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Flour-mill fumigation using hydrogen cyanide insecticide gas

Owing to their good penetration properties, fumigants are still one of the key components of integrated pest control programmes in flour mills in many countries. Hydrogen cyanide (HCN) is commercially available and registered in some EU countries as a biocide for mill and aeroplane fumigation. Although it is known (mostly from laboratory studies) that HCN has good biological activity on all pest stadia including eggs, currently there is insufficient information concerning biological HCN efficacy in relation to the CT-products reached during the real-world flour mill fumigations. The aim of this study was to (i) determine the extent of variation of HCN CTproducts at various floors of flour mill building during a ‘real world’ commercial fumigation, (ii) determine HCN efficacy on 5 species of stored products pests, viz. Tribolium castaneum (Herbst), Tribolium confusum (L.), Cryptolestes turcicus (L.), Sitophilus oryzae (L.) and Rhyzopertha dominica (Fabricius) in the fumigated mill, and (iii) determine HCN biological efficacy on the confused flour beetle Tribolium confusum du val exposed to fumigant under ‘naked’ (i.e. pests enclosed in open empty vials and covered by mash lid) and ‘obstructed’ (i.e. pests enclosed in the same vials but containing various layers of wheat (Triticum aestivum L.) flour conditions. Although CT-products estimated for HCN were less than half of the labelled HCN rate (240 g h m-3), 100% mortality was recorded for larvae and adults of T. confusum in all of the mill floors and locations tested. Regardless of the floor and CT variations, all adults and larvae of exposed T. confusum were dead. Contrary to the general belief that HCN is usually is poorly penetrative fumigant, we found 100% mortality of T. confusum enclosed in the vials containing wheat flour.