Development and optimization of plant-derived gel baits to control Blattella germanica

Cockroaches (Blattella germanica) are among the most persistent and problematic pests in urban and domestic environments worldwide and are also known to transmit infectious diseases such as hepatitis, cholera, and tuberculosis. Thus, this study aimed to develop insecticidal gel baits targeting B. germanica. The proposed formulations were based on plant extracts, that is, essential oils from spearmint, lavender, and clove, and alkaloids and fatty oil extracted from Peganum harmala seeds. The bioactivity of the gel baits and that of the pure plant materials used for their production were tested in terms of the mortality rate induced on adult cockroaches. The bioassays demonstrated that lavender essential oil, predominantly composed of linalool, exhibited the highest toxicity among the tested extracts. The alkaloid fraction C of P. harmala (0.5 g), characterized by a high concentration of harmine, resulted in complete mortality at 72 h, whereas its fatty oil achieved 100% mortality at a dose of 300 µL within 48 h. About the gel baits, all formulations showed a significant insecticidal effect, mainly within 24 h of treatment, nevertheless, from the main components. Lastly, to optimize the preparations, a response surface methodology study with a 6-factor Box-Behnken design was applied, correlating the observed mortality rate with the tested plant ingredients. All these findings confirm the synergistic effect of phytochemicals on bioactivity against B. germanica, suggesting their use in eco-friendly, sustainable insecticide baits compared to dangerous, toxic alternatives, including synthetic compounds.