The use of soapy water and freezing as secondary steps for euthanasia in cave (Blaberus giganteus) and Madagascar hissing (Gromphadorhina portentosa) cockroaches.

Objective: To evaluate methods for euthanizing cave cockroaches (CCs; Blaberus giganteus) and Madagascar hissing cockroaches (MHCs; Gromphadorhina portentosa). It was hypothesized that both suggested methods would be effective for humane mass euthanasia of both species.

Sample: Approximately 800 CC.

Methods: The CCs were separated into replicate groups of 25, 50, 75, 100, and 150 grams and placed into 3.8-L plastic bags. Twenty-seven MHCs were divided into groups of 2 to 3. The study took place from January to March 2023. All CC groups were exposed to 100% carbon dioxide (CO2) at a rate of 4 L/min until the bag was full. Madagascar hissing cockroaches were similarly anesthetized using either CO2 or 2 mL of isoflurane on a cotton ball in a 1-L container or a combination of CO2 and isoflurane. Once cockroaches were immobile, secondary euthanasia steps were performed. One bag of CCs per weight category was exposed to soapy water (5% Dawn dishwashing liquid), and the second was placed into a -80 °C freezer. The containers of MHCs were evenly exposed to the 2 euthanasia methods. Individuals remained in their secondary euthanasia method for 30 minutes.

Results: Regardless of the weight of the CCs within each bag, there was no impact on time (1.8 ± 0.4 minutes [mean ± SD]) to immobility. The failure rates for both species were 0.2% CI (-0.1% to 1.5% [1/413]) for soapy water and 0.5% CI (0.005% to 1.9% [2/414]) for the freezer method. These results support the use of both 2-step euthanasia methods in CCs and MHCs.

Clinical relevance: These methods will serve as an evidence-based alternative for humane mass euthanasia in cockroaches.