Toxicity tests, bioaccumulation and residuality of pyrethroid insecticides commonly used to control conifer bark...

Effectiveness of pyrethroid insecticides against pests including bark beetles (Dendroctonus spp.) is well known, but little is known about their (a) residuality and persistence in forests after application to control an outbreak and (b) ability to bioaccumulate in insects, which could cause adverse effects on the trophic chains. The 24 h lethal toxicity, bioaccumulation factors, and lethal body burdens of the pyrethroid insecticides bifenthrin, deltamethrin, and cypermethrin were evaluated in the bark beetle Dendroctonus mexicanus. The residuality and persistence of the insecticide bifenthrin in the forest ecosystem (soil, water, and sediment) was also monitored after its application in a region infested by bark beetles. We determined whether contamination of soil, water, and sediments occurred near the sanitation site. For D. mexicanus, the most toxic insecticide for adults was bifenthrin for topical application (LC₅₀ = 0.94 mg/L) and cypermethrin for bark application (LC₅₀ = 5.04 mg/L). The insecticide that bioaccumulated the most in the insect body was deltamethrin (622.41 μg g^-1 dw) and the insecticide that bioaccumulated the least amount was cypermethrin (183.09 μg g^-1 dw). However, cypermethrin was the active substance that presented the lowest body burdens, and therefore required a lower dose to cause death of D. mexicanus adults. Our results demonstrate that prolonged presence of bifenthrin in the forest ecosystem could lead to bioaccumulation in soil, sediment, and insects.