Population Dynamics and Control Potential of the Soil-Dwelling Stages of the South African Citrus Thrips, Scirtothrips aurantii (Thysanoptera: Thripidae), on Avocado

Abstract

Scirtothrips aurantii (Thysanoptera: Thripidae) is a recently confirmed economic pest of avocado (Persea americana). Damage by S. aurantii, through their feeding on avocado fruit results in corky tissue development (scarring), making the fruit unsuitable for export. The study aimed to monitor S. aurantii population dynamics during the critical early fruiting period by means of dispersal/emergence (D/E) traps and fruit infestation indices. The field efficacy of biologicals (Beauveria bassiana, Steinernema feltiae), the pyrethroid beta-cyfluthrin, and the semi-synthetic spinosyn, spinetoram, against soil-dwelling stages of S. aurantii during early fruit development were determined. Finally, the study aimed to establish the pupation sites of S. aurantii in avocado. Above ground, population dynamics fluctuated directly in response to the host plant's phenological changes and were modified by rainfall. Control of soil-dwelling stages by the insecticides and the effectiveness of D/E traps in monitoring S. aurantii populations were not demonstrated, probably because the populations trapped using the D/E traps were not representative of the above-ground populations, as evidenced by fruit infestation indices. Under laboratory conditions, 81.60 % of mature larvae pupated away from the soil, demonstrating that S. aurantii does not passively drop to the ground in an avocado orchard, but actively seeks out dark, sheltered areas to pupate.