Biocontrol for Weed & Insect Pests
Weed Control Programs
The Insectary has ongoing biological control programs for many noxious or problem weed species. They include: leafy spurge, diffuse and spotted knapweed, tall larkspur,puncturevine, musk thistle, yellow and Dalmatian toadflax, bull thistle, Canada thistle, purple loosestrife, andfield bindweed. Approximately 30 weed predators are being cultured, released, and established on weed infestations throughout the State. In addition to the biological weed control programs, this section conducts control programs for the alfalfa weevil, and Oriental fruit moth, with a total of twelve beneficial species.
The main function of the Biological Pest Control Section is the rearing and releasing of natural enemies for control of specific plant and insect pests. To request biological pest control please contact our office at 1-866-324-2963. This section also acts as the State's receiving station for biological control agents. New biological control programs are being developed primarily by agencies of the United States Department of Agriculture. Foreign exploration produces several new species each year that are known to control introduced plant and insect pests. These exotic species are exposed to a strict quarantine procedure before they become available to cooperating states for general release. This insures that potentially hazardous species are not accidentally introduced with the beneficial insects.
(Photos courtesy of Kelly Uhing)
ABOUT THE NATURAL ENEMIES OF:
LEAFY SPURGE (Euphorbia esula)
In 1989, two leafy spurge biocontrol agents, Aphthona flava and Aphthona nigriscutis, were obtained from collections in Canada and Europe. The adults of these flea beetles defoliate the spurge plants while the larvae feed on the roots. In 1991, a third flea beetle species, Aphthona cyparissiae, was obtained from Canada and released. In 1992, a long-horned beetle, Oberea erythrocephala, was obtained and released. The adults of the beetle feed on the aboveground parts of the plant while the larvae bore into the stem and root crown. In 1993, a fourth flea beetle, Aphthona czwalinae\lacertosa, was obtained and released in the State. The larvae of A. czwalinae\lacertosa feed on the roots and the adults feed on the leaves of leafy spurge. A final flea beetle species, Aphthona abdominalis, was released in 1996. This is the smallest of the flea beetles and causes similar damage to the plants as the other Aphthona species. Aphthona nigriscutis, A. cyparissiae and A. czwalinae\lacertosa have all become established at field insectary sites and can be collected in large numbers. These beneficial organisms are now available for redistribution in the state and can be obtained by requesting releases through the Department of Agriculture.
|
Leafy Spurge Images |
DIFFUSE AND SPOTTED KNAPWEED
(Centaurea diffusa and C. maculosa )
The Colorado Department of Agriculture has released a number of biocontrol agents against diffuse and spotted knapweed including a two root boring beetles, two seed head feeding flies, seed head feeding weevils and seed head feeding moths. Several of these are well established in Colorado and are probably having an impact on the knapweeds.
The most successful agent for use against diffuse knapweed is the seed head feeding weevil, Larinus minutus. The beetle feeds on the seed heads but is also a foliage feeder as an adult. Large scale control against diffuse knapweed has been seen at a number of locations along the Front Range. The Colorado Department of Agriculture currently releases this agent as the primary biocontrol for diffuse knapweed.
The root boring weevil Cyphocleonus achates weakens plants by destroying the root system. This large weevil has been effective against both diffuse and spotted knapweed and collectable populations have recently been seen on the Front Range. The Department of Agriculture will distribute these beetles as number allow.
|
Diffuse knapweed Images Spotted knapweed Images
|
TALL LARKSPUR (Delphinium occidentale )
Tall larkspur is a native plant and the biocontrol agent is also a native true bug, Hoplomachus affiguratus. This insect feeds on tall larkspur and the feeding damage makes the plant less palatable to cattle. This is good since tall larkspur is poisonous The goal of this program is not the elimination of tall larkspur but the inhibition of grazing by cattle. The program is small and arrangements for collection and redistribution can be made by calling the Insectary. These insects are not shipped out for general use.
PUNCTUREVINE (Tribulus terrestris )
The most successful biological control agents are Microlarinus lareynii, a seed feeding weevil, and Microlarinus lypriformis, a stem boring weevil. M. lareynii and M. lypriformis have been collected from established colonies around the state. Redistribution of M. lareynii and M. lypriformis is available upon request. As part of two beneficial insect exchange programs, these weevils were sent to Oregon and Washington State.
|
Puncturevine
|
MUSK THISTLE (Carduus nutans )
The musk thistle seed weevil, Rhinocyllus conicus, was released in Colorado over 30 years ago and can now be found throughout the state. In many areas it has significantly reduced the density of musk thistle. The department of Agriculture has discontinued widespread distribution of this insect since it is found almost everywhere in the state, plus there are concerns since this insect will feed on native thistles.
Another weevil, Trichosirocalus horridus, feeds in the crowns of musk thistle, killing the apical meristem and reducing the flowering potential of the plant. This insect is currently established in many areas around the state and is still being distributed by the Insectary.
|
Musk thistle
|
TOADFLAX - Yellow and Dalmatian
(Linaria vulgaris and L. genistifolia ssp. dalmatica )
Calophasia lunula is a toadflax-feeding noctuid moth which has been released for control of both toadflax species. C. lunula larvae feed extensively on leaves and flowers of toadflax, severely damaging the plants. It is established in Colorado and is available upon request. Large scale impacts on toadflax populations have not yet been documented in Colorado with this biocontrol agent.
Mecinus janthinus is a stem boring weevil that has shown good promise for control of Dalmatian toadflax. This beetle is capable of killing a large portion of the above-ground plant by boring into and killing the stems where the larvae live and feed. These beetles have proven very effective against Dalmatian toadflax at a number of sites around the state. We now have collection sites where we can obtain large enough numbers for redistribution.
The Colorado Department of Agriculture is a member of the International Toadflax Consortium and through the Consortium we have obtained a small population of a root-galling weevil Rhinusa linariae which we will use to establish field insectaries. This weevil has been shown to be effective against yellow toadflax in Canada, so we are hopeful that soon we will have another insect to use against this ever-spreading weed.
|
Dalmatian toadflax
Yellow toadflax
|
BULL THISTLE (Cirsium vulgare )
Urophora stylata, a fly predator, is used to help control this thistle. The female fly lays eggs in the seed head of the thistle. The maggot then consumes the seed in the flower. This species has overwintered in Colorado but the limited numbers will not allow for general redistribution.
|
Bull thistle
|
CANADA THISTLE (Cirsium arvense )
The primary biocontrol agent currently in use against Canada thistle is the stem-gall forming fly, Urophora cardui. Urophora lays eggs in the stems of Canada thistle and large galls develop around the stem-dwelling larvae. Larvae pass through the winter within the protective galls and emerge in the spring as adults. This agent is not effective in killing the plant but may weaken the plant, making it more susceptible to other stresses.
A stem mining weevil, Ceutorhynchus littura, has been released in Colorado but reliably collectable populations have yet to be established. Since there is some evidence that these beetles may be effective in combination with the gall flies the Department of Agriculture is working to establish collection sites for C. littura for use in combination with U. cardui.
|
Canada thistle
|
PURPLE LOOSESTRIFE (Lythrum salicaria )
Purple loosestrife is a list A species in Colorado which means that it is scheduled for eradication and biological control is an inappropriate control method. The Colorado Department of Agriculture does rear biocontrol agents for purple loosestrife as part of a nationwide cooperative program. Hylobius transversovittatus is a large weevil that develops within the roots of purple loosestrife. They require one to two years to develop on plants but at the Insectary they are reared on an artificial diet where they can go from egg to adult in just ten weeks. These weevils have been shipped from Colorado to new homes in several other states.
|
Purple loosestrife
|
FIELD BINDWEED (Convolvulus arvensis)
Two species of natural enemies are presently being released in Colorado for the suppression of field bindweed. The first, a small eriophyid mite, Aceria malherbae, is a microscopic wormlike mite that causes gall formation along the midribs of the leaves, petioles and stem tips, stunting the plant and reducing seed production. They are established in Colorado and are available upon request.
The bindweed moth, Tyta luctuosa, is also being reared at the Insectary for release to the field. Larvae of this noctuid moth defoliate bindweed plants by consuming both leaves and flower buds. The moth has now been found to overwinter in the Grand Valley, the first place in the United States where establishment has been documented.
|
Field bindweed
|