Molecular diagnostics of insecticide resistance in Australian Tetranychus urticae Koch (Acari: Tetranychidae) quarantine intercepts

Australian ports are continuously exposed to exotic and invasive mite and insect species associated with imported fresh produce. Much effort is focused on preventing the exotic species from entering Australia by product fumigation or destruction in a timely manner. However, quarantine intercepts of invasive species may contain unwanted resistance to pesticides or carry viruses that can undermine Australian agricultural sustainability. We examined pesticide resistance status in 1275 Tetranychus urticae samples from quarantine intercepts from the Department of Agriculture, Fisheries and Forestry originating from some 29 countries spread over 6 main continents (Africa [4], Asia [12], Europe [3], North America [2], Oceania [4] and South America [4]). We used a high-throughput multiamplicon sequencing platform to screen major target-site mutations that cause acaricide resistance in T. urticae. These included G119S, A201S, T280A, G328A and F331Y (Ace-1) associated with mode of action (MoA) 1 insecticide (organophosphates and carbamates); M918, L925I, L1014F and F1538I (VGSC) associated with MoA 3 insecticide (pyrethroids); G314D (GluCl1) associated with MoA 6 insecticide (avermectins and milbemycins); and finally, H92R (PSST) associated with MoA 21 insecticide (fenpyroximate, pyridaben and tebufenpyrad). The results revealed that four known mutations (G119S, T280A, G328A and F331W) were abundant in the quarantine samples including those from Norfolk Island and New Zealand. The mutations L1024V, F1538I and L925V (VGSC) associated with pyrethroid resistance were widespread through many samples, but the super Kdr mutation M918 was not detected. Similarly, H92R (PSST) that causes resistance to fenpyroximate, pyridaben and tebufenpyrad was found in most of the T. urticae intercept samples. We conclude that resistance alleles entering Australia through quarantine intercepts are common, suggesting that unwanted or rare alleles could enter Australia via this route. However, exotic quarantine breaches carrying such alleles remain of most serious concern.