Characters differentiating immature stages of two introduced Centaurea solstitialis L. (Asterales: Asteraceae) seedhead-attacking Tephritidae

Authors: CURTISS, ROBERT - Washington State University; Tonkel, Kirk

Submitted to: Proceedings of the Entomological Society of Washington
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2024
Publication Date: 10/9/2024
Citation: Curtiss, R.T., Tonkel, K.C. 2024. Characters differentiating immature stages of two introduced Centaurea solstitialis L. (Asterales: Asteraceae) seedhead-attacking Tephritidae. Proceedings of the Entomological Society of Washington. 126(2), pp. 137–148. https://doi.org/10.4289/0013-8797.126.2.137.
DOI: https://doi.org/10.4289/0013-8797.126.2.137

Interpretive Summary: Yellow starthistle is an invasive noxious weed that infests millions of hectares in the United States. Biological control efforts resulted in the introduction of a suite of natural enemies, including two seed-feeding fruit flies in the genus Chaetorellia. These flies, Chaetorellia australis and C. succinea, can account for significant yellow starthistle seed mortality. In this study we set out to obtain high resolution scanning electron microscope images to analyze species-level morphological differences in the immature stages. This information allows for definitive determinations of the identity of Chaetorellia australis and C. succinea individuals without rearing adults, which is of value to monitoring efforts of biocontrol practitioners and others working with introduced Chaetorellia flies on yellow starthistle.

Technical Abstract: Yellow starthistle, Centaurea solstitialis L. (Asterales: Asteraceae), has invaded over 8 million ha of the United States. As a target of biological control in North America since the 1950’s, seven insect species were intentionally released, and one was accidentally introduced into the western United States. Two introduced fruit flies (Diptera: Tephritidae), the yellow starthistle peacock fly, Chaetorellia australis Hering, and the false peacock fly, Chaetorellia succinea (Costa), attack Ce. solstitialis seedheads as immatures. Separation of the immature stages of these two flies in infested seedheads is difficult without rearing the adults. The puparial exuviae of these flies are retained in the seedhead for months following adult fly emergence, so they may be useful in forensic species diagnosis if differentiating characters exist. In this study, the vacant puparial exuviae of C. australis and C. succinea were evaluated using scanning electron microscopy to assess morphological differences in these species. It was found that the clusters of branched posterior spiracular hairs retained on the puparial exuvia can be used diagnostically to separate these species: C. succinea has 5.91 ± 0.43 and C. australis has 2.67 ± 0.25 spiracular hair branches between posterior spiracles. These differences provide a diagnostic tool that expands monitoring capabilities for these important biological control agents.