A contribution to the biology, phenology and host specificity of Chaetorellia hexachaeta Loew (Dipt., Tephritidae), a possible candidate for the biological control of yellow starthistle (Centautea solstitialis L.)

Abstract

The biology and host specificity of the tephritid Chaetorellia hexachaeta Loew, the larvae of which live in the flower heads of Centaurea solstitialis and some related Centaurea spp. was studied in Northern Greece. The species has at least three generations per year. Previous research revealed that under laboratory conditions adults lived up to 60 days and up to 243 eggs were deposited by a female. Under cage conditions, particularly under oviposition pressure, the threshold of acceptance was lowered and eggs were laid into the flower heads of several non‐host plants. However, the larvae did not survive on 3 non‐hosts tested (Cirsium spp., Zinnia elegans). When caged with safflower (Carthamus tinctorius) and yellow starthistle heads (two—choice test), adults showed a 100% preference for yellow starthistle (YST). On the average, a single larva destroys 86.3% of the achenes of the attacked YST flower head. The species is recommended for consideration as a candidate for the biological control of Centaurea solstitialis but additional host specificity studies are needed before a definitive decision as to its introduction to North America can be made. Zusammenfassung Ein Beitrag zur Biologie, Phänologie und Wirtsspezifität von Chaetorellia hexachaeta Loew (Dipt., Tephritidae) und ihre potentielle Eignung für die biologische Bekämpfung von Centaurea solstitialis Die Bohrfliege Chaetorellia hexachaeta Loew ist in Nordgriechenland, wo sie in 3 oder mehr Generationen jährlich auftreten kann, eine wichtige Art im Phytophagenkomplex von Centaurea solstitialis. Im Freiland ist ihr Wirtskreis auf einige zumeist nah verwandte Centaurea‐Arten beschränkt. Im Labor lebten die adulten Tiere bis zu 60 Tage und legten bis zu 243 Eier/Weibchen. Die Eiablage erfolgt unter die Brakteen der Wirtspflanze. In Labortests konnte auch an verschiedenen, nicht zum Wirtskreis der Art gehörenden, Compositen eine Eiablage induziert werden, jedoch waren die Larven nicht in der Lage, sich in den drei eingehender untersuchten Testpflanzen (Cirsium creticum, C. vulgare und Zinnia elegans) zu entwickeln. Es konnte gezeigt werden, daß das Fehlen geeigneter Wirtspflanzen die Akzeptanzschwelle der Weibchen senkt und zur Eiablage in “Nicht‐Wirten” führen kann. Im Durchschnitt zerstört eine einzige C. hexachaeta‐Larve über 80% der Achanenproduktion eines Centaurea solstitialis‐Blütenkopfes. Im Zweifach‐Wahlversuch bevorzugen die Weibchen zu 100% ihre Wirtspflanze gegenüber Carthamus tinctorius. Damit sprechen die biologischen Befunde sowie die Ergebnisse unserer Versuche zur Wirtsspezifität dafür, diese Art zur biologischen Bekämpfung von Centaurea solstitialis einzusetzen, jedoch sind noch weitere Sicher‐heitstests notwendig, bevor über eine Einfuhr dieser Art nach Nordamerika entschieden werden kann.

Chaetorellia australis(Diptera: Tephritidae) for biological control of yellow starthistle,Centaurea solstitialis(Compositae), in the western USA: establishment and seed destruction

“…The first adults to emerge from the overwintered generation do so in April, before yellow starthistle capitula are generally available for oviposition, thus oviposition in this generation of C. australis occurs chiefly on the earlier flowering Centaurea cyanus in Greece (Sobhian & Pittara, 1988). Oviposition by the next two generations (includes overwintering larval progeny) of Chaetorellia australis in Greece occurs on yellow starthistle (Sobhian & Pittara, 1988). White & Marquardt (1989) found intergenerational colour and morphometric differences between the generations that attack Centaurea cyanus versus yellow starthistle in Greece.…”

“…To examine the importance of C. cyanus for Chaetorellia australis, we will continue to monitor fly establishment at yellow starthistle sites with and without Centaurea cyanus, and at yellow starthistle-only sites different distances from sites containing both hosts. In northern Greece, Sobhian & Pittara (1988) reported that Chaetorellia australis infestation frequencies in yellow starthistle ranged from 3 to 17% at five sites without Centaurea cyanus (distances to the nearest C. cyanus sites not provided), and 30 to 47% at three sites also supporting C. cyanus populations.…”

“…Chaetorellia australis has three generations per year in its native range in northern Greece (Sobhian & Pittara, 1988). The first adults to emerge from the overwintered generation do so in April, before yellow starthistle capitula are generally available for oviposition, thus oviposition in this generation of C. australis occurs chiefly on the earlier flowering Centaurea cyanus in Greece (Sobhian & Pittara, 1988). Oviposition by the next two generations (includes overwintering larval progeny) of Chaetorellia australis in Greece occurs on yellow starthistle (Sobhian & Pittara, 1988).…”

“…Although the total number of flies released was similar at the Merlin and Colfax sites (table 1), and the Merlin site was sampled three years after the initial (table 1). Chaetorellia australis has three generations per year in its native range in northern Greece (Sobhian & Pittara, 1988). The first adults to emerge from the overwintered generation do so in April, before yellow starthistle capitula are generally available for oviposition, thus oviposition in this generation of C. australis occurs chiefly on the earlier flowering Centaurea cyanus in Greece (Sobhian & Pittara, 1988).…”

“…Females oviposit just beneath the involucral bracts on closed capitulum buds. Following their penetration into the capitulum interior, larvae feed by mining through multiple developing seeds, destroying most of them (Sobhian & Pittara, 1988). Mature larvae overwinter in hibernacula in host capitula, and pupariate and emerge as adults the following spring.…”