n African Entomology - Sterile insect releases for control of (Lepidoptera: Tortricidae) : an assessment on semi-commercial scale




False codling moth, (Meyrick) (Lepidoptera: Tortricidae), is indigenous to sub-Saharan Africa. It infests a large number of wild plants and can be a pest of commercial concern in cultivated fruit and nuts. A limited number of insecticides, as well as biological control and mating disruption can be applied as control measures in citrus, but they often do not reduce pre- and post-harvest crop loss adequately. The potential of the sterile insect technique (SIT) for the control of was investigated between 2002 and 2006 in Citrusdal, Western Cape Province, South Africa, and entailed studies on radiation biology and F1 sterility, compatibility with the egg parasitoid Nagaraja (Hymenoptera: Trichogrammatidae), and field cage experiments to determine sterile:fertile moth overflooding ratios. Promising results justified a pilot experiment conducted on semi-commercial scale in citrus orchards in Citrusdal during 2005-06. One thousand mixed sex moths were treated with 150 Gy ionising radiation and released in 35 ha of Washington navel oranges twice a week for 28 weeks during the production season. The moths were released by hand from an all-terrain vehicle, with release rows 40 m apart and the numbers of released and feral moths monitored weekly with pheromone traps. Released moths dispersed well and fully overlapped between release rows. The target overflooding ratio of released to feral males (10:1) was exceeded by wide margins and a mean overflooding ratio of 41:1 was maintained during the experiment. Fruit drop assessments were conducted once a week in the SIT-treated and control orchards. Crop loss due to infestation was reduced by 95.2 % in the SIT-treated area compared to the control orchard. The project resulted in the commercialisation of the SIT for on citrus.


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