Toxicity and Laboratory Performance of Insecticides to Field-Collected German Cockroaches (Dictyoptera: Blattellidae)
Type of DegreeMaster's Thesis
DepartmentEntomology and Plant Pathology
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The toxicity and resistance levels of five technical grade insecticides (permethrin, chlorpyrifos, propoxur, imidacloprid, and fipronil) were determined for adult males of seven strains of the German cockroach, Blattella germanica (L.). One laboratory reared susceptible strain combined with six field-collected strains. Using topical application methods, fipronil was the most toxic insecticide to all seven strains. The LD50 values of fipronil to the susceptible strain and the field-collected strains B, D, E, G, H, and I were 1.33, 2.62, 11.53, 5.07, 7.66, 5.15, and 10.15 ng/insect, respectively. The field-collected strains were most resistant to permethrin among the five insecticides, except for strain H. The resistance ratios of strains B, D, E, G, and I to permethrin were 31.8, 37.3, 51.9, 34.9, and 37.5, respectively. With a resistance ratio of 6.4, the field-collected strain H was most resistant to chlorpyrifos. The field-collected strains had nearly no resistance to propoxur. Strains B, H, and I were not significantly resistant to imidacloprid when compared to the susceptible strain. Based on the different resistance ratios for each insecticide, we conclude that the field-collected strains had different treatment histories. The repellency and performance of five selected insecticide formulations (each of which included one of the above insecticides) were determined using Ebeling choice boxes against male adult German cockroaches. Permethrin was the most repellent insecticide to the susceptible strain and field-collected strains B, E, G, and I with mean repellency of 55.97%, 66.89%, 85.92%, 27.16%, and 53.66%, respectively. Fipronil was the most repellent to strain D with repellency of 41.72%, and the five insecticides were similar in their repellency against strain H. Fipronil reached PI values of 100 during the 14 d experiment and tPImax/2 < 2 d. Chlorpyrifos reached PImax 100 for the susceptible strain and field-collected strains D and H during the 14 d experiment as well. Permethrin, propoxur, and imidacloprid did not reach PI values of 100 during the 14 d experiment. According to the repellency and performance index, fipronil may provide effective control in field, while other insecticides may be incapable of providing good field performance.