Ultrastructure of sensilla on antennae and maxillary palps in three Mesembrinellidae species

Ultrastructure of Antennal Sensory Organs in Nine Flesh Flies (Diptera: Sarcophagidae): New Insight into the Definition of Family Sarcophagidae

Simple Summary

The antennal sensilla of species in all three subfamilies of Sarcophagidae are studied for the first time via scanning electron microscopy. The morphology, density, and distribution of each type are described for each species. A total of eight types of antennal sensilla (chaetic sensilla, setiferous plaques, pedicellar buttons, trichoid sensilla, basiconic sensilla, coeloconic sensilla, clavate sensilla, bottle-shaped sensilla) and sensory pits are found in both sexes. The existence of bottle-shaped sensilla in the sensory pits in all three subfamilies of the sarcophagid species suggests a potential synapomorphy of sarcophagids and a new morphological diagnosis character of the family Sarcophagidae.

Abstract

The antennae are the main olfactory organ of flies, playing key roles in their survival and the success of all life stages. Antennal ultrastructural morphology has been well described in the representative species of most calyptrate families, yet only a few studies have focused on Sarcophagidae species, those with ecological and medical relevance. Antennal morphology and the types, shapes, distribution, and density of the antennal sensilla of nine Sarcophagidae species are studied in detail with scanning electron microscopy, including Miltogramminae: Metopia campestris (Fallén) and Mesomelena mesomelaena (Loew), Paramacronychiinae: Agria mihalyii (Rohdendorf & Verves), Wohlfahrtia bella (Macquart), and W. magnifica (Schiner); Sarcophaginae: Sarcophaga (Parasarcophaga) albiceps Meigen, S. (Bercaea) africa (Wiedemann), S. (Boettcherisca) peregrina (Robineau-Desvoidy), and S. (Liosarcophaga) portschinskyi (Rohdendorf), covering all three subfamilies of this family. The morphology of the three segments of the antennae has been described. The scape has only one type of chaetic sensilla, while three subtypes of chaetic sensilla were detected on the pedicel. The postpedicel has four types of sensilla: trichoid sensilla, coeloconic sensilla, clavate sensilla, and three subtypes of basiconic sensilla. Bottle-shaped sensilla were observed in sensory pits on the postpedicel in all nine species. These sensilla have not been discovered in other calyptrate species, suggesting that they are a potential sarcophagid synapomorphy.

Fine Structure of Maxillary Palps in Adults of Hermetia illucens (Diptera: Stratiomyidae)

A relevant species in waste management but also in forensic, medical, and veterinary sciences is the black soldier fly, Hermetia illucens (Linnaeus; Diptera: Stratiomyidae). An ultrastructural study by scanning electron microscopy (SEM) was conducted for the first time on maxillary palps of both sexes, describing in detail the morphology and distribution of sensilla and microtrichia. The maxillary palps, composed of two segments, show sexual dimorphism in length and shape. In both sexes, the first segment is covered only by microtrichia, but the second one is divided into two parts: the proximal one, covered only by microtrichia, and the distal one containing both microtrichia and sensory structures. These structures include two types of sensory pits and one of chaetic sensilla. Due to sexual dimorphism in palp size, females have a higher number of sensory pits. The sexual dimorphism of palps and the presence and role of sensilla in H. illucens was discussed in comparison to other species of the family Stratiomyidae and of other Diptera. This study may represent a base for further investigations on mouthpart structures of this species, involved in key physiological activities, such as feeding, mating and oviposition.

Characterization of the Expression and Functions of Two Odorant-Binding Proteins of Sitophilus zeamais Motschulsky (Coleoptera: Curculionoidea)

Odorant-binding proteins (OBPs) are important in insect chemical communication. The objective of this research was to identify the functions of two OBPs in Sitophilus zeamais. qRT-PCR and western blot (WB) were performed to investigate the expression profiles at the transcript and protein levels, respectively. Fluorescence competitive binding assays were used to measure the ability of the OBPs to bind to host volatiles, and a Y-tube olfactometer was used to verify the results (attraction/no response) via behavioral experiments. The RNAi was used to verify the function by knocking down the ability of proteins to bind odorants. qRT-PCR showed the highest expression SzeaOBP1 and SzeaOBP28 at the low-instar larva (LL) and eclosion adult (EA) stages, respectively. WB showed that both SzeaOBP1 and SzeaOBP28 were highly expressed in the EA stage. Fluorescence competitive binding assays indicated that SzeaOBP1 exhibited extremely high binding affinity with cetanol. SzeaOBP28 exhibited a pronounced binding affinity for 4-hydroxy-3-methoxybenzaldehyde. The behavioral experiment showed that the adult S. zeamais responded strongly to 4-hydroxy-3-methoxybenzaldehyde and valeraldehyde from Sorghum bicolor. The RNAi knockdown individuals displayed behavioral differences between normal insects and dsRNA (SzeaOBP1)-treated insects. We infer that they both have functions in perception and recognition of host volatiles, whereas SzeaOBP28 may also have other functions.