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Global warming has gradually reduced the control efficacy of <i>Agasicles hygrophila</i> against the invasive weed <i>Alternanthera philoxeroides</i>. To better understand the summer collapse of <i>A. hygrophila</i> populations, we cloned the cDNA sequences of the high temperature-sensing <i>TRPA1</i>, <i>Painless</i>, and <i>Pyrexia</i> from <i>A. hygrophila</i>, and analyzed their temporal expressions and the impacts of high temperatures on their expression in eggs, the most vulnerable stage of <i>A. hygrophila</i> to hot temperatures. All the three genes obtained had the signature domains of TRPA channels and were constitutively expressed in eggs, larvae (L1, L2, L3), pupae, and adults, but <i>AhPainless</i> had the highest expression, followed by <i>AhPyrexia</i>, and <i>AhTRPA1</i>. The lowest and highest expression stages were adult and pupae for <i>AhTRPA1</i>, egg and L3 for <i>AhPainless</i>, and pupae/adult and L2 for <i>AhPyrexia</i>. The expressions of <i>AhTRPA1</i>, <i>AhPainless</i>, and <i>AhPyrexia</i> remained low at the preferred temperature range of 25–28 °C, elevated to their peak levels at 37.5, 30, and 30 °C, respectively, then fell to their 25–28 °C levels (<i>AhTRPA1</i>, <i>AhPainless</i>) or a lower level (<i>AhPyrexia</i>) at one or more temperatures >30 or 37.5 °C. These results suggest that their temperature-sensing roles and importance may be different, stage-specific, and their expression may be decoupled from their activation.