INSECTICIDAL ACTIVITY AND CHEMICAL CONSTITUTION: ANALOGUES AND ISOSTERES OF DDT

A number of isosteres of DDT and related compounds have been synthesized and examined for insecticidal activity using the grain-weevil, locust and cotton stainer. A marked loss of activity follows replacement of the chlorine atoms of DDT by methyl and hydroxyl groups. In the nitroalkane series, the optimum structure for maximum toxicity was present in i:i-di-/>-chlorophenyl-2-nitropropane. The significance of these results has been reviewed in the light of current theories of DDT structure and activity. Many of the compounds expected to be toxic were found not to be so, and this inactivity can be attributed either to the initial hypotheses being invalid or to the operation of biological factors preventing concentration of the compound at the site of action.     

The response of macroinvertebrate production to a pollution gradient in a headwater stream

1. This study quantified patterns of macroinvertebrate secondary production and stored benthic organic matter along a gradient of pollution and habitat channelisation over a 3‐km reach of Goosefare Brook, a first‐order stream in southern Maine (U.S.A.). 2. Whole‐community invertebrate production decreased from 26.4 g ash‐free dry mass (AFDM) m⁻² year⁻¹ at the reference station to 1.1 g AFDM m⁻² year⁻¹ at stations with the greatest levels of pollution. Production decreased along the pollution gradient for most taxa, although decreases were partly offset by production increases in tolerant taxa. Biomass turnover rates (P/B) were less affected by the stresses than was production. 3. Differences in functional characteristics of the community were evident at stations with channelised habitat, but overall production declined in a linear pattern that mirrored the pollution gradient. Stored organic matter showed a decline along the gradient, but was also lower at channelised stations. Populations of taxa with documented pollution tolerance were more likely to maintain or increase production and P/B. 4. Decreasing biomass because of decreasing stored organic matter and lethal effects of pollutants resulted in shifts in the pathways of energy flow observed at stations exposed to moderate physical or chemical stress, to the loss of most taxa and an extreme (96%) decrease in production at the stations receiving the highest levels of metal pollution. 5. The shifting prominence of different taxa along a continuum of stress in Goosefare Brook shows that describing the nature of an impairment in a functional context requires consideration of chemical stressors, habitat alterations and food resources.     

FUNGICIDAL ACTIVITY AND CHEMICAL CONSTITUTION

A series of 5- n -alkyl oxines was tested against the mycelium of Aspergillus niger. As non-chelated molecules, they showed maximum fungistatic activity at a chain length of 5–6 carbon atoms. Values of Ferguson's thermodynamic activity coefficient, obtained from spore germination tests with Sclerotinia laxa , indicated that the mechanism of toxicity of the lower homologues is predominantly chemical, whilst that of the n -amyl and higher members is mainly physical.
The ED 50 value of 5- n -amyl-6-hydroxyquinoline, which is incapable of chelation, was found to be eighty times greater than that of 5- n -amyl oxine (in the non-chelated form). The optimum initial pH for fungistatic activity of the latter was 5.4–5.6.
In the presence of metals the pattern of fungistatic activity was markedly altered: maximum activity in the presence of Cu²⁺, Fe²⁺and Zn²⁺was found with oxine and 5-methyloxine.     

FUNGICIDAL ACTIVITY AND CHEMICAL CONSTITUTION

2:3–Dichloro-1:4-naphthahydroquinone and several derivatives were prepared and tested in aqueous acetone solution against four fungi using a spore germination technique. The hydroquinone showed the same order of fungicidal activity as 2:3-dichloro-1: 4-naphthaquinone, but was no less phytotoxic. Whilst the dibenzoyl ester and the dimethyl ether proved virtually inactive, the diacetyl ester was found to be as effective as 2:3-dichloro-1:4-naphthaquinone against Sclerotinia laxa, Botrytis fabae and Cladosporium fulvum , and also less phytotoxic to plum fruitlets and tomato and broad bean foliage. Reduced fungicidal activity was shown when the substance was formulated as an aqueous suspension suitable for field application.
The rates of alkaline hydrolysis of these esters have been determined, and a relationship between ease of hydrolysis and fungicidal activity is apparent. It is suggested that these compounds, whilst not inherently active, are similarly hydrolysed to 2:3-dichloro-1:4-naphthahydroquinone in the presence of a fungal esterase.
* Byrde, R. J. W., Crowdy, S. H. & Woodcock, D., 'Studies on Systemic Fungicides. III', Ann. appl. Biol . 40 , 152, is regarded as Part I of this series.     

The Buttressed Blue Marble Tree: Wood and Growth Characteristics of Elaeocarpus angustifolius (Elaeocarpaceae)

Elaeocarpus angustifolius, a forest tree native to Australia,was introduced into the Hawaiian Islands and is now naturalizedlocally. The main purpose of this study was to test the hypothesisthat a radial increase in wood specific gravity was presentin trunk wood of these trees, which grow quite large (diameterat breast height=200 cm) and have massive buttress systems.Information on buttress height and number and specific gravityof the outer trunk wood (sampled at breast height), as wellas anatomical characteristics pertaining to conduction (vesseldiameter and density), was obtained from a range of different-sizedtrees. Both buttress height and number increase with increasingtree diameter. Wood specific gravity has a median value of 0.49and increases more than 50% over the range of tree diametersstudied. Vessel diameter increases over two-fold and vesselfrequency decreases with increasing tree diameter, althoughvery large trees (diameters>70 cm) exhibit more variability.Trees have buttresses spaced evenly around the circumference(maximum of 15–20) and exhibit no difference in wood specificgravity on the leeward and windward sides in spite of theirlocation in the trade wind belt. Radial increases in specificgravity of the type documented here may be important in evaluatingthe carbon present in forest stores. Copyright 2000 Annals ofBotany Company Buttresses, wood specific gravity, vessel diameter and density, Elaeocarpus angustifolius.