Biological control of two sporadic grapevine pests, Plangia graminea and Lobesia vanillana, using entomopathogenic nematodes.

Du Preez, Francois (2019-03)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Plangia graminea (Serville) (Orthoptera: Tettigoniidae) and Lobesia vanillana (De Joannis) (Lepidoptera: Tortricidae) are two sporadic, minor pests of wine grape vineyards in the Western Cape province of South Africa. Recent years have seen an increase in their abundance and damage, which necessitates their control. Little is known about the biology, ecology and distribution of these insects. The aim of this study was to collect their basic ecological data and to evaluate entomopathogenic nematodes (EPN) as potential biocontrol agents. Nymphs of P. graminea were evaluated against 12 in vivo-cultured EPN species, of which Heterorhabditis zealandica (SF41), H. indica (SGS), Steinernema jeffreyense (J192), S. yirgalemense (157-C) and H. baujardi (MT19), resulted in > 82 % mortality after 48 h. Larvae of L. vanillana were evaluated against S. jeffreyense (J192) and S. yirgalemense (157-C), sourced from both in vivo and in vitro-cultures of the same isolates. Results show that they were susceptible to all treatments, resulting in > 72% mortality, and that there was no significant difference in mortality between in vivo and in vitro-cultured nematodes of the same EPN species, but that in the in vitro-culture, S. yirgalemense (98%) performed significantly better than S. jeffreyense (73%). Cadavers from screening bioassays were dissected to evaluate the presence of infective juveniles (IJ), which in turn confirmed insect mortality by EPN infection. The ability of IJs to complete their lifecycle in vivo, and their ability to produce a new cohort of IJs, suggests that they may be able to provide persistent control in favourable environments. Observations on the biology and ecology of P. graminea in grapevine, suggests that they do not have a soil stage and only a single generation per year. Plangia graminea were mainly reported from the Cape Winelands region in the Western Cape province of South Africa, from where they were collected in an attempt to establish a laboratory colony. They did not perform well in captivity, therefore field collected individuals had to be used in laboratory bioassays. Observations on L. vanillana suggests that this species also does not have a soil stage. They seem to have a generational life cycle of 4-5 weeks and to overwinter as pupae. Lobesia vanillana was successfully reared from field-collected larvae using an agar-based modified codling moth diet. The present study contributes to new knowledge of P. graminea and L. vanillana, and indicates that EPNs are promising as biological control agents when considered as part of an integrated pest management program.

AFRIKAANSE OPSOMMING: Plangia graminea (Serville) (Orthoptera: Tettigoniidae) en Lobesia vanillana (De Joannis) (Lepidoptera: Tortricidae) is twee, minder belangrike, sporadiese peste van wyndruiwe in die Wes-Kaap provinsie van Suid Afrika. In die laaste paar jaar was daar ʼn toename in hul teenwoordigheid en skade opgemerk, wat beheermaatreëls noodsaak vir hulle beheer. Min is bekend oor hierdie insekte se biologie, ekologie en verspreiding. Die doel van hierdie studie was om hul basiese ekologiese inligting te versamel en om entomopatogeniese nematodes (EPN) as potensiële biologiese beheer agent te evalueer. Nimfe van P. graminea was geëvalueer teen 12 in vivo gekweekte EPN spesies, waarvan Heterorhabditis zealandica (SF41), H. indica (SGS), Steinernema jeffreyense (J192), S. yirgalemense (157-C) en H. baujardi (MT19), meer as 82% mortaliteit na 48 uur veroorsaak het. Larwes van L. vanillana was geëvalueer teen S. jeffreyense (J192) en S. yirgalemense (157-C), afkomstig vanaf beide in vivo en in vitro kulture van dieselfde isolate. Resultate toon dat hulle vatbaar was vir alle behandelinge, wat meer as 72% mortaliteit veroorsaak het, en dat daar geen beduidende verskil tussen in vivo en in vitro gekweekte kulture was nie, maar dat binne die in vitro kultuur, S. yirgalemense (98%) beduidend beter gevaar het as S. jeffreyense (73%). Kadawers van laboratoriumtoetse was gedissekteer om die teenwoordigheid van invektiewe onvolwassenes te evalueer, wat dus insekmortaliteit deur EPN infeksie bevestig het. Die vermoë van hierdie invektiewe onvolwassenes om hul lewenssiklus in vivo te voltooi, en hul vermoë om ʼn nuwe gros invektiewe onvolwassenes te vorm, dui daarop dat hulle moontlik die vermoë het om voortgesette beheer te kan uitoefen in gunstige omstandighede. Waarnemings ten opsigte van die biologie en ekologie van P. graminea op wyndruiwe, dui daarop dat hulle nie ʼn grondgebonde fase het nie en slegs ʼn enkele generasie per jaar. Plangia graminea was hoofsaaklik gerapporteer vanuit die Kaapse Wynland distrik in die Wes-Kaap provinsie van Suid Afrika, en van daar versamel is met die doel om ʼn laboratoriumkolonie te stig. Plangia graminea het nie goed presteer in gevangenisskap nie, wat dit genoodsaak het om individue uit die veld te versamel en te gebruik vir laboratoriumtoetse. Waarnemings van L. vanillana in die veld dui daarop dat hierdie insek ook nie ʼn grondgebonde lewensstadium het nie. Dit wil voorkom dat hulle ʼn lewenssiklus van 4-5 weke het en oorwinter as ʼn papie. Veld versamelde L. vanillana was suksesvol geteel op ʼn gewysigde agar-gebaseerde kodling mot dieet. Die huidige studie dra by tot nuwe kennis van P. graminea en L. vanillana, en dui daarop dat EPNs as belowende agente vir biologiese beheer oorweeg kan word, indien dit deel vorm van ʼn geïntegreerde plaagbeheer program.

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