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Chapter 9
Delia antiqua (Meigen), Onion Maggot
(Diptera: Anthomyiidae)
F.L. McEWEN
The onion maggot, Delia anliqua (Meigen), is the most destructive pest of onions
throughout the temperate regions of the northern hemisphere and in Canada causes
losses of 50-90% (Finlayson 1959). Effective control was not achieved until the late
1940s when the cyclodiene insecticides became available. These, when applied in the
furrow with the seed, provided excellent control of the first generation and additional
treatments of DDT against the second and third generation adults reduced damage to a
minimum. Resistance to these insecticides developed and the cyclodienes were
replaced about 1960 by such organophosphorus components as ethion and diazinon.
Subsequently chlorfenvinphos, fensulfothion, carbofuran, fonofos, and chlorpyrifos
have been used in the seed furrow; and parathion, diazinon, naled, or malathion have
been used as sprays against the adults of the second and third generation. Resistance
to several of these insecticides has developed and, while the level of resistance has not
been as great as with the cyclodienes, commercial control is becoming increasingly
difficult (Harris & Svec 1976).
The use of the sterile-male approach for insect control was first successfully applied
(Knipling 1960) against a livestock pest and since then its use has been explored for
many insect species. In the case of the onion maggot, McClanahan & Simmons
(1966) and Noordink (1966) showed that the insect could be sterilized without serious
effects on the longevity of the adult. In Holland, Noordink and his associates
continued studies on the sterile-male method for control, and by 1980 had completed
laboratory and field testing to the point where a commercial venture in marketing the
programme to the growers is now in place (Noordink 1971, 1974; Ticheler el al. 1974;
Loosjes 1976).
In Canada, research on sterile-male control for the onion maggot began as a
cooperative venture between Agriculture Canada (C.R. Harris) and the University of
Guelph (F.L. McEwen) in 1971. In the initial stages of the study, mass rearing
procedures were perfected (Harris & Svec 1976), and laboratory tests determined that
when pupae reared under diapausing conditions were irradiated (Cobalt 60) after 6
days post-diapause (24°C) at 2 or 4 krad, the males were sterilized and the females
made unreproductive. Tests established that males produced from these pupae were
competitive and lived about as long as those emerging from non-irradiated pupae.
Initial field releases of sterilized pupae were begun in 1973 and, using fluorescent
dyes as markers on released flies, the field distribution pattern was also determined.
The survival of released flies was monitored and eggs collected in the field and hatch
determined. The initial results indicated that the flies did not disperse widely (most
recaptures were within 75 m of release site) and that the hatchability of eggs in the
release area was reduced. In addition, an economic study was undertaken that showed
that if the sterile-male programme was effective, it was an economically sound
approach (King 1973).
Field tests were expanded with 6000000 pupae released in 1974 and 10 000 000 in
1975. While it was clear that egg hatch was reduced, bird predation on released pupae
and immigration of wild flies into the release area resulted in inconsistent results.
Extensive monitoring indicated, however, that when the ratio of wild to released flies
approached 1: I, the egg hatch was reduced near 50%.
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