Fluxametamide differentially affects population growth of the predatory mite Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae)

Abstract

Fluxametamide, an isoxazoline compound, is a novel broad-spectrum insecticide and acaricide with a neurotoxic mode of action, is intended for use against lepidopteran, thysanopteran, coleopteran, hemipteran and dipteran pest species, as well as spider mites. Its effects on life-history and population parameters of the predatory mite Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) were assessed in demographic bioassay using the age-stage two-sex life table. Fluxametamide was applied against 24-h old adult females at LC10 and LC30 (the concentrations obtained in previously conducted acute toxicity bioassay) and the effects were evaluated on their offspring. Three cohorts (two acaricide treatments and a control) of 45 eggs each were formed. The eggs were laid by the females exposed for 24 h to fluxametamide residues on bean leaf discs. Developmental time, survival, and the number of eggs laid were checked daily, until all individuals were dead. To provide a food supply for the predator, 4–6 Tetranychus urticae Koch immatures were added several times per day. The raw life history data were analyzed using the TWOSEX MSChart software. The following parameters were estimated: pre-adult developmental time (Pa, days), total preoviposition period (TPOP, days), fecundity (eggs female-1), adult longevity (days), oviposition period (days), total life span (days), gross reproductive rate (GRR, eggs laid), net reproductive rate (R0, eggs mite-1), intrinsic rate of increase (r, days-1) and finite rate of increase (λ, days-1). Standard errors of the parameters were estimated by the bootstrap technique with 100,000 replicates, and the differences between control and treatments were compared by the paired bootstrap test. Fluxametamide differentially affected population growth of A. swirskii. Applied at LC10, the acaricide significantly reduced GRR (8.78), R0 (7.68), r (0.122) and λ (1.130), compared to the control (GRR = 14.25, R0 = 12.24; r = 0.142; λ = 1.152), and this reduction was largely the consequence of significant reduction in adult longevity (females: 22.10, males: 20.36; in the control: 24.31 and 22.09) and fecundity (11.93; in the control: 19.00). On the other hand, the application at LC30 caused a significant increase in GRR (18.16), R0 (16.25), r (0.188) and λ (1.207), compared to the control, mainly due to a significant shortening of TPOP (8.68; in the control: 10.17) and a significant increase in fecundity (22.64).