Structural constraints in expansion segments from a midge 26S rDNA

DNA sequences representing approximately 40% of the large-subunit rRNA gene from the lower dipteran Chironomus thummi were analyzed. Once aligned with their Drosophila counterparts, sequence and base content comparisons were carried out. Sequence identity was found to be high overall, except for six regions that displayed a local bias in nucleotide composition toward AT. These regions were identified as expansion segments D3, D4, D5, D6, D7a, and D12. Besides base sequence divergence, differences in length were observed between the respective variable domains of the two species, particularly for D7a. Prediction of secondary structure showed that the folding of the Chironomus expansion segments analyzed is in agreement with the general patterns proposed for eukaryotic LSU rRNA. The comparison with Drosophila revealed also that the Chironomus secondary structures of the variable domains are supported by multiple compensatory substitutions or even compensatory insertions. Chironomus D7a displayed an unusual structural feature with respect to the insect D7a models that have been inferred up to now. The structural constraint observed in the expansion segments of Diptera so distantly related as midges and Drosophila suggests that these regions contribute to some functional role. Concerning the D7a of insects so far analyzed, there can be, in addition to a conserved secondary structure, a nucleotide composition constraint that might be important for the process giving rise to the alpha and beta halves of the 26S rRNA. Correspondence to: E. Gorab     

An ultrastructural study of the larval integument of the midge,Chironomus riparius meigen (Diptera: Chironomidae)

Summary The larval integument of the midge, Chironomus riparius Mg., is unusually thin although it conforms with the normal insect pattern. The cuticle of the post-cephalic segments is about 3 m thick and overlies an epidermis which has an irregular basal plasma membrane resulting in spaces occurring between it and the basement membrane. The ventral tubuli have a similar epidermis but the cuticle is somewhat thinner. The anal papillae have the thinnest cuticular covering with a uniquely folded epicuticle of variable thickness, and their epidermis has the characteristics of a transporting epithelium. No evidence of pore canals could be found in the cuticle of any part except the head capsule which has a remarkably smooth epicuticle and a distinct layer which may represent the exocuticle. There are no spaces between the basement membrane and basal plasma membrane of the epidermis in the head. Ultrastructural evidence would suggest that gaseous exchange can occur across most of the post-cephalic integument.The author is indebted to Mrs. L. Rolph and Mr. R.L. Jones for their technical assistance     

Large variation among photoreceptors as the basis of visual flexibility in the common backswimmer

The common backswimmer, Notonecta glauca, uses vision by day and night for functions such as underwater prey animal capture and flight in search of new habitats. Although previous studies have identified some of the physiological mechanisms facilitating such flexibility in the animal''s vision, neither the biophysics of Notonecta photoreceptors nor possible cellular adaptations are known. Here, we studied Notonecta photoreceptors using patch-clamp and intracellular recording methods. Photoreceptor size (approximated by capacitance) was positively correlated with absolute sensitivity and acceptance angles. Information rate measurements indicated that large and more sensitive photoreceptors performed better than small ones. Our results suggest that backswimmers are adapted for vision in both dim and well-illuminated environments by having open-rhabdom eyes with large intrinsic variation in absolute sensitivity among photoreceptors, exceeding those found in purely diurnal or nocturnal species. Both electrophysiology and microscopic analysis of retinal structure suggest two retinal subsystems: the largest peripheral photoreceptors provide vision in dim light and the smaller peripheral and central photoreceptors function primarily in sunlight, with light-dependent pigment screening further contributing to adaptation in this system by dynamically recruiting photoreceptors with varying sensitivity into the operational pool.     

Orientation of males of sorghum midge,Contarinia sorghicola to sex pheromones from virgin females in the field

The orientation of males of the sorghum midge,Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) towards virgin female baited sticky traps was studied in the field. Male response increased linearly with an increase in the number of virgin females in the sticky traps. Five females per vial were optimum for monitoring midge populations in the field. Numbers of males trapped were significantly greater in traps placed at 0.5 and 1.5 m above ground level compared with those placed at 2.5 m. Peak trap catches occurred at 0900 h. The number of males trapped decreased significantly after 1400 h; male catches continued till sunset. Trap catches followed the same pattern as the number of ovipositing females on sorghum panicles at the half-anthesis stage. Midge activity decreased with an increase in temperature and a decrease in relative humidity. Peak midge density was observed during the second fortnight of October in the rainy season and during February-March in the post-rainy season. Sex pheromones can be used to monitor midge population dynamics for integrated pest management and to screen for host plant resistance to this insect.     

Novel organelle associations in photoreceptors of a serpulid polychaete worm

Cerebral and branchial eyes of serpulid polychaetes have been studied by electron microscopy for the first time. In one species both eye types possess a novel ultrastructure. The receptor cells of the simple cerebral ocelli are rhabdomeric and display a close structural and functional relationship between ciliary rootlets and mitochondria. The receptors of the compound branchial eyes contain both a rhabdom and a stack of photosensitive ciliary membranes.     

Inheritance of resistance against biotype 2 of the Asian rice gall midge, Orseolia oryzae

The inheritance of resistance in the rice cultivars Phalguna, ARC5984, ARC 5158, Veluthacheera, and T1477 to the Asian rice gall midge biotype 2 was studied under both natural and artificial infestation conditions against the susceptible cultivars Jaya and IR20. A single recessive gene in Veluthacheera and two recessive complementary genes in T1477 control resistance. Phalguna and ARC5984 possess a single dominant gene while ARC5158 has a single dominant and a single recessive gene for resistance. Allelism studies showed that genes for resistance in Veluthacheera and T1477 are allelic but non-allelic to the resistance genes in Phalguna and ARC5984, which are allelic to each other. Genes for resistance in ARC5158 are allelic to resistance genes of the other four donors. There was no cytoplasmic inhibition of resistance by the susceptible parents.     

A female sex-pheromone in the pea midge, Contarinia pisi

Experiments designed to demonstrate the existence of a female sex-pheromone in the pea midge, Contarinia pisi Winn. (Diptera: Cecidomyiidae) are described. Recordings from antennal receptors of males showed that extract of virgin females elicited an increase in spike activity. Field trapping experiments showed that traps containing virgin females or crude extract of virgin females caught large numbers of males.

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Résumé L'antenne des mâles de Contarinia pisi répond par électro-antennogramme à un courant d'air contaminé par des femelles vierges. Des pièges contenant des femelles attirent de nombreux mâles.

     

Light-activated single channel currents in Limulus ventral nerve photoreceptors

Light-activated single channel currents were measured in Limulus ventral photoreceptors in the cell-attached configuration at 14°C. The results show three channel types with conductances of 6.2, 10.4 and 28.7 pS. The most active channels have the 10 pS conductance; the open time histograms of these channels could be best fitted by the sum of two exponentials with time constants (and weights) of 0.58 ms (0.78) and 4.32 ms (0.22), suggesting two populations of channels or two open states. The mean open time was 1.38 ms. The open time histogram of the channels with the 29 pS conductance could be best fitted by a single exponential with a time constant of 3.35 ms. First latencies of the 10 pS channels were between 40 and 280 ms but those of the 29 pS conductance channels were 300 ms. These findings suggest that the two channel types are gated by two different intracellular transmitters or mechanisms. Offprint requests to: K. Nagy     

Field testing of BACTICIDE®, PHYTOVERM® and CHITINASE for control of the raspberry midge blight in Siberia

Three products based on compounds of biological origin were tested for their ability tocontrol the raspberry midge blight in theSiberian region of Russia. Bacillusthuringiensis subsp. israelensis(BACTICIDE^®) and Streptomycesavermitilis metabolites (PHYTOVERM^®) were used against Thomasiniana theobaldi (ageneral member of the midge blight) andCHITINASE was used against fungi (mainly Didymella applanata) associated with T. theobaldi. The BACTICIDE^®(0.2%) and PHYTOVERM^® (0.2%) sprays caused a 2-fold decrease in midge blight severity and the sameeffect was obtained with chemical insecticides.The CHITINASE (1%) spray caused a 4-folddecrease in the severity of midge blight. Inaddition, CHITINASE and PHYTOVERM^®caused a significant suppression of theindependent spur blight. These studies form thebasis for further evaluation of ecologicallysafe control of the raspberry midge blight.     

A structural study of the anal papillae of the midge Chironomus riparius Meigen (Diptera: Chironomidae)

Larvae of the midge, Chironomus riparius Mg., have four anal papillae arranged as two pairs, one dorsal to and the other ventral to the anus. Structural study with light and electron microscopes has revealed that their integument consists of a thin cuticle overlaying a thick, syncytial epidermis which is specialised to facilitate ion transport. There is a distinct neck or collar region at the junction of each papilla with the rest of the body wall. Although in many respects these structures resemble those in mosquitoes, there are both morphological and physiological features which suggest that differences exist in the means by which ion exchange with the environment is controlled and effected in the two families.     

Kinetic properties of single-ion channels activated by light in Limulus ventral nerve photoreceptors

Previous results on Limulus ventral photoreceptors have suggested that besides inositol trisphosphate, another unknown transmitter may also work in the transduction cascade. This assumption has been supported by the finding of two light-activated channel types. The present report furnishes further evidence of the dual transmitter mechanism in phototransduction by analyzing the kinetic properties and voltage dependency of these cation channels with conductances of 12 pS and 30 pS. Single-channel currents were recorded in Limulus ventral nerve photoreceptors in cell-attached configuration at 14°C. At V _m + 80 mV the open-time histograms of both channels were fit best by the sum of two exponentials; time constants (and weights) were: 0.81 ms (0.62) and 6.20 ms (0.38) for the 12 pS channels and 2.38 ms (0.43) and 19.4 ms (0.57) for the 30 pS channels. At this potential the mean open times were 2.7 ms for the 12 pS and 13.3 ms for the 30 pS channels, about two-times larger than at hyperpolarizing potentials. The deactivation kinetics were also different for the two channels. The time constants of the decay of the channel activity, after switching off the light, were 2.5 s for the 12 pS and 12.9 s for the 30 pS channels. The 12 pS channel exhibits bursting and subconductance states at positive potentials. The subconductances are about 20%, 46% and 72% of the fully open state. Results show that the two types of light-activated channels have different kinetic parameters, voltage dependence and gating mechanisms. The two channels are suggested to be gated by different transmitters or processes. It is proposed that for the 30 pS channel the transmitter could be calcium ion or a calcium-dependent transmitter.     

Hyperpredation by generalist predatory mites disrupts biological control of aphids by the aphidophagous gall midge Aphidoletes aphidimyza

Biological control of different species of pest with various species of generalist predators can potentially disrupt the control of pests through predator-predator interactions. We evaluate the impact of three species of generalist predatory mites on the biological control of green peach aphids, Myzus persicae (Sulzer) with the aphidophagous gall midge Aphidoletes aphidimyza (Rondani). The predatory mites tested were Neoseiulus cucumeris (Oudemans), Iphiseius degenerans (Berlese) and Amblyseius swirskii Athias–Henriot, which are all commonly used for pest control in greenhouse sweet pepper. All three species of predatory mites were found to feed on eggs of A. aphidimyza, even in the presence of abundant sweet pepper pollen, an alternative food source for the predatory mites. In a greenhouse experiment on sweet pepper, all three predators significantly reduced population densities of A. aphidimyza, but aphid densities only increased significantly in the presence of A. swirskii when compared to the treatment with A. aphidimyza only. This stronger effect of A. swirskii can be explained by the higher population densities that this predator reached on sweet pepper plants compared to the other two predator species. An additional experiment showed that female predatory midges do not avoid oviposition sites with the predator A. swirskii. On the contrary, they even deposited more eggs on plants with predatory mites than on plants without. Hence, this study shows that disruption of aphid control by predatory mites is a realistic scenario in sweet pepper, and needs to be considered when optimizing biological control strategies.     

Increase in activity of acetylcholinesterase by 20-OH-ecdysone in a Chironomus tentans cell line

Summary An epithelial cell line from Chironomus tentans exhibits acetylcholinesterase activity (specific activity 0.05–0.2 nkat/mg protein), which rises 30– to 40-fold after addition of 10^–6 M 20-OH-ecdysone. The first visible increase occurs after 4 days of incubation with hormone. The enzyme has an apparent K _m of 2.3±0.2×10^–4 M for acetylthiocholine iodide as substrate and is inhibited by eserine and BW284 C51 (50% inhibition at 5×10^–7 M for both inhibitiors) as well as by high concentrations of substrate, but not by tetraisopropylpyrophosphamide. The sensitivity against inhibitors is the same in extracts from hormone-treated cells and from controls. The cholinesterase activity correlates with morphological changes (shape and cell arrangement) and is indepenent of neuronal differentiation. We therefore propose a function for this activity during morphogenesis.     

Novel observations of midge and mosquito larval population dynamics in leaves of the northern pitcher plant,Sarracenia purpurea L.

The invertebrate communities in Sarracenia purpurea were characterized by surveying the contents of 474 leaves from six pitcher plant populations in the eastern United States. More than 8200 invertebrate specimens, both living and dead, were recovered. Midge and mosquito larvae comprised 7907 (96%) of the specimens, with a mean of 16.9 dipteran larvae per leaf. Although midge larvae were present at all collection sites, mosquito larvae were absent from two of the sites. In the latter sites, the number of midge larvae per leaf was greater. This report documents for the first time that there is no statistical difference between the average number of Diptera larvae per leaf for sites that contain both midge and mosquito larvae compared to sites that contain only midge larvae. It appears that pitcher plants maintain an average number of larvae per leaf based on a number of interacting factors which we do not fully understand. This investigation documents that in the absence of mosquito larvae, more midge larvae are found per leaf per leaf than would be predicted based on data from sites that contain both larval taxa.     

Hypersensitive reaction and induced resistance in rice against the Asian rice gall midge Orseolia oryzae

Rice seedlings of the resistant variety Phalguna showed premature tillering, browning of central leaf, and tissue necrosis at the apical meristem following artificial infestation with avirulent biotype 1 of the Asian rice gall midge, Orseolia oryzae (Wood-Mason) (Diptera: Cecidomyiidae). Tissue necrosis representing a typical hypersensitive reaction (HR), accompanied by maggot mortality, was observed within 4 days after infestation. However, reinfestation of secondary tillers subsequent to HR in primary tiller, did not lead to HR in secondary tillers though maggot mortality was seen. Artificial infestation with the weed gall midge O. fluvialis did not result in HR either in gall midge susceptible TN 1 or resistant Phalguna rice varieties. Resistance in Phalguna against the virulent biotype 4 could be induced by either prior, simultaneous, or subsequent infestation with the avirulent biotype 1. The duration of effectiveness of such induced resistance varied with the sequence and time lag between infestations.     

Extracellular mannanases and galactanases from selected fungi

Summary Eight thermophilic fungi were tested for production of mannanases and galactanases. Highest mannanase activities were produced byTalaromyces byssochlamydoides andTalaromyces emersonii. Mannanases from all strains tested were induced by locust bean gum except in the case ofThermoascus aurantiacus, where mannose had a greater inducing effect. Locust bean gum was also the best inducer of -mannosidase and galactanase except in the case ofT. emersonii where galactose was a better inducer of both these enzymes. Highest mannanase activity was produced byTalaromyces species when peptone was used as nitrogen source whereas sodium nitrate promoted maximum production of this enzyme byThielavia terrestris andT. aurantiacus. The pH optima of mannanases from the thermophilic fungi were in the range 5.0–6.6 and contrasted with the low pH optimum (3.2) of the enzyme fromAspergillus niger. Galactanases had pH optima in the range 4.3–5.8. The mannanase fromT. emersonii and the galactanase fromT. terrestris were most thermostable, each retaining 100% activity for 3 h at 60°C.     

Spontaneous activity of the light-dependent channel irreversibly induced in excised patches from Limulus ventral photoreceptors

We have studied the properties of membrane patches excised from the transducing lobe of Limulus ventral photoreceptors. If patches are excised into an "internal" solution that resembles the ionic composition of the cytoplasm, channel activity is typically absent, but can be turned on by cyclic GMP (cGMP). In contrast, if patches are excised directly into sea water and subsequently examined in internal solution, they exhibit a high channel activity in the absence of any second messenger (spontaneous channel activity). Because these patches contained only light-dependent channels when examined before excision and because these spontaneous channels have properties in common with the light/cGMP-dependent channel, we believe that the spontaneously active channels represent light/cGMP-dependent channels that have been damaged by exposure to sea water, perhaps due to proteolysis activated by the high Ca2+ levels of the sea water. One type of the spontaneously active channel resembles the light/cGMP-dependent channel in open time, reversal potential, conductance states and voltage dependence. Application of micromolar Ca2+ to this channel produces a reversible decrease in the opening rate, indicating a high affinity binding site for Ca2+ on this channel. Another type of spontaneously active channel has a conductance state and reversal potential similar to the light/cGMP-dependent channel, but has apparently lost its dependence and sensitivity to Ca2+ and voltage.     

Extracellular laccase activity in Tetraploa aristata

Tetraploa aristata CLPS 419 produced maximum extracellular laccase activity at over 9 mU ml^–1 in shaking cultures supplemented with glucose and 3.5 mU ml^–1 in sucrose-grown ones. Laccase activity did not exceed 0.7 mU ml^–1 in stationary cultures with glucose and was not detected in similar cultures with sucrose or in ones grown on lignin.     

Extracellular enzymatic activity ofMicrosporum canis isolates

The enzymatic activity of 70 feline and canineMicrosporum canis isolates was determined by the Api-Zym^® test. The liquid phase of cultures, inoculated into Tryptic Soy Broth, was used to examine 19 enzymes. Considerable differences were observed among the extracellular enzymatic patterns. All the isolates produced alkaline phosphatase and beta-glucosidase, while lipase (C14), trypsin, chymotrypsin, beta-glucuronidase, and alpha-fucosidase activity was never revealed. Esterase (C4) activity was present in 57 samples (81%), esterase lipase (C8) in 31 (44%), leucine arylamidase in 35 (50%), valine arylamidase and cystine arylamidase in 7 (10%), acid phosphatase in 64 (91%), naphthol-AS-BI-phosphohydrolase in 60 (86%), alpha-galactosidase in 5 (7%), beta-galactosidase in 6 (8%), alpha-glucosidase in 25 (36%), N-acetyl-beta-glucosaminidase in 41 (58%), and alpha-mannosidase in 51 (73%). The beta-galactosidase activity ofM. canis has not been reported previously. Remarkable variations of intensity for each enzymatic activity were also detected. It is believed that these results could provide basic data for further investigations on the pathogenic role of enzymes secreted byM. canis.     

Extracellular proteolytic enzyme activity ofHistoplasma capsulatum var.duboisii

Histoplasma capsulatum var.duboisii is the etiological agent of African histoplasmosis, an important deep mycosis in West Africa. Not much is known about the physiological properties of this fungus. This communication reports on the extracellular proteolytic enzyme activity of this fungus. Five isolates of this fungus tested hydrolyzed azocasein and bovine serum albumin at pH 6.8 and 8.0. Assay of the crude enzyme showed that proteolytic activity increased with age and peaked on the 10th day and then again on the 13th day for the yeast form, and on the 11th day of growth for the mycelial form. The optimum temperature and pH for maximum enzyme activity were 35 °C and 6.8 respectively. The proteinase activity was more pronounced with the yeast form than with the mycelial form. The action of enzyme inhibitors suggested the presence of an aspartyl proteinase.