Pupation in Zophobas atratus is dependent on isolation and this provides a model for study of the onset of metamorphosis in beetles. We have analyzed the effects of isolation vs grouping on certain developmental parameters; the number of larval instars; their duration and weight. Sex differences were detected, such as the occurrence of regressive moults in females. Moreover, the development of Z. atratus is discussed in relation to Tenebrio molitor, the physiological timing of which appeared in part extendable to Z. atratus. Experiments show that 4-6 days of isolation are required for commencement of metamorphosis, as indicated by an immobile crooked posture observed at the end of this period, characterizing the beginning of prepupal development. During this period, return to grouped conditions, as well as applications of a juvenile hormone analogue (ZR 515) prevented metamorphosis and precipitated another larval moult. This suggests that grouped conditions may delay the onset of metamorphosis through the modulation of juvenile hormone titres.
