Effects of long-term chlorpyrifos exposure on moulting and growth of Armadillo officinalis Dumèril, 1816 (Crustacea, Isopoda, Oniscidea)

Abstract

The aim of this study was to evaluate the long-term effects of the insecticide chlorpyrifos on the moulting and growth of the terrestrial isopods Armadillo officinalis. Adult woodlice were exposed to chlorpyrifos at concentrations of 5, 10, 20, 40 mg/kg dry soil and compared to a control. During 100 days of exposure, effects on moulting and growth were investigated. The duration of premoult, ecdysis and intermoult stages were estimated. Also, the cuticle width (CW) and length (CL) were measured and their size increase and specific growth were calculated. The results showed that exposure to chlorpyrifos induced adverse effects on moulting in the terrestrial isopod Armadillo officinalis, mainly at the higher concentrations (20 mg and 40 mg/kg dry soil). Indeed, it decreased the percentage of moulting animals, delayed moulting, decreased the number of completed moult, extended the premoult stage, prolonged ecdysis, and reduced intermoult duration. Furthermore, these findings showed that chlorpyrifos exposure impaired also growth of Armadillo officinalis, mainly at the highest concentration (40 mg/kg dry soi), by decreasing weight gain (0.94 ± 2.14 mg), cuticle length gain (0.26 ± 0.06 mm) and specific growth rate (SGR) (0.04 ± 0.01 mm/days) compared to the control (Weight gain = 16.5 ± 1.84 mg; CL gain = 0.65 ± 0.07 mm; SGR = 0.08 ± 0.01). The present study highlighted the adverse effects of chlorpyrifos on moulting and growth of Armadillo officinalis, which raises concern about consequences of chlorpyrifos exposure on population dynamic of this species.