Developing practical phosphine fumigation strategies to manage Callosobruchus maculatus F. in stored mungbeans: Laboratory and silo-scale evaluations

Abstract

The current research was aimed to establish phosphine efficacy data in the laboratory and field for the management of Callosobruchus maculatus F., a serious pest of pulses. Responses of eggs, adults, and mixed-age populations of two C. maculatus strains were determined against a range of phosphine concentrations at 25 °C. A farm-scale trial involving a sealable silo 11.1 m³ (8 t capacity) containing mungbeans was also undertaken to evaluate the effectiveness of the currently registered rate of tablet formulation of aluminium phosphide in Australia. Multiple field-collected populations of C. maculatus were also screened at two phosphine dose rates to validate the effectiveness of the established protocols. No significant difference was observed between the response of eggs of two reference strains to phosphine, however, nearly two-fold differences were noticed at LC₅₀ between the adults. For mixed-age populations, there was a significant effect of strain, dose, and exposure period on progeny reduction, as well as a significant interaction between these factors. The efficacy tended to increase with increasing dose and exposure period. There was complete progeny reduction in mixed-age populations fumigated in the silo, where consistently high concentrations [>720 ppm (1 mg L⁻¹)] were recorded over the 7-day fumigation. Moreover, the complete control of 10 field populations at the current label rate of phosphine (7 days at 1 mg L⁻¹) confirmed the lack of resistance development in C. maculatus. Future research should focus on establishing a discriminating dose for resistance monitoring and developing alternative management strategies for bruchids.