Particulate organic matter in a mountain stream in the south-western Cape,South Africa

The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a second-order, perennial mountain stream in the south-west Cape, South Africa, between April 1983 and January 1986. Although the endemic, riparian vegetation is sclerophyllous, low and evergreen, inputs of allochthonous detritus to the stream (434 to 500 g m^–2y^–1) were similar to those recorded for riparian communities worldwide, as were calorific values of these inputs (9548 to 10 032 KJ m^–2y^–1). Leaf fall of the riparian vegetation is seasonal, occurring in spring (November) as discharge decreases, resulting in retention of benthic organic matter (BOM) on the stream bed during summer and early autumn (maximum 224 g m^–2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g m^–2). Therefore, BOM was predictably plentiful for about half of each year and predictably scarce for the other half. Coarse BOM (CBOM) and fine BOM (FBOM) constituted 46–64% of BOM standing stock, ultra-fine BOM (UBOM) 16–33% and leaf packs 13–24%. The mean annual calorific value of total BOM standing stock was 1709 KJ m^–2. Both standing stocks and total calorific values of BOM were lower than those reported for streams in other biogeographical regions. Values of C:N ratios decreased with decrease in BOM particle size (CBOM 27–100; FBOM 25–27; UBOM 13–19) with no seasonal trends. The stream is erosive with a poor ability to retain organic detritus. Its character appears to be dictated by abiotic factors, the most important of which is winter spates.     

Maintenance of innate feeding preferences by a polyphagous insect despite ingestion of applied deleterious chemicals

The question of whether the appearance of a novel deleterious chemical in a preferred host plant could alter the relative degree of preference by a polyphagous insect during its lifetime was considered. The behavioral preference of fall armyworm, Spodoptera frugiperda (J. E. Smith), for corn (Zea mays L.) over red kidney bean Phaseolus spp. was quantified in a two-way choice test, and followed by a no-choice test in which the same larvae were fed either treated or untreated corn. Each treatment consisted of one of 15 compounds, including 13 naturally occurring allelochemicals and two synthetic insecticides. None of the test chemicals had any inherently deterrent effect at the rates tested. Deleterious effects on the larvae during exposure included reduced growth, reduced size, irritancy, and in some cases death. After this exposure the two way choice test was repeated. All test compounds failed to elicit a change in relative preference during the final two-way choice test. However, larvae exposed to gossypol and chrysanthemum monocarboxylic acid ester fed less than expected during the latter stages of no-choice conditions. The degree of aversion learning by each larva was related to the degree of prior sickness it had experienced.

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Résumé Nous avons examiné si l'introduction d'une substance chimique nocive dans la plante-hôte préférée pouvait modifier la hiérarchie des choix durant le reste de la vie d'un insecte phytophage. Le comportement de préférence de Spodoptera frugiperda pour le maïs (Zea mays) vis à vis des Phaseolus, a été quantifié dans un dispositif à choix binaire, ont suivi des expériences au cours desquelles les chenilles devaient s'alimenter, soit sur maïs sain, soit sur maïs traité. Chaque essai concernait un composé chimique (15 au total), 13 étant des substances allélochimiques naturelles, 2 des insecticides de synthèse. Aux concentrations étudiées, aucun des produits n'a eu d'effet dissuasif. Les effets nocifs pendant l'exposition sur les chenilles comprenaient une croissance et une taille réduites, une irritation et, dans quelques cas, la mort. Aucune des expériences de choix binaire, avec des chenilles ayant subi cette exposition, n'a modifié les préférences. Cependant les chenilles, qui avaient été exposées au gossypol ou à l'acide monocarboxylique éthyl ester de chrysanthemum, ont consommé moins pendant les stades ultérieurs que ce que l'on pouvait attendre en absence de choix. Le degré d'aversion acquis par chaque chenille dépendait de l'importance des maux qu'elle avait subis précédemment.

     

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia

Summary Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m^-2), although litter fall was high; 822 and 1022 g·m^-2·y^-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m^-2·y^-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m^-2·y^-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m^-2) and crabs removed less litter; 173 g·m^-2·y^-1 or 33% of the annual litter fall of 519 g·m^-2·y^-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m^-2·y^-1 or 32% of annual litter fall), and tides exported 107 g·m^-2·y^-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.Contribution No. 445 from the Australian Institute of Marine Science     

Ectoparasitic Acugutturid Nematodes of Adult Lepidoptera

Noctuidonema guyaneme is an interesting ectoparasite of adult Lepidoptera that feeds on hosts from at least five families with its long stylet. Noctuidonema guyanense spends its entire life on the adult moth and is sustained as it is passed from moth to moth during host mating. Overlapping host generations are essential for parasite survival. This nematode occurs throughout tropical and subtropical America and is transported by at least one of its hosts, Spodoptera frugiperda, during migration to northern sites in the United States each spring. Noctuidonema guyanense debilitates its hosts. Research conducted to help determine the biological control importance of this nematode is reviewed. Two additional species, N. daptria and N. dibolia, are now known for Noctuidonema.     

Dry matter and nutrient inputs through litter fall in a dry tropical forest of India

The present paper elucidates the pattern of leaf and non-leaf fall and quantifies of the total annual input of litter in a dry tropical forest of India. In addition, concentration of selected nutrients in various litter species and their annual return to the forest floor are examined. Total annual input of litter measured in litter traps ranged between 488.0–671.0 g m^-2 of which 65–72% was leaf litter fall and 28–35% wood litter fall. 73–81% leaves fall during the winter season. Herbaceous litter fall ranged between 80.0–110.0 g m^-2 yr^-1. The annual nutrient return through litter fall amounted (kg ha^-1): 51.6–69.6 N, 3.1–4.3 P, 31.0–40.0 Ca, 14.0–19.0 K and 3.7–5.0 Na, of which 71–77% and 23–29% were contributed by leaf and wood litter fall, respectively for different nutrients. Input of nutrients through herbaceous litter was: 13.0–16.6 for N, 1.0–1.4 for P, 4.0–5.0 for Ca, 7.9–10.5 for K and 0.8–1.0 kg ha^-1 yr^-1 for Na.     

Effects of Azadirachtin on reproduction in the African armyworm (Spodoptera exempta)

Azadirachtin, applied topically to final instar larvae of the African armyworm (Spodoptera exempta, Walker) (Lepidoptera: Noctuidae), adversely affected oogenesis and reproductive maturation in subsequent female moths. Moths obtained from such treated larvae failed to mature their oocytes, probably as a result of interference of azadirachtin with vitellogenin synthesis and/or its uptake by developing oocytes. Such larval treatment also caused substantial decreases in fecundity and although fertility in affected females was not decreased significantly, emerging larvae were less viable, less than 40% reaching the fourth instar.Closer examination revealed that protein levels as well as fat body development in female moths were suppressed by azadirachtin. Prospects for field control of this pest with neem are discussed in the light of these findings.

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Résumé L'application locale d'azadirachtine sur des chenilles de dernier stade de S. exempta Walker nuit à l'ovogenèse et à la maturation des ovaires des futures femelles. Les papillons provenant des chenilles traitées ne produisent pas d'ovocytes mûrs, probablement par suite de l'interférence de l'azadirachtine avec la synthèse de la vitellogénine et/ou son incorporation dans les ovocytes en développement. De tels traitements larvaires provoquent aussi une diminution importante de la fécondité et bien que la fertilité des femelles touchées ne diminue pas significativement, les chenilles néonates sont moins viables, moins de 40% atteignant le 4^e stade. Un examen plus précis a révélé que la teneur en protéines et le développement du corps gras des papillons femelles étaient altérés par l'azadirachtine. Des perspectives d'utilisation du NEEM dans la lutte contre cet insecte ont été discutées à la lumière de ces résultats.

     

Inhibitory effects of different quantitative compositions of Hymenaea leaf resins on a generalist herbivore Spodoptera exigua

The hypotheses that quantitative variation in leaf resins in the leguminous genus Hymenaea may partially be a response to insect predation was tested in feeding experiments with the generalist herbivore, the beet armyworm, Spodoptera exigua Hübn (Noctuidae). Leaf resins of all Hymenaea species are comprised of essentially the same suite of sesquiterpene hydrocarbons, but discrete quantitative patterns have been classified as Compositional Types based on the amounts of major components. In this work pure extracts of leaf resins of Type I (high - and β-selinene), Type II (intermediate amounts of -and β-selinene and caryophyllene) and Type III (high caryophyllene) were incorporated into an artificial diet for the insects at 1 and 3.2% (dry wt). Resin Type treatments produced differential dose-dependent effects on growth rate (lower larval weights and increased time to pupation) and in mortality. More significant inhibitory effects occurred in Compositional Types with a predominance of a single compared (i.e. Types I and III). Significantly higher mortality occurring in Type III treatments suggests that caryophllene may have higher potential toxicity than - and β-selinene for S. exigua. These experiments indicate that feeding by generalist herbivores could be a factor determining quantitative compositional variation: (a) among populations; (b) during the development of leaves; (c) in the spatial distribution within the leaves; and (d) between parent tree and seedling progeny.     

Downwind migration of the African army worm moth, Spodoptera exempta, studied by mark-and-capture and by radar

Abstract. 1. About 166,000 African armyworm moths, Spodoptera exempta (Walk.), were marked at an emergence site near Nairobi when they fed at night on trees baited with dyed molasses.
2. Six marked moths were captured in pheromone traps, including one at 90 km after flying for only one night, and another at 147 km.
3. Moth flight trajectories deduced from radar and from marking showed that migration was downwind.
4. During migration, moths become dispersed; hence the high densities that lead to outbreaks must be produced by concentration.
5. Some moths were ready to mate on the same night they completed their long-distance flight.     

Morphological and immunohistochemical study of the midgut and fat body of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: noctuidae) treated with essential oils of the genus Piper

ABSTRACT

Essential oils are a promising alternative to insecticides. We investigated the LD₅₀ of oils extracted from Piper corcovadensis, P. marginatum, and P. arboreum after 48 h topical contact with Spodoptera frugiperda larvae using morphometry, histochemistry and immunohistochemistry of the midgut and fat body. Chromatography revealed that E-caryophyllene was the principal compound common to the Piper species. The essential oils of P. corcovadensis, P. marginatum and P. arboreum caused deleterious changes in the midgut of S. frugiperda larvae. P. corcovadensis oil produced the lowest LD₅₀ and significant histopathological alterations including elongation of the columnar cells, formation of cytoplasmic protrusions, reduction in carbohydrate, increased apoptotic index and decreased cell proliferation. P. arboreum oil caused histopathological alterations similar to P. corcovadensis, but caused the highest rate of cell proliferation and increased regenerative cells, which indicated rapid regeneration of the epithelium. Our findings demonstrated the insecticidal potential of P. corcovadensis for control of S. frugiperda owing to the significant damage it inflicted on S. frugiperda midgut.     

Automatic individual calibration in fall detection – an integrative ambulatory measurement framework

The objective of the current study was to demonstrate the utility of a new integrative ambulatory measurement (IAM) framework by developing and evaluating an individual calibration function in fall detection application. Ten healthy elderly persons were involved in a laboratory study and tested in a protocol comprising various types of activities of daily living and slip-induced backward falls. Inertial measurement units attached to the trunk and thigh segments were used to measure trunk angular kinematics and thigh accelerations. The effect of individual calibration was evaluated with previously developed fall detection algorithm. The results indicated that with individual calibration, the fall detection performance achieved approximately the same level of sensitivity (100% vs. 100%) and specificity (95.25% vs. 95.65%); however, response time was significantly lower than without (249 ms vs. 255 ms). It was concluded that the automatic individual calibration using the IAM framework improves the performance of fall detection, which has a greater implication in preventing/minimising injuries associated with fall accidents.