Insect-fungal ecology on selected new crops in South Africa

Abstract

English: This study investigates insect-fungal-plant interactions on three new crops (viz. cactus pear, pistachio and pigeonpea) in South Africa. Isolation of Drosophila. melanogaster and D. hydei flies from cactus pear (Opuntia ficus-indicay orchards showed that these two species harbour fungi. Inoculations of specific fungi obtained from the two Drosophila species onto fruit and cladodes of cactus pear showed that some of the fungi had the ability to cause rot and may even be pathogenic. Scanning electron microscopy (SEM) confirmed the harbouring of fungi on the bodies by of the two Drosophila species and it also showed that most of the fungal propagules were present on the legs of the flies. An insect succession study showed that both Drosophilidae flies and Nitidulidae beetles play a vital role in the degradation of the fruit by contributing to the rate of fruit decomposition and by spreading yeasts and fungi that cause rot. Further to this a dissemination potential experiment with Drosophilidae also showed that these flies are capable of transmitting fungi, which are capable of causing rot on 0. ficus-indica fruit. Isolation of Nysius natalensis bugs collected in Pistacia vera (pistachio) orchards showed that this species harbours fungi. Additionally, isolation of the heads and faeces of Sparrmannia flava beetles collected in pistachio orchards showed that this species also harbours fungi. More specifically, both these species harbour fungi known to be pathogenic to P. vera. SEM of N. natalensis confirmed that they harbour fungi on the exoskeleton and that most of the fungal propagules were present on the legs of the insects. It was also shown that N. natalensis cause feeding lesions on pistachio nuts, thereby providing access for fungal infection. Analysis of N. natalensis confirmed that their numbers are higher in late summer and that cover crops and surrounding vegetation have an influence on their population dynamics. Analysis of S. flava showed that they have a peak season during summer and that their flight activity is influenced by a combination of temperature, rainfall, windspeed, soil type and lunar phases. Isolation of Clavigralla tomentosicollis bugs collected in a Cajanus cajan (pigeonpea) cultivation showed that this speceis harbours fungi. Some of these fungi are known to be pathogenic to C. cajan. Scanning electron microscopy (SEM) confirmed the harbouring of fungal propagules on the exoskeleton of C. tomentosicollis. It was also shown that fungal propagules were present all over the body, most importantly the mouthparts. A dissemination potential experiment showed that this species is capable of transmitting fungal proapgules to pigeonpea plants. C. tomentosicollis prefers some pigeonpea cultivars above others.

Afrikaans: Hierdie studie ondersoek die insek-swam-plant interaksie op drie nuwe gewasse (tewete turksvy, pistachio en duifert) in Suid-Afrika. Isolering van Drosophila melanogaster en D. hydei vlieë vanaf turkvy (Opuntia ficus-indicaï boorde toon dat hierdie twee spesies swamme huisves. Inokulasies van spesifieke swamme, wat vanaf die twee Drosophila spesies verkry is, op die vrugte en blaaie van turksvye toon dat sommige van die swamme die vermoë besit om verrotting te veroorsaak en dat hulle selfs patogenies mag wees. Skandeer elektron mikroskopie (SEM) bevestig dat swamme op die liggame van die twee Drosophila spesies gehuisves word en toon ook dat die meeste van die swampropagules op die bene van die vlieë voorkom. 'n Insek suksessie studie toon dat beide Drosophilidae vlieë en Nitidulidae kewers 'n belangrike rol vervul in die degradasie van die vrugte deur by te dra tot die tempo van vrugontbinding en deur die giste en swamme wat verrotting veroorsaak te versprei. Bykomend tot hierdie toon 'n verspreidingspotensiaal eksperiment met Drosophilidae ook dat hierdie vlieë die vermoë besit om die swamme, wat die verrotting van turksvyvrugte veroorsaak, oor te dra. Isolering van Nysius natalensis besies wat in Pistacia vera (pistachio) boorde versamel is toon dat hierdie spesie swamme huisves. Daarby toon die isolering van die koppe en faeses van Sparrmannia flava kewers, wat ook in pistachio boorde versamel is, dat hierdie spesie ook swamme huisves. Beide hierdie spesies huisves spesifieke swamme wat daarvoor bekend is dat hulle patogenies op P. vera is. SEM van Nysius natalensis bevestig dat hierdie spesie swamme op hul eksoskelet huisves en dat die meeste van die swampropagules op die bene van die insekte voorkom. Daar is ook aangetoon dat N. natalensis voedingsletsels op pistachio neute veroorsaak, wat toegang tot swaminfeksies verskaf. 'n Voorkomsanalise van N. natalensis bevestig dat hul getalle gedurende laat somer hoër is en dat dekgewasse en omliggende plantegroei In invloed op hul populasiedinamika het. In Voorkomsanalise van S. flava toon dat hulle In piekseisoen gedurende die somer het en dat hul vlugaktiwiteit deur In kombinasie van temperatuur, reënval, windspoed, grondtipe en maanfase beïnvloed word. Isolering van Clavigralla tomentosicollis besies, wat in In Cajanus cajan (duifert) aanplanting versamel is, toon dat hierdie spesie swamme huisves. Sommige van hierdie swamme is daarvoor bekend dat hulle patogenies op C. cajan is. SEM bevestig die voorkoms van swampropagules op die eksoskelet van C. tomentosicollis. Daar is ook getoon dat swampropagules orals op die insekliggaam, en veral belangrik op die monddele, voorkom. In Verspreidingspotensiaal eksperiment toon dat hierdie spesie die vermoë besit om swampropagules na duifert oor te dra. C. tomentosicollis verkies sekere duifertkultivars bo ander.