UC Riverside

Five strains of German cockroaches, WM, RG386, Ryan, CDR, and SY, were collected from field sites in California. Resistance to five bait insecticides was assessed in laboratory arenas and compared to the UCR susceptible strain, revealing increased survivability towards baits. Contact resistance towards bait active ingredients and deltamethrin was found in all strains from topical applications of the 3 x LD95 and 10 x LD95 of the UCR strain. The physiological resistance mechanisms of deltamethrin and fipronil resistance were assessed. The involvement of metabolic detoxification was evidenced by increases in topical toxicity of deltamethrin or fipronil diagnostic doses with the synergists piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF), and diethyl maleate (DEM). Elevated general esterase and glutathione-S-transferase activities were detected with biochemical assays of whole-body homogenates. The pyrethroid resistance-conferring L993F kdr mutation and the fipronil resistance-conferring Rdl mutation of the GABA chloride channel was found in all field-collected strains.Sucralose is an artificial sweetener that has garnered attention as a potential safe insecticide. The oral toxicity of sucralose was found to be concentration dependent for the UCR, WM, and RG386 strains through provisions of 5, 10, and 20% solutions in water. Pre-exposure to 20% sucralose solutions for 2 d did not affect the topical toxicity of deltamethrin, fipronil, or hydramethylnon but improved the performance of a hydramethylnon bait. There was no initial preference for contacting or consuming sucralose or water in the UCR and WM strains, but RG386 cockroaches preferred to consume water. Because sucralose cannot be metabolized, it has been hypothesized that mortality is caused by a buildup in the hemolymph, osmotic imbalance in the alimentary system, and subsequent dehydration through water excretion. When provided with 20% sucralose solutions, body water decreased by 23.0–30.29% by 6 d, and sucralose acted ~2–3 d faster against 2 d dehydrated cockroaches. Evidence of alimentary disruption was demonstrated with the significant loss of bacterial diversity in the guts of treated cockroaches.