Sublethal effects and direct mortality of flucythrinate and fenvalerate to (Tetranychus urticae) koch: A dissertation submitted in partial fulfilment of the requirement for the degree of Bachelor of Horticultural Science (Hons.) in the University of Canterbury.

Abstract

Mite outbreaks occur after use of pyrethroid insecticides. Dosage mortality data of two pyrethroid insecticides, fenvalerate and flucythrinate, was obtained for the two spotted-spider mite (Tetranychus urticae Koch). LC₅₀'s were determined using slide dip and leaf disc techniques. The leaf disc method was used to measure sublethal effects such as repellency and changes in oviposition. There was a four fold difference between LC₅₀'s for flucythrinate derived by slide dip and leaf disc methods (0.43 g a.i.l⁻¹ and 0.11 g a.i.l⁻respectively). LC₅₀'s for fenvalerate derived by slide dip and leaf disc methods were similar (0.34 g a.i.l⁻¹ and 0.45 g a.i.l⁻¹ respectively). Both flucythrinate and fenvalerate repelled T. urticae . At 1 g a.i.l⁻¹ of flucythrinate mean run off was 3.9+0.5 compared to 3.3±0.9 from leaf discs treated with the same concentration of fenvalerate. Mean run off from untreated controls was 0.45 ± 0.60 and 0.3 ± 0.5 for flucythrinate and fenvalerate treatments respectively. Flucythrinate was not directly toxic to TSM. Mean direct mortality of the untreated control and the highest concentration of flucythrinate (2 g a.i.l⁻¹ ) was the same (0.3±0.5). Oviposition was reduced by fenvalerate and flucythrinate. At 1 g a.i.l⁻¹ of flucythrinate mean egg production per surviving female was 0.1±0.3 compared to 1.1±0.7 at 1 g a.i.l⁻¹of fenvalerate. There were no differences in repellency, direct mortality or egg production of T. urticae treated with various formulations of flucythrinate.