Genotype-by-environment interactions for mean performance and trait variation in house fly larvae reared on two diets

Some insect species have been proposed as a sustainable alternative to traditional animal-based food and feed sources. Optimisation of insect production can generally be achieved using two main approaches: optimising environmental conditions and improving traits of interest through selective breeding. These avenues are not inseparable as performance of a genotype might differ between environments due to phenotypic plasticity and because genotypes can respond differently to environmental changes, that is genotype-by-environment interactions (G × E). In insect production, diets can be of variable quality and consist of waste- and by-products of low nutritional value, which might result in decreased performance and/or increased trait variability within a population. Therefore, it is of interest to investigate how genotypes perform across various diets. Here, we investigated plasticity and G × E for mean performance and trait variation, which we define as the ability of a genotype to produce consistent phenotypes within and across environments. We did this by rearing 190 full-sib families of house fly larvae, Musca domestica L. (Diptera: Muscidae), on two diets based on either alfalfa, Medicago sativa L. (Fabales: Fabaceae), or deproteinated grass. Four larval traits were assessed: egg-to-larva viability, surface area, dry weight and relative lipid content. Reaction norms were used to investigate the effects of diet on full-sib family mean and trait variation within and across environments. We found that families reared on the grass-based diet had higher performance across all investigated traits than families reared on the alfalfa-based diet. For both mean performance and trait variation, we found G × E for all investigated traits. These findings suggest that there is genetic variation for plasticity (slope of reaction norms) for both trait mean and trait variation, and thus that there is a potential to breed for genotypes with high performance as well as for genotypes with low trait variation within and across diets.