Locational dynamics of concentration and efficacy of phosphine against Pulse Beetle, Callosobruchus maculatus Fab.

Abstract

Phosphine is considered as an effective substitute to methyl bromide (MB), an ozone depleting fumigant which was phased out honouring ‘Montreal Protocol’. Limited field studies are available on phosphine toxicity against storage insects of pulses under different climatic conditions in India. In the present study phosphine efficacy was investigated against laboratory cultured and field populations of Callosobruchus maculatus by organising field fumigation trials of 5 MT pulse stacks, each in triplicate, under varied climatic conditions. The trials were conducted at three locations, Jaipur for Cicer arietinum (chickpea), Cuttack for Vigna radiata (green gram) and Mumbai for Lathyrus aphaca (yellow pea) using conventional 56% Aluminium phosphide (AlP) tablets (2 tab/MT and 3 tab/MT) application; and gas derived from on-site phosphine generator with 77.5% granular (1.0 g and 1.5 g phosphine/m3) formulations for two exposure periods (7 and 10-days) for each dosage including untreated control. Phosphine gas concentration was monitored daily until the exposure periods using gas monitoring equipment. No emergence of adults was observed until 60 days after treatment indicating 100% insect mortality of both populations (laboratory and field) for both exposure periods using all dosages. The minimum effective phosphine gas concentration for controlling C. maculatus was observed as 300–500 ppm for 7-days exposure using 1.5 g phosphine/m3 depending on climatic conditions. A significant variation was observed in gas concentration monitored during fumigation of pulses at different locations. Average concentration-time (Ct) product for green gram was higher than that of chickpea and yellowpea. The loss of gas concentration was found to be significantly low in yellowpea treated with phosphine at moderately hot and humid climate.