Biological Control Agent: Brachypterolus pulicarius L.
Invasive Plant Species Attacked: Dalmatian toadflax (Linaria dalmatica), yellow toadflax (L. vulgaris) and narrow-leaved Dalmatian toadflax (L. genistifolia spp. dalmatica)
Type of Agent: Seed feeding beetle
Description and Biology
The beetles are shiny black, elongate to oval, 2.4 x 1.0 mm, and sparsely covered with hairs. Short wing covers expose the last abdominal segments of their bodies. Females have slightly longer covers than the males. Rear legs are darker than the other legs. Near equal male/female ratio adults begin to appear in early May, usually when the plants are 15 – 20 cm tall. Adults congregate and feed on pollen, flowers and on young foliage, sometimes completely consuming terminals. Mating occurs in June when the plants begin to bud. Heavy feeding can cause significant flower loss, which may delay oviposition until the second flowering cycle in July. Eggs are laid individually or in small clusters of up to three into unopened floral buds. Adults live one to three months and populations begin to subside by August.
The eggs are white and measure 0.6 mm long. Just prior to hatching, the eggs turn yellow.
Larva and pupa:
Pale yellow larvae with brown heads emerge and begin feeding on the reproductive parts of the flowers and move between flowers and developing buds. Smaller flowers are less nutritious than larger ones and, therefore, the quantity of floral damage each larva destroys relates to bloom size. Older larvae will feed on seeds. Mature larvae move into the soil to pupate. Yellow pupae measure 2. 8 x 2. 0 mm and develop for three weeks.
Most overwinter as pupae, however, adults can overwinter in climates with long growing seasons.
Location and effectiveness of attack
Adults feed first on early succulent terminal growth, causing extensive damage and later move onto flowers and floral buds as they become available. Stem and terminal damage initiates branching. Heavy attack causes delayed bloom until July or August. Larvae feed on the reproductive parts of the plants and developing seeds. Brachypterolus pulicarius feeding reduces the first bloom by 95%; the second by 82%; and, the third by 52%. Overall seed production is reduced by 74% and each beetle is responsible for destroying 76.5 seeds. Heavy foliar feeding can help reduce plant vigour.
Predicted and native habitat
The adventive agent, B. pulicarius was found in Saskatchewan by 1950. It is believed to have entered into Canada via the accidental introduction from New York, where it was first noticed in 1919. Now it is abundant and common in all Canadian provinces that support yellow and Dalmatian toadflax varieties. It shows a preference for yellow toadflax but is commonly found on both. It has a broad range of climatic and habitat preferences, from warm to hot open sites, to warm, slightly moist semi-shaded locations. Sites with coarse sandy and poor soils are common with the plant and B. pulicarius.
It Europe B. pulicarius is wide spread.
British Columbia Experiences
The first B. pulicarius release in BC was made near Grand Forks in 1989. It has self dispersed and is commonly found throughout the toadflax infestations and appears to have no preference for one variety over the other. Although it may not be present in its adult form at the same time as other biocontrol agents, it is often found sharing sites with Rhinusa spp., Calophasia lunula, and Mecinus janthinus.
Collection for redistribution
Wide dispersal of this agent eliminates the need to collect and release B. pulicarius in most circumstances. Adults can be swept from plants in early summer. Aspirating adults is efficient and less destructive to plants.
B. pulicarius directly competes with Rhinusa antirrhini and R. neta.
Harris, P. 1961. Control of toadflax by Brachypterolus pulicarius (L.) (Coleoptera: Nitidulidae) and Gymnaetron antirrhini (Payyk.) (Coleoptera: Curculionidae) in Canada.
Harris, P. 2005. Classical biological control of weeds established biocontrol agent Brachypterolus pulicarius L. flower-feeding beetle. Gov. of Can., Agriculture and Agri-Food Canada. February 1, 2007. http://res2.agr.ca/lethbridge/weedbio/agents/abracpul_e.htm
Hervey, G. E. R. No date. A European Nitidulid, Brachypterolus pulicarius L. (Coleoptera, Family, Nitidulidae). Journal of Economic Entomol., Vol. 20: 809-814.
MFR staff comments and observations
Powell, G. W., A. Sturko, B. Wikeem and P. Harris. 1994. Field guide to the biological control of weeds in British Columbia. B.C. Min. For. Res. Prog.
Rees, N. E., Quimbly, Jr., P. C., G. L. Piper, E. M. Coombs, C. E. Turner, N. R. Spencer, L. V. Knutson (editors). 1996. Biological control of weeds in the west.
Smith, J. M. 1959. Notes on insects, especially Gymnaetron spp. (Coleoptera: Curculionidae), associated with toadflax, Linaria vulgaris Mill. (Scrophulariaceae), in North America. The Can. Entomol., Vol. XCI, No. 2. Pp. 118-119.