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frequently asked questions
SIT is literally birth control for insects. It is used primarily to control or eradicate insect pests, usually crop pests. The target insect is reared in great numbers and the males sterilised, using gamma radiation. The sterile males are released in high numbers in target areas throughout the year. They mate with wild females which results in infertile eggs and provided that other population management practices are properly carried out, the wild population declines rapidly.
The existing wild Medfly population first needs to be managed down to very low levels (an average over the year of ± 1 FTD*) over one season using sound, basic Integrated Pest Management (IPM) practises such as year-round fruit fly baiting and good host plant management. Only when the seasonal Medfly population level is low enough can sterile male releases be started.
*FTD = Flies per Trap per Day
FFA has a special strain of Medfly that enables the production of a separate ‘stream’ of male-only eggs. We also have a quality control process that monitors the purity of the male stream. Only males from the male-only stream are irradiated and released.
A special radiation-sensitive sticker is placed on every container of male pupae that is irradiated to gauge if the required radiation dose has been applied. FFA also conducts post-radiation quality control tests on irradiated male pupae to ensure that all the flies in that batch conform to the sterilisation requirement.
During the growing season from October to May, sterile flies are released by helicopter on a weekly basis, over all planted hectares of fruit in designated SIT areas, while from June to September sterile males are released in bags by hand, concentrating on gardens and other fruit fly hotspots.
Male fruit flies do not have an ovipositor (egg-laying device) as in the female, and therefore cannot damage fruit in any way.
Very definitely! Fruit flies ignore boundary fences, and if there is ripe or ripening fruit on your farm, fruit flies will soon become your problem too.
Traps baited with a fruit fly lure are placed in orchards and vineyards throughout the SIT area according to standard procedures. During the growing season, from September to end of May, all traps are read weekly. During the winter months, from June to end of August, the focus of our monitoring shifts towards all gardens (on farms and in towns) and other fruit fly hotspots. Trap counts and identified hotspots are communicated to producers and other stakeholders accordingly.
The sterilized male pupae are treated with a purple fluorescent dye. When the adult males emerge, some of this dye is automatically transferred onto them. When flies from a trap are placed under an ultra-violet light, sterilized males shine purple from the dye, while wild flies do not.
Ideally, females should be monitored as well, using bucket traps with a so-called food lure that attracts both sexes, together with a piece of Vapona strip to kill flies thus trapped. Trimedlure traps are also used in SIT orchards in addition to bucket traps in order to monitor the distribution of the released sterile males.
The winter months are in fact the best (and easiest) time to control fruit fly populations – a low fruit fly count at the end of winter means lower populations during the following growing season. Bait all fruit trees as well as good shade trees in all home and farm gardens and around labourers’ houses every 7 to 10 days. Ideally, strip off all winter fruit such as loquats and guavas while they are still green, unless these are routinely baited through the winter. Destroy or bury any fallen fruit.
|Medfly and Cape fly
|With a Delta trap:
Fruit Fly lure (Trimedlure) with a sticky pad (replaced every 6 weeks); or
With a Bucket trap:
Biolure with Vapona (Dichlorvos) (replaced every 6 weeks)
|Oriental Fruit Fly
|With a Bucket trap:
Methyl Eugenol lure with Vapona (Dichlorvos) (replaced every 6 weeks)
|False Codling Moth (FCM)
|With a Delta trap:
FCM lure with a sticky pad (replaced every 3 months)