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Maart 2016
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FOCUS
Seed
Special
‘O
utbreaks of rodents occur worldwide; the factors that
cause them are less than fully understood. In Southern
Africa, rodents such as gerbils can undergo population
explosions or outbreaks in agricultural situations as a
result of various circumstances. Abnormal population increases re-
sult from excessive food availability such as access to stored grain
or animal feed, or because of wastage during harvesting.
‘Outbreaks follow years when good rains occur late in the wet sea-
son with high vegetation growth resulting in an unusually good food
supply during the dry season. Outbreaks also occur during sustained
periods of good rainfall and thus good food supply, after periods of
intense drought. Predator numbers decline during drought and as
they produce slower than rodents, the population growth of rodents
proceed unchecked once improved feeding conditions return.’ (Ken
Willan, 1992)
Throughout South Africa, rodents of the genus
Gerbilliscus
(gerbils,
nagmuis
, also referred to as
springhaasrotte
, but not to be confused
with the springhare or
springhaas
,
Pedetes capensis
, which is also a
rodent) have caused concern with regards to the damage they inflict
on field crops at planting.
The wide geographic distribution where the damage had been noted
and reported in recent years, has also led to various tongue-in-the-
cheek rumours and myths. We aim to debunk some of these myths
with scientific published facts, recent research observations from
on-farm situations and suggestions to reduce the long-term impact
of the pest.
The genus
Gerbilliscus
is widespread in sub-Saharan Africa and rep-
resents one of the main components of the rodent fauna of arid open
habitats. The
Gerbilliscus
now comprises all the African species of
gerbilline
that were formerly included in the genus
Tatera
. The genus
Gerbilliscus
includes eleven species and is grouped into three geo-
graphically defined clades: Western, eastern and southern, based
on their chromosomal and phylogenetic characteristics, with the
estimated age of divergence from three to seven million years ago.
The southern clade comprises three species. Two species are en-
demic of the Southern African region:
Gerbilliscus afra
(Gray, 1830)
and
G
.
brantsii
(Smith, 1836), while the distribution of the third,
G
.
leucogaster
(Peters, 1852), overlaps with the eastern African region.
Highveld gerbil
Gerbilliscus brantsii
(Highveld gerbil or
Hoëveldse nagmuis
) (
Photo 1
)
was first described in 1836, from specimens collected ‘near the
sources of the Caledon River’ (Lesotho and eastern Free State)
and subsequently from other areas. The Highveld gerbil occurs in
the following regions: North-eastern parts of the Eastern Cape to
the western and north-eastern parts of KwaZulu-Natal, southern
Mpumalanga, throughout the Free State, Gauteng and North West
Province, the south-western parts of Limpopo, in the northern half
of the Northern Cape, Lesotho, Botswana and the eastern and
northern Namibia (
Figure 1
).
Bushveld gerbil
Gerbilliscus leucogaster
(Bushveld gerbil or
Bosveldse nagmuis
) was
first described in 1852 from specimens collected in Mozambique,
and then from almost all over southern Africa. The Bushveld ger-
bil is distributed widely in east and south-east Africa, Mozambique,
Zimbabwe, Botswana and northern Namibia, and in South Africa in
Limpopo, the North West Province, northern Gauteng, Mpumalanga,
the western and southern parts of the Free State, and the Northern
Cape, north of the Orange River. These two gerbils are indigenous
and common to most of the summer rainfall region of South Africa.
Cape gerbil
Gerbilliscus
afra
(Cape gerbil of
Kaapse nagmuis
) is endemic to
South Africa, and is confined to the limits of the south-western Cape
sub-region, from Nieuwoudtville in the Northern Cape southwards
to the fynbos biome in the Western Cape and eastwards to Herold’s
Bay. The Cape gerbil has caused considerable damage to wheat in
the Western Cape in recent years.
Habitat
All three species are predominantly associated with light sandy soils
or sandy alluvium, with exceptions such as hard substrate in mopane
woodland and peaty soils around marshes and pans.
Ecologically based
rodent management in maize
EMIL VON MALTITZ
and
FRIKKIE KIRSTEN,
ARC-Plant Protection Research Institute and
LUSHKA LABUSCHAGNE,
Centre for Wildlife Management: University of Pretoria
Figure 1: Distribution of three gerbil species in Southern Africa.