HYPOGASTRURA SUCCINEA (COLLEMBOLA: HYPOGASTRURIDAE) DISPERSED BY ADULTS OF THE CABBAGE MAGGOT, DELIA RADICUM (DIPTERA: ANTHOMYIIDAE), INFECTED WITH THE PARASITIC FUNGUS STRONGWELLSEA CASTRANS (ZYGOMYCETES: ENTOMOPHTHORACEAE)

In the course of investigations of the cabbage maggot, Delia radicum (L.) (= brassicae Wiedemann, brassicae Bouché), a pest of canola (rapeseed) in northern Alberta, an epidemic of the parasitic fungus Strongwellsea castrans Batko and Weiser (see Humber 1976) was documented during July 1983. Infected flies (mostly females) can be recognized by the presence of one or more cavities in the abdominal membrane, into which the fungus discharges its spores (conidia). The flies continue to feed (as vital organs are not attacked), but their eggs fail to mature, apparently because of inadequate nutrition. The presence of this fungus as a pathogen of the cabbage maggot in Canada is well known (Nair and McEwen 1973).

ECOLOGY OF THE CABBAGE MAGGOT, HYLEMYA BRASSICAE (DIPTERA: ANTHOMYIIDAE), IN RUTABAGA IN SOUTHWESTERN ONTARIO, WITH SOME OBSERVATIONS ON OTHER ROOT MAGGOTS

The cabbage maggot, Hylemya brassicae (Bouché), had three generations per year from 1970 to 1973 inclusive, a partial fourth was noted in most years. A small proportion of first generation pupae entered aestivation in 1971.Thermal units required for fly emergence from overwintered pupae fell within a narrow range (174 to 199), but there was little correlation between thermal units and fly emergence in subsequent generations. Lack of adequate moisture delayed establishment of larvae in roots in some generations. Lack of adequate soil moisture delayed establishment of larvae in roots in some generations, and this appeared to be the chief reason for the lack of correlation between thermal units and fly peaks.Throughout this investigation the over-all population remained remarkably constant. Parasitism by a staphylinid, Aleochara bilineata Gyll., and a fungus, Strongwellsea castrans Batko and Weiser, and soil moisture were the most important biological and climatic factors affecting survival. Parasitism of the adult by a nematode, Heterotylenchus sp., was recorded for the first time.Although large numbers of seed maggot adults, Hylemya florilega (Zett.) and H. platura (Meig.), were recorded, few infested rutabaga. Other species trapped included Euxesta notata (Weid.) and Muscina spp.

Observations on feeding and egg development of the wheat bulb fly Leptohylemyia coarctata (Fall.)

The crops and guts of adults of Leptohylemyia coarctata (Fall.) from different parts of England and Scotland contained spores of Septomyxa affinis. This fungus is widespread on dead wheat leaves and grass in wheat fields and is an important food for the flies, especially in south and east England during July and August. Of all flies dissected in 1967, 1968 and 1969, 57%, 39% and 45%, respectively, contained Septomyxa spores. Spores of other fungi, pollen grains, bacteria and yeasts were also ingested. All solid food was ingested in water or honeydew. The weight of the newly emerged female fly almost doubled with the ripening of the first batch of eggs, whereas males remained the same weight or became lighter. Different individuals had different numbers of ovarioles, so the number of eggs ripe and ready to lay at the same time also differed between individuals. The mean numbers, 25·6 ± 0·8 in 1968 and 28·6 ± 0·4 in 1969 were fewer than the usually accepted 32. During August, before all the eggs had been laid, many flies were killed by Entomophthora muscae and Strongwellsea castrans.