Toxicity effect of the edible pigment carmoisine on Polyrhachis vicina Roger (Hymenoptera: Formicidae)

Carmoisine belongs to a water-soluble synthetic dye and is often used as a food additive. Previous research has shown that carmoisine is toxic to rats and zebrafish, but there have been few reports on the effect of carmoisine on soil-dwelling social insects. The present study evaluated carmoisine toxicity in Polyrhachis vicina Roger. We found that the effects of different concentrations of carmoisine on the mortality of workers were dose-dependent. The 10% lethal dose (LD₁₀), 50% lethal dose (LD₅₀) and 90% lethal dose (LD₉₀) of carmoisine to workers at 96 h was calculated to be 0.504, 5.491 and 10.478 g/L, respectivily. LD₁₀ of workers were selected to treat the fourth instar larvae, pupae and adults for 10 days. The results showed that the survival rate of all ants, except for females, was significantly reduced, especially larvae and workers. The body weight of larvae, pupae and males decreased significantly, while weight gain was observed in the females and workers. The appearance of larvae, pupae and workers changed after carmoisine treatment, such as body darkening and epidermis shrinking of larvae and pupae, as well as body segment expansion of workers. Furthermore, carmoisine altered the expression of the estrogen-related receptor, tailless and homothorax of P. vicina (Pv-ERR, Pv-tll and Pv-hth) to varying degrees in larvae and adults. We believe that variations in body weight can lead to a decrease in survival rate and appearance changes in the ants, which may be related to abnormal gene expressions caused by carmoisine treatment. Therefore, we confirm that carmoisine has negative effects on the growth and development of P. vicina.