Effect of commercialBacillus thuringiensistoxins onTyrophagus putrescentiae(Schrank) fed on wolfberry (Lycium barbarumL.)

A laboratory study was conducted at the Traditional Chinese Medicine Center in Huazhong Agricultural University, Wuhan, China. Two commercial Bacillus thuringiensis (Bt) toxins (var. israelensis and tenebrionis) were used in this study at six concentrations (0, 2, 4, 8, 16 and 32 mg kg−1). We evaluated the growth and some biological properties of Tyrophagus putrescentiae (Schrank) fed on one Chinese herb (wolfberry) in the dark at 25°C and 80% relative humidity (RH). Mortalities of T. putrescentiae on wolfberry were examined after 1, 2, 3 and 4 weeks. The results indicated that the chosen Bt toxins had similar governing effects on the growth of T. putrescentiae and its biology. Increase of Bt toxin concentrations caused marked decreases in fecundity and longevity of T. putrescentiae. Development time and mortality of T. putrescentiae also increased with Bt dosage. The highest mortalities (81.22% and 90.91%) of T. putrescentiae adults were recorded due to the use of Bt toxins (Bt1 and Bt2) at the rates of 32 mg kg−1 after 4 weeks, so this dosage might be the best for controlling T. putrescentiae and maintaining quality of dried wolfberry fruits.