Insecticidal Efficacy Against Bed Bugs

Three technical grade insecticides belonging to neonicotinoid and pyrethroid groups were tested: acetamiprid (99.5%), imidacloprid (98.9%), and deltamethrin (93.2%). All materials were purchased from Chem Service Inc., West Chester, PA, USA. In topical assays, a feather weight forceps (available at www.amazon.com, accessed on 27 December 2022) were used to place 10 male adults of unknown age in a clean Petri dish (5.5 cm diameter and 1.5 cm height, Fisher Scientific, Pittston, PA, USA) lined with filter paper (Grade P8, Fisher Scientific, Pittston, PA, USA). Only male bed bugs were used in the topical assays because female bed bugs suffer injuries from traumatic insemination during mating. The wound on the abdomen of females may affect the results. Bed bugs were then anesthetized by placing the Petri dish on ice for 1 min prior to topical assay. An insecticide-acetone solution (1 µL) was applied onto the dorsal surface of the abdomen using a micro-applicator (Burkard Manufacturing Co. Ltd., Rickmansworth, UK) equipped with a 25-µL glass syringe (Burkard Manufacturing Co. Ltd., Rickmansworth, UK). Treated bed bugs were held with a forceps until the applied insecticide solution had dried then gently placed in a clean Petri dish. Control insects received 1 µL of acetone only. The concentrations of insecticides used were acetamiprid: 0.1–50 ppm; imidacloprid: 1–10 ppm; and deltamethrin: 0.04–1 ppm. At least three concentrations causing 1–99% mortality were included for each chemical. Each concentration was replicated three times. After treatment, insects were maintained in Petri dishes in an environmental chamber at 25 ± 1 °C, 45 ± 10% RH and 12:12 L:D photoperiod. Mortality was recorded after 72 h. An insect was considered dead if it could not move when touched with a pair of forceps.
After calculating the values of lethal dose (LD) for each insecticide, a discriminating dose (10 times of LD₉₀; 10 × LD₉₀) [46 (link)] of three insecticides was tested against all bed bug populations using topical assay. Similar to the previous topical assays, ten males were transferred to a clean Petri dish lined with filter paper. Each insect was treated with 1 µL insecticide-acetone solution. Insects in the control were treated with 1 µL acetone. Each population was replicated three times. The number of knockdown and dead insects was recorded every 5 min for the first hour and subsequently every 10 min until 2 h or until 90% of tested insects were knocked down. A bed bug was considered knocked down if it could not right itself when gently flipped over with a pair of forceps. Final mortality was recorded after 72 h. All tests were conducted in 2022.