Agriculture Reference
In-Depth Information
be able to survive the physical disruption and other stresses (
e.g.,
greater diurnal
temperature fluctuations and periodic drought) normally associated with the conversion
of land to arable use, or be able to colonise the disturbed areas rapidly and effectively.
Termite damage is often greatest to exotic plant species (commonly species of such
genera as
Pinus
and
Eucalyptus
), to stressed plants, particularly young plants and those
subject to drought, as at the end of the intertropical dry season. Such stress may also
derive from the alteration of drainage regimes. Termites frequently gain entry to trees
through areas that have been physically damaged: such injury may result from the effects
of large mammals, through pruning scars and incisions (Wood, 1996) or through fire
scars, all of which allow fungi to attack the damaged tissues and make them vulnerable
to termite attack (Perry
et al.,
1985).
As indicated in Section IV.5.3.2.1, a few examples exist of grass-harvesting termites
apparently denuding areas subject to drought or overgrazing although they usually have
only small effects on long term plant cover. Few species attack the leaves of living plants:
species of the Neotropical genus
Syntermes
may defoliate nursery trees, sugarcane and
other plants (Mill, 1992) and the northwestern Australian harvester species
Schedorhino-
termes derosus
(family Rhinotermitidae) unusually harvests living grasses (Watson, 1969).
Most grass-harvesting and litter-feeding species feed on hayed-off, nutrient-depleted,
above-ground materials. Similarly, litter feeders may not cause severe damage directly
to plants unless their feeding habits are broad or flexible enough to extend into other
food materials, as illustrated in Section IV.5.3.2.1.
Most of the termites that directly damage plants are wood-feeding or polyphagous
species. Damage may be minor to severe and can occur in a variety of ways, often being
expressed through feeding on the roots, hollowing, severing or ring barking the stems.
Colonies of many species may establish in larger trees and gradually eat out the centres
of the stems; in species of the intermediate life type, colony members also extend their
attacks to adjacent trees. The polyphagous Australian termite
Mastotermes darwiniensis
may kill mature trees by ring barking, often forming a characteristic cincture around
the stem (Hill, 1942). In crop species, damage may occur directly to the plant or the
product may be attacked, as illustrated below.
Termite attack may entrain damage by other organisms. In groundnut (
Arachis hypogea
)
crops, damage to subterranean pods may lead to infection and spoilage by various fungi
to such an extent that affected crops become unsaleable (Wood, 1996).
The biology and population dynamics of termites attacking crops is now well docu-
mented, especially in Africa and parts of South America (Black and Wood, 1989; Cowie
and Wood, 1989; Cowie
et al
., 1989; Mill, 1992; Sen-Sarma, 1986; Wood and Pearce,
1991; Wood, 1996). A very wide range of crops are at risk, including cereals (especially
maize), groundnuts, dryland rice, cotton, yam, cassava, tea, cocoa, coconut, coffee,
rubber and a range of fruit producing species. Seedlings of fast-growing exotic tree
species, including softwoods, are also highly vulnerable and termites may therefore
adversely impact timber plantations and agroforestry schemes.
The soil-wood feeders and the soil feeders cause little damage to living plants or their
products. However, some soil-wood feeding species may occasionally damage timber
and a few soil feeders may browse the root tips of certain crop species (Mill, 1992).
