Toxicant translocation and colony impact in the Pharaoh ant (Hymenoptera: Formicidae) after consumption of gel bait-killed German cockroach (Blattodea: Ectobiidae) cadavers

This study investigated the translocation of cockroach bait toxicants to the Pharaoh ant, Monomorium pharaonis (L.), through feeding on cadavers of German cockroaches, Blattella germanica (L.), which were killed by commercial gel baits. The cockroaches were first treated with 1 of 4 gel baits: Advion Trio (0.6% indoxacarb, 0.1% pyriproxyfen, 0.1% novaluron), Maxforce FC Magnum (0.05% fipronil), Alpine Rotation 1 (0.5% dinotefuran), and Vendetta Nitro (0.5% clothianidin, 0.5% pyriproxyfen) before the Pharaoh ants were allowed to forage on the cadavers. The effects of the toxicants on the Pharaoh ant colonies were examined. Ants that fed on cadavers killed by Maxforce FC Magnum showed significantly higher (P < 0.05) mortality rates among queens and brood. Advion Trio initially led to the rapid reduction of queens, workers, and brood; however, the Pharaoh ant colony later recovered as the workers abandoned treated cockroach cadavers in favor of the regular diet. Examination of the queen ovaries revealed that, in the Vendetta Nitro-treated group, the size of mature oocytes was significantly reduced (P < 0.05). However, no structural damage was observed on any oocyte, as all exhibited a visible nucleus, multiple nurse cells, and well-developed follicular epithelium. The horizontal transfer efficacy of different cockroach gel bait toxicants is discussed.