What are the observed trends in phosphine resistance development so far?
The frequency of strong resistance to phosphine is increasing in four of the five major insect pest species. This resistance was first detected in 1997. About 5% of insect populations contain individuals with this strong resistance. Strong resistance occurs throughout Eastern Australia but has not yet been detected as endemic in the western grain region. The highest level of resistance occurs in the lesser grain borer (Rhyzopertha dominica). The Department of Employment, Economic Development and Innovation’s (DEEDI) Stored Grain Team have based our new recommendation for use of phosphine on this lesser grain borer resistance. Several resistant strains of tiny grain pests called psocids have been found, particularly in South Australia. We expect that the number of resistant insects found will increase rapidly over the next five years. Resistance is likely to appear in all grain growing areas in that time.
