Paralyzing effects of CO₂ and hypothermia on Madagascar hissing and dubia cockroaches

Cockroaches are often used as experimental subjects in a diverse range of biological studies. It can be necessary to temporarily immobilize an individual cockroach for measuring or marking purposes; in such cases, hypothermia or CO₂ can serve as paralyzers. Immersion in cold water is a commonly used technique: a cockroach, when put into cold water, starts to lose the ability to move and respond to stimuli over time. However, this method requires a relatively long time to paralyze a cockroach and leads to a slow recovery. We aimed to find a more ethical and efficient way to temporarily paralyze a cockroach by comparing the results of two methods: one that uses hypothermia as a paralyzer and an analogous method that uses high concentrations of CO₂ instead. Cockroaches, like most insects, have a trachea system, which allows the CO₂ gas to easily penetrate their breathing system. Thus, changes caused by CO₂ manifest in an insect’s body quicker than the effect of cold. We hypothesized that the paralyzing effect of CO₂ would be more time-efficient than that of hypothermia. Our results support this hypothesis given that the time required for immobilization using CO₂ was decreased compared to that using cold water. This research aims to contribute to the usages of laboratory animal ethics, especially cockroaches.