Sustainable Agriculture and Food: Four volume set (Earthscan Reference Collections)

Multi-Function Agricultural Biodiversity 321

pathologists as a way of slowing the spread of diseases (e.g. in rice, Wolfe, 2000),
but its potential impact on insect pests is illustrated by a recent study of the willow
beetle (Phratora vulgatissima (L.)). Beetle density, oviposition and damage were
lower in mixtures of up to five willow (Salix spp.) varieties and species than in
monocultures (Peacock and Herrick, 2000). This example illustrates that enhance-
ment of natural enemy density is not a prerequisite for effective pest management.
Its findings are consistent with the resource concentration hypothesis.

Table 17.1 Examples, with increasing levels of complexity, of biodiversity enhancement
benefiting pest management

Level of complexity Nature of diversification Example

Diversification within a

monoculture

Make crop itself

structurally more diverse

Alternating harvests of lucerne

strips to give structural diversity

and preserve habitat for natural

enemies of Helicoverpa spp.

(Hossain et al, 2001)

‘Relax’ the

monoculture

Grow a mix of varieties or

closely related species

Willow beetle numbers and

damage reduced in mixed

plantings of willow (Peacock and

Herrick, 2000)

Allow non-crop

vegetation within the

monoculture

Allow weed growth within

areas of the crop

Weed strips increase natural

enemy density (Lys et al, 1994)

Diversify vegetation

bordering the

monoculture

Sow non-crop vegetation

in field margin

Phacelia strips beside wheat as

pollen source for hoverfly, natural

enemies of aphids (Hickman and

Wratten, 1996)

Abandon monoculture Grow two or more crops

within the field

Lucerne strip within cotton act as

decoy for mirids and habitat for

natural enemies of cotton pests

(Mensah and Kahn, 1997)

Diversify vegetation

beyond the field

margin

Sown or naturally

generated vegetation in

fallow fields adjacent to

crops

‘Complex, structurally rich ... large

old fallows’ adjacent to rape

increased parasitism of rape pollen

beetle and reduced crop damage

(Thies and Tscharntke, 1999)

Farm-wide

diversification

Agroforestry integrated

with cropping and

livestock

Increasing arthropod densities by

use of a ‘silvoarable agroforestry

system’ (Peng et al, 1993)

Landscape level

changes

Landscapes with areas of

woodland

Parasitism rates of armyworm

lower in crops within complex

landscapes (Marino and Landis,

1996)