Completion of diapause in field populations of the cabbage root fly (Delia radicum)

The various diapause and post-diapause stages entered by cabbage root fly pupae during the overwintering period are shown schematically. Although diapause induction started in mid-Aug., the early-pupating insects did not develop further but were maintained in diapause by the warm autumn temperatures. Therefore, diapause development was simultaneous in all Wellesbourne pupae, whether of second or third generation origin. Diapause development started only in mid-Oct., when mean soil temperatures fell below 10°. In the field, 90% of the overwintering population of cabbage root fly pupae had completed pleted diapause by 5 March 1980, 17 Feb. 1981 and 18 Feb. 1982. This was equivalent to a duration of 19 weeks from mid-Oct. onwards, during the winters of 1979–80, 1980–81 and 1981–82 respectively. A further break between the completion of diapause and the warm conditions required to start post-diapause development also helps to condense the emergence of flies in the spring. Hence, an accurate forecast of the time of spring attack by populations of flies similar to those at Wellesbourne should be possible.This study was financed partly by the Commission of the European Communities as CEC Contract No. 0771.     

Neuropeptides of the cotton fleahopper, Pseudatomoscelis seriatus (Reuter)

The cotton fleahopper, Pseudatomoscelis seriatus (Reuter), is an economically important pest of cotton, and increasing concerns over resistance, detrimental effects on beneficial insects and safety issues associated with traditional insecticide applications have led to an interest in research on novel, alternative strategies for control. One such approach requires a more basic understanding of the neurohormonal system that regulates important physiological properties of the fleahopper; e.g. the expression of specific messenger molecules such as neuropeptides. Therefore we performed a peptidomic study of neural tissues from the fleahopper which led to the first identification of the sequences of native peptide hormones. These peptide hormones include the following neuropeptides: corazonin, short neuropeptide F (sNPF), myosuppressin, CAPA-pyrokinin and CAPA-PVK peptides. The CAPA-pyrokinin, sNPF, and CAPA-PVK peptides represent novel sequences. A comparison of fleahopper neuropeptides with those of related heteropteran species indicates that they are quite different. The sNPF of P. seriatus shows, among others, a novel substitution of Leu with Phe within the C-terminal region; a modification that sets it apart from the known sNPFs of not only other Heteroptera but of other arthropod species as well. The identity of the neuropeptides native to the fleahopper can aid in the potential development of biostable, bioavailable mimetic agonists and antagonists capable of disrupting the physiological functions that these neuropeptides regulate.     

Influence of background on host-plant selection and subsequent oviposition by the cabbage root fly (Delia radicum)

The behaviour of female cabbage root flies during host plant selection was studied in the laboratory using brassica plants growing in backgrounds of bare soil, clover, grass, peas and four non-living materials. Gravid females landed about twice as often on brassica plants growing in bare soil than on comparable plants growing amongst non-host plants. Once a receptive female landed on a brassica plant, the female made, on average, four ‘spiral flights’ and two jumps on and off the plant before laying alongside the plant. Surrounding a brassica plant with a diverse background altered the behaviour of the flies, so that the spiral flights around the host plant were replaced by short hops between nearby vertical objects. The loss of contact and recontact with the host plant then prevented the females from accumulating sufficient contacts with the host plant to be stimulated to lay. Spiral flights around host plants appear to determine whether or not flies will lay alongside host plants. Flies in mixed plantings have a reduced rate of settling on the host plant, and a higher rate of locomotion, because they land frequently on non-host plants. Hence, visual stimuli appeared to have greater effects than, chemical or mechanical barriers in deterring flies from laying alongside brassica plants in diverse backgrounds. In ‘choice’ situations, backgrounds of real plants reduced oviposition alongside brassica plants by at least 50%. In ‘no-choice’ situations, flies laid similar numbers of eggs alongside all brassica plants irrespective of plant background or plant size. If numbers of fly eggs are to be reduced on commercial brassica crops by undersowing the crops with clover, plants growing in bare soil may also have to be included to provide the flies with sites preferred for oviposition.     

Immunological evidence for an allatostatin-like neuropeptide in the central nervous system of Schistocerca gregaria,Locusta migratoria and Neobellieria bullata

Methanolic brain extracts of Locusta migratoria inhibit in vitro juvenile hormone biosynthesis in both the locust L. migratoria and the cockroach Diploptera punctata. A polyclonal antibody against allatostatin-5 (AST-5) (dipstatin-2) of this cockroach was used to immunolocalize allatostatin-5-like peptides in the central nervous system of the locusts Schistocerca gregaria and L. migratoria and of the fleshfly Neobellieria bullata. In both locust species, immunoreactivity was found in many cells and axons of the brain-retrocerebral complex, the thoracic and the abdominal ganglia. Strongly immunoreactive cells were stained in the pars lateralis of the brain with axons (NCC II and NCA I) extending to and arborizing in the corpus cardiacum and the corpora allata. Although many neurosecretory cells of the pars intercerebralis project into the corpus cardiacum, only 12 of them were immunoreactive and the nervi corporis cardiaci I (NCC I) and fibers in the nervi corporis allati II (NCA II) connecting the corpora allata to the suboesophageal ganglion remained unstained. S. gregaria and L. migratoria seem to have an allatostatin-like neuropeptide present in axons of the NCC II and the NCA I leading to the corpus cardiacum and the corpora allata. All these data suggest that in locusts allatostatin-like neuropeptides might be involved in controlling the production of juvenile hormone by the corpora allata and, perhaps, some aspects of the functioning of the corpus cardiacum as well. However, when tested in a L. migratoria in-vitro juvenile hormone-biosynthesis assay, allatostatin-5 did not yield an inhibitory or stimulatory effect. There is abundant AST-5 immunoreactivity in cell bodies of the fleshfly N. bullata, but none in the CA-CC complexes. Apparently, factors that are immunologically related to AST-5 do occur in locusts and fleshflies but, the active protion of the peptide required to inhibit JH biosynthesis in locusts is probably different from that of AST-5.     

Distribution and characterization of Corazonin in the central nervous system of Triatoma infestans (Insecta: Heteroptera)

The distribution of corazonin in the central nervous system of the heteropteran insect Triatoma infestans was studied by immunohistochemistry. The presence of corazonin isoforms was investigated using MALDI-TOF mass spectrometry in samples containing the brain, the subesophageal ganglion, the corpora cardiaca-corpus allatum complex and the anterior part of the aorta. Several groups of immunopositive perikarya were detected in the brain, the subesophageal ganglion and the thoracic ganglia. Regarding the brain, three clusters were observed in the protocerebrum. One of these clusters was formed by somata located near the entrance of the ocellar nerves whose fibers supplied the aorta and the corpora cardiaca. The remaining groups of the protocerebrum were located in the lateral soma cortex and at the boundary of the protocerebrum with the optic lobe. The optic lobe housed immunoreactive somata in the medial soma layer of the lobula and at the level of the first optic chiasma. The neuropils of the deutocerebrum and the tritocerebrum were immunostained, but no immunoreactive perikarya were detected. In the subesophageal ganglion, immunostained somata were found in the soma layers of the mandibular and labial neuromeres, whereas in the mesothoracic ganglionic mass, they were observed in the mesothoracic, metathoracic and abdominal neuromeres. Immunostained neurites were also found in the esophageal wall. The distribution pattern of corazonin like immunoreactivity in the central nervous system of this species suggests that corazonin may act as a neurohormone. Mass spectrometric analysis revealed that [Arg⁷]-corazonin was the only isoform of the neuropeptide present in T. infestans tissue samples.     

The cardiacal neurosecretory system and associated organs of an adult mosquito, Aedes aegypti

Unlike most other insects, mosquitoes do not possess discrete corpora cardiaca composed of neuropile, intrinsic neurosecretory cells and glial cells. Cells homologous with the intrinsic neurosecretory cells of other insects are located at the junction of the neck and thorax of mosquitoes, close to the corpora allata. These cells are named cardiacal neurosecretory cells. Axons run forwards from the cardiacal neurosecretory cells into the allatal nerves. Neurosecretory release sites occur over almost the whole of the nervi corporum cardiacorum, allatal nerves and oesophageal nerves, and these nerves constitute a very extensive neurohaemal organ for many of the cerebral neurosecretory cells. The neurosecretory release sites of the cardiacal neurosecretory cells appear to be in the allatal nerves and possibly also on the perikarya of these cells.     

Localization of cholecystokinin-like immunoreactivity in the central nervous system of Triatoma infestans (Insecta: Heteroptera)

The distribution of cholecystokinin-like immunoreactivity was studied in the central nervous system of the heteropteran insect Triatoma infestans using high-sensitivity immunocytochemistry. In the protocerebrum, CCK-IR somata were observed in the anteromedial, anterolateral and posterior cell-body layers. The neuropils displayed different densities of immunoreactive neurites. Few immunoreactive somata were found in the optic lobe in both the medial and lateral soma rinds, as well as in the proximal optic lobe. Immunoreactive fibers were present in the medulla and lobula neuropils. The sensory deutocerebrum contained a higher number of immunopositive perikarya than the antennal mechanosensory and motor center. The antennal lobe glomeruli displayed a moderate density of immunoreactive fibers. With regard to the subesophageal ganglion, numerous CCK-IR somata were found close to the root of the mandibular nerve; others were present in the soma rind of the remaining neuromeres. CCK-IR perikarya were present in both thoracic ganglia, with the abdominal neuromeres containing the highest number of positive somata. The neuropils of both ganglia showed moderate densities of immunopositive processes. The distribution of CCK-LI in somata and neuropils of central nervous system of T. infestans is widespread suggesting that a CCK-like peptide may act mainly as a neuromodulator in the integration of information from distinct sensory receptors.     

Environmental triggers to cryoprotectant modulation in separate populations of the gall fly, Eurost a solidaginis (Fitch)

Northern and southern populations of the gall fly Eurosta solidaginis utilize quantitatively distinct adaptive strategies when exposed to a laboratory simulation of winter temperatures. Both populations are freezing tolerant and rely in part on the temperature-dependent accumulation of glycerol and sorbitol, and static but elevated levels of trehalose for protection. The accumulation triggers are time-temperature dependent. For northern and southern populations, exposure to 5°C for periods exceeding 24 hr, but less than 5 days or 5°C with a gradual reduction (1°C/day) results in the accumulation of sorbitol at 1.5 μg/mg/day. Glycerol levels remain essentially constant between 10° and ?25°C in each population. However, the concentration of glycerol in the Minnesota population is 3–4 times greater that that of the Texas specimens. Haemolymph melting points varied quantitatively with changing cryoprotectant levels. No significant difference was noted between the supercooling points of each population. This suggests that ice-nucleator levels were comparable throughout the exposure period.     

Ultrastructure of the funicular sensilla of the cabbage root fly,Delia radicum L. (Diptera : Anthomyiidae)

A transmission electron microscope study of the funicular sensilla of the cabbage root fly, Delia radicum, (Diptera : Anthomyiidae), showed 4 types of surface sensilla and 5 types of pit sensilla. The ultrastructure of the surface sensilla indicated all had a primary olfactory function. These include thick-walled multiporous trichoid sensilla, thin-walled multiporous basiconic sensilla (with 2 subtypes), thin-walled multiporous clavate sensilla, and grooved sensilla with channels at the base of each of the grooves. Clavate sensilla had 2 types of dendrites, one tubular, the other “scrolled”. This 2nd type may indicate an additional thermosensitive function. The dorsal pits contained thin-walled multiporous basiconic sensilla with a tapered tip. The ventral pits contain 3 types of sensilla, which have no wall pores and an inflexible socket. These may contain thermo- and/or hygroreceptors and include smooth-walled conical-, smooth-walled tapered- and striated pit sensilla. The 4th type is a grooved pit sensillum similar to the surface type.     

Morphology of the antennal sensilla of the cabbage root fly,Delia radicum L. (Diptera : Anthomyiidae)

The antennal sensilla of Delia radicum L. (Diptera : Anthomyiidae) were studied by scanning electron microscopy. On the scape and pedicel, grooved socketed bristles and setiferous plaques were found. There are 4 types of surface sensilla on the funicle: trichoid, basiconic, clavate, and grooved. Their numbers and distribution are described. There are 3–4 single-chambered pits on the dorsal surface of the funicle of both sexes and these contain basiconic sensilla. On the ventral surface, there is one multi-chambered pit, which contains 5 types of sensilla: grooved s., smooth-walled conical s., smooth-walled tapered s., striated s. and a novel type, flattened sensilla. These results are compared with previously published studies on several other fly species.     

Identification of diacylglycerol-O-(N,N,N-trimethyl)-homoserine in the halotolerant alga, Dunaliella parva

An unusual zwitterionic polar lipid component isolated from the halotolerant alga, Dunaliella parva Lerche, has been identified as 1(3),2-diacylglyceryl-3(1)-O-4′-(N,N,N-trimethyl) homoserine by means of infrared spectrometry, ¹H- and ¹³C-NMR spectrometry and field desorption mass spectrometry of the intact lipid, as well as by its TLC mobilities and staining behaviour. Mass spectrometry of this lipid indicated the presence of the following major molecular species: 16:0–18:0 (24%); 18:3–18:3 (19%); 16:0–18:2 (16%); 16:0–18:1 (8%).     

Inflammatory changes in the central nervous system are associated with behavioral impairment in Plasmodium berghei (strain ANKA)-infected mice

Experimental cerebral malaria is a neuroinflammatory condition that results from the host immune response to the parasite. Using intravital microscopy, we investigated leukocyte recruitment in the brain microcirculation and the temporal relationship of this process to the behavioral changes observed in Plasmodium berghei (strain ANKA)-infected C57Bl/6 mice. We found that leukocyte recruitment was increased from day 5 post-infection (p.i.) onwards. Histopathological changes and increased levels of inflammatory cytokines in the brain were also observed. Behavioral performance evaluated by the SHIRPA protocol showed functional impairment from day 6 p.i. onwards. Thus, early leukocyte migration into the brain and associated inflammatory changes may be involved in neurological impairment in parasite-infected C57Bl/6 mice.     

Oviposition behavior of the cabbage root fly,Delia radicum (L.), influenced by host plant extracts

An ethanolic extract of cabbage leaves (Brassica oleraceavar. capitata,Golden Acre)and derived fractions were tested on natural and surrogate leaves in order to study the oviposition behavior of the cabbage root fly Delia radicum(Diptera: Anthomyiidae). On surrogate plastic leaves coated with a thin layer of paraffin wax and treated with 0.1 gram leaf equivalent (gle) of an ethanolic raw cabbage extract, the females displayed the same sequence of behavioral patterns as on a natural host plant. The quantified oviposition behavior correlated well with the actual number of eggs laid. The extract-treated surrogate leaves received at least as many eggs as natural leaves with a similar surface area. Previous exposure to surrogate or natural leaves seemed not to induce a specific preference. The three fractions (hexane, butanol, and water) of the raw extract stimulated the oviposition behavior. This was taken as evidence for the presence of a multicomponent mixture or a chemical pattern in the cabbage leaves stimulating oviposition. At the tested concentration each fraction alone could stimulate in some individuals the complete behavior. No effect of volatile components of the raw extract could be detected. This is thought to be due to the extraction procedure, which limits the production of attractive, volatile compounds, such as isothiocyanates.     

Cyclic nucleotide binding and protein kinase in the central nervous system of Galleria mellonella (L.)

The binding of cyclic AMP, IMP and GMP by the central nervous system of Galleria mellonella was studied. The K_m for cyclic AMP was 1 · 10^?7 and that for cyclic GMP 1 · 10^?8. The results suggest a different binding protein and cyclic nucleotide-stimulated protein kinase for each of these nucleotides. In addition a cyclic IMP-dependent protein kinase may also be present.     

Serotonin in the central nervous system of the cockroach, Periplaneta americana

Studies on serotonin in the insect nervous system has long been neglected, although serotonin is a putative neurotransmitter. During the course of this study the serotonin content was found to be significantly higher than that found in mammalian midbrain. Parachlorophenylalanine was found to inhibit the first step of the biosynthetic pathway by inhibiting tryptophan-hydroxylase enzyme and leading to alterations in the concentrations of metabolites such as 5-hydroxy tryptophan, 5-hydroxy indole acetic acid and tryptophan. Using a dose of 15 μg/g the inhibitory effect was not long lasting and recovery was observed to restore the normal levels. Higher trytophan levels were observed after a certain period of P-chlorophenylalanine treatment because there was a block in the biosynthetic path and tryptophan could not be utilized for 5-HT synthesis. A negative correlation between brain tryptophan and protein content was observed in both the cases of P-chlorophenylalanine and reserpine treatments.     

Limits for the detection of (poly-)phosphoinositides by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS)

Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been recently established as a powerful tool for the analysis of biomolecules. Here, MALDI-TOF MS was used for the detection of (poly-)phosphoinositides (PPI). PPI possess higher molecular weights than other phospholipids and a high phosphorylation-dependent negative charge. Both features affect the MALDI detection limits expressed as the minimum of analyte on the sample plate resulting in a signal-to-noise-ratio of S/N=5. Using 2,5-dihydroxybenzoic acid (DHB) as matrix the detection limit for phosphatidylinositol (PI) is seven times higher than for phosphatidylcholine (PC) and further increases with increasing phosphorylation or in mixtures with other well-detectable phospholipids. For phosphatidylinositol-tris-phosphate (PIP₃) in a mixture with PC, the limit is about 20 times higher than for PI. The consequences for the experimental conditions are discussed. It is advisable to pre-separate PPI from biological lipid mixtures prior to the application of MALDI-TOF MS.     

Ocellar projections within the central nervous system of the worker honey bee,Apis mellifera

Summary The projections of ocellar fibres within the brain and thorax of the honey bee, Apis mellifera, were established using a modified cobalt sulphide technique, supplemented by serial sectioning of the brain for the light microscope.The results are: 5 large fibres in each lateral nerve and 12 in the median nerve have wide-field terminal arborisations in ocellar association areas on either side of the posterior slope area. 9 medium-sized fibres in each lateral nerve and 12 in the median nerve form a second ocellar association area on each side of the perioesophageal foramen. A group of fine fibres, stained via the ocellar nerves, arborise just below and anterior to the protocerebral bridge. 10 medium-sized fibres run from the level of the ocellar nerve tracts to the first and second thoracic ganglia, branching in a number of discrete areas within each ganglion. These fibres also form a restricted ocellar association area within the suboesophageal ganglion. A few fibres run between the higher-order optic centres and the ocellar tract. The large- and mediumsized fibres give off short, stout spines from their axons within the ocellar tracts.     

The structure of the postantennal organ in Onychiurus sp. (Insecta: Collembola) and its connection to the central nervous system

Summary The postantennal organ in Onychiurus (group armatus) is a sensory organ comprising one sensory cell, several enveloping cells and cuticular structures.The perikaryon of the sensory cell is located in the central nervous system and distally gives off a dendrite in which one inner and two outer segments are distinguishable. Two ciliary structures connect the outer dendritic segments with the inner segment. The outer segments divide repeatedly, basal to the cuticular structures, into small branches which end distally beneath the cuticular wall. The wall of the cuticular structures is very thin and is pierced by numerous funnel-shaped pores. The pores are filled with electron-dense material which forms a continuous sheath underneath the cuticle. This material encases the small dendritic branches and the processes of the enveloping cells which occupy the lumen of the cuticular structures. There are three types of enveloping cells: one inner, several outer and one basal. Their processes differ in the manner in which they envelop the various regions of the dendrite.At the beginning of moulting outer dendritic branches are not found within the cuticular structures of the organ. They may be assumed to retract inwardly. However, in the later stages, when the cuticle is fully formed, the outer dendritic segments appear to divide. It is assumed that the small dendritic branches reach their targets before ecdysis. The electrondense material which clogs the intermoult cuticular pores is absent until the final stages of the moulting cycle.Supported by a grant from the Deutscher Akademischer Austauschdienst.