HOST SPECIFICITY AND BIOLOGY OFUROPHORA CARDUI(DIPTERA: TEPHRITIDAE). A BIOCONTROL AGENT FOR CANADA THISTLE (CIRSIUM ARVENSE)

Abstract The biology ofUrophora cardui(L.) (Diptera: Tephritidae) and its suitability as a biocontrol agent for Canada thistle (Cirsium arvense(L.) Scop.) were investigated. The incubation period of the eggs was 4.3 days at 27 °C. Crowding did not significantly reduce the longevity of the adults, the number of eggs laid, or the egg hatch.U.carduioverwinters as a mature larva in the gall but pupation and further development ensue when the larvae are exposed to air by opening the gall. The roots of single and double-galled plants weighed 65 and 78% less and the combined weights of the stem and leaves 47 and 58% less respectively than plants without galls.U.carduiis monophagous: it oviposits into Canada thistle and if kept without this host, into the closely related weedsCirsium vulgare(Savi) Ten. andCarduus acanthoidesL.U.carduiis a promising biological control agent and should be released in Canada. Canada thistle (Cirsium arvense(L.) Scop.) is a widespread noxious weed in Canada and the northern United States. This paper reports on the biology ofUrophora cardui(L.), a European tephritid, and its suitability for introduction into Canada to aid in the control of the thistle.