Arthropod communities of Proteaceae with special emphasis on plant-insect interactions

Thesis (PhD) -- Stellenbosch University, 1989.

ENGLISH ABSTRACT: Arthropod communities of five proteaceous species viz. Protea repens. P. neriifolia. P.cynaroides, Leucospermum cordifolium and Leucadendron /aureolum were studied. A faunal list of the insects was compiled according to the feeding guilds of insects. Six phytophagous guilds were recognized: flower visitors, thrips, endophages, ectophages, sap-suckers, and ants. The guild composition, species packing and seasonal distribution for the free-IMng insects, spiders and other arthropods were investigated on the different plant species. The ants, flower visitors and sap-sucking species found on the plant species, were very similar, but the number of leaf chewing species common to all the plant species was low, suggesting that some species were monophagous. Insect abundance increased during the wet winter months when the plants were in flower. Of the total number of herbivores collected, flower visitors represented 69,5%, leaf feeders 14,5% and sap-suckers 16,1 %. The chewers constituted 60,1% of the total herbivore. biomass. Leaf damage increased with age ; young leaves were practically free of herbivore damage, while older leaves were stm acceptable as food. The degree of insect damage differed amongst the plant species varying from 2% to 15%. The following leaf characteristics were investigated to determine the factors involved in defence against insect herbivory : total phenolic content, protein precipitating ability, cyanogenesis, nitrogen content, leaf toughness, woodiness and fibre content lt appears that the plant species use different mechanisms to protect their leaves. The infructescences of Protea repens were exploited by the larvae of four Coleoptera and four Lepidoptera species. The community structure of these phytophagous insects was determined largely by negative interactions. Various strategies are followed (e.g. niche segregation in time and space) to lessen interspecific competition.

AFRIKAANSE OPSOMMING: 'n Studie van die arthropoocl gemeenskap op vyf proteasoorte, naamlik Protea repens. P. neriffolia. P. cynaroides. Leucospennum cordffolium en Leucadendron laureolum is gedoen. 'n Faunalys van insekte volgens hul voedingsgDdes is saamgestel. Die insekte is in ses fitofage gDdes verdeel naamlik blombesoekers, blaaspootjies, endovoeders, ektovoeders, sapsuiers en miere. Die samestelling van die gDdes, spesie-rangskikking en seisoenale verspreiding is bepaal vir die vrylewende insekte, spinnekoppe en ander arthropode. Die miere, blombesoekers en sapsuierspesies wat op die plantsoorte gevind is, is byna dieselfde, maar verslalle in die blaarvoederspesies is gevind wat 'n aanduiding is dat sommige spesies monofaag mag wees. Gedurende die nat wintermaande toon die insekgetalle 'n toename. Blombesoekers verteenwoordig 69,5%, blaarvoeders 14,5% en sapsuiers 16,1% van die aantal insekherbivore wat versamel is. Die kouers vorm 60,1% van die totale herbivoor biomassa Soos die blare verouder, neem die skade op die blare toe; jong blare toon byna geen skade nie, terwyl ouer blare steeds geskik is vir insekvoedsel. Die insekskade op die blare wissel by die verslallende plante tussen 2% en 15%. Om te bepaal watter blaareienskappe moontlik 'n rol kan speel in blaarverdediging teen insekte is die volgende ondersoek: totale fenoliese inhoud, die vermoe om proteiene te presipiteer, sianogenese. stikstofinhoud, blaartaaiheid, houtagtigheid en veselinhoud. Dit wil voorkom asof die plante verskillende meganismes gebruik om die blare te beskerm. Saadkoppe van Protea repens word deur vier Coleoptera en vier Lepidoptera spesies benut Die gemeenskapstruktuur van die boarders word tot 'n groat mate bepaal deur negatiewe interaksies. Verskeie strategiee word gevolg (bv. nissegregasie in ~ en ruimte) om kompetisie tussen spesies te verminder.

Doctoral