Insect tissue culture systems: models for study of hormonal control of development

Summary The regulation of growth and development of insects is under endocrine control and involves both juvenile hormones and ecdysteroids. Neuropeptides are master regulators which control the secretion of these hormones. Most experiments in insect endocrinology have been conducted in vivo, but tissue culture methodology is playing an increasing role due to the great interest in simpler model systems for the study of complex processes that occur in vivo. The availability of appropriate media has allowed the culture of a variety of insect organs and cell lines of defined origin which have kept certain properties of the parent tissues. Tissue culture approaches have been useful for studying hormonal control of morphogenetic processes. Cell lines are particularly suited to the study of hormonally regulated mechanisms of macromolecular biosynthesis and gene expression. Thus, the value of in vitro analysis in studies of regulation of hormone production is now recognized. Results obtained from tissue culture allow more precise definition of the hormonal requirements of insect cells and tissues for growth and differentiation and might make possible the discovery of new growth regulators.     

Trophic diversity of the otter (Lutra lutra L.) in temperate and Mediterranean freshwater habitats

Aim To analyse the geographical patterns in the composition and diversity of otter's (Lutra lutra L.) diet and their relationship with climatic characteristics. Location European freshwater habitats under Mediterranean and temperate climatic regimes. Methods Thirty‐seven otter diet studies were reviewed, twenty‐one from temperate and sixteen from Mediterranean areas. All studies were based on spraint analysis and their results expressed as relative frequency of occurrence of seven main prey categories. Principal Component Analysis was performed to extract the main gradients of diet composition. Pearson's correlation and t‐tests were used to assess the relationship between diet characteristics (composition, diversity and taxonomic richness) and geographical and climatic variables. Results A clear latitudinal gradient in diet composition was observed. Otter diet was more diverse and featured more prey classes in southern localities, while the species was more piscivorous towards the north, where it predated upon a higher number of fish families. This pattern was similar when temperate and Mediterranean localities of Europe were compared. Mediterranean otters behaved as more generalist predators than temperate ones, relying less on fish, and more on aquatic invertebrates and reptiles. Main conclusions Geographical differences in otter feeding ecology in Europe seem to be related with the two contrasted climatic conditions affecting prey populations. The otter can act as a highly specialized piscivorous predator in temperate freshwater ecosystems, which do not suffer a dry season and have a comparatively stable water regime compared to Mediterranean ones. However, the unpredictable prey availability in Mediterranean areas, affected by strong spatial and temporal water shortages, favours a diversification of the otter's diet.     

Stable isotopes in fish otoliths discriminate between lagoonal and oceanic residents of Taiaro Atoll (Tuamotu Archipelago, French Polynesia)

 The fully enclosed Taiaro lagoon is hypersaline (42.5 psu) and non-tidal; constant salinity and water level result from strong evaporation balanced by low percolation through the lagoon floor. Seawater can flow over the atoll rim during exceptionally high seas and may then replenish lagoonal communities with propagules of oceanic origin. The distinctive water chemistry of the lagoon suggests a possible way of identifying these immigrants. We established this potential by analysing stable isotopes of carbon and oxygen in the recent growth layers of otoliths of two adult reef fishes, Chaetodon ulietensis and Acanthurus triostegus, collected from both sides of the atoll rim. Fish from the two locations were discriminated by their isotopic signatures, suggesting that analysis of the microchemical signatures deposited during the larval development could be used in future work to determine which individuals and species complete their life-cycles in this unusual lagoon. Accepted: 28 August 1997     

Effects of Juvenoids and Retinoic Acid on Development of Larvae and Nymphs in the Tick Ixodes ricinus L. (Acari,Ixodidae) and Regeneration of Haller's Organ during Metamorphosis

Larvae and nymphs of the tick Ixodes ricinus L. display similar reactions to analogs of the insect juvenile hormones (methoprene and pyriproxyfen), which induce at both stages juvenalization of the Haller's sense organ regenerates. Similar effects were also described for retinoic acid. Unlike juvenoids, retinoic acid can affect not only regeneration, but also normal development of the Haller's organ and cause changes corresponding to so-called regenerative induction. Amputation of the leg and treatment with retinoic acid do not affect the duration of larval or nymphal development, while juvenoids somewhat accelerate their development.     

Non-native fishes in the Mediterranean from the Red Sea,by way of the Suez Canal

The opening of the Suez Canal in 1869 caused a migration generally from the Red Sea to the Mediterranean, rarely the opposite direction, and 63 lessepsian fish species penetrated into the Mediterranean by way of this canal. These species usually spread northward and most of them can establish wide populations in this area, but some of them can not be successful with respect to establishment. Thus, it is clearly seen that there are a lot of factors influencing the success of species with respect to migration, spreading and establishment. So, the lessepsian migration has been formed by the effects of these factors. Lessepsian species also have the ability to adapt to the ecological conditions of their new environment. Therefore, the influential factors, their effectiveness and the observed changes in lessepsian species due to the effects of these factors have been discussed by considering fishes in this paper.     

Methoprene modulates the effect of diet on male melon fly,Bactrocera cucurbitae,performance at mating aggregations

The effect of access to dietary protein (P) (hydrolyzed yeast) and/or treatment with a juvenile hormone analogue, methoprene (M), (in addition to sugar and water) on male aggregation (lekking) behaviour and mating success was studied in a laboratory strain of the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Six‐day‐old males were treated with (1) protein and methoprene (M+P+), (2) only protein (M?P+), or (3) only methoprene (M+P?), and compared with 14‐day‐old sexually mature untreated males (M?P?). The lekking behaviour of the four groups of males when competing for virgin sexually mature females (14 –16 days old) was observed in field cages. The following parameters were measured at male aggregations: lek initiation, lek participation, males calling, male–male interaction, female acceptance index, and mating success. For all these parameters, the M+P+ males significantly outperformed the other males. Moreover, for all parameters, there was a similar trend with M+P+ > M?P+ > M?P? > M+P?. More M+P+ males called and initiated and participated in lek activities than all other types of male, which resulted in higher mating success. They had also fewer unsuccessful copulation attempts than their counterparts. Whereas treatment with methoprene alone had a negative effect in young males with only access to sugar, access to dietary protein alone significantly improved young male sexual performance; moreover, the provision of methoprene together with protein had a synergistic effect, improving further male performance at leks. The results are of great relevance for enhancing the application of the sterile insect technique (SIT) against this pest species. The fact that access to dietary protein and treatment of sterile males with methoprene improves mating success means that SIT cost‐effectiveness is increased, as more released males survive to sexual maturity.