Musk thistle and Canada thistle
Musk thistle, Carduus nutans Identification & origins Eurasian origin Sometimes called the nodding thistle : long slender stems bear heavy flowers Flowers are broader at the base & larger than those of Canada thistle
Musk thistle Biology Biennial: First year = rosette only; Second year = bolting or flowering stem growth Propagates mainly by seed Seeds released 7 10 after flowering Large, terminal heads produce 1,200 1,500 each Smaller, lateral blossoms produce less than 25 seeds each
Canada thistle, Cirsium arvense Origins & identification Eurasian origin Perennial Flowering stems are more slender than other noxious thistles Flowers are smaller than those of musk thistle
Canada thistle Biology Leaves emerge in spring as a rosette 3 weeks later, bolting (vertical flowering stem growth) occurs 40 80 seeds per flower Once established by seed, reproduce by below ground vegetative growth
Canada thistle, dioecious Male & female flowers Flowers small & spineless Only dioecious thistle = separate male & female plants Male flowers: smaller, do not produce fluffy pappus Females: larger; produce fluffy pappus that make seeds airborne
Canada thistle is only dioecious thistle Female flowers Male flowers
Differences in flowers of two most common noxious thistles Musk thistle Canada thistle
Insects Insects most successful organisms General traits: Exoskeleton of chitin Advantages? Six jointed legs Advantages?
Insect body plan Insecta, means cut into Head, thorax, abdomen Head: sensory Thorax: locomotion Abdomen: metabolism & physiology
Biocontrol insects Nearly all USDA released biocontrol agents are beetles Beetles are most successful organism Every 5 th living species (including fungi, plants, animals) is a beetle
Beetle external anatomy Beetles have head, thorax that bears forewings & hindwings & abdomen Forewings are shell like & called elytra Hindwings are folded beneath elytra & are used for flight
Life cycle of beetles
Weevils Thistle biocontrol beetles are weevils or snout beetles Elongate proboscis Antennae often arise on proboscis All weevils are herbivorous
Fly identication Order Diptera = two wings Only 2 functional wings Hindwings are now tiny halteres used as gyroscopes to aid in flight
Fly life cycle
Rhinocyllus conicus, Seedhead weevil Seedhead weevil Parallel sides Setae (hairs) on all surfaces, including legs Coloration varies; usually, brown to dark brown with light spots
Seedhead weevil Eats seeds of all thistle species Spring: mating occurs & females oviposit on developing flowers After ovipositing, females chews thistle leaf material & places a cap of chewed material over the oviposition opening Called egg caps, brown coloration
Seedhead weevil Larvae hatch from eggs & feed on developing seeds for 25 40 days Enters pupal stage that lasts 8 14 days Adults emerge, mate & continue life cycle
Trichosirocalus horridus, crown root weevil Setae (hairs) on all surfaces, including legs Tick like appearance Smaller than R. conicus & has thick scales on back Coloration varies; dark brown to black
T. Horridus life cycle Attacks rosette & roots Overwinters in the adult, egg and larval stages. Adults emerge in late winter and early spring to lay eggs on young thistle rosettes. Spring: mating occurs & females oviposit on rosettes Eggs hatch in about 10 12 days. Larvae feed for 6 8 wks. 3 rd instar larva leaves plant to pupate in the soil in pupation chambers. Adults emerge in 12 20 days. New generation of adults appears in June in SW Colorado & go into hiding until the fall, when they emerge to feed. Some start ovipositing until the first frost before hibernation. There is usually one generation per year.
Trichosirocalus horridus damage to musk thistle
Ceutorhynchus litura, stem weevil of Canada thistle Setae (hairs) on all surfaces, including legs Tick like appearance Smaller than R. conicus & has thick scales on back Coloration varies; dark brown to black with distinctive light patches
C. litura stem damage
Urophora cardui, canada thistle gall fly
Urophora cardui