Insight into the larva of the greater wax moth Galleria mellonella as a model organism, with a pictorial key for identifying larval stages

A thorough knowledge of the larval stages of a model organism such as the greater wax moth Galleria mellonella is essential for researchers in various fields in the biological, pharmaceutical, medical and agricultural sciences. This is particularly important for the correct identification of the different larval stages: this will ensure reproducibility of results when individuals of a given stage are used in experiments. Knowledge of their morphology also has potential value in phylogenetic analyses. To address the urgent need for such knowledge, the development of G. mellonella larvae was tracked from the first to the eighth stage. This paper provides (i) a detailed description of the morphology, including the chaetotaxy, of the hitherto completely unknown first-stage (L1) larvae, with particular emphasis on adhesive structures, including those described for lepidopterans for the first time; (ii) a supplement to Smith’s (1965) description of the morphology of the last stage (L8); (iii) a list of macroscopic and ultrastructural features of morphological structures that undergo changes during larval development from the first stage to the eighth; and (iv) a pictorial, user-friendly key to all the larval instars (from L1 to L8) which has been developed based on metric and qualitative diagnostic characters, chiefly the head capsule width, the colour of the pronotum and the presence of an ecdysial line on it, the body shape and the presence of club-shaped setae, the arrangement of crochets on the prolegs, and the colour of the dorsal sclerites.