Phenology and behaviour of the clearwing moth, Monopetalotaxis candescens (Lepidoptera: Sesiidae), associated with cultivated rooibos, Aspalathus linearis (Fabaceae), in South Africa
Production of 'rooibos' or red bush tea from Aspalathus linearis (Burman f.) Dahlgren (Fabaceae) is unique within the greater Cederberg region, Western Cape Province, South Africa. One of the principal insect pests associated with A. linearis production is the root-boring clearwing moth, Monopetalotaxis candescens Felder & Felder (Lepidoptera: Sesiidae). Annual moth flights peak during November/December, resulting in young plantations being targeted during the hot, dry summer conditions prevailing at this time. Average infestation levels progressively increased from 28 ± 2 % in year 1, to 53 ± 2 % and 72 ± 1 % in years 2 and 3, respectively. A second, 4-6 years old plantation during the three-year survey period was found to be severely infested (average 92 ± 1 %) with virtually no additional infestation over time. Estimated losses to borer infestation were calculated at 4, 24, 27 and 36 % in plantations that were 1-4 years old, respectively. Significantly more eggs were laid on leaves (66 ± 4 %) compared to woody tissue, stems and twigs. Most eggs hatched between 02:00 and 04:00, with neonates migrating down to the stem base and entering the root just below the soil surface. A control strategy, exploiting aspects of neonate migratory and feeding behaviour, should result in both yield increases and prolonged survival of plantations beyond the typical 4-5-year cycle.