Trimen’s false tiger moth, Agoma trimenii (Lepidoptera: Agaristidae) : biology and potential control options

Morris, Courtney Anne (2019-04)

Thesis (MScConsEcol)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Trimen se valstiermot, Agoma trimenii (Lepidoptera: Agaristidae), het pesstatus bereik in wingerde in die Noord-Kaap en Limpopo (Groblersdal area) provinsies van Suid-Afrika. Die larwes voed op nuwe wingerd groei wat kan lei tot grootskaalse blaarverlies en mislukte oeste, indien dit nie vroeg genoeg opgemerk word nie. Uitbrake is sporadies en die vlak van infestasie wissel. Min is bekend oor die biologie en gedrag van Trimen se valstiermot en geen offisiële metodes vir monitering of ekonomiese drempels bestaan al nie, wat beteken dat baie min opsies vir die beheer en bestuur van die mot bestaan. Daar word dus baie aandag gegee aan die gebruik van omgewingsvriendelike, alternatiewe pesbeheer tegnologie. Hierdie studie het, deur middel van waarnemingsstudies en visuele opnames, waardevolle insigte gelewer tot die biologie, seisoenale ontwikkeling en gedrag van A. trimenii. Die gebruik van feromoon lokvalle, lewendige aas lokvalle en lig lokvalle was getoets as potensiële monitering strategieë vir A. trimenii. Die potensiaal van verskillende biologiese beheermiddels was ook getoets teen A. trimenii vir moontlike gebruik in latere geïntegreerde pes bestuur (GPB) sisteme. Die middels wat getoets was, was entomopatogeniese nematodes (EPNs), entomopatogeniese swamme (EPSe), patogeniese bakterieë en insek groei reguleerders. Die gebruik van feromoon lokvalle, lig lokvalle en visuele waarnemings was getoets in die veld as potensiële metodes vir die monitering van A. trimenii. Verskeie lewensfases van A. trimenii was geïdentifiseer, piek vlugtye was vasgestel, oorvleuelende generasies was waargeneem en die gedragskenmerke van elke lewensfase was gedokumenteer. Ultraviolet blou lig lokvalle was uiteindelik die mees belowende potensiële monitering strategie en ‘n A. trimenii lokmiddel het potensiaal getoon as ’n alternatiewe monitering strategie. Die vatbaarheid van larwes en papies van A. trimenii tot EPNs van die Steinernematidae en Heterorhabditidae families, asook twee kommersieel beskikbare EPSe was getoets in laboratorium omstandighede. Die patogenisiteit van twee plaaslike EPN spesies, Steinernema yirgalemense en Heterorhabditis noenieputensis, was getoets op larwes en papies van A. trimenii teen ‘n konsentrasie van 100 infektiewe larwes in 50 μl water. Na 48 uur is 100% mortaliteit aangeteken by die larwe fase, maar geen infeksie van papies is gevind nie. Die patogenisiteit van twee kommersieel beskikbare EPS isolate, Metarhizium anisopliae en Beauveria bassiana, was getoets op larwes en papies teen ‘n konsentrasie van 0.2 ml/500 ml water en 0.5 g/500 ml water, onderskeidelik. Teen 15 dae na behandeling was 100% mortaliteit by larwes aangeteken, maar geen by die papies. Die vatbaarheid van larwes tot drie kommersiële produkte, Delegate®WG, Steward®150 EC en drie verskillende dosisse van DiPel®DF was ondersoek onder laboratorium omstandighede. Semi-veld proewe was uitgevoer om die potensiaal van DiPel ® DF te toets teen larwes by verskillende water volumes (50g/1000L/ha en 42g/1200L/ha), asook om die sproei dekking te vergelyk op die boonste en onderste blare van die wingerde. Die residuele aktiwiteit van DiPel®DF, wanneer dit aangewend is teen verskillende water volumes, was daagliks ondersoek en vergelyk tussen boonste en onderste blare, oor ‘n tydperk van 7 dae. Vir die biotoets proewe het Delegate®WG, Steward®150 EC en die aanbevole dosis van DiPel®DF 100% mortaliteit in larwes getoon na 7 dae. Delegate®WG en die aanbevole dosis van DiPel®DF was egter die produkte wat die vinnigste gewerk het. Die aanbevole dosis van DiPel®DF (0.25g/500 ml gedistilleerde water) was die mees effektiewe behandeling (in vergelyking met gehalveerde en verdubbelde dosisse) en het 100% mortaliteit veroorsaak na 5 dae. Toename in die water volume van ‘n sproei toediening van DiPel®DF het geen beduidende toename getoon in die mortaliteit van larwes in die boonste en onderste blare gesamentlik nie. Oor die algemeen het onderste blare hoër mortaliteit by larwes getoon in vergelyking met boonste blare wanneer dit behandel was met enige van die twee water volumes. ‘n Afname in insek aktiwiteit was aangeteken vir DiPel®DF aangewend by beide water volumes, tussen blare gepluk 4 dae na behandeling en blare gepluk 5 dae na behandeling. Geen mortaliteit was gevind na dag 6 nie. Onderste blare het hoër mortaliteit in larwes getoon oor die 7 dae tydperk vir beide water volumes van DiPel®DF, in vergelyking met boonste blare, wat ‘n moontlike aanduiding is van hoër residuele aktiwiteit op die onderste blare van wingerde. Toekomstige navorsing moet fokus daarop om die sproei dekking en residuele aktiwiteit van DiPel®DF te verhoog, asook om die produkte wat getoets was te gebruik as deel van ‘n geïntegreerde pes bestuur (GPB) program. Resultate van die studie kan gebruik word as aanbevelings vir produsente om A. trimenii effektief en biologies te monitor en te beheer, wat verder sal bydra tot ‘n GPB sisteem vir die mot.

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