Thermal physiology and predicted distribution of Zygogramma bicolorata (Chrysomelidae), a promising agent for the biological control of the invasive weed Parthenium hysterophorus in South Africa.
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Date
2008
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Abstract
Parthenium hysterophorus (Asteraceae), classified as an emerging weed in South Africa,
has become abundant throughout large parts of southern and eastern Africa. In South
Africa it has invaded areas in KwaZulu-Natal, Mpumalanga, the North West Province
and Limpopo. A biological control programme against parthenium weed was launched in
South Africa in 2003, based on the success achieved in Australia. Zygogramma
bicolorata, a leaf-feeding beetle native to Mexico, was imported into South Africa via
Central Queensland, Australia where it was released in the 1980s. This thesis examines
aspects of the thermal physiology of Z. bicolorata which, in conjunction with its native
and exotic geographical distribution, was used to predict the potential distribution of the
agent in South Africa, in relation to climate. To determine Z. bicolorata’s physiological
capability, several physiological parameters were examined for mechanistic modelling
purposes. These parameters included the beetle’s lethal thermal limits, critical thermal
limits, lethal humidities (Chapter 2) and developmental rate at constant temperatures
(Chapter 3). In Chapter 4, these physiological parameters were entered into the dynamic
modelling program CLIMEX (CLIMEX programme ver. 2, CSIRO Entomology ©) and a
map of the areas that are acceptable for the establishment of Z. bicolorata was produced.
The CLIMEX model predicted that most of South Africa is favourable for the
establishment of the beetle, except in the west of the country and in the north of Lesotho,
extending into South Africa. All areas in which parthenium currently occurs were
predicted to be very favourable for Z. bicolorata establishment and proliferation.
Optimal release sites aimed at initial establishment were earmarked at three areas in the
northeastern part of South Africa (Jozini, Ndumu Game Reserve and along the road from
Swaziland to Mozambique). It is concluded that Z. bicolorata is climatically suited to
South Africa, increasing the likelihood that populations will establish and proliferate
when released.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.
Keywords
Chrysomelidae--South Africa., Thermal tolerance (Physiology)--South Africa., Chrysomelidae--Geographical distribution--Climatic factors--South Africa., Parthenium hysterophorus--Biological control--South Africa., Insects as biological pest control agents--South Africa., Theses--Entomology.