Browsing by Author "Morris, Courtney Anne"
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- ItemTrimen’s false tiger moth, Agoma trimenii (Lepidoptera: Agaristidae) : biology and potential control options(Stellenbosch : Stellenbosch University, 2019-04) Morris, Courtney Anne; Johnson, Shelley; De Waal, Jeanne Y.; Malan, Antoinette P.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Trimen’s false tiger moth, Agoma trimenii (Lepidoptera: Agaristidae), has developed pest status in vineyards in the Northern Cape and Limpopo (Groblersdal area) provinces of South Africa. Larvae feed on new vine growth and, if not detected early, the subsequent defoliation of vineyards can be severe, resulting in crop losses. Outbreaks are sporadic, and infestation levels vary. Little is known about the biology and behaviour of Trimen’s false tiger moth, and no official monitoring methods or economic thresholds yet exist. Consequently, management and control options are lacking. Hence, attention has been drawn to the use of environment-friendly alternative pest control technologies. In this study, observational studies and visual scouting provided insight into the biology, seasonal development and behaviour of A. trimenii. The use of pheromone traps, live bait traps and light traps was tested as potential monitoring strategies of A. trimenii. The potential of different biocontrol agents, including entomopathogenic nematodes (EPN), entomopathogenic fungi (EPF), pathogenic bacteria and insect growth regulators were tested against A. trimenii, to be considered for later use in an integrated pest management (IPM) system. The use of pheromone traps, light traps and visual scouting as potential monitoring strategies of A. trimenii was tested in the field. Various life stages of A. trimenii were identified, peak flight times were established, overlapping generations were determined, and the behavioural traits of all life stages were documented. Ultraviolet blue light traps proved to be the most promising potential monitoring strategy, with the prospect for an A. trimenii pheromone lure holding potential as an alternative monitoring strategy. The susceptibility of larvae and pupae to EPNs of Steinernematidae and Heterorhabditidae and two commercially available EPF isolates, under laboratory conditions, were tested. The pathogenicity of two local species, Steinernema yirgalemense and Heterorhabditis noenieputensis, was screened against larvae and pupae of A. trimenii, using a concentration of 100 infective juveniles in 50 l of water. After 48 h, 100% mortality of the larval stage was found. However, in the case of the pupae, no infection with EPNs was observed. The pathogenicity of two commercially available EPF isolates, Metarhizium anisopliae and Beauveria bassiana, was screened against larvae and pupae by means of a dipping test undertaken at a concentration of 0.2 ml/500 ml water and 0.5 g/500 ml water, respectively. At 15 days post treatment, 100% larval mortality was recorded. However, no mortality of the pupae was observed. The susceptibility of larvae to three commercial products, Delegate®WG, Steward®150 EC and three different doses of DiPel®DF under laboratory conditions was examined. Semi-field trials were performed to test the potential of DiPel ® DF against larvae, applied at different water volumes (50g/1000L/ha and 42g/1200L/ha) and to compare spray coverage between top and bottom leaves on the vines. The residual activity of DiPel®DF when applied at different water volumes was investigated daily and compared between top and bottom leaves over a 7-day period. For the bioassay trials, Delegate®WG, Steward®150 EC and the recommended dose of DiPel®DF showed 100% larval mortality within 7 days, however Delegate®WG and the recommended dose of DiPel®DF proved to be the fastest acting products. The recommended dose of DiPel®DF (0.25g/500 ml distilled water) proved the most effective (in comparison to halved and doubled dosages) and showed 100% mortality after 5 days of application. Increasing the water volume of a spray application of DiPel®DF showed no significant increase in larval mortality for combined top and bottom leaves. Generally, bottom leaves displayed higher larval mortality compared to top leaves when treated with either water volume. A reduction in insecticidal activity for DiPel®DF applied at both water volumes was established between leaves picked 4 days after spraying and leaves picked 5 days after spraying, and no mortality was established after day 6. Bottom leaves displayed higher larval mortality throughout the 7-day period for both water volumes of DiPel®DF in comparison to top leaves, suggesting higher residual activity on bottom leaves of vines. Future research should be aimed at increasing spray coverage and residual activity of DiPel®DF, as well as using all tested products within an IPM system. Results from the study can be used as recommendations for growers to monitor and control A. trimenii effectively and biologically, further contributing towards an IPM system for the moth.