Initial investigation of Trichogrammatoidea lutea (Hymenoptera: Trichogrammatidae) as biological control agent of codling moth, Cydia pomonella (Lepidoptera: Tortricidae), in apple and pear orchards, under sterile insect technique (SIT)
Date
2008-12
Authors
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Stellenbosch : Stellenbosch University
Abstract
Codling moth (CM), Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is the major pest of
apples and pears in the South Western Cape, South Africa. Apart from conventional insecticide
sprays, area-wide biologically intensive control methods, such as Sterile Insect Technique (SIT) and
pheromone mediated mating disruption (MD) are currently in use on two farms in the Elgin valley. The
indigenous parasitoid Trichogrammatoidea lutea Girault (Hymentoptera: Trichogrammatidae) attacks
eggs of false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), as
well as CM and has been found to have considerable parasitism potential on both. Elevated host egg
numbers, as achieved by SIT are thought to support establishment of populations of these natural
enemies in the orchards.
For rapid and secure Trichogrammatoidea species identification, the ITS2 sequences of
Trichogrammatoidea lutea and T. cryptophlebiae Nagaraja (an indigenous FCM parasitoid on citrus)
were determined and species specific primers were developed.
Lifetable studies of T. lutea indicated an optimal temperature for reproduction at around 20 °C.
Food was provided by the application of honey-solution soaked cotton wool, behind fine netting. The
effect of food provision by this method was found to be dependent on temperature. The acceptance of
CM eggs from sterilized vs. fertile parents and of radiation-sterilized eggs vs. fertile ones was
assessed in choice trials. While no difference was observed between radiated and fertile eggs, sterile
eggs from irradiated parents were significantly less attractive than eggs from fertile parents.
In several field studies the dispersal capacity and population sustainability of released T. lutea
were investigated. Trials took place in apple and pear orchards in the Elgin valley that formed part of
an area-wide sterile CM SIT program. Most of the wasp releases were carried out within blocks of up
to 1 ha. A square grid of up to 36 monitoring trees per block allowed spatial distribution analysis.
Following single central point releases, parasitism of sentinel eggs was recorded until the end of all
experiments, the longest of which lasted 37 weeks. T. lutea females were found to disperse up to 73
m, within one week.
Studies concerning toxicity of four commonly used insecticides and one fungicide to immature and
adult T. lutea indicated no to low susceptibility of wasps at egg- to first-instar-stage within host eggs.
Contact toxicity of the tested materials to adults differed significantly, depending on the compound. All
five pesticides caused significantly higher mortality among adults relative to the control. The overall aim of above studies was to determine the potential of T. lutea for broad-scale releases
against CM, within a broader integrated pest management program in apple and pear orchards in the
Western Cape.
Description
Thesis (MScAgric (Conservation Ecology and Entomology))--Stellenbosch University, 2008.
Keywords
Trichogrammatoidea lutea, Biological control, Codling moth, Parasitoid, Dissertations -- Conservation ecology and entomology, Theses -- Conservation ecology and entomology