Regal Fritillary - Reproduction and Life Cycle

Reproduction and Life Cycle

The regal fritillary is univoltine, having a single generation per year (Selby 2007). Adult male butterflies emerge in early June along with the first milkweed plants. Adult females emerge shortly after and mating takes place in late June and early July. After mating, females enter a 6 to 8 week period of reproductive diapause, or a suspended period of development. The ovaries remain undeveloped during this time. Oogenesis does not initiate until late August when juvenile hormone sharply increases (Kopper et al. 2001). Once oogenesis takes place, the eggs are fertilized and soon after, oviposition occurs. The female lays over 1,000 eggs and possibly more than 2,000 (Vaughan and Shepherd, 2005). The small larvae hatch in late September and into October. Immediately after hatching, the tiny larvae seek protective covering in the leaf litter and overwinter there. At this stage the larvae delay development over the winter months and this is known as larval diapuase (Kopper et al. 2001). Once spring arrives, the larvae emerge and begin feeding on violets. They grow and mature through six instar stages until late May when they pupate (Selby 2007).

The life cycle of the regal fritillary is quite unique and is thought to be an adaptation to the phenology, or seasonal timing and nature of their larval food plant, the violet (Kopper et al. 2001). These small perennial violets produce abundant foliage in the spring for the growing larvae. However, in most areas they senesce in the heat of the summer and become unavailable to the larvae at that time. When this occurs, the regal fritillary is entering into its adult life and is no longer dependent on the violet. The fact that the violets remain unable to support larvae throughout the rest of the summer helps to explain the regal fritillary’s univoltine life cycle. It is through larval diapause coupled with the adult female reproductive diapuase that enables the larvae to maximize the benefits of fresh and abundant violet foliage when they are active in the spring (Kopper et al. 2001).