamy between floral morphs, pollination and reproductive success were not impaired. Floral features, which allowed pollination by complementary groups of pollinators, may explain the absence of anomalies in the isoplethy and distylous features in the studied population, anomalies which have been observed in other sympatric distylous Rubiaceae.     

Bacillus thuringiensis protein production, signal transduction, and insect control in chemically inducible PR-1a/cry1Ab broccoli plants

In an effort to develop a chemically inducible system for insect management, we studied production of Cry1Ab Bacillus thuringiensis (Bt) protein and control of the diamondback moth (DBM), Plutella xylostella L., in inducer-treated and untreated tissues of a broccoli line transformed with a PR-1a/cry1Ab expression cassette. Spraying leaves of these plants with the inducer acibenzolar-S-methyl (= 1,2,3 benzothiadiazole-7-thiocarboxylic acid-S-methyl-ester) (ASM) triggered expression of the cry1Ab gene and produced a high level of Cry1Ab protein within 2–3 days. Cry1Ab protein persisted in leaves for at least 8 weeks, providing prolonged protection from P. xylostella attack. Signals generated in inducer-treated leaves were transferred to untreated newly emerged leaves or heads, as seen by production of Cry1Ab protein and/or protection from insect damage in these plant parts. Signal transduction proceeded in an attenuated manner up to the sixth newly emerged leaf. No Cry1Ab protein was detectable by ELISA in uninduced young leaves, but small amounts of the protein were present in uninduced leaves older than 3 weeks and caused some insect mortality. Such basal expression of Bt genes without induction may favor the evolution of resistant insect populations and therefore limits the application of the PR-1a/cry1Ab system for insect management. However, the rapid production and steady maintenance of a high level of transgenic protein upon induction, the signal transduction observed, and the fact that the chemical inducer can be used in field conditions make the PR-1a promoter attractive for chemical regulation of other agriculturally or pharmaceutically important genes for which low expression in the absence of induction is not a concern.     

Cloning and nucleotide sequencing of three heat shock protein genes (hsp90, hsc70, and hsp19.5) from the diamondback moth, Plutella xylostella (L.) and their expression in relation to developmental stage and temperature

Heat shock protein genes, hsp90, hsc70, and hsp19.5, were cloned and sequenced from the diamondback moth, Plutella xylostella (L.) by RT-PCR and RACE method. The cDNA sequence analysis of hsp90 and hsp19.5 revealed open reading frames (ORFs) of 2,151 and 522 bp in length, which encode proteins with calculated molecular weights of 82.4 and 19.5 kDa, respectively. Analysis of cDNA from hsc70 revealed an ORF of 1,878 bp coding a protein with a calculated molecular weight of 69.3 kDa. Furthermore, the analysis of genomic DNA from hsc70 confirmed the presence of introns while no introns were apparent in hsp90 and hsp19.5. Southern blot analysis suggested the presence of multiple copies of each gene family in the DBM genome. Detectable expression of hsp19.5 was observed at the pupal stage while expression of hsp90 and hsc70 was detected at both pupal and adult stages. At adult stage, females showed a higher expression of hsp90 and hsc70 than males. An increased expression was observed in all three genes after exposure to a high temperature in both sexes. These results suggest that in addition to a heat shock response, these HSP genes might be involved in other functions during the course of development in DBM.     

Seasonality in neotropical populations of Plutella xylostella (Lepidoptera): resource availability and migration

The present study aimed to verify (1) whether seasonal increases in neotropical populations of Plutella xylostella are directly provoked by regular influxes of migrants, and (2) whether temporal variation in food availability is the ecological process behind such predictable events. Over 3 years, plants that P. xylostella prefers were cultivated and irrigated in order to provide a continuous and abundant supply of food. Nevertheless, seasonal oscillations in the population of the herbivore still occurred. The hypothesis of seasonal availability of host plants could not explain the population pattern. In April, when the insect was practically extinct from the area, an artificial infestation (immigration) with 10,000 pupae established a precocious population. Therefore, the start of the natural cycles of population growth, during July–August, seems to be due to external factors, rather than an improvement in local conditions for resident individuals. In the beginning of the natural cycles, the increase in the density of adults significantly preceded the increase in immatures. Plutella xylostella does not diapause, and therefore immigration is the proximate cause of the seasonal population increases. Hypotheses about local factors are suggested to explain the decreasing phase of the predictable population cycles.     

Coordination of wing motion and walking suggests common control of zigzag motor program in a male silkworm moth

The male silkworm moth, Bombyx mori, exhibits a zigzagging pattern as it walks upwind to pheromones. This species usually does not fly, but obvious wing-beating accompanies the pheromone-mediated walking. Males supported by a `sled', after having their legs removed, also moved upwind in a pheromone plume along zigzagging tracks, indicating that wing-generated thrust and torque result in locomotory paths similar to those observed from walking moths. Using a high-speed video system we investigated the correlation between the wing movements and zigzag walking. The wing ipsilateral to the direction of the turn showed a greater degree of retraction with respect to the contralateral wing. The timing of the wing retraction pattern was synchronized with changes of direction in the walking track. Coordination of wing movements and walking pattern was not dependent on visual feedback or sensory feedback generated from neck movements associated with turning. The results presented here, taken together with our previous studies of descending interneurons suggest that the coordination of wing movements with the walking pattern may result from the activity of a set of identified interneurons descending from the brain to the thoracic ganglia and/or may be coordinated by coupling of oscillating circuits for walking and wing beating. Accepted: 15 May 1997