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UK: Large narcissus fly forecasts

The forecasts below predict the timing of narcissus fly activity. They do not predict the number of insects present in the crop, as this depends on the size of the local fly population. For control purposes, the pest is considered to have become active when 10% of the insects have emerged/laid eggs and that the peak of activity has occurred when 50% have emerged/laid eggs.

Once they have emerged, adult large narcissus flies need warm sunny days to mate and lay their eggs. Provided these conditions occur, egg laying will start 4-5 days after emergence at the earliest. Mating, and therefore egg laying, will be delayed if air temperatures are lower than the activity threshold, which is close to 20^oC. The period between egg-laying and egg hatching, after which the larvae invade bulbs, will be about 9-11 days depending on temperatures.

For more information:
www.syngenta.com