Thesis (MScAgric (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / 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.

The African bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), is a polyphagous pest that attacks many crops in sub-Saharan Africa. The pest is currently managed through chemical control, and by planting Bt-transgenic cotton. Trichogrammatoidea lutea Girault (Hymenoptera: Trichogrammatidae) is an indigenous egg parasitoid of H. armigera in southern Africa. The study was undertaken to determine the potential of T. lutea as a biological control agent for augmentative releases as an alternative to chemical control, and to pave the way for the development of a mass-rearing method. The biology of T. lutea was examined in the laboratory on H. armigera, Chilo partellus (Swinhoe), and Cadra (formerly Ephestia) cautella (Walker) (Lepidoptera: Pyralidae). The objectives of the study were to determine (i) the exposure time of UV-irradiation required for killing the embryos of the hosts and the effect of UV-irradiated eggs on life history parameters of T. lutea, (ii) which host(s) and temperature(s) (18, 21, 24, 27, 30 and 35 °C) are suitable for mass-rearing of T. lutea, and (iii) the longevity and age-related reproductive biology of T. lutea on H. armigera. Findings of this study showed that 13 minutes of UV-irradiation were sufficient to kill embryos of all three host species. Life history parameters were not influenced by UV-irradiation but by host species. Parasitism, number of progeny per parasitized egg, proportion of females, and developmental time of T. lutea aried on different host species at temperatures ranging from 18 to 30 °C. Trichogrammatoidea lutea did not develop at 35 °C. Overall parasitism by T. lutea was higher on H. armigera and Cadra cautella compared to Chilo partellus. The number of progeny per parasitized egg was highest on H. armigera compared to Cadra cautella and Chilo partellus. The proportion of females was highest on Chilo partellus, intermediate on Cadra cautella, and lowest on H. armigera. For all species and temperatures tested, parasitism and number of progeny per parasitized egg by T. lutea was highest on H. armigera at 27 °C. The lower threshold for development of T. lutea on all hosts was approximately 12 °C. Female T. lutea parasitized eggs of H. armigera soon after eclosion, with the highest parasitism achieved on the day of eclosion. Though T. lutea parasitized eggs for up to 14 days, it may not be economically viable to keep them in cultures for more than three days since progeny became male biased three days after eclosion. The average longevity of female and male T. lutea was 9 and 6 days, respectively. The life table parameters of T. lutea, the net replacement rate (Ro), mean generation time (T), and instantaneous rate of population increase (rm) were 25.5, 9.79, and 0.33, respectively. The timing of inundative releases of T. lutea must be synchronised with the time that eggs of H. armigera are abundant in the field. The results of this study indicate that T. lutea is a good candidate for further testing for augmentative biological control of H. armigera in the field. If successful, T. lutea may provide opportunities for expanding tactics in the management of H. armigera in southern Africa. Copyright / Dissertation (MSc)--University of Pretoria, 2011. / Zoology and Entomology / unrestricted