Chaetorellia species in Lebanon: Ovipositor Morphology and DNA Barcoding

Abstract

The genus Chaetorellia (Hendel, 1927) belongs to the Family Tephritidae, subfamily Tephritinae, within the Diptera. It is mainly found in the Palearctic and consists of 12 species. In Lebanon, only two species are prevalent. Chaetorellia carthami infests the flower heads of Carthamus species while C. conjuncta exploits the flower heads of Centaurea iberica, and is rarely found on Carthamus tenuis, a new and unusual host. In both species, adults have four characteristic bands on their wings, and their identification can be challenging. They can be recognized by the number of dark spots on their thorax, 8 in C. conjuncta and 10-12 in C. carthami. The females use their ovipositor to deposit eggs in the flower heads of their host plants, and the larvae feed and destroy a few seeds. The ovipositor is an important structure to distinguish tephritid species. The ultrastructure of Chaetorellia ovipositor has not been documented. This study aimed at estimating the extent of intra- and interspecific variations in the two species by examining the morphology of the ovipositor and sequencing the mitochondrial COX1 gene. Morphological studies using light microscopy and nine measurements showed significant differences in the two species regarding ovipositor length, ovipositor tip width and length, and the position of the ventrolateral grooves with respect to the tip. Scanning electron microscopy revealed that the ovipositor tip in the two species was associated with 4-5 pairs of highly elevated campaniform sensilla. Differences between the two species were observed in the acanthae’s shape on the eversible membrane, pointed in C. carthami and ovate in C. conjuncta, and in the distribution of the sensilla on the ventral and dorsal processes. Females of C. carthami had longer ovipositor with a blunt end suited for oviposition in the narrow, longer and tubular heads of Carthamus species while C. conjuncta females had shorter ovipositor with narrow and pointed tip, adapted to the smaller and globular heads of Centaurea iberica. Phylogenetic analysis using COX1 gene showed that the populations of the two species fell into two distinct clades and proved that this gene is useful as a DNA marker for distinguishing between the two species. Future studies should focus on sampling more flies from more sites to fully document the extent of intraspecific variations within Chaetorellia species.