Evaluation of the toxicological effect of bean flour on the mortality and population dynamics of two storage mites

A laboratory study was carried out to demonstrate the efficiency of bean flour in the control of two storage mites: Tyrophagus putrescentiae (Schrank, 1781) and Aleuroglyphus ovatus (Troupeau, 1878) fed on two dried Chinese herbs: coix seed (Coix lachrymal-jobi) and Chinese hawthorn (Crataegus pinnatifida). Five concentrations of bean flour (0%, 0.01%, 0.1%, 1% and 10%) were used at 25 °C and 85 ± 5% relative humidity (RH) under darkness. The results indicated that the controlling effect of bean flour on T. putrescentiae was higher than that on A. ovatus and became more noticeable when its concentration was increased. Low dose of bean flour (0.01%) generally had no toxic effect on T. putrescentiae and A. ovatus when they fed on C. lachrymal-job and C. pinnatifida. Mortalities of T. putrescentiae on C. pinnatifida varied from 15% to 40% and from 26% to 61% on C. lachrymal-job due to the use of 0.1% of bean flour. Moreover, in the case of A. ovatus, the mortalities ranged from 6% to 26% and from 15% to 51% on C. pinnatifida and C. lachrymal-job, respectively. After 28 days, the concentration of 1% bean flour caused 81% and 52% mortalities of T. putrescentiae and A. ovatus on C. pinnatifida and 92% and 69% on C. lachrymal-job. Addition of bean flour at 10% on C. pinnatifida and C. lachrymal-job killed all individuals of T. putrescentiae and A. ovatus.The results showed also that population dynamics of T. putrescentiae and A. ovatus, which is explained by the rate of increase (r values) on C. pinnatifida and C. lachrymal-job did not change considerably at 0% and 0.01% concentrations of bean flour. On the other hand, r values of T. putrescentiae and A. ovatus reread on C. pinnatifida and C. lachrymal-job sharply decreased at other concentrations of bean flour (0.1%, 1% and 10%) after 21 days. It can be concluded that 1% of bean flour is a good concentration to control T. putrescentiae after 28 days on C. pinnatifida and C. lachrymal-job, but it is not good enough in the case of A. ovatus.