Flavonoids from Kalanchoe ×laetivirens Impair Survival and Immunity of Atta sexdens (Hymenoptera: Formicidae)

The active secondary metabolites of various Kalanchoe species are promising for controlling insects and other agricultural pests. This study aimed to evaluate the mortality and immune responses of the leafcutter ant Atta sexdens (L.) after treatment with Kalanchoe ×laetivirens (Desc.) aqueous extract. The effects on an aquatic organism used as a bioindicator, Chironomus xanthus (Rempel), were also evaluated. Different K. ×laetivirens concentrations were prepared by dilution in honey to assess the toxicity and determine the median lethal concentration (LC50) for A. sexdens workers. The haemocytes of workers treated with a sublethal concentration (0.005 g/mL) were counted. The plant extracts induced high mortality in A. sexdens workers. All concentrations, except 0.001 g/mL, increased mortality rates. The sublethal concentration negatively affected the immune system of A. sexdens workers 48 and 72 h after ingestion. The flavonoids 4″″-acetylsagittatin A, sagittatin A and the nucleosides uridine and adenosine were identified. The LC50 of the K. ×laetivirens (128.1 mg /L) was determined for the non-target organism, C. xanthus. These natural compounds can be used in future research to plan alternative control strategies for leafcutter ants in forests and other agroecosystems.