Katydid (Orthoptera: Tettigoniidae) bio-ecology in Western Cape vineyards

Thesis (MScConsEcol)--Stellenbosch University, 2017.ENGLISH ABSTRACT: Many orthopterans are associated with large scale destruction of crops, rangeland and pastures. Plangia graminea (Serville) (Orthoptera: Tettigoniidae) is considered a minor sporadic pest in vineyards of the Western Cape Province, South Africa, and was the focus of this study. In the past few seasons (since 2012) P. graminea appeared to have caused a substantial amount of damage leading to great concern among the wine farmers of the Western Cape Province. Very little was known about the biology and ecology of this species, and no monitoring method was available for this pest. The overall aim of the present study was, therefore, to investigate the biology and ecology of P. graminea in vineyards of the Western Cape to contribute knowledge towards the formulation of a sustainable integrated pest management program, as well as to establish an appropriate monitoring system. No detailed surveys have as yet been undertaken to assess the assemblage structure of katydids in vineyards and to verify their taxonomic status. By conducting a survey in vineyards located in the greater Stellenbosch region of the Western Cape, the identities of the katydid species present and their pest status was determined. A monitoring method was developed by adapting a generic sampling system for monitoring key arthropod pests in vineyards. Due to the perfect camouflage of adult katydids within the vine canopy, surrogate methods for monitoring this pest were investigated. Besides determining the basic biology and ecology of P. graminea within vineyards, aspects of its physiological ecology with implications on its mating behaviour were investigated. Furthermore, natural enemies that could potentially be used as environmentally-friendly biological control agents against this pest were identified. Three Phaneropterinae species were identified, namely P. graminea, Eurycorypha lesnei Chopard and a Phaneroptera species. Due to the similarity between the Plangia and Eurycorypha species, an ID-key was compiled for easy identification by growers. Plangia graminea was found to be the primary katydid pest in vineyards monitored. There was only one generation per year, with an overwintering egg stage. The monitoring of katydid eggs could potentially be used to monitor P. graminea, as eggs were positively and significantly correlated with katydid numbers and could allow early prediction estimates of katydid populations in vineyards. Temperature appeared to be an important environmental factor enhancing population outbreaks, as it influenced katydid development, but could also affect mating success of male katydids. It was found that there was a significant metabolic cost associated with the mating calls of P. graminea males. This study identified two natural control agents that could potentially be incorporated into an integrated pest management program for the control of P. graminea, namely hymenopteran egg parasitoids and an entomopathogenic fungus. The outcomes of this study aim towards the development of a practical, sustainable and environmentally-friendly integrated pest management program. Future research should focus on validating a monitoring method in the field, establishing an economic threshold, testing the efficacy of entomopathogenic fungi in the laboratory and in the field, and investigating the mechanisms involved in habitat preferences of hymenopteran egg parasitoids.AFRIKAANSE OPSOMMING: Baie sprinkaanagtiges is geassosieerd met grootskaalse vernietiging van gewasse en weivelde. Plangia graminea (Serville) (Orthoptera: Tettigoniidae), plaaslik bekend as “krompokkels,” word beskou as ‘n sporadiese plaag in wingerde in die Wes-Kaap Provinsie, Suid-Afrika, en was die onderwerp van die huidige studie. In die afgelope paar seisoene (vanaf 2012) het P. graminea ansienlike skade aangerig in wingerde, wat tot groot kommer onder die wynboergemeenskap van die Wes-Kaap gelei het. Baie min inligting is bekend oor die biologie en ekologie van die plaag. Geen moniteringsmetode is vir die plaag beskikbaar nie. Die algehele doel van die studie was daarop gemik om die biologie en ekologie van P. graminea in wingerde in die Wes-Kaap te ondersoek, om verworwe kennis beskikbaar te maak vir die formulering van ‘n volhoubare geïntegreerde plaagbestuurprogram, asook om ‘n geskikte moniteringsisteem te ontwerp. Tot dusver was daar nog geen gedetailleerde opname van die groeperingsstruktuur van krompokkels in wingerde, en hul taksonomiese status nie. Die studie het beoog om die krompokkel spesies in wingerde te identifiseer, en om hul plaagstatus te bepaal deur ‘n opname in wingerde geleë in die groter Stellenbosch streek van die Wes-Kaap uit te voer. ‘n Moniteringsmetode, gebasseer op ‘n generiese steekproefnemingsisteem vir die monitering van sleutel artropode wingerdplae was ontwerp. Aangesien volwasse krompokkels baie goed gekamoefleerd is tussen wingerdblare, is surrogaat metodes vir die monitering van die plaag ondersoek. Benewens die bepaling van die insek se biologie en ekologie, is ondersoek ook uitgevoer aangaande die fisiologiese-ekologie van die insek in verband met implikasies rakende die insek se paringsgedrag. ‘n Verdere doel van die studie was om die natuurlike vyande, teenwoordig in wingerde, te identifiseer wat moontlik gebruik kan word as omgewingsvriendelike biologiese beheermetodes teen die plaag. Drie Phaneropterinae spesies was geïdentifiseer, naamlik P. graminea, Eurycorypha lesnei Chopard, en ‘n Phaneroptera spesies. Weens die groot ooreenkomste tussen Plangia en Eurycorypha spesies, is ‘n ID-sleutel saamgestel wat deur die wingerdboere gebruik kan word vir maklike identifikasie. Plangia graminea was die primêre krompokkel plaag in die wingerde wat gedurende die studie gemoniteer was. Net een generasie was teenwoordig, met ‘n oorwinterende eier-stadium. Die monitering van krompokkel eiers kan potensieel gebruik word vir die monitering van P. graminea, aangesien daar ‘n positiewe en beduidende korrelasie was tussen die getal eiers en die aantal krompokkels. Die eiers kan ook gebruik word vir vroegtydige voorspellingsberamings van krompokkel populasies in wingerde. Dit blyk dat temperatuur ‘n belangrike omgewingsfaktor is tot bevolkingsuitbrake, aangesien dit ‘n invloed gehad het op die ontwikkeling van krompokkels, asook die paring sukses van mannetjie krompokkels. Daar is bevind dat daar ‘n beduidende metaboliese koste geassosieer is met die paringsroepe van P. graminea mannetjies. Die studie het twee natuurlike agente geïdentifiseer wat moontlik in ‘n geïntegreerde plaagbestuurprogram ingesluit kan word vir die beheer van P. graminea, naamlik, eier parasiterende wespies en ‘n entomopatogeniese swam. Die doelstellings van die huidige studie mik na die ontwikkeling van ‘n praktiese, volhoubare en omgewingsvriendelike geïntegreerde plaagbestuurprogram. Toekomstige navorsing kan fokus op (i) die ontwerp en toepassing van ‘n moniteringsmetode in die veld, (ii) die bepaling van ‘n ekonomiese drempelwaarde, (iii) om die effektiwiteit van die entomopatogeniese swam in die laboratorium en in die veld te toets, en (iv) om die meganismes betrokke by habitatsvoorkeure van eier parasiterende wespies te ondersoek