Detection of aphid remains in predatory insects and spiders by ELISA

An ELISA was developed which would detect and quantify ingested aphids in predators found in and around cereal crops. The detection limit of the assay was less than one hundredth of an homogenised adult aphid. Tests with 13 species of aphid showed that those which had been used as the principal immunogens reacted most strongly in the assay. Nearly a hundred species of invertebrates, both predators and alternative prey, have been tested in the assay and no evidence of significant cross-reaction was found with any of these species or with a number of samples of plant material on which aphids may be found. Aphid material could still be detected in predators which had been stored for up to 7 days in 4% formalin or 70% ethanol.     

GENETIC STUDIES OF ALLOZYME VARIATION IN LEUCINE AMINOPEPTIDASE IN THE LAND SNAIL HELIX ASPERSA (MULLER)

In the land snail H. aspersathe enzyme LAP has two loci, LAP-1and LAP-2, both of which arc monomeric enzymes under the controlof multiple alleles, the alleles being codominant. None of theobserved ratios in the pheno types in the experimental progenywere significantly different from Mendelian expectation. ^* Present Address: Bournside School, Cheltenham, Glos. (Received 1 September 1981;     

The Increase in Anchorage with Tree Size of the Tropical Tap Rooted TreeMallotus wrayi, King (Euphorbiaceae)

The mechanical development of the anchorage system of the taprooted tropical speciesMallotus wrayiKing (Euphorbiaceae) wasinvestigated by pulling over and examining trees with a diameterat breast height (d_bh) of 4.2 cm to 14.3 cm. The mode of mechanicalfailure depended upon the size of the tree: thicker trees (d_bhapprox.9 cm) failed in the ground with their tap roots pushing intothe soil on the winchward side; in smaller trees (d_bhapprox.7 cm) the trunk snapped before anchorage failure; and in verysmall trees (of d_bh<6 cm) neither type of failure occurredand the trees returned to their original upright position undamagedafter the test. The anchorage strength of the trees was correlatedwith the second power of trunk diameter rather than with thethird power that theory suggests is optimal because tap rootsdid not show an isometric increase in length or diameter. Thereforeas trees grow larger the ‘factor of safety’ againstanchorage failure falls, making them prone to fail in theirroots. These results suggest that only relatively small treespecies can rely solely on the tap root to prevent uprooting.It may be for this reason that most larger trees develop thicklateral roots.Copyright 1998 Annals of Botany Company Anchorage, tap roots, scaling,Mallotus wrayi, isometric growth, functional development, windthrow, root systems.     

Eucalyptus leachate inhibits reproduction in a freshwater fish

1. Dissolved organic carbon (DOC) can induce lethal and sub‐lethal effects in exposed biota via hypoxic blackwater events and the toxicity of leached compounds. Little is known of how DOC exposure affects fish reproduction despite the fact that its release can coincide with spawning‐associated flow pulses. 2. River red gum (Eucalyptus camaldulensis) leaf leachate is a major source of DOC in Australian freshwaters and includes the toxic plant secondary metabolites polyphenols and tannins. High concentrations of leachate are released when leaves on floodplains or dry stream channels are inundated by water. 3. Southern pygmy perch (Nannoperca australis) from naturally high and naturally low Eucalyptus leachate environments in south‐east Australia were exposed to elevated leachate levels to investigate the effects of DOC on reproduction and to explore whether response patterns were consistent with populations becoming locally adapted to historical leachate levels. 4. Fish exposed to leachate were half as likely to reach sexual maturity as control fish. Fish from a naturally high‐exposure population tended to reach sexual maturity earlier than those from a naturally low‐exposure population. Leachate exposure had no effect on either egg size or fecundity. 5. Our results suggest that leachate‐exposed mothers did not reproduce because they were physiologically stressed or perceive the environment to be unsuitable, which raises the potential of plastic or adaptive responses to this stressor. The negative sub‐lethal effects observed have important fitness implications for individuals, the viability of populations and the management of environmental flows and riparian zones.     

Comparative ecophysiology of CAM and C3 bromeliads. III. Environmental influences on CO2 assimilation and transpiration

Abstract Field measurements of the gas exchange of epiphytic bromeliads were made during the dry season in Trinidad in order to compare carbon assimilation with water use in CAM and C₃ photosynthesis. The expression of CAM was found to be directly influenced by habitat and microclimate. The timing of nocturnal CO₂ uptake was restricted to the end of the dark period in plants found at drier habitats, and stomatal conductance in two CAM species was found to respond directly to humidity or temperature. Total night-time CO₂ uptake, when compared with malic-acid formation (measured as the dawn-dusk difference in acidity, ΔH⁺), could only account for 10–40% of the total ΔH⁺ accumulated. The remaining malic acid must have been derived from the refixation of respired CO₂ (recycling). Within the genus Aechmea (12 samples from four species), recycling was significantly correlated with night temperature at the six sample sites. Recycling was lowest in A. fendleri (54% of ΔH⁺ derived from respired CO₂), a CAM bromeliad with little water-storage parenchyma that is restricted to wetter, cooler regions of Trinidad. Gas-exchange rates of C₃ bromeliads were found to be similar to those of the CAM bromeliads, with CO₂ uptake from 1 to 3 μmol m^?2 s^?1 and stomatal conductances generally up to 100 mmol m^?2 s^?1. The midday depression of photosynthesis occurred in exposed habitats, although photosynthetically active radiation (PAR) limited photosynthesis in shaded habitats. CO₂ uptake of the C₃ bromeliad Guzmania lingulata was saturated at around 500 μmol m^?2 s^?1 PAR, suggesting that epiphytic plants found in the shaded forest understorey are shade-tolerant rather than shade-demanding. Transpiration ratios (TR) during CO₂ fixation in CAM (Phase I and IV) and C₃ bromeliads were compared at different sites in order to assess the efficiency of water utilization. For the epiphytes displaying marked uptake of CO₂, TR were found to be lower than many previously published values. In addition, the average TR values were very similar for dark CO₂ uptake in CAM (42 ± 41, n= 12), Phase IV of CAM (69 ± 36, n= 3) and for C₃ photosynthesis (99 ± 73, n= 4) in these plants. It appears that recycling of respired CO₂ by CAM bromeliads and efficient use of water in all phases of CO₂ uptake are physiological adaptations of bromeliads to arid microclimates in the humid tropics.