Initial Sublethal Exposure to an Argentine Bacillus thuringiensis Strain Induces Chronic Toxicity and Delayed Mortality in Alphitobius diaperinus (Coleoptera: Tenebrionidae)

<i>Bacillus thuringiensis</i> is the most extensively studied entomopathogenic bacterium worldwide; however, its sublethal effects on beetles remain poorly characterized. The aim of this study was to evaluate the toxicity of a previously selected Argentine strain of <i>B. thuringiensis</i> on second-instar <i>Alphitobius diaperinus</i> larvae during an initial 14 days of exposure, and to assess its effects at day 14 and throughout the remainder of the life cycle until death. Three treatments were applied: control, LC₃₀, and LC₅₀. Larval, pupal, and adult weight and body surface area were recorded, and nutritional composition was quantified using colorimetric methods. Insect status was monitored every 48-72 h over a total period of 540 days, until the death of the last individual. Among the evaluated variables, statistically significant differences between control and treatment groups were detected in larval area and weight, in the survival analysis and in two nutritional components: total protein and lipid content per larva. Overall, the results demonstrate that initial sublethal exposure to <i>B. thuringiensis</i> induces chronic lethal effects with delayed mortality in <i>A. diaperinus</i>, indicating irreversible physiological damage. This provides valuable information not only for understanding the biology of this insect but also for stakeholders involved in the productive scaling of beetle-targeted bioinputs.