Are galling insects better protected against parasitoids than exposed feeders?: a test using tenthredinid sawflies

ABSTRACT.

• 1 Data mostly from the published literature were used to assess the effect of galling on the number of parasitoid species per host species in the phylogeny of nematine sawflies from free external feeders (colonial and solitary) to leaf gallers and shoot gallers.
• 2 The strongest effects of galling were the total elimination of the species-rich cocoon-attacking guild of parasitoids, and eonymphal parasitoids, from the parasitoid community on shoot gallers, all of which are in the genus Euura.
• 3 All tachinid larval parasitoids were also eliminated by the galling habit.
• 4 The cumulative effects of these exclusions resulted in a decline in mean number of parasitoid species per host species from almost sixteen species on external colonial feeders to 4.0 species on shoot gallers.
• 5 General patterns in per cent parasitism by non-tachinid and tachinid larval parasitoids, eonymphal and cocoon parasitoids, on exposed feeders to shoot gallers, showed declines in non-tachinid attack and elimination of tachinid, eonymphal and cocoon parasitoids. But leaf gallers tended to be attacked more than exposed feeders by non-tachinid larval parasitoids.
• 6 The galling habit had a long-term impact by reducing the number of parasitoid species attacking nematine sawfly gallers and per cent mortality inflicted, so that natural enemies may have been important as a selective factor in the evolution of galling nematine sawflies.

     

Foraging rate of ants collecting honeydew or extrafloral nectar, and some possible constraints

ABSTRACT.

• 1 In a given ant species, the number of ants collecting honeydew in an aphid colony or extrafloral nectar on a plant is proportional to the productivity of the colony or plant. Thus, the number of ants per resource unit and the ingestion rate per ant are constant for a species.
• 2 Mean number of ants per resource unit and ingestion rate per ant differed considerably between the investigated species. The ingestion rate increases with the body size of the species and decreases with an increase of the mean number of ants per resource unit.
• 3 Ingestion rates were higher in ants foraging singly at the resource than in ants foraging in the normal way in a group.
• 4 It is suggested that the ingestion rate per ant is reduced below a maximum level by the number of ants present per resource unit because a certain number of ants is needed to defend the resource against alien ants. Small species need more individuals for this purpose than large species, and consequently suffer a larger reduction of their ingestion rate.

     

New land tortoises (Testudines: Testudinidae) from the Miocene of Africa

The described fossil testudinids from the Miocene of Africa are reviewed. Geochelone stromeri sp. nov . is described from Lower Pliocene (Langebaanweg) and Miocene (Namib) specimens. Kinixys erosa , an extant species, is reported from Songhor Hill. Chersina sp. is reported from Arrisdrift. Impregnochelys pachytectis gen. et sp. nov . is described from Rusinga Island, Kenya, and is unique in having the anterior shell opening orientated ventrally and in having struts on the internal surface of the neurals, but shares with Kinixys a unique epiplastron shape, a high number of axillary scutes and unique orientation of the head of the femur.     

Polyamine Depletion Following Exposure to DL-α-Difluoromethylornithine Both In Vivo and In Vitro Initiates Morphological Alterations and Mitochondrial Activation in a Monomorphic Strain of Trypanosoma brucei brucei

ABSTRACT. DL-α-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase (ODC), rapidly depletes cells of intracellular putrescine. When administered to animals and humans, DFMO cures acute infections of trypanosomiasis. In order to determine if the mechanism of drug action is related to initiation of transformation and biochemical alterations subsequent to polyamine depletion, trypanosome morphology and mitochondrial activation were studied in a monomorphic strain of Trypanosoma brucei brucei. Exposure of trypanosomes to DFMO in vivo in infected rodents or in vitro in culture resulted in a depletion of intracellular putrescine and a cessation of cell division without specific cytotoxicity. These events were followed by a transformation of the long slender bloodstream form to a short stumpy form via an intermediate morphology. Putrescine, the product of the ODC reaction, abrogates this effect. When introduced into SDM-79 medium, the intermediate form is capable of further transformation to an "insect" procyclic trypomastigote whereas the long slender form and short stumpy form are not. Short stumpy forms are incapable of binary fission and have lost their infectivity for the vertebrate host. In addition, the mitochondrial marker enzyme, NAD diaphorase, was found only in the short stumpy and intermediate forms. We hypothesize that the short stumpy phenotype may not be a viable stage in the natural transformation of the trypanosome from its mammalian host to the insect vector.     

Embryonic Induction

"Spemann's" lecture treats experiments on the separation ofthe first two cells of a frog, or sea urchin, or salamanderembryo; the induction of a lens in a frog embryo by an opticvesicle (primordium of the eye); and the primary organizer thatis a dynamic center, establishing the basic organization ofthe embryo and inducing the nervous system and sense organs."Spemann" goes beyond science in speaking poetically of thebeauty and order in the universe, and to illustrate how a goodscholar should work he uses a lovely metaphor of piecing togetherthe fragments of a broken vase. "Spemann" concludes with a stirringplea for academic freedom.     

Separation and Purification of Protoplast Types from Commelina communis L. Leaf Epidermis

Guard cell and epidermal/subsidiary cell protoplasts obtainedby enzymic digestion of peeled Commelina communis leaf epidermiswere separated and purified by discontinuous density gradientccntrifugation with media based on Percoll (Pharmacia Fine ChemicalsAB, Uppsala, Sweden). The cell types were recovered over 99.9%pure at yields exceeding 50% efficiency, and mesophyll contaminationcould be virtually eliminated when desired. Osmotic characteristicsof the protoplast types were evaluated and compared to in vivovalues, and the viability of the protoplasts, assessed usinga range of criteria, was found to be high. Purified Commelinaguard cell protoplasts were able to evolve O₂ when illuminated,and this was substantially reduced in the presence of the inhibitorDCMU, indicating that they possess photosystem II activity.Specific advantages of this method of protoplast purification,and the potential uses of separate suspensions of guard cellsand epidermal/subsidiary cells in experiments on stomatal physiologyare discussed. Key words: Commelina communis, Protoplasts, Epidermis     

Boundary Layer Effects in Ion Absorption by Roots and Storage Organs of Plants

In plant nutrition studies with culture solutions it is tacitly assumed that replenishment of ions at the root surface is guaranteed by the turbulence of the stirred solution. That this belief may be erroneous is demonstrated in this study with barley roots and discs of beet roots and potato tubers. At very low concentrations of RbCl (in presence of CaCl₂) the uptake of Rb by roots is strongly controlled by the rate of stirring. The results are interpreted in the light of the Nernst hydrodynamic boundary film which surrounds solids and through which ions must diffuse to reach the root surface. “Film-controlled” and “root-controlled” ion uptake is visualized.     

Ultrastructure of Acrasis rosea,a Cellular Slime Mold,During Development*

SYNOPSIS. An ultrastructural study of the myxamoebae of Acrasis rosea in the vegetative, aggregative and culminative stages was made. An intracytoplasmic system of microfibrillar bundles develops as the cells enter the aggregative stage and commence the morphogenetic sequence leading to the construction of a fruiting body. The fibrillar bundles disappear in the cells of the mature fruiting body. No relevant ultrastructural differences were observed between spores, stalk cells and microcysts. Each of these cells is surrounded by a single-layered coat of fibrillar material that is oriented parallel to the cell surface. Tubular structures were observed between the plasma membrane and the cell coat. The tubules may be layered along the cell periphery or they may be recessed in pockets formed by the plasma membrane. They resemble lomasomes typical of fungal cells. The myxamoebae of A. rosea clearly differ from the Dictyostelium-type myxamoebae in mitochondrial structure, the presence of lamellate structures in the nucleolus and the absence of prespore vacuoles.