Sublethal Effects of a Commercial Imidacloprid Formulation on Histopathological, Biochemical, and Haematological Parameters in Periplaneta americana (L.)

The “American” cockroach has been fairly well characterized in the literature as both a pest and model organism for toxicological studies. This study highlights the effects of the commercial formulation of imidacloprid (Zevictra TC) on P. americana, addressing an important gap in the literature, as most previous studies have focused on pure compounds rather than actual formulations. We deliberately wanted to study an actual formulation, which more accurately represents how chemicals impact the recipient in the field. After 24-h exposures, we estimated sub-lethal (LC10) and median lethal (LC50) doses using probit analysis. Our data showed clear, dose-dependent toxicity across numerous physiological systems. Histological examination of the midgut tissue from the LC50 group showed developmentally altered tissue, as well as disorganization of the muscle layers and fragmentation of the peritrophic membrane. In addition, biochemical assays detected distinct, dose-dependent decreases in total proteins, trehalose, and lipids, also suggesting extreme metabolic stress/damage and possibly cellular energy depletion. The Total Haemocyte Count (THC) data showed significant and dose-dependent decreases in the THC and indicated a considerable degree of immunosuppression and severe disruption to the immune response across the doses. Taken together, our results strongly suggest that even sub-lethal exposure to commercial formulation of imidacloprid significantly depressed the digestive, metabolic, and immune systems of P. americana. The results of this study indicate the need to explore systemic sub-lethal effects in the design of sustainable, and effective, management strategies for urban pests.