Abstract
While inspection of wheat stores situated in districts Jehlum and Faisalabad, it was revealed that phosphine gas released from solid formulation of aluminium phosphide failed to control infestation of Liposcelis bostrychophila (Badonnel). Failure of fumigation as well as interception of this pest created a lot of fretfulness as the pest was not reported earlier from food godowns in Pakistan. Live presence of the pests was a proof that they survived the toxicant. Results of the godowns with fumigation failure were analyzed minutely. Survival of the pest in the treated godowns opened a window of new questions about the fate of phosphine, intensity and degree of resistance of the pest as well as status of this insect as grain pest. However, control of the pest became a top priority. This time one of the godowns was refumigated with the Split Dosage Technique which involved application of aluminum phosphide tablets @ 720 ppm (1 tablet/cubic meter) as first dose supplemented by 360 ppm (0.5 tablet/cubic meter) after 24, 48 hours and 240 ppm (0.33 tablet/cubic meter) each after 96, 120, and 240 hours, respectively. The other godown having the same storage capacity was fumigated with the routine practice of the Food Department, i.e., 1080 ppm (1.5 tablet/cubic meter) as first dose, supplemented by 1080 ppm (1.5 tablet/cubic meter) after 48 hours. The sealed godowns were kept closed and the results of refumigation were checked after 25 and 15 days of the initial dose administration, respectively. The technique proved successful and the infestation of psocids was completely controlled. The key to psocid survival of phosphine has been attributed to the high tolerance of their eggs. Split Dosage Technique, however, addressed this problem resulting in 100% control of all stages of the pest. The technique is feasible not only for Asian but also for African and other countries of the world where storage facilities are leaky and the insect pests have developed resistance against phosphine fumigant ultimately posing a threat to the food security and safety.