Susceptibility of different developmental stages of the root-knot nematode, Meloidogyne incognita, to the nematicide oxamyl

Oxamyl (6.25 μg ml^-1 soil water) was applied to cucumber roots containing Meloidogyne incognita at different stages of nematode development. Oxamyl was more effective in reducing the proportion of juveniles which developed into females when applied soon after infection to second stage juveniles than when applied later (to third and fourth stage juveniles). Early application of oxamyl also significantly reduced the proportion of females with egg masses, whereas late application had no such effect. However, the number of eggs per egg mass and the size of the young adult females was significantly reduced by all oxamyl treatments - the earlier the application the greater the effect. These results support the hypothesis that actively feeding second stage juveniles of Meloidogyne spp. are more susceptible to systemic nematicides than are the non-feeding third and fourth stage juveniles.     

ALCOHOL, ALCOHOLIC BRAIN DAMAGE, AND GABAA RECEPTOR ISOFORM GENE EXPRESSION

Selective variations in cerebral GABA_A receptor pharmacology and function are observed in experimental animals subjected to a number of alcohol-treatment and -withdrawal paradigms, and where human alcoholics with and without a range of concomitant diseases are compared with non-alcoholic cases. Recombination studies have shown that variations in GABA_A receptor pharmacology and function can result from altering its subunit isoform composition. This commentary examines the rôle of subunit isoform expression in the response to long-term alcohol administration in animals, and in the pathogenesis of alcoholism-related brain damage in human cases. Copyright © 1996 Elsevier Science Ltd     

PIGMENT TRANSACTIONS BETWEEN ANIMALS AND PLANTS

1. Animals, in common with plants, are capable of elaborating their own supplies of tetrapyrrolic pigments, i.e. the porphyrins and bilichromes, as well as pterins and certain indolic biochromes, including melanins and indigoids. But they must depend upon plants for the primary synthesis of other vitally important biochromes including flavins, flavonoids, quinones, and notably the carotenoids. These must be assimilated by animals, directly or ultimately from the plant kingdom. 2. Colour is expressed in certain large organic molecules as a consequence of chemical resonance, evoked by the presence of unsaturated intra-molecular bonds. This condition, allied closely with chemical instability and metabolic reactivity, thus underlies certain biocatalytic functions, fulfilled for example by some biochromic molecules, such as oxidative enzymes, and some vitamins and hormone-like regulators. 3. Commonest examples of such biocatalysts include the several classes named above, conspicuously such porphyrinic tetrapyrroles as chlorophyll, haemoglobin, and the oxidases and peroxidases, including cytochromes and catalase. Among the open-chained members or bilichromes, we find some of these in red algae; phyto-chrome initiates numerous vital biochemical processes in green plants; and bilirubin and biliverdin are found in blood and bile of animals. 4. Among the pterins are members which simulate closely some physiological functions of vitamins B₁ and B₂. Some promote sexual activity in aphids, and in the royal jelly of honeybees, they determine whether a hatchling shall develop into a queen or a neuter worker. 5. Riboflavin, acquired in minute but fundamentally necessary amounts by animals' consumption of plants, whether directly or indirectly, is a unit of the vitamin B₂ complex, and is stored either unmodified or conjugated with the animal's protein. 6. Flavonoids and quinones are similarly acquired from ultimate plant sources. Such compounds may or may not undergo minor chemical modifications within the bodies of consumers. Quercitin, a flavonoid, favours normality of the eye-lens, skin and blood capillaries, while, among the naphthoquinones, the K vitamins ensure blood coagulability. The benzoquinones include the Q-enzymes or ubiquinones, which serve as metabolic oxidative catalysts. 7. Integumentary melanins, derived from oxidative degeneration of tyrosine, chiefly by animals as well as by certain plants, may serve usefully in screening underlying tissues against injurious light rays or, in insects, as well as in some cold-blooded vertebrates, may be capable of effecting either concealment or advertisement. Related to these so-called indole pigments are the indigoids which are breakdown products of tryptophan, and are encountered chiefly in excretory materials, some especially under pathological conditions. Dibromindigo, an ancient dye recovered from certain marine gastropods, is something of an enigmatic exception. 8. Among the carotenoids, manufactured de novo only by plants, are found the known precursors of the A vitamins. It is these compounds that represent by far the most prominent members of the world's pigment crop. In their handling of ingested carotenoids, animals emphasize any of several metabolic alternatives, e.g. (a) non-selective assimilation of all types; (b) rejection of all classes from any storage; (c) selective uptake of the hydrocarbon or carotene kind; or (d) solely of the alcoholic or other oxygen-containing members (xanthophylls); or finally (e) oxidative conversion of carotenes or xanthophylls into innovated red or other richly coloured derivatives. Some animals are without A vitamins among any carotenoids they may store. Numbers of arthropods so characterized nevertheless exhibit photokinetic responses. Plants are without vitamin A per se, carrying only carotenoid precursors thereof; however, single-celled phototactic phytoplankton, e.g. dinoflagellates, respond to light by their diurnal vertical migrations. It seems reasonable to suppose that animals, evolving from the primitive plant world, must have inherited therefrom many similarities in their cytoplasmic constitution and basic metabolic needs, but not in all instances the means of fully supplying them. They must, accordingly, continue to rely upon the plant world for the synthesis, de novo, of materials such as carbohydrates (for fuel, inter alia) and many amino acids for their protein upkeep, as well as certain biocatalysts, notably of the bio-chromic type, such as vitamins, e.g. B₂ (riboflavin), B₁₂ (cyanocobalamin), thenaphthoquinone K vitamins, and the A provitamin pigments, including carotenes and close chemical relatives thereof, although the animals have developed the capacity to split such pigments, deriving thus for themselves the A vitamins proper.     

Delayed setting of the photoperiodic response in recombinant clones of the aphid species Sitobion avenae

1. To explore the possible causes of apparent changes in reproductive mode from obligate to cyclical parthenogenesis over time in recombinant clones of the aphid Sitobion avenae Fabricius, all F1 progenies from various crosses were tested for several consecutive years for sexual morph production, after several weeks' exposure to a short photoperiod. 2. Variable proportions of the F1 progenies from selfing and outcrossing holocyclic clones did not produce mating females when induction was attempted in the year of hatching, but only after further induction, the following year or after. This ‘delayed setting of the photoperiodic response’ (DSPR) was much stronger in recombinants from crosses involving only clones from oceanic regions than in those involving one clone from a region with a continental climate. 3. F1 progenies resulting from crosses between one holocyclic and one intermediate clone did not show DSPR. It appeared again in the F2. 4. DSPR preferentially affected the latest hatched clones in a given progeny. 5. This phenomenon is neither an experimental artefact nor as a result of clone contamination. It appears to be because of a genetically controlled quantitative trait affecting the length of the ‘interval timer’, and may represent an adaptation of holocyclic aphid clones from oceanic regions to unpredictable winter climates.     

Molecular and chemical characters to evaluate species status of two cuckoo bumblebees: Bombus barbutellus and Bombus maxillosus (Hymenoptera,Apidae, Bombini)

Many methods, based on morphological, molecular or chemical characters, have been used to address the question of species taxonomic status. Integrative taxonomy aims to define stronger supported taxonomic hypotheses by considering complementary datasets from different characters. By following an integrative approach, the present study includes molecular, chemical and morphological criteria to establish the taxonomic status of two rare and doubtful cuckoo bumblebee taxa: Bombus (Psithyrus) barbutellus and Bombus (Psithyrus) maxillosus. These two sympatric taxa are discriminated by few morphological criteria (mainly wing darkness and hair length). We used these morphological character diagnoses to establish an a priori status of our samples (23 specimens). We developed a combined molecular dataset from one nuclear gene, elongation factor 1α (EF‐1α), and one mitochondrial gene, cytochrome c oxidase subunit I (COI), spanning 1623 bp, and a chemical dataset of sexual marking pheromones (73 compounds). The molecular data were subjected to maximum‐likelihood and Bayesian phylogenetic inference under partitioned model and maximum parsimony. The chemical data were analysed by clustering and the two‐group k‐means method to test divergences between the two species. The resulting phylogenetic trees show no consistent divergence between the two taxa. Moreover, we found no divergence in the sexual marking pheromones in the clustering and two‐group k‐means analyses. These converging results support the conspecificity of both taxa. Nonetheless, our determinations using the traditional morphological criteria separated our samples into two taxa. We conclude that the morphological criteria seem to relate to intraspecific variations: B. maxillosus is regarded as a syn.n. of B. barbutellus.