Pheromone perception in the tsetse fly Glossina morsitans morsitans

The perception of cuticular female sex pheromone (15, 19, 23-trimethylheptatriacontane=morsilure) in Glossina m. morsitans was studied electrophysiologically and behaviourally. Electrophysiological studies indicated no sensitivity of the tibial sensilla or the contact chemoreceptive hairs on the legs of males to the pheromone. However, electroantennograms were recorded during stimulation of antennae from male flies with the odour of morsilure, which indicated that the pheromone is detected by the insect via olfactory receptors on the antennae. This was further confirmed by behavioural experiments in which the antennal movements of intact males stimulated with the odour of both synthetic pheromone and female decoys were studied. Behavioural responsiveness to morsilure increased with increasing starvation and was not due to a general sensitivity to paraffins. These studies indicate that tsetse flies may be able to recognize conspecifics at close range using their sense of olfaction.

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Résumé La perception de la phéromone sexuelle des femelles de Glossina m.morsitans, la morsilure (15, 19, 23-triméthylheptatriacontane) a été examinée par électrophysiologie et par le comportement. L'électrophysiologie n'a pas révélé de sensibilité des sensilles tibiales, ni des poils chimioréceptives de contact sur les pattes des mâles à la phéromone. Cependant, les électroantennogrammes recueillis pendant la stimulation des antennes des mâles par l'odeur de morsilure, ont montré que la phéromone est décelée par l'insecte grâce aux récepteurs olfactifs des antennes. Ceci a été confirmé ultérieurement par des expériences de comportement au cours desquelles ont été examinés les mouvements antennaires de mâles intacts stimulés par l'odeur de phéromone synthétique et de femelles.La réponse comportementale à la morsilure a augmenté avec le jeûne, elle n'était pas due à une sensibilité générale aux paraffines.Ces études montrent que les mouches tsé-tsé peuvent être capables de reconnaître leurs congénères à faible distance grâce à l'olfaction.

     

Factors associated with neonatal lamb mortality

Three factors were associated with lamb neonatal mortality: birthweight (P<0.003), number of lambs born per ewe (P<0.001) and lamb sex (P<0.32). Lamb birthweight had the greatest predictive power for survival during the neonatal period. The neonatal mortality rate was 14.3%. The age specific mortality for lambs one day old was 7.9% (P<0.05). Seventy-nine percent of the lambs that died, did so by the end of the fourth post-natal day. Starvation was associated with 58.3% (P < 0.05) of the lamb deaths.     

Variation in sex determination in natural populations of a shrimp

Strategies of sex determination were studied in Gammarus duebeni, a brackish water shrimp (Crustacea, Amphipoda). Animals from Budle Bay, northern England, have environmental sex determination (e. s. d.), in accord with a population studied in Germany. Males are produced in long day photoperiods and females in short days. By contrast, animals from southern England show no significant sex ratio variation with daylength. This is the first report of such variation in sex determination for an invertebrate. Detailed studies of Budle Bay animals show that sex is determined several weeks after young are released by the mother; that the critical daylength is longer at Budle Bay than in Germany; and that the critical response is cued at the onset of a photophase. The nature of sex determination in G. duebeni may be associated with population dynamics. Males gain greater relative fitness by large size than females. E. s. d. is then adaptive where the breeding season produces significant growth differences between early and late animals, but where generations do not overlap. Comparisons are drawn with the flexible sex determining system in Menidia menidia (Pisces).     

Flow sorting of X and Y chromosome-bearing mammalian sperm: Activation and pronuclear development of sorted bull,boar, and ram sperm microinjected into hamster oocytes

Flow cytometric techniques were used to measure relative DNA content of X and Y chromosome-bearing bull, boar, and ram sperm populations and to separate the two sex-determining populations. Neat semen was prepared for flow cytometric analysis by washing, light sonication, and staining with 9 μM Hoechst 33342. Computer analysis of the bimodal histograms showed mean X-Y DNA differences of 3.9, 3.7, and 4.2% for bull, boar, and ram, respectively. Flow cytometric reanalysis of sorted bull, boar, and ram sperm showed purities greater than 90%. Bull, boar, and ram sperm nuclei were microinjected into hamster oocytes. Microinjected sperm were either unsorted, sorted, unsorted plus dithio-threitol (DTT) exposure, or sorted plus DTT exposure. Following microinjection, eggs were incubated 3 hr, fixed, and stained. A total of 579 eggs was observed for sperm activation (decondensation or formation of a male pronucleus). A lower percentage of sorted than unsorted (3 vs. 23%) boar sperm was activated (P <.05). However, sorted and unsorted DTT-exposed boar sperm or sorted and unsorted bull or ram sperm, regardless of DTT treatment, did not differ significantly. Sorted sperm nuclei of both rams and bulls exhibited higher activation rates than sorted boar sperm (P <.05). Treatment of sperm with DTT increased the activation rate (P < .05) for sorted boar sperm but not for bull or ram sperm. These data represent the first separation of bull, boar, and ram X and Y chromosome-bearing sperm populations and the first evidence that sperm of domestic animals sorted on the basis of DNA by flow cytometric procedures have the ability to decondense and to form pronuclei upon injection into a hamster egg.     

Seasonal changes in the population of the mite Unionicola intermedia (Hydrachnellae,Acari) from the freshwater mussel Anodonta anatina (Unionidae)

Although numbers were low in winter, males of Unionicola intermedia were found throughout the year. A mean of 2.5 (±0.26 SE) males per mussel was found with a range of 0 to 20. Females had a mean of 13.07 (±0.87 SE) per mussel and a range from 0 to 57, with the highest mean in August. The incidence of males was much lower than that of females. Nymphs and females were highly aggregated and males showed aggregation at a lower level of significance for nine months of the year. Although the primary sex ratio is unknown, the tertiary sex ratio is 86% female and on a monthly basis ranged from 68.9% to 96.7% female. It is speculated that reproduction is arrhenotokous. The sex ratio and the significant seasonal variations of the active stages may be influenced by the dispersal pattern of this species and by the biology of its host.     

Sex allocation in an hermaphroditic plant: the case of gynodioecy in Thymus vulgaris L.

Resource allocation to male and female functions was investigated in Thymus vulgaris L. (thyme), a gynodioecious species, in which females produce twice as many seeds as hermaphrodites. Negative correlations were found between male and female fertility of hermaphrodites, providing evidence of a trade-off. There was a high variability in sexual investment, some of the hermaphrodites functioning almost as males, and others almost as females. Estimation of the relative cost of male and female gametes showed that the female advantage in seed production was mainly due to reallocation of the resources not allocated to male function into female function. The determination of sex allocation was shown to have a genetic component, and there were some evidence that an interaction between nuclear and cytoplasmic genomes was involved.     

Sex pheromone components of female Cornutiplusia circumflexa

Capillary gas chromatography indicated the presence of (Z)-7-dodecenyl alcohol and (Z)-7-dodecenyl acetate in the abdominal tip extracts of female Cornutiplusia circumflexa (L.) (Lepidoptera: Noctuidae: Plusiinae) moths. Gas chromatography combined with mass spectrometry and dimethyl disulfide derivatization confirmed the structure of these two principal pheromone components. In a flight-tunnel bioassay, a 5:1 blend of alcohol and acetate elicited the complete courtship sequence by males. The response was comparable to that evoked by a live virgin female, but males spent significantly longer time at calling females than at the synthetic source. The 5:1 blend was also attractive to male C. circumflexa in the field, as indicated by catches in traps baited with this mixture. (Z)-7-dodecenyl alcohol alone was slightly attractive whereas (Z)-7-dodecenyl acetate alone was completely inactive. C. circumflexa is the first reported Plusiinae species which utilizes (Z)-7-dodecenyl alcohol as the major pheromone component.     

Sex pheromones of Spilonota ocellana and Spilonota laricana

The sex pheromones of Spilonota ocellana D. & S. and Spilonota laricana Hein. (Lepidoptera: Tortricidae) were identified by chemical analysis and field trapping. Female moths of the two species produce (Z)-8-tetradecenyl acetate, (Z)-8-tetradecen-1-ol and dodecyl acetate in almost the same proportions (98:1:1 and 97:3:1). Males of both species were best attracted to a blend of 10:1 to 1:1 Z8-14Ac:Z8-14OH. This indicates that mating barriers other than sex pheromones exist between sympatric populations.     

Egg allocation of the autoparasitoid encarsia tricolor at different relative densities of the primary host (Trialeurodes vaporariorum) and two secondary hosts (Encarsia formosa and E. tricolor)

Parasitism, offspring sex ratio and superparasitism of the facultative autoparasitoid Encarsia tricolor Foërster (Hymenoptera: Aphelinidae) when given access to arenae with different proportions of the primary host (Trialeurodes vaporariorum (Westwood)) and two species of secondary hosts (E. tricolor and Encarsia formosa Gahan) were studied.Parasitism and offspring sex ratio were not affected by female age in the range 3–10 days old. When the secondary hosts were young E. tricolor pupae, eggs were mostly laid on primary hosts, so the offspring sex ratio was more female-biased than expected, and secondary hosts were not superparasitized at all. When the secondary hosts were fully grown E. formosa larvae, superparasitism was small and offspring sex ratio was more male-biased than expected. E. tricolor females were able to discriminate between hosts previously parasitized by themselves and non-parasitized hosts.     

Nocturnal behaviour of female Mythimna convecta

Nocturnal behaviour of Mythimna convecta (Walker) (Lepidoptera: Noctuidae) virgin females was studied in the laboratory under 20 °C and 16:8 LD conditions. The periodicity of activity, feeding, calling, pre-oviposition extrusion and oviposition varied with female age and hour of the scotophase. Females called for the first time between the 2nd and 11th scotophases with the peak in the 4th scotophase. Maximum calling occurred on the 7th hour of the scotophase. Young moths called more frequently with shorter bouts while old moths called less often but with longer bouts. In the presence of older females, moths spent significantly more time in pre-oviposition extrusion and resting and less in activity and feeding than they did when only females of the same age or younger were present. There were no significant differences for calling suggesting that pheromones of older calling females did not affect calling of younger females.