THE USE OF PROTECTIVE FILMS OF INSECTICIDE IN THE CONTROL OF INDOOR INSECTS, WITH SPECIAL REFERENCE TO PLODIA INTERPUNCT‐ELLA Hb. AND EPHESTIA ELUTELLA Hb.

Abstract

GENERAL SUMMARY AND CONCLUSIONS1. A series of experiments and a field scale trial have been made of a 61m spraying method for the protection of stored goods from infestation by E. elutella and P. interpunctella.2. It is shown that where the goods have been efficiently sterilized before storing, reinfestation by these two species in the warehouse can be prevented completely, as far as could be ascertained.The procedure is to spray the interior of the warehouse and the cases stored in it with an insecticide consisting of a solution of 0.8% pyrethrins in a white oil, the constitution of which is given. The apparatus and method of spraying are described. Spraying should be started some time before the moths are expected to emerge; in England about 15 May, and should be continued twice a week throughout the period of moth emergence, which may continue until 30 September.3. The laboratory and semi‐field scale experiments, together with data obtained during the commercial working of the process, show that control is obtained by a protective 61m of insecticide, which is formed and maintained throughout the period of moth emergence.A film of about 0.006‐0.007 g. of insecticide per sq. in., which is about the amount applied in practice in a single heavy spraying or two light sprayings, on an absorbent wood such as Canadian hemlock, will remain effective against moths of the two species for at least 26 days. It is highly effective against the migrating larvae for a week or longer.The moths were paralysed and ultimately killed by an exposure to the insecticide of not more than 30 min.; the larvae need to be exposed to the action of the film for periods of 1–24 hr., depending on the age of the film.4. It was shown that the oil plays very little part in the toxic effect of the film.5. A short series of experiments indicate that the method of using a protective film of insecticide might be usefully applied in the control of other indoor insects. Probably its most useful application is in cleaning up the residual infestation in empty warehouses and other buildings, in cases where fumigation is not practicable or desirable.6. The effectiveness of this method of prevention of infestation by E. elutella and P. interpunctella has been proved by its adoption for the protection of 30,000 tons of dried fruits in warehouses in London, Liverpool, Manchester and Glasgow, with complete success.7. The method has also been adopted for the protection of cacao and tobacco in London and elsewhere. In these instances, although a great reduction of infestation was observed, it was not possible to assess the results accurately, because the goods were not sterilized before being brought into store and therefore fresh infestation was continuously brought into the warehouse.8. The advantages of the method are that it can be used without interference with the normal routine of storage and involves no extra handling of the goods.It is also a continuous protection from infestation during periods when this is likely to occur. This is a very important point when goods are stored in places where other infested goods may also be stored.This method has the further advantage, that it will localize and check the spread of infestation if this is brought into a building in which the method is used.Finally, compared with fumigation, it is cheap and is devoid of risk to human beings.9. Although the insecticide described in this paper has been successful, it is not necessarily the only possible one for use in this method. Preliminary trials have shown that one of the organic thiocyanates, β butoxy β thiocyanodiethylether has a marked toxicity when applied in this way and may compare favourably with pyrethrum for some purposes.