Agriculture Reference
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Fig. 5.9. Relationships between temperature and development rate for the four life
stages of the onion fly Delia antiqua ; shaded circles represent data from constant
temperature experiments, and open circles from fluctuating temperatures. The lines
are derived from equations fitted to the data (from Otto, 2002, Fig. 26).
debris, the mutual isolation of onion, garlic and leek fields and a 2- (or more)
year rotation between allium crops. Numerous predators and parasites of D.
antiqua have been identified, including fungal pathogens and nematode
parasites, and these are important particularly in reducing numbers in the
second and third annual generations. The insecticide cyromazine, which is
now approved for use as a seed-coating (see above) on onions in the USA, is
highly effective against diptera like the onion fly, but is relatively non-toxic to
other insects, including beneficials (Taylor et al ., 2001).
Cultivars differ in their content of the precursors of volatiles and in their
colonization by non-pathogenic, surface bacteria that increase volatile
emission. Decreases in these factors have been shown to correlate with
increased varietal resistance to fly attack. However, egg-laying preferences may
not be so important if flies are presented with one such 'resistant' line rather
than with several lines differing in volatile production. To reduce volatile
production by plants in the field, and thereby their attractiveness to egg-laying
females, plant damage during cultivation and herbicide application should be
minimized. IPM has become important for onion fly control because past
practices - including routine spraying and the continuous cropping of onions
on the fertile 'muck' soils of New York and Ontario and elsewhere - have led to
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