Formation of a ventral cavity in lepidopteran insect pupae

Abstract

A cavity exists between the thorax and abdomen in Pieris brassicae (Lepidoptera: Pieridae) and Pieris rapae crucivora pupae. In this paper, it was investigated whether air swallowing occurs at the pupal ecdysis and the relationship between the swallowed air and cavity formation by MRI measurements of P. brassicae and six other lepidopteran species after pupation. In P. brassicae, air swallowing was observed at the pupal ecdysis with air found in the esophagus immediately after pupation. The size of the air pocket was larger in non-diapause pupae than diapause pupae; however, no marked cavity was found between the thorax and abdomen in both diapause and non-diapause pupae. As time lapsed, the air pocket became smaller and moved towards the abdomen with a reduction in the size of the digestive tract. The air disappeared within 6 to 18 h after pupation. Conversely, the cavity became larger 12 h after pupation in both diapause and non-diapause pupae. Twenty-four hours after pupation, a distinct cavity was formed. The swallowed air appears to be involved in cavity formation. In six lepidopteran species, air was also found in the esophagus immediately after pupation. The size of this air pocket was also larger in non-diapause than diapause pupae in all species with a diapause stage. This is the first paper to describe that lepidopteran species swallow air at the pupal ecdysis and the air pocket is larger in non-diapause pupae than diapause pupae.