Development of new treatments for the protection of stored grain against insect pests

Abstract

Strong resistance to phosphine is an increasing problem, with Cryptolestes ferrugineus requiring very high doses or extended fumigation times to achieve control. As a result, sulfuryl fluoride (SF) is used as an alternative fumigant, but its use is limited by cost and the potential for residues. To overcome these limitations, we have tested both simultaneous and sequential co-treatment with phosphine and SF. Both strategies control all life stages of the four major grain pests more rapidly than phosphine and at reduced chemical concentrations, reducing cost and potential residues.
We have reinvestigated the model of SF toxicity that has prevailed for more than 50 years - that fluoride released from SF is the toxic entity that kills both vertebrate and invertebrate organisms.
We have clearly demonstrated that this mechanism is false. We find that fluorosulfate, which is also released from SF, is not only much more toxic than fluoride, but acts much more rapidly as well.
Based on the mechanism of action of phosphine, we have identified a range of potent synergists.
We also find evidence that resistance to phosphine is associated with permanent activation of stress defence systems, which actually limits the adaptability of resistant animals. We are in the preliminary stages of testing a synergistic gas using our knowledge to maximise its effectiveness.