Determination of the Natural Host Status of Avocado Fruit to Pestiferous Thrips (Thysanoptera: Thripidae) in KwaZulu-Natal, South Africa

Abstract

The South African avocado industry is export-oriented, with approximately 3.0 % of international market share and with a five-year mean annual production of 118 000 t from 17 500 ha. Feeding by thrips results in fruit scarring and corky tissue development, making the fruit unsuitable for export. The study aimed to identify the spectrum of thrips in avocado flowers and more importantly, to confirm the identity of the thrips species responsible for damaging fruit. Thrips were collected from flowering panicles and identified using taxonomic keys. Frankliniella occidentalis (Pergande), Scirtothrips aurantii (Faure), Thrips gowdeyi (Bagnall), Thrips pusillus (Bagnall), Thrips tenellus (Trybom), Haplothrips gowdeyi (Franklin), Haplothrips bedfordi (Jacot-Guillarmod) and Megalurothrips sjostedti (Trybom) were consistently collected from May to September 2018. The minute size of thrips warranted a pre-season trial to determine the best netting material to contain thrips. Insect screen (149 µm), nylon netting (250 µm), chiffon (210 µm), voile (250 µm), organza (500 µm), tea filter paper (74 µm) and coffee filter paper (53 µm) were evaluated. The experiment was laid out as a randomised complete block design with six replications and the trials repeated twice. Only coffee filter paper and tea filter paper contained at least 85 % of the thrips and were therefore chosen for thrips exclusion trials. Surveillance by fruit sampling was undertaken to determine the natural host status of avocado to thrips. Avocado fruitlets were randomly sampled and incubated under laboratory conditions. Scirtothrips aurantii (Faure) (the South African citrus thrips) emerged from fruitlets and was sustained on that fruit to adulthood. This is the first study to demonstrate that avocado is a natural host to this pest in South Africa.