THE EFFECT, ON OYSTER SPATFALL, OF CONTROLLING BARNACLE SETTLEMENT WITH DDT

During the summer of 1955 experiments were made with DDT to control barnacle fouling of oyster spat collectors. Results showed that effective control of barnacles on artificial collectors doubled the yield of oyster spat. Shell cultch treated in the same way gave less conclusive results, partly because of the poor spatfall experienced.
Oyster spat on treated artificial collectors were approximately 40% bigger, at the end of 2 1/2 months, than those on controls. Evidence from shells, however, indicated that DDT initially inhibited the growth of oyster spat. Apparently spat become stunted in natural conditions, because they are unable to compete effectively for food with the dense barnacle populations. Competition amongst barnacles themselves also causes stunting.
The dense population of Elminius modestus on the east coast oyster grounds may have a long-term effect on both the yield and growth of oysters.     

ULTRASTRUCTURE OF BARNACLE GIANT MUSCLE FIBERS

Increasing use of barnacle giant muscle fibers for physiological research has prompted this investigation of their fine structure. The fibers are invaginated by a multibranched system of clefts connecting to the exterior and filled with material similar to that of the basement material of the sarcolemmal complex. Tubules originate from the surface plasma membrane at irregular sites, and also from the clefts They run transversely, spirally, and longitudinally, making many diadic and some triadic contacts with cisternal sacs of the longitudinal sarcoplasmic reticulum. The contacts are not confined to any particular region of the sarcomere. The tubules are wider and their walls are thicker at points of contact with Z material. Some linking of the Z regions occurs across spaces within the fiber which contain large numbers of glycogen particles. A-band lengths are extremely variable, in the range 2.2 µm–20.3 µm (average 5.2 µm) Individual thick filaments have thin (110 Å) hollow regions alternating with thick (340 Å) solid ones. Bridges between thick filaments occur at random points and are not concentrated into an M band The thin:thick filament ratio is variable in different parts of a fiber, from 3:1 to 6:1. Z bands are basically perforated, but the number of perforations may increase during contraction.     

ANNONA SPECIES AS INSECTICIDES

By extraction and precipitation from several solvents the toxic principle present in Annona reticulata and A. squamosa seeds and roots has been concentrated up to one hundred-fold. A preliminary chemical examination of this concentrate is described, leading to the conclusion that the toxicity is due to a glyceride or glycerides of a hydroxylated unsaturated acid or acids of high molecular weight.
These extracts have been examined for contact and stomach poison and ovicidal properties in a variety of media. When used as a contact insecticide against Aphis fabae, Macrosiphoniella sanborni and Macronphum solanifolii , the concentrate exhibited a toxicity of the same order as that of rotenone, but against Oryzaephilus surinamensis the toxicity was considerably less. As a stomach poison the ether extract was both toxic and repellent to Plutella maculipennis larvae, but was neither toxic nor repellent to Diataraxia oleracea larvae. Ovicidal tests against the eggs of Plutella maculipennis and of Ephestia kühniella were inconclusive. The potency of this concentrate is therefore of a limited nature and although of roughly the same order as that of rotenone to certain aphides, it has neither the intensity of effect nor the range of insecticidal action of that compound.     

A DIRECT-SPRAY TECHNIQUE FOR THE BIOLOGICAL EVALUATION OF PYRETHRUM-IN-OIL INSECTICIDES FOR USE AGAINST STORED PRODUCT INSECTS IN WAREHOUSES

A direct-spray technique for the biological assay of pyrethrins in Shell oil P31 is described, together with the experiments leading to its adoption. The technique is such that film effects are reduced to the minimum practicable, but it is otherwise as similar as possible to the film technique described by Parkin & Green (1943). Methods for statistical analysis of the results are discussed. For the biological assay of pyrethrins in Shell oil P31, the direct-spray method is slightly superior to Parkin & Green's film method, but both techniques should have their uses in general experimental work.     

NEWER INSECTICIDES AND SCABICIDES

Experimental and clinical data show that taking thiamine chloride internally protects against flea bites. Application of DDT powder to the breeding places of fleas controls infestation.Clinical data appear to show that the use of an ointment containing gamma isomer hexachlorocyclohexane is an effective and pleasant means of treating scabies.     

PREDATOR-INDUCED SHELL DIMORPHISM IN THE ACORN BARNACLE CHTHAMALUS ANISOPOMA

Field experiments were conducted in order to determine the nature of shell dimorphism in the acorn barnacle Chthamalus anisopoma and the adaptive significance of the atypical form. The typical morph has the conical shape which is characteristic of acorn barnacles, while the atypical morph appears bent over, with the rim of its aperture oriented perpendicular to its base. The experiments showed that: 1) the bent-over morphology is an environmentally-induced developmental response to the presence of a carnivorous gastropod (Acanthina angelica) and 2) that “bents” are more resistant than “conics” to specialized predation by this snail. The results also showed that predation by A. angelica is patchy and heaviest in the near vicinity of cracks and crevices, which it uses as refuges during periods of tidal inundation. Because predation is patchy and bents are less fecund and grow slower than conics, the conditional developmental strategy is likely to be favored over strict genetical control of shell morphology.