γ-Radiation studies of two strains of Trichoplusia ni: Sensitivity of the compound eye and induced sterility

The visual response of laboratory-reared wild-type and yellow-eyed mutant (lacking pigments) cabbage loopers, Trichoplusia ni, was studied by standard electroretinogram (ERG) techniques. The ERG waveform, time to dark-adapt, maximum sensitivity, and flicker fusion frequency (FFF) of both strains and sexes were compared with those of moths treated with 15 and 30 krad of γ-radiation. From the rate of dark adaptation, yellow-eyed moths were initially more sensitive than wild-type moths, but no significant differences were apparent in the ERG waveform, total time to dark-adapt, and FFF between strains, sexes, or treatment groups. However, both sexes of both strains exhibited increased sensitivity (required less light to evoke a threshold response when fully dark-adapted) to light stimulus when they had been treated with 15 krad of γ-radiation.A comparison of the effects of irradiation on the fertility and fecundity of the two strains showed no significant differences between the number of eggs oviposited by inseminated females. However, the lower egg hatch by yellow-eyed females at most dose levels indicated reduced egg viability for the yellow-eyed genotype. Thus, a significant dose × strain interaction was found when the percentage of egg hatch of the two strains was compared.     

The flicker fusion frequencies of six laboratory insects, and the response of the compound eye to mains fluorescent 'ripple'

ABSTRACT. The ERG response of the compound eye to single, brief, light pulses, to sustained stimulation for 2 s, and the dark adapted flicker-fusion frequency (FFF) under stroboscopic light was measured in six species: Locusta migratoria (FFF range: 40–90 Hz), Periplaneta americana (25–60 Hz), Saturnia pavonia (65–85 Hz), Antheraea pernyi (25–70 Hz), Glossina morsitans (85–205 Hz) and Drosophila hydei (60–100 Hz). The first four species have typical 'slow-eyed', monophasic ERG responses; the two flies typical 'fast-eyed', biphasic responses. The FFF proved to be dependent on the state of light adaptation, being 40–70% higher than the above figures after only 2 min exposure to as little as 300 lx. Adult male Glossina , but not Locusta nymphs, showed a clear 100 Hz ERG ripple in response to single-phase, mains fluorescent lighting. To three-phase fluorescent lighting no 300 Hz ERG ripple was detected, but the 100 Hz component was still evident.     

Olfactory responses of tsetse flies to phenols from buffalo urine

Abstract A comparison was made of the EAG responses of males and females of Glossina morsitans morsitans Westwood, G.austeni Newstead and G.tachinoides , Westwood to various doses of compounds known to be components of ox and buffalo urine fractions which are attractive to tsetse in the field (phenol, 3- and 4-methylphenol, 3- and 4-ethylphenol, 4-n-propylphenol, dimethylsulfone). All three species did not respond to dimethylsulfone. The overall responses to the phenolic substances were higher in females than in males in G.m.morsitans and higher in males than in females in G.austeni and G.tachinoides. Response spectra of the species for the phenolic substances suggested that G.m.morsitans and G. austeni were most responsive to 3- and 4-methylphenol and 3-ethylphenol, whereas G. tachinoides was most sensitive to 3-ethylphenol and 3-methylphenol, and only moderately sensitive to 4-methylphenol.
Cross-adaptation experiments, in which l-octen-3-ol, acetone, 4-heptanone and 3-nonanone were also included, revealed that all phenolic compounds stimulated one and the same class of receptors, which differed from the class of receptors activated by l-octen-3-ol. The ketones also had their own receptors. Hence, the flies can obtain information about the presence of attractants by at least three different receptor classes. It was concluded that phenol and any individual alkylphenol found in ox and buffalo urine should be attractive to tsetse flies, provided that stimulus intensity is above threshold and not beyond optimum. One class of receptors may respond more strongly in males than in females, whereas another class is more responsive in females than in males. This may result in a change in sex ratios in catches depending on the odour bait used.     

Characteristics of Drosophila rhodopsin in wild-type and norpA vision transduction mutants

The properties of the major visual pigment of Drosophila melanogaster were evaluated. The visual pigment was isolated from other protein components using acrylamide gel electrophoresis and spectral identification. Sodium dodecyl sulfate (SDS) acrylamide gels of the isolated visual pigment gave a single protein subunit with a mol wt of 37,000 daltons. The rhodopsin480 molar extinction coefficient was 35,000 liter/mol-cm (+/- 2,700 SE). The metarhodopsin580 molar extinction coefficient was approximately 56,000 liter/mol-cm. Microspectrophotometry was used to compare the rhodopsin concentrations in wild-type flies and norpA vision transduction mutants. At 2 days of age (12 h dark-12 h light cycle, 19 degrees C) all of the norpA flies exhibited a similar rhodopsin concentration (75% of the wild-type strain). By 21 days of age some of the norpA alleles showed substantially reduced rhodopsin concentrations (16-43% of normal), whereas others showed no major age-dependent decreases (68-77%). Temperature and light-dark cycle affected the reduction. Alleles with no receptor potential exhibited the largest decreases in rhodopsin concentration. The data indicate that the norpA phototransduction mutant has a defect in the system responsible for maintaining the rhodopsin480 concentration. This defect in the rhodopsin maintenance system does not appear to be the cause of the reduced electroretinogram (ERG) amplitude observed in some of these mutants, but instead is a consequence of the decrease in ERG amplitude, or the flaw(s) responsible for the decrease in ERG amplitude.     

Genetics of hybridization of Glossina swynnertoni with Glossina morsitans morsitans and Glossina morsitans centralis

Abstract Reciprocal crosses were performed with Glossina swynnertoni and Glossina morsitans morsitans and with G. swynnertoni and Glossina morsitans centralis , using strains that carried marker genes in all three linkage groups. Glossina swynnertoni males can inseminate, but not fertilize, G.m.morsitans; all other crosses produced some fertile females. Hybridization did not cause sex ratio distortion among F_{ flies. Most F and backcross females were fertile, but all F, males were sterile. Sterility among backcross males was also high (99% in BXj, 85% in Bx₂, and about 50% in Bx₃ to Bx₅). Chromosome transmission by hybrid females usually conformed to Mendelian expectations, but genetic recombination was lower than observed in G.m.morsitans. The reduction in fertility among backcross females was not associated with heterozygosity in any linkage group. Sterility among hybrid and backcross males was associated with heterozygosity of sex chromosomes and probably autosomes. The results support the systematic placement of G.swynnertoni closer to G.mxentralis than to G.m.morsitans.     

Spectral responses of the tsetse fly, Glossina morsitans morsitans

Spectral responses of male Glossina morsitans morsitans Westw, were investigated using behavioural and electrophysiological techniques. Phototactic responses to monochromatic lights of different wavelengths but equivalent intensities (measured either in energy or quantal units) were tested in an apparatus which permitted the simultaneous presentation of pairs of lights to groups of flies. Near ultraviolet light was the most attractive, followed by blue and red, with green and far red light giving no significant responses above control levels. The spectral sensitivity of the compound eye was also determined from the electroretinogram (ERG) recorded from electrodes implanted in the eye which was stimulated with flashes of monochromatic light. Three areas of maximum sensitivity were found by this method in the UV, blue/green and red. The relationship between the behavioural and electrophysiological sensitivity characteristics is explained with reference to visual systems of other Diptera which have previously been described.     

Effects of age, sex and hunger on the antennal olfactory sensitivity of tsetse flies

Abstract The effects of age on electroantennogram (EAG) responses were investigated in male and female Glossina morsitans morsitans and comparative studies on the effects of starvation and sex on the EAG in G.m. morsitans, G.austeni, G.tachinoides and G.fuscipes fuscipes were made. Stimuli were the vapours of l-octen-3-ol, 4-heptanone, 3-nonanone and acetone. EAG decreased with age in both sexes of G.m.morsitans , responses in 5-day-old flies already being significantly lower than those in 1-day-old flies. In G.m.morsitans and G.tachinoides , EAG responses of males were higher than those of females. In G.austeni and G.f.fuscipes , however, the reverse was found. With increasing starvation EAG sensitivity increased in both sexes of G.m.morsitans and G.tachinoides. In G.austeni and in G.f.fuscipes no clear effects of starvation were observed. Response spectra of the individual species to the four odour substances did not change with increasing hunger. It is concluded that receptor sensitivity may be modulated depending on the insect's needs. Possible mechanisms of regulation and significance of this modulation are discussed.     

The effect of eye colour pigments on the action spectrum of Drosophila

In vivo absorption spectra for Drosophila melanogaster eye colour pigment classes (drosopterins and ommatins) were constructed by subtracting the whole eye electroretinographic (ERG) spectral sensitivities of cn and bw respectively from the sensitivities of white-eyed strains. In situ microspectrophotometric (MSP) absorption spectra were also obtained. Both the ERG and MSP drosopterin spectra show a visible peak at 500 nm compared to the 480 nm peak of in vitro drosopterins. For the ommatins, the ERG absorption spectrum peaks at 450 nm while the MSP spectrum peaks at 400 and 525 nm. The ERG spectrum is similar to the in vitro absorption spectrum of xanthommatin while the MSP spectrum is similar to the in vitro absorption spectrum of reduced xanthommatin. The ERG absorption spectra for the drosopterins and the ommatins yield an accurate prediction of the effect of the combined pigments in wild-type eyes. Newly emerged and 7 day post-emergence bw flies show quantitatively similar pigment absorption effects while the drosopterins depress the sensitivity of newly emerged cn flies to a greater extent than that of cn flies 7 days after emergence.     

Spectral sensitivity of ground squirrel cones measured with ERG flicker photometry

Summary Ground squirrels have dichromatic color vision. The spectral sensitivities of the two classes of cones found in the retinas of two species of ground squirrel were measured using ERG flicker photometry. The spectral sensitivity curves for these cone classes were closely fit by curves from wavelength-dependent visual pigment nomograms. One cone type had an average peak sensitivity of 518.9 nm (California ground squirrels,Spermophilus beecheyi) or 517.0 nm (thirteen-lined ground squirrels,Spermophilus tridecemlineatus). The second type of cone found in these ground squirrels had an average peak sensitivity of 436.7 nm. An examination of the variation in spectral sensitivity among individual animals suggests that the sensitivity peaks for the middle-wavelength cone cover a range of not greater than 4 nm.     

Effects of light on pigment development in the echiuran worm, Bonellia viridis

In rhe echiuran Bonellia viridis the green pigment first develops in the gastrula, before the formation of the trochal rings, and the trochophores acquire a deep green pigmentation before hatching. Eggs that were cultured under continuous illumination (2000–4000 lx) did not develop any green pigment, and although the trochophores hatched normally, they lacked pigment entirely. The unpigmented trochophores that were kept under continuous illumination developed into unpigmented males and females. The far-blue (380–400 nm) and red (620–640 nm) regions were more effective in preventing pigment development than the blue, green and yellow regions of the spectrum. Illumination of the eggs before the gastrula stage did not affect the development of pigment when these were subsequently returned to the dark. When unpigmented trochophores, that had been cultured in the light, were placed in the dark they acquired a slight pigmentation, but this was much less intense than that of trochophores that had been cultured in the dark throughout. Pigmented trochophores were more vulnerable to high light intensities than unpigmented ones.     

Temporal properties of the lens eyes of the box jellyfish Tripedalia cystophora

Box jellyfish (Cubomedusae) are visually orientating animals which posses a total of 24 eyes of 4 morphological types; 2 pigment cup eyes (pit eye and slit eye) and 2 lens eyes [upper lens-eye (ule) and lower lens-eye (lle)]. In this study, we use electroretinograms (ERGs) to explore temporal properties of the two lens eyes. We find that the ERG of both lens eyes are complex and using sinusoidal flicker stimuli we find that both lens eyes have slow temporal resolution. The average flicker fusion frequency (FFF) was found to be approximately 10 Hz for the ule and 8 Hz for the lle. Differences in the FFF and response patterns between the two lens eyes suggest that the ule and lle filter information differently in the temporal domain and thus are tuned to perform different visual tasks. The data collected in this study support the idea that the visual system of box jellyfish is a collection of special purpose eyes.     

Trypanosoma brucei 29-13 strain is inducible in but not permissive for the tsetse fly vector

Using green fluorescent protein as a reporter, we have shown that the strain 29-13 of Trypanosoma brucei, widely used for inducible down-regulation of mRNA, is inducible in, but not permissive for the tsetse flies Glossina palpalis gambiensis and Glossina morsitans morsitans. Within two weeks post-infection, 42% males and females of teneral and non-teneral tsetse flies harboured intestinal infections, yet not a single infection progressed into the salivary glands.     

Metabolic rates of tsetse flies in the field as measured by the excretion of injected caesium

ABSTRACT Teneral tsetse flies, Glossina morsitans morsitans Westw., were injected with labelled caesium (¹³⁷Cs) <18 h after emergence and released in the Zambezi Valley of Zimbabwe between May 1983 and June 1984, and again in February 1985. Radioactivity in flies recaptured time t days after injection indicated a three-stage exponential loss of caesium, identical for both sexes. For t≫4 the estimated rate constant (-0.119 per day) was significantly lower than for 4≫t≫12 (–0.252 per day). By day 15 about 97% of the isotope had been excreted; thereafter the loss rate fell by an order of magnitude. The data for t>4 days were well fitted by the sum of two exponentials but no smooth function was found to fit all three phases. The loss rate from the rapidly metabolized pool increased exponentially with temperature at the same rate as for male tsetse kept in the dark in the laboratory. However, the loss rate in the field was lower at every temperature, suggesting that these flies live at 2–6^oC lower than the average Stevenson screen temperature. Published estimates of hunger cycle and daily flight durations, made on the basis of measured rates of caesium excretion, are invalid because they use the assumption that flies are living in the field at screen temperatures. The data suggest that both sexes have the same metabolic rate up to the age of about 15 days, which implies that the females (being larger and having to nourish a larva in the latter stages of this period) must be less active and/or live at even lower temperatures than the males.     

The eel retina. Receptor classes and spectral mechanisms

Light and electron microscopy revealed that there are both rods and cones in the retina of the eel Anguilla rostrata. The rods predominate with a rod to cone ratio of 150:1. The spectral sensitivity of the dark-adapted eyecup ERG had a peak at about 520 nm and was well fit by a vitamin A2 nomogram pigment with a lambdamax = 520 nm. This agrees with the eel photopigment measurements of other investigators. This result implies that a single spectral mechanism--the rods--provides the input for the dark-adapted ERG. The spectral sensitivity of the ERG to flicker in the light-adapted eyecup preparation was shifted to longer wavelengths; it peaked at around 550 nm. However, there was evidence that this technique might not have completely eliminated rod intrusion. Rod responses were abolished in a bleached isolated retina preparation, in which it was shown that there were two classes of cone-like mechanisms, one with lambdamax of 550 nm and the other with lambdamax of less than 450 nm. Ganglion cell recording provided preliminary evidence for opponent-color processing. Horizontal cells were only of the L type with both rod and cone inputs.     

Age, sex ratio and timing of the catch of kelts and ascending Atlantic salmon in the subarctic River Teno

By 15 June, 82% of the catch of Atlantic salmon Salmo salar kelts had been taken from the middle part of River Teno, northern Scandinavia. The median date of capture was 4 June for males and 8 June for females. Salmon of 1–4 sea–winters (SW) of both sexes survived spawning to return to sea as kelts. Among males, 1 SW kelts were caught earliest in the spring and 3 SW latest, but among females 4 SW were earliest, then 3 SW and finally 1 and 2 SW. There were 17 river and sea–age combinations among the kelts compared with 23 among the ascending salmon. The smolt age distribution and the mean smolt age differed significantly only between female 2 SW ascending salmon (3·97 years) and kelts (4·14 years). The proportion of 1 SW females was higher and that of 3 SW males lower among kelts than among ascending salmon. The proportion of males among 1 SW ascending salmon was 80% but among kelts only 57%. Similarly, the proportion of males among 3 SW fish was 21% for ascending salmon but only 7% for kelts. Hence overwinter mortality was higher among males. Male and female kelts of 1 and female kelts of 2 SWhad a greater mean length than ascending salmon in corresponding groups indicating a better survival of larger fish within an age group. Grilse ascend rivers after most kelts have left, but the main catch of ascending 2–3 SW salmon takes place concurrently with kelts leaving the river, inadvertently targeting kelts in the fishery.     

Activation of three species of tsetse (Glossina spp.) in response to host derived stimuli

Recordings were made of the activation of hungry Glossina morsitans morsitans Westwood, G. pallidipes Austen, and G. austeni Newstead in response to odours from ox breath and ox urine, and a moving visual stimulus, in a wind tunnel. The spontaneous activity of G.m.morsitans was very low (less than 4% of males and 2% of females active per min during control periods). That of G.austeni and G.pallidipes was in the region of 20% except for G.pallidipes females when in excess of 40% were active during control periods. Addition of ox urine odours to the airstream had no effect on activity in any of the species investigated but addition of ox breath odours to the airstream significantly increased activity of G.pallidipes and of G.m.morsitans, although for the latter only approximately 12% of flies were active. For G.austeni the addition of ox breath odours resulted in a significant increase in activity of females but not of males. The moving visual stimulus resulted in a significant increase in the activity of both sexes of G.austeni and G.m.morsitans but no change in the activity of G.pallidipes. The low level of spontaneous activity and the low response to ox breath odours in a strain of G.m.morsitans maintained in the laboratory since 1969 was compared with a new colony of this species which originated from puparia collected in Zimbabwe in 1991. No differences in either spontaneous activity or the response to ox breath odour was recorded, but females from the new colony were significantly more responsive to a moving visual stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of sex and fly species on the development of trypanosomes in tsetse flies

Unlike other dipteran disease vectors, tsetse flies of both sexes feed on blood and transmit pathogenic African trypanosomes. During transmission, Trypanosoma brucei undergoes a complex cycle of proliferation and development inside the tsetse vector, culminating in production of infective forms in the saliva. The insect manifests robust immune defences throughout the alimentary tract, which eliminate many trypanosome infections. Previous work has shown that fly sex influences susceptibility to trypanosome infection as males show higher rates of salivary gland (SG) infection with T. brucei than females. To investigate sex-linked differences in the progression of infection, we compared midgut (MG), proventriculus, foregut and SG infections in male and female Glossina morsitans morsitans. Initially, infections developed in the same way in both sexes: no difference was observed in numbers of MG or proventriculus infections, or in the number and type of developmental forms produced. Female flies tended to produce foregut migratory forms later than males, but this had no detectable impact on the number of SG infections. The sex difference was not apparent until the final stage of SG invasion and colonisation, showing that the SG environment differs between male and female flies. Comparison of G. m. morsitans with G. pallidipes showed a similar, though less pronounced, sex difference in susceptibility, but additionally revealed very different levels of trypanosome resistance in the MG and SG. While G. pallidipes was more refractory to MG infection, a very high proportion of MG infections led to SG infection in both sexes. It appears that the two fly species use different strategies to block trypanosome infection: G. pallidipes heavily defends against initial establishment in the MG, while G. m. morsitans has additional measures to prevent trypanosomes colonising the SG, particularly in female flies. We conclude that the tsetse-trypanosome interface works differently in G. m. morsitans and G. pallidipes.     

Genetics of Glossina morsitans morsitans (Diptera: Glossinidae). X. A mutant (sabr) having long scutellar apical bristles in females

A line of Glossina morsitans morsitans Westwood was established in which females have scutellar apical bristles approximately three times as long as normal. In other respects the flies appear normal. The mutant allele, sabr, is recessive to the wild-type allele. The locus for sabr is located in linkage group III, 50 or more map units from the locus for malic dehydrogenase. Scutellar apical bristles in mutant flies are longer in flies emerging from puparia maintained at 30 degrees C than in flies emerging from puparia maintained at 25 degrees C.     

Rod-Driven OFF Pathway Responses in the Distal Retina: Dark-Adapted Flicker Electroretinogram in Mouse

Purpose

The rodent retina does not exhibit a positive OFF-response in the electroretinogram (ERG), which makes it difficult to evaluate its OFF-pathway functions in vivo. We studied the rod-driven OFF pathway responses by using a dark-adapted 10-Hz flicker ERG procedure in mouse.

Materials and Methods

Conventional ERGs and 10-Hz dark-adapted flicker ERGs were obtained in wild-type mice (C57BL/6), in mice with pure rod (cpfl1) or pure cone (rho^−/−) function, and in nob1 mice which have a selective ON-pathway defect. To isolate the response from ON or OFF pathway, glutamate analogs 2-amino-4-phosphobutyric acid (APB, an ON pathway blocker) and cis-2, 3-piperidine-dicarboxylic acid (PDA, an OFF pathway blocker), were injected intravitreally.

Results

The amplitude-intensity profile of the dark-adapted 10-Hz flicker ERG in the wild-type mice exhibits two peaks at middle and high light intensities. The two peaks represent rod- and cone-driven responses respectively. In APB-treated C57BL/6 mice and in nob1 mice, the dark-adapted ERG b-waves were absent. However, both rod- and cone-driven OFF pathway responses were evident with flicker ERG recording. At middle light intensities that activate only rod system, the flicker ERG responses in saline-injected nob1 mice were similar to those in APB-injected cpfl1 mice and wild-type mice. These responses are sensitive to PDA. The amplitudes of these rod-driven OFF pathway responses were approximately 20% of the total rod-driven flicker ERG responses.

Conclusion

We demonstrate that the rod-OFF bipolar cell pathway is functional in the outer retina. The dark-adapted flicker ERG is practical for the evaluation of rod- and cone-driven responses, and the residual OFF pathway signals in subjects with ON pathway defects.