Efficacy of a mixture of phosphine/carbon dioxide on eight species of stored product insects

Using laboratory fumigation chambers 28.42L, we determined efficacy on all life stages of Lepidoptera: Plodia interpunctella (Hubner), Amyelois transitella (Walker); Coleoptera: Tribolium castaneum (Herbst), Tribolium confusum (Jacquelin du Val); Trogoderma variabile (Ballion), Orzaephilus surinamensis (Linnaeus), Lasioderma serricome (Fabricius), Carpophilus hemipterus (L.), using phosphine (PH sub(3)) directly from a gas cylinder mixture, carbon dioxide 98% and PH sub(3) 2%, ECO sub(2)FUME registered Fumigant gas, (Cytec Industries Inc., Niagara Falls, ON Canada). We investigated the efficacy of PH sub(3)/CO sub(2) at various temperatures in a 24-hour fumigation period. Starting dosages tested were 250, 500 and 1,000 ppm PH sub(3). The egg stage was most tolerant to PH sub(3) fumigation. At 26.7 degree C for 24-hour exposure and a CT Product (ppm) x time of 11,659 plus or minus 4,584, a mean mortality of 92.4% plus or minus 3.2 (SEM) mortality to eggs (1-3 days old) for the eight species was obtained. Under the same conditions for 36-hour exposure with CT Product, (mean plus or minus SEM) of 17,556 plus or minus 7,028, mean egg mortality was 95.2% plus or minus 4.1. Temperatures of 30 degree C, 32.5 degree C, and 35 degree C for 24-hour exposure and CT Products of 13,224 plus or minus 5,299, 12,997 plus or minus 5,427 and 13,654 plus or minus 5,676 produced a mean mortality of 93.8% plus or minus 3.1, 97% plus or minus 2.7 and 99.8% plus or minus 0.0 to eggs, respectively. A mean mortality of 98.9% plus or minus 1.0 (SEM) was found for larvae, 98.8% plus or minus 0.54 for pupae and 100% for adults treated for 24- or -36 hour exposures at 26.7 degree C under the same concentrations as those for the eggs. The order of susceptibility to the treatments was eggs, pupae, larvae, adults. Trogoderma variabile was most tolerant to the treatments followed by Tribolium confusum and Lasioderma serricome. The data indicated that phosphine/CO2 could effectively be used to fumigate multiple insect stages at elevated temperatures in less than 48 hours.