Optimisation of <i>Tenebrio molitor</i> reproduction: assessing the impact of different factors on larval yield, performances and mating preferences of beetles

Optimising reproduction of Tenebrio molitor (TM) is a key factor for improving farm productivity. Three experiments were conducted to investigate how beetles size influences reproductive performance of TM. Experiment 1 (1a and 1b) assessed size-based mate preferences among 14–day-old beetles. In 1a, beetles were grouped into four weight categories across 18 replicates; 1b involved two groups with 76 replicates. Mating behaviour was analysed among mixed-size males and females. Experiment 2 compared reproductive output across three weight classes (80–100 mg, 101–120 mg, 121–140 mg) in groups of 10 males and 10 females; outcomes included larval number, weight, and daily gain. Experiment 3 examined parental weight effects on larval traits and estimated heritability. Results indicated that both large and small males preferentially mated with larger females during initial mating events (66.7% and 72.2%, respectively). Male competition to mate first was evident, independent of female size. Beetle size did not consistently affect the number of larvae produced. However, larger beetles generated significantly heavier larvae, with this weight advantage maintained up to 8 weeks (137 mg vs 130 mg and 121 mg), potentially enhancing production efficiency. Paternal weight influenced larval weight more than maternal weight. Heritability of larval weight was estimated at 12.8% (maternal) and 13.2% (paternal), suggesting potential for genetic selection. Findings of the present study suggest that a preference towards large females is present. Furthermore, larger beetles increased larval yield by producing heavier individual larvae, thereby enhancing the efficiency of TM farming.