Effect of Phosphine on Mites, Insects, and Microorganisms1

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Abstract
Phosphine (PH3) produced from Phostoxin® (aluminum phosphide) tablets was used to fumigate 2 bins, each containing about 450 bushels of Selkirk wheat with wellestablished natural infestations of 10 species of mites and insects. The history of the grain bulk ecosystems was studied for 5¾ years prior to fumigation. The distribution and persistence patterns of phosphine in the interstitial air, as measured by gas chromatography at periodic intervals for 7 days following fumigation, indicated stratification with greater amounts of the gas at the 4-foot levels than at the 1- and 2-foot levels when measured from the top; no phosphine was detected after 7 days. No live insects or mobile mites, except Aëroglyphus robustus (Banks), were detected 6 days after fumigation. However, Acarus siro L., Glycyphagus destructor (Schrank), and Spinibdella bifurcata Atyeo reappeared in both bins within 1-3 months and continued to thrive for 6 months afterward, as in previous years. It is suggested that elimination of the natural predator Cheyletus eruditus (Schrank) by phophine would permit unusual increase in numbers of G. destructor and thus disrupt the natural balance in the ecosystems. Such a trend was observed for G. destructor. While phosphine was ineffective against A. robustus, it was effective against all stages of C. eruditus, Haemolaelaps casalis (Berlese). Tarsonemus sp., Tydeus interruptus Thor, and insects Lepinotus reticulatus Enderlein and Oryzaephilus surinamensis (L.)., Adults of Cryptolestes ferrugineus (Stephens), Rhyzopertha dominica (Fauvel), Sitophilus granarius (L.), Tribolium castaneum (Herbst), and larvae of Plodia interpunctella (Hübner) and Trogoderma parabile Beal were killed upon 6 days’ exposure in test cages to phosphine concentrations as encountered 2½ feet below the bin surface. Phosphine had no detectable effect on the germination and the microflora of the stored grain.

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