Production of trophic eggs by virgin workers in the ponerine ant Gnamptogenys menadensis

Abstract. Most colonies (thirty-five out of thirty-seven) of the ant Gnamptogenys menadensis (Mayr) (Hymenoptera: Formicidae: Ponerinae) lack queens. Mated workers produce reproductive eggs, whereas virgin workers can lay only smaller trophic eggs (350 ovipositions observed). These two egg types are morphologically distinct (e.g. in the pattern of oogenesis and ultrastructure of membranes and micropyle) and relate to different ovarian characteristics (ovariole length, number of yolky oocytes and yellow bodies). When reproductives are removed, a small number of virgin workers switch to producing reproductive eggs, although only 3% of these develop into larvae. Once workers are mated, up to 50% of their eggs develop further. Trophic eggs are generally absent in social insects lacking physical castes, and we review adaptive explanations of its occurrence in G. menadensis .     

Observations of flagellates in colonies of Phaeocystis globosa (Prymnesiophyceae); a hypothesis for their position in the life cycle

Flagellates of Phaeocystis globosa were observed inside coloniesin North Sea samples in 1992. Field data suggest that low phosphateconcentrations (     

In-Situ Optical and Acoustical Measurements of the Buoyant Cyanobacterium P. Rubescens: Spatial and Temporal Distribution Patterns

Optical (fluorescence) and acoustic in-situ techniques were tested in their ability to measure the spatial and temporal distribution of plankton in freshwater ecosystems with special emphasis on the harmful and buoyant cyanobacterium P. rubescens. Fluorescence was measured with the multi-spectral FluoroProbe (Moldaenke FluoroProbe, MFP) and a Seapoint Chlorophyll Fluorometer (SCF). In-situ measurements of the acoustic backscatter strength (ABS) were conducted with three different acoustic devices covering multiple acoustic frequencies (614 kHz ADCP, 2 MHz ADP, and 6 MHz ADV). The MFP provides a fast and reliable technique to measure fluorescence at different wavelengths in situ, which allows discriminating between P. rubescens and other phytoplankton species. All three acoustic devices are sensitive to P. rubescens even if other scatterers, e.g., zooplankton or suspended sediment, are present in the water column, because P. rubescens containing gas vesicles has a strong density difference and hence acoustic contrast to the ambient water and other scatterers. After calibration, the combination of optical and acoustical measurements not only allows qualitative and quantitative observation of P. rubescens, but also distinction between P. rubescens, other phytoplankton, and zooplankton. As the measuring devices can sample in situ at high rates they enable assessment of plankton distributions at high temporal (minutes) and spatial (decimeters) resolution or covering large temporal (seasonal) and spatial (basin scale) scales.     

Dolichopodidae (Diptera) of a Nymphaeid‐Dominated system in the Netherlands: Species composition,diversity, spatial and temporal distribution

The composition of the Dolichopodid fauna was studied at various sites within nymphaeid stands during one growth season in an oxbow lake with the aid of adhesive traps; additional observations were made by means of hand-net collecting at various localities within nymphaeid stands. The first method gave the best results.

With this method the species composition, diversity, spatial and temporal distribution of the Dolichopodid fauna within nymphaeid stands could be described.

Nine species appeared to be common, viz. )in order of decreasing numbers( Hydrophorus praecox )Lehm.(, Dolichopus latilimbatus Mcq.¹(, Campsicnemus picticornis )Zett.(, Rhaphium antennatum )Carl.(, Dolichopus nubilus Mg., Hydrophorus litoreus Fall., Campsicnemus pectinulatus Lw., Campsicnemus lumbatus Lw. and Rhaphium elegantulum )Mg.(. With respect to the spatial distribution within the nymphaeid zone both Hydrophorus species were found in large numbers on sites bordering on the open water, while the largest numbers of all other species mentioned above were caught on sites near the helophyte zone. A distinct succession of Dolichopodid species with respect to their numbers could be observed during the growth season on the floating leaves in the sequence Hydrophorus, Campsicnemus, Rhaphium and Dolichopus spp.

The reasons for these distribution patterns are discussed on the basis of what is known of the ecology and behaviour of the various species.