Browsing by Author "Mugala, Thabu"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Ecology and biocontrol options of the leaf miner, liriomyza huidobrensis, on potatoes in the Western Cape province
    (Stellenbosch : Stellenbosch University, 2021-04) Mugala, Thabu; Addison, Pia; Malan, Antoinette P.; Visser, Diedrich; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The potato leaf miner, Liriomyza huidobrensis Blanchard (Diptera: Agromyzidae), is a devastating pest of potatoes, worldwide. However, little knowledge of the biology and ecology of this pest in South Africa exists, with both factors being cardinal elements in implementing an effective integrated pest management (IPM) programme. Control of the pest relies on the extensive use of chemical insecticides. Concerns regarding insect resistance, human safety and environmental impacts have, however, encouraged the development and use of alternative environmental control strategies, including the use of entomopathogenic nematodes (EPNs) and fungi (EPF). The present study focuses on the population dynamics of L. huidobrensis during the winter and summer period, a parasitoid survey and biological control using EPNs and EPF. The study showed differences in adult leaf miner populations in both the potato fields and the natural vegetation for both the winter and summer monitoring periods. The abundance and population densities of leaf miners increased during summer, while being very low during the winter monitoring period. The observed trend was that the leaf miner populations increased during crop development, with damage regularly being spotted on the potato leaves two weeks after plant emergence. Five parasitoid species associated with L. huidobrensis were identified during the monitoring periods, with Diglyphus isaea being the most abundant species. After assessing the occurrence of entomopathogens in the soil samples collected from the potato fields, one EPN species Heterorhabditis zealandica, one insect-associated nematode Acrobeloides sp. and two EPF species, Metarhizium robertsii and Metarhizium majus were isolated from the 16 surveyed potato fields. Four EPN species were screened for pathogenicity against the larval and pupal stages using different concentrations of infective juveniles (IJs) in the laboratory, which included Heterorhabditis bacteriophora, Heterorhabditis baujardi and Steinernema yirgalemense and which were obtained from the collection of the Department of Conservation Ecology and Entomology, Stellenbosch University, with the fourth species Heterorhabditis zealandica being isolated from the potato fields. The pathogenicity results of all the EPNs at 200 IJs/50 μl of distilled water solution indicated insect mortality of > 40 % for both the leaf mining larvae and the pupae. However, pupae and larvae trials indicated that the best performing treatment was found to be H. baujardi with more than 57 % of pupae mortality and > 71 % larvae mortality. The findings, thus, indicate the EPNs potential for adoption as part of an IPM strategy. On the other hand, two different species of EPF, namely Metarhizium robertsii and Beauveria bassiana, were tested for pathogenicity against the pupae of the potato leaf miner. The EPF were able to cause 67 % mortality. The study also screened five different isolates of M. robertsii found during the monitoring period, with the results obtained indicating very high pupae mortality of more than 80 % of pupae. The study provided a positive forecast for the management of potentially damaging populations using entomopathogens as biocontrol agents against L. huidobrensis, in potato cultivation, in South Africa. This study was a laboratory assessment and thus a first step towards further development of a management strategy.