Biological Control of Invasive Species

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 Invasive Species

Invasive species, also known as alien species when introduced into natural or semi natural habitat, thrives and threatens the native species. 

Invasive species are those species that causes ecological and economical harm where it it not native.

The major characteristics of invasive species are:

  1. Fast growth
  2. Rapid reproduction
  3. High tolerance
  4. Ability to survive on wide range of food types
  5. Phenotype plasticity (the ability to alter growth form to suit current conditions) 
  6. Rampant spreading capacity
  7. Ability to outcompete native species

Ballast water from oceangoing ships, purposeful and unintentional releases of aquaculture species, aquarium specimens or bait, and other methods are the major cause that introduces invasive species to a new location.

Cases of invasive species control by biological methods

a.  Water Hyacinth in the Lake Victoria

Lake Victoria, also known as Victoria Nyanza, is Africa's largest lake and the Nile's main reservoir, located primarily in Tanzania and Uganda and bordering Kenya. It covers a total area of 26,828 square miles (69,484 square km).

Water hyacinth, Eichhornia crassipes was first observed in Lake Victoria in 1989.

The lake's biodiversity was reduced, and its activities were disrupted: fisherman caught fewer fish, the plants interfered with water transit, and the plants hindered hydroelectric generating turbines.

The scientists’ control strategy involving the weed weevils Neochetina bruchi and Neochetina eichhorniae, natural enemy of water hyacinth. 

Using this method, the scientists successfully eradicated 90 per cent of the water hyacinth in Africa’s Lake Victoria.

Both adult and larval form of weed weevils feed on the water hyacinth and decreasing its buoyancy, causing plant to decay at faster rate.

Weed Weevil


b. Hawkweeds on the Native American Pastures

Open fields, mountain meadows, forest clearings, permanent pastures, cleared wood units, abandoned cropland, roadsides, and other disturbed environments are the most common places to find hawkweed Hieracium aurantiacum). Usually found in well-drained, coarse-textured, low-nutrient soils.

Hawkweed are highly tolerant & directly hinders the growth of native species.

Once established, it quickly spreads by seed, aboveground stems (stolons), and below ground stems (rhizomes), developing dense patches that displace native vegetation.

Two agents have been released in Canada the gall wasp Aulacidea subterminalis in 2011 and the hoverfly Cheilosia urbana in 2017.

These insects damage the stolons, roots, and stems of the plant impacting seed production and limiting the spread.

Gall wasps diminish the amount of flower heads on hawkweed plants and prevent them from blossoming.

Different portions of the hawkweed plant are affected by the two hover flies (Cheilosia urbana and Cheilosia psilophthalma). 

C. urbana affects the roots, but C. psilophthalma consumes the plant portions above ground.

Hawkweed






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