Journal of Taiwan Agricultural Research

Fig. 1.　Locations where Rhyzopertha dominica adults were collected from paddy rice warehouses in Taiwan. The red spot denotes R. dominica populations with a high degree of deltamethrin resistance.

Author:Wen-Bin Feng, Chi-Yang Lee, and Me-Chi Yao*

Abstract:

The lesser grain borer, Rhyzopertha dominica (Fabricius) is one of the most common stored product pests found in the paddy rice warehouses in Taiwan. Both larvae and adults can bite through the husk of paddy rice, causing serious losses. Currently, 0.055% dustable powder of deltamethrin is the only insecticide applied in the paddy rice warehouses to control the lesser grain borer in Taiwan. Deltamethrin has been recommended to control the stored product pests for 21 years since 2002. The long-term use of insecticides may lead to the development of insect resistance. In this study, we collected 21 R. dominica populations from paddy rice warehouses and obtained the deltamethrin resistance ratio of R. dominica with the rice-mixing method. The highest resistance ratios to deltamethrin were found in Wufeng, Hemei, Lukang, Minxiong, Liujiao, Houbi, Wandan, Dongshan, Yilan and Sanxing with the resistance ratios exceeding 117.65-fold. Results showed that R. dominica populations have developed high resistance to deltamethrin after a decade-long use of deltamethrin in Taiwan. To solve effectively control the lesser grain borer, it is necessary to find the alternative insecticides for controlling the stored product pests in paddy rice warehouses in Taiwan.

Key words:Paddy rice warehouse, Rhyzopertha dominica, Deltamethrin, Lethal concentration 50, Resistance ratio.