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.