Internal morphological changes during metamorphosis in the sheep nasal bot fly, Oestrus ovis

Abstract

During the larval stage, oestrid flies (Diptera: Oestridae) are obligate parasites, whereas during the adult stage they are free-living and do not feed. Like other cyclorrhaphous flies, oestrids undergo metamorphosis inside an opaque puparium, formed by the contracted and hardened cuticle of the third-instar larva. The present study documents the internal morphological changes taking place during metamorphosis of the sheep nasal bot fly, Oestrus ovis L., using non-invasive, micro-CT-based virtual histology and provides quantitative data of volumetric changes in specific organs. Virtual histological sections allowed visualisation of the progression and completion of the apolyses, which delimit the different intra-puparial stages, and the connection to the tracheal system of a large gas bubble, which plays an essential role during early metamorphosis. Overall, our results show that the sequence of morphological and volumetric changes in tissues and organs is similar to those found in other cyclorrhaphous flies, but they also reveal developmental differences that result in an adult vestigial digestive tract. Future studies could develop non-invasive, reliable methods for aging the intra-puparial forms of different oestrid species of veterinary importance, based on both qualitative and quantitative markers, thus improving our knowledge of their development and the efficiency of control strategies.

Ultrastructural and Morphological Observations of the External and Internal Structures of the Adult Midge <em>Culicoides grisescens</em> Edwards (Diptera: Ceratopogonidae)

“…There is no gastric caecum structure in the digestive tract of C. grisescens and the existence and number of this structure are quite different among Diptera [20,21]. Because the main function of the gastric caecum is to increase the surface area of the midgut to assist its digestion and absorption, insects that feed on liquid food do not have this structure.…”

Larval anatomy of the digestive and excretory systems of the pharyngeal bot fly, Pharyngomyia picta (Diptera: Oestridae)

“…In holometabolous insects, the lifecycle distinction between the larval feeding and growing stage and the adult reproductive stage is particularly clear, but in insects like the Oestridae, where the adult mouthparts are vestigial and some digestive organs do not develop during metamorphosis (Martín-Vega et al, 2020), such a distinction becomes even more evident. Feeding during the larval stage is therefore crucial in oestrid flies, and, considering that oestrid subfamilies differ in the type of tissues they infest, larvae show specific anatomical adaptations to parasitism in both external and internal structures (Colwell, 2006a(Colwell, , 2006b.…”

“…Nevertheless, the development of optimal protocols for the fixation and preparation of samples for micro‐CT scanning is strongly needed. Previous studies had shown that hot water fixation of larval and intra‐puparial specimens results in good contrast images that allow for the identification of internal soft tissues (Martín‐Vega et al, 2020, 2021). Although it is not within the aims and scope of this study (and it would need a proper replication and analysis of different larval instars), the resulting scans suggest that similar good contrast between tissues might be achieved with fixation in Kahle's solution, whereas glutaraldehyde may not be a suitable fixative as it resulted in poor contrast images here.…”

The pederin‐producing bacteria density dynamics in Paederus fuscipes at different developmental stages

“…Indeed, evidence from interspecific transfer experiments also revealed that successful colonisation by PPB endosymbionts in different Paederus beetles depends on the number of (+)‐eggs consumed by the larvae (Kellner, 2003). Incidentally, P. fuscipes has distinct larval and adult stages separated by metamorphosis (Figure 1), which entails dramatic remodelling of external and internal body structures during the pupal stage (Martín‐Vega et al, 2020). This may explain why a sharp decrease in PPB density could be observed from the pupae to newly emerged adults.…”