Abstract
The compatibilities of 10 acaricides with Beauveria bassiana SG8702 varied significantly in 24 h liquid cultures including three chemical rates. Pyridaben, hexythiazox and propargite were found highly compatible with the fungus even at field application levels. Four bioassays were performed with Tetranychus cinnabarinus eggs using a non-touch leaf method. The ≤18 h-old eggs laid on detached fava bean leaves were exposed to gradient conidial sprays of B. bassiana alone in Assay 1 or together with the pyridaben rates of 0.05, 1.0 and 2.5 a.i. μg/ml in Assays 2–4, respectively. The percentages of hatched eggs decreased with the increase in conidial concentrations and increased over post-spray days at a given concentration but had no more change from Day 9 onwards. Final egg mortalities reached 65.4, 72.3, 77.7 and 85.3% at ~1,000 conidia/mm2 in Assays 1–4. Ovicidal activity of B. bassiana [LC50 with 95% CI: 546 (406–818) conidia/mm2] was enhanced significantly by fungal sprays including pyridaben [LC50s: 322 (220–527), 199 (144–282), and 75 (48–103) conidia/mm2]. The effects of both agents and their interactions on the hatch rate of the mite eggs over post-spray days were illustrated by modeling the time-concentration-hatch relationship. The results indicate an alternative to utilize interactions of both agents against spider mites.
