Genetic parameters of larval weight and length in yellow mealworm under tropical conditions: heritability and implications for breeding programmes

Understanding the genetic architecture of growth and larval productivity is essential for developing breeding programmes for Tenebrio molitor in tropical regions, where environmental conditions differ markedly from the temperate systems in which most genetic studies have been conducted. We analysed larval weight, larval length, family-level larval counts, and proportional survival in a population reared under tropical conditions. Growth traits were recorded at the individual level (60 and 130 days postmating), whereas family-level traits were based on square-root-transformed counts (√IPF30, √IPF60, √IPF130) and logit-transformed proportions (logitT, logit130). Variance components were estimated using univariate and multivariate animal models fitted with REML. Heritabilities were moderate for weight (0.27-0.33 ± 0.05) and low to moderate for length (0.19-0.21 ± 0.04). Additive genetic correlations between weight and length at each age were very high (0.90-0.999 ± 0.05). Family productivity showed moderate heritability at early stages (0.19-0.23) and high heritability for √IPF130 (0.61 ± 0.12). In contrast, proportional survival traits exhibited low and imprecise heritabilities (logitT ≈ 0.34 ± 0.18; logit130 ≈ 0.006 ± 0.03). Pearson correlations between family means and Estimated Breeding Values were high for growth traits (> 0.70) but weak for productivity and survival traits. These results indicate that larval weight and length are robust targets for genetic improvement in tropical environments, with family-level productivity providing complementary information. Survival traits, as defined in this study, require refined phenotype definitions before they can be used for direct selection. The genetic parameters reported here provide a foundation for developing structured breeding programmes for Tenebrio molitor in tropical production systems.