View report page

While these conditions are fulfilled in ship construction, the repeated process of eradication must
continue and every effort made to discover and apply better antidotes which will exterminate the
resident pests as effectively, quickly and economically as possible. So far, a reasonable measure
of success has been achieved and this policy has considerably reduced the prevalence of gross
infestations known to seamen twenty years ago. The menace associated with ship-borne rat
populations has declined because of the drastic measures adopted for the suppression of rats at
regular intervals and a growing tendency to deny them breeding harbourages in the compartments
by a technique of "rat-proofing". Deratting of ships is gradually becoming the exception
rather than the rule.
The insect problem presents some difficulties which cannot be so ruthlessly overcome. The
harbourage sought by insects need not be remote though obscure, for they can thrive and breed
in conditions generally found in the accommodation. The cavities and crevices provided by wood
linings, sheathing, cabinets, open joints, heating installations, etc., are readily available, and
these are considered essential units in the design. It remains, therefore, to carry out "insectproofing"
by reducing accessible harbourages to a minimum compatible with comfort and
amenity and by treating the inevitable harbourages in such a manner as to make life
impossible for any insect which might use it, including the "steam fly" or German cockroach,
hitherto so difficult to eradicate.
The details of construction being the prerogative of the ship designer has left the inseeticidal
treatment open to development and it is intended to describe now a formulation and technique
which has been applied to many cockroach infested ships during the past three years and which
has exterminated the infestations for at least two years by a single treatment. No subsequent
treatment has been required of the crew during the periods when these observations have been
made.
Insecticidal Lacquer.
For a considerable time research workers have sought to discover a durable film or coating
which could be impregnated with an insecticide possessing persistent properties. These
characteristics led scientists to explore the field of urea-formaldehvde resins which were originally
developed for moulding purposes, since synthetic resins of this type are thermosetting and are
characterised by rapidity of cure under conditions of heat. In this form the resins are not
suitable for surface coatings because they are only soluble in special solvents. However, modified
resins suitable for surface coatings can be prepared by condensing urea and formaldehyde in the
presence of monohydric or complex polvhydric alcohols. These modified urea resins are used in
stoving finishes, but they can also be made to polymerise, cure or "set" in the presence of added
acidic catalysts which render these products suitable for air-drying applications. Since films
obtained from cured urea-formaldehyde resins alone are brittle, very hard and lack adhesion
qualities, it is the general practice to combine them with more elastic film-forming resins and
these are usually alkyd resins. Alkyd resins are formed by the condensation of polybasic acids or
anhydrides with polvhydric alcohols and since the most common member of this group is a
glycerol-phthalic acid polymer, the specific name "glyptal" is frequently used for alkyd resins.
The primary use for these resins is in surface coating materials, also in cements and binders.
Alkvds too can be modified by the addition of other synthetic resins, with advantages derived
from the properties of each component.
At the Government Research Station, Paul Bracey used a standard lacquer of the following
components:-
Urea formaldehyde resin BE610 50 parts by weight
Castor oil alkyd resin BA502 50 do.
Butanol 27.5 do.
Xylol 22.5 do.
Insecticide 12 do.
This formula produced a free-flowing and clear lacquer containing 40% solids, which was stable to
long storage at room temperatures ranging from freezing to 85°F.
The proportion of insecticide was always based on the weight of resin solids and, in the
foregoing formula, a solid coating containing 20% by weight of insecticide was obtained, although
the resin in the form of a clear liquid can dissolve 50% DDT without impairing its clarity. To
produce a satisfactory air-drying lacquer from this formulation and a finished surface of correct
hardness, an acid accelerator known as AC54 should be added. The accelerator consists of 10%
concentrated sulphuric acid in butanol and should be added to the lacquer just before the application
in the proportion of one part of accelerator to twenty parts of lacquer. The hardness of
the film of lacquer is very important, since this factor governs the durability of the coating and
the rate of inseeticidal activity. A cleaning medium mixture of four parts of Xylol and one part
of butanol is very effective for cleaning any equipment used in this process of lacquering.
Insecticidal Formulations.
When assessing the value of insecticides consideration should be given to such factors as
relative toxicity to man, specific insecticidal properties, possible contamination of foodstuffs by
contact or taint, nature of odour, fire hazard, and any losses which may be sustained by decorative
or fabric deterioration. Economics will also play a decisive part and the final decision will
invariably demand a form of single treatment which gives an immediate "knock-down" and will
continue to kill off any insects for as long a period as possible, using materials which are always
readily available and the overall cost of the operation is fair and reasonable when compared with
the results achieved.
Attention has so far been concentrated on four proven insecticides, e.g. DDT, BHC, Aldrin
and Dieldrin and from a practical viewpoint it has proved advantageous to incorporate two
insecticides to complement one another in a formulation. Both Aldrin and BHC have a higher
vapour pressure than either DDT or Dieldrin, therefore such combinations as DDT + BHC "and
Aldrin + Dieldrin have been used very effectively.
22