Weed Control News

Effect of Fire on Leafy Spurge Natural Enemy

The flea beetle Aphthona nigriscutis is a potentially useful agent for biological control of leafy spurge (Euphorbia esula) in grasslands devoted to wildlife conservation. However, the effects of other grassland management practices on the persistence and dynamics of populations of this flea beetle are not well understood.

Small plot tests were conducted to evaluate the effect of prerelease burning on establishment of A. nigriscutis colonies and the ability of established A. nigriscutis colonies to survive prescribed fire.

More colonies established on plots that were burned prior to beetle release (83% establishment) than on unburned plots (37% establishment), possibly due to litter reduction and baring of the soil surface. However, most colonies established with the aid of fire did not survive past the first generation unless the habitat was otherwise suitable for the species. The primary benefit of prerelease burning is a higher increase in numbers during the first few generations.

Established colonies were not harmed by burns in October and May. Both spring and fall burns resulted in an increase in leafy spurge stem density during the first growing season, but stem density declined to the preburn level by the second growing season.

Source:

Fellows, D. P., and W. E. Newton. 1999. Prescribed fire effects on biological control of leafy spurge. J. Range Manag. 52(5):489-493.

Houndstongue Natural Enemy

Houndstoungue (Cynoglossum officinale) is a Eurasian plant that has become an invasive weed of rangelands in the United States and Canada. It was probably introduced into North America in the middle of the 19th century as a contaminant of cereal. It is a herbaceous, short-lived perennial that germinates in the spring, produces rosettes in the first year and flowers in the second or subsequent years. This colonizer of disturbed areas now occurs in all Canadian provinces and most mainland U.S. states, with the highest densities in the northwestern states.

Since there are no satisfactory means of control of houndstongue, a biological control project was initiated in 1988. The first species introduced for the control of houndstongue is a root-mining weevil, Mogulones cruciger, which was first released in Canada in 1997. The flea beetle Longitarsus quadriguttatus is another below-ground herbivore species considered for the biological control of houndstongue. 

This flea beetle feeds on aerial plant parts as adults and the larvae mine the roots. The adults emerge in late May to mid-June, living until October. The females lay eggs at the bases of petioles or at the root crown. The three larval instars develop during late summer and fall, mining in the cortex of the tap root and in secondary roots. They overwinter in the roots, complete development in early spring and pupate in the soil in April.

Previous host-specificity investigations with 49 European test-plant species demonstrated that larval development of the flea beetle is limited largely to plant species within the tribe Cynoglosseae in Boraginaceae. However, those investigations did not include any native North American Boraginaceae species, nor examine results of earlier tests for plant species that were susceptible to attack by the flea beetle. Therefore, additional host-range investigations were conducted between 1994 and 1996. Different no-choice and choice tests were conducted with 7 plant species that showed susceptibility to attack in previous tests and 5 native North American plant species. 

L. quadriguttatus was host specific in these tests. Two European test-plant species outside the genus Cynoglossum and 2 native North American Cynoglossum species supported complete development of the flea beetle to some extent, but in all cases the test plants were significantly less suitable hosts than houndstongue. The remaining 5 European and 3 native North American test-plant species did not support development and/or survival of L. quadriguttatus

This flea beetle is host specific to species within the genus Cynoglossum, and has a strong preference for houndstongue. The introduction of L. quadriguttatus into Canada was approved in 1998 and individuals were released that year.

Source:

Schwarzlander, M. 2000. Host specificity of Longitarsus quadriguttatus Pont., a below-ground herbivore for the biological control of houndstongue. Biological Control 18(1):18-26.


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