Warmer temperatures reduce chemical tolerance in the redlegged earth mite (Halotydeus destructor), an invasive winter‐active pest

Abstract

BACKGROUND: Quantifying how chemical tolerance of pest arthropods varies with temperature is important for understanding the outcomes of chemical control, for measuring and monitoring resistance, and for predicting how pesticide resistance will evolve under future climate change. We studied the redlegged earth mite, Halotydeus destructor (Tucker), a winter-active invasive agricultural pest in Australia. Using a replicated block experiment, we tested the effect of different thermal conditions on the expression of chemical tolerance to a pyrethroid and two organophosphates. Our chemical bioassays were conducted on two redlegged earth mite populations: one possessed organophosphate resistance, whilst the other was susceptible to pesticides. Mites were first acclimated at cool (4 °C) and warm (14 °C) conditions and then exposed to pesticides in both cool ( 11°C) and warm (18 °C) test conditions. RESULTS: Warm test conditions generally reduced chemical tolerance to all pesticides relative to cool test conditions. Median lethal dose (LD 50 ) values of mites tested under cool conditions were 1.12-3.57-fold greater than of mites tested under warm conditions. Acclimation had a variable and small impact on chemical responses. Thermal factors (ratio between test temperatures) were similar between populations for each active ingredient. Despite reduced chemical tolerances under warm test conditions for individual mite populations, resistance factors (ratio between resistant and susceptible mite populations) were relatively consistent. CONCLUSION: Our data provides context for prior theoretical work demonstrating climatically constrained pesticide resistances in Australian redlegged earth mites. Estimates of temperature dependent toxicity measured in this study may be useful in parameterizing models of redlegged earth mite control under an increasingly warm and more variable climate.

From laboratory to field: laboratory-measured pesticide resistance reflects outcomes of field-based control in the redlegged earth mite, Halotydeus destructor

“…In a previous experiment, we undertook a series of laboratory bioassays to understand how temperature affects the chemical response of H. destructor (see Thia et al 2022b ). As part of this study, mites were collected from a field known to contain OP resistance (herein referred to as ‘Res-pop’) and from a nearby field known to contain mites that are susceptible to OPs (herein referred to as ‘Sus-pop’).…”

“…As part of this study, mites were collected from a field known to contain OP resistance (herein referred to as ‘Res-pop’) and from a nearby field known to contain mites that are susceptible to OPs (herein referred to as ‘Sus-pop’). In the current study, we re-analysed a sub-set of the laboratory bioassay data from Thia et al ( 2022b ) and so briefly summarise the relevant methods below and detail the statistical analysis we undertook.…”

“…For the purposes of the current study, we were only interested in those treatments where mites were held at 4 °C prior to testing and incubated at 18 °C during pesticide exposure (i.e., acclimation treatment = ‘Acclim cool’ and test treatment = ‘Test warm’; see Thia et al 2022b ). This is the standard methodology for pesticide laboratory bioassays involving H. destructor (Hoffmann et al 1997 ; Umina 2007 ; Maino et al 2018 ).…”

Ace and ace‐like genes of invasive redlegged earth mite: copy number variation, target‐site mutations, and their associations with organophosphate insensitivity

“…All Western Australia populations (Manjimup, Tambellup, Treeton, and Yongarillup) were found to be resistant to organophosphates. Victoria populations included two from Colbinabbin, one with evolved resistance to organophosphates (herein referred to as Colbinabbin Res) and the other susceptible to organophosphates (herein referred to as Colbinabbin Sus) 32 . A third Victorian population was collected from Wantirna South and was previously used to assemble the reference genome for H. destructor 29 .…”

“…Victoria populations included two from Colbinabbin, one with evolved resistance to organophosphates (herein referred to as Colbinabbin Res) and the other susceptible to organophosphates (herein referred to as Colbinabbin Sus). 32 A third Victorian population was collected from Wantirna South and was previously used to assemble the reference genome for H. destructor. 29 Although not phenotypically screened in this study, mites from Wantirna South are known to be susceptible to organophosphates.…”