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

Abstract

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.

Possible aversion learning in the Pacific Coast wireworm

“…Wireworms used in bioassays were either naïve, or had been preconditioned by approximately 3 h of morbidity caused by exposure to ungerminated wheat seeds treated with Tefluthrin 20SC plus Dividend (as above) in Eppendorf tubes, as described previously by van Herk & Vernon (2007a). Wireworms were introduced into the soil bioassays approximately 30 min or 21 h after recovering from morbidity.…”

“…It is observed also that, for some insecticides (e.g. tefluthrin), brief (<2 min) direct contact without feeding with treated wheat seeds alone is sufficient to induce temporary (<12 h) morbidity in wireworms (van Herk & Vernon, 2007a, 2008).…”

Wireworms’ Management: An Overview of the Existing Methods, with Particular Regards to Agriotes spp. (Coleoptera: Elateridae)

“…Chemicals identified as eliciting repellency should be tested to determine whether the attractive cues of host plants dominate repellent stimuli [ 171 ]. Moreover, the ability of wireworms to recover from an active substance-induced morbidity may seriously limit the efficacy of the substance, as it has been shown for L. canus and tefluthrin-treated seeds [ 172 ]. Their sensitivity to repellent compounds may decrease when repeatedly made moribund.…”

Wireworm Management I: Stand Protection Versus Wireworm Mortality With Wheat Seed Treatments

“…In contrast, the phenyl pyrazole Þpronil, at sublethal acute dosages, caused no apparent ill effects for several months during which time feeding could occur, but after which latent morbidity effects and mortality occurred (van Herk et al 2008a, Vernon et al 2008). In addition, recent studies also demonstrated that the pyrethroid teßuthrin applied to wheat, Triticum aestivum L. seed was repulsive to A. obscurus (van Herk and Vernon 2007a) and L. canus (van Herk et al 2008c) in soil bioassays; and although morbidity was often observed after contact with treated seed, both species fully recovered within 24 h ( van Herk and Vernon 2007b, van Herk et al 2008c), and actually recovered more quickly after multiple exposures (van Herk and Vernon 2007b). Repulsion of wireworms also has been reported to certain OCs and OPs, including terbufos (Belcher and Tenne 1987), chlordane, chlorpyrifos, and fonofos (Missonnier andBrunel 1979, Horne andHorne 1991) and lindane (Long and Lilly 1958, van Herk et al 2008b), although these insecticides also were shown to kill wireworms in the Þeld.…”