Effect of lengthy storage on the palatability and efficacy of zinc phosphide wheat bait used for controlling house mice

Abstract

The palatability and efficacy of 2.5% zinc phosphide (ZP) wheat bait that had been in dry storage for about 3.5 years was tested against house mice in canola crops in the central wheatbelt region of Western Australia. Before baiting, mouse numbers in these crops were around 90 mice ha^-1. Mouse numbers were reduced by 89% in the crop where the stored bait was applied at 1 kg ha^-1 by aerial broadcast. The palatability of the stored bait was also determined in additional crops by comparing the amount taken with that of `fresh' ZP wheat bait. Bait (200 g) was offered in two different types of bait station: (1) in 45-cm lengths of 50-mm-diameter plastic agricultural drainage pipe, and (2) on 40-cm-diameter plastic saucers. Regardless of station type, mice often consumed significantly more of the stored product than the `fresh' bait, particularly on Day 1. This was attributed to the stored product lacking the typical, strong ZP odour that was initially present in the fresh bait. Mouse numbers on the bait station grids (1.28 ha each) were reduced by approximately 65% after 4 days of baiting. The shelf-life and palatability of ZP wheat bait seem to be relatively unaffected by prolonged storage. If any decrease in palatability occurs, then this seems to be transient and did not reduce the overall effectiveness of the stored bait.