Morbidity and recovery of the Pacific Coast wireworm, Limonius canus, following contact with tefluthrin-treated wheat seeds

Late instars of the Pacific Coast wireworm, Limonius canus (LeConte) (Coleoptera: Elateridae), were exposed to wheat seeds treated with tefluthrin at 5, 10, 15, 20, or 30 g active ingredient (a.i.) per 100 kg wheat seed for 1, 2, 4, 8, or 16 min. All wireworms were moribund within 20 min of first exposure and recovered fully within 12 h. The time required for recovery (t(r)) after a single exposure increased with duration of exposure (e) and concentration (c), but decreased with wireworm weight (w), expressed as (t(r))(0.5) = 5.2812 + 0.9407e - 0.0259e(2) + 0.1569c + 0.0254ec - 0.0174w - 0.0057ew. For wireworms exposed to treated seeds for 2 min, the time required for induction of morbidity decreased as concentration of tefluthrin increased and as wireworm weight decreased, expressed as (t(i))(0.5) = 2.613 - 0.039c + 0.018w, where t(i) is the induction time of morbidity, and c and w are as above. Wireworms re-exposed to tefluthrin-treated seeds after recovery from previous exposure were again moribund within 20 min of exposure, but recovery was significantly more rapid if the second exposure was 2, 4, 6, 8, 12, 18, 24, and 48 h after recovery from first exposure. Recovery from a second exposure was not significantly faster when the second exposure was 96 h after recovery from the first exposure. The ability of wireworms to recover from tefluthrin-induced morbidity may seriously limit the efficacy of this insecticide in actually reducing wireworm populations in the field.