Oblique Flower Fly
Head: Face entirely yellow on male, pointed at top where red eyes join. Female has yellow stripe up inner eye margin, rest brown; eyes separated at top. Face does not protrude in either male or female. Hind eye margin indented near middle, covered with white hair.
Antenna: Female antenna dark. Male antenna light yellowish-brown.
Thorax: Segment 1 (scutum) metallic bronze to greenish – no longitudinal lines. Wide yellow stripe on side edges, broken at wing base. Segment 2 (scutellum or half-moon) yellow, sometimes tinted with obscure reddish brown. Thorax sides black with many oblong yellow spots covering surface.
Wings: Clear, veins black. Halteres yellow.
Legs: Front and mid legs yellow. Hind legs dark, mixed with some yellow rings. Feet dark. Toes yellow.
Abdomen: Black with yellow to yellow-orange marks.
Segment 1: Very short, mostly at each side of scutellum. Base has wide yellow stripe bending around scutellum. Lower margin black.
Segment 2: Thin yellow stripe at base, broken at center. Another wider yellow stripe across middle of segment.
Segment 3: Thin yellow stripe at base, slightly broken at center. Another very wide yellow stripe across middle of segment, somewhat curved on female; much wider and more curved on male.
Segment 4: Thin yellow stripe entire across base, with 2 longitudinal lines down middle of segment. Another long, oblong mark on each side. Main ID.
Segment 5: Thin yellow stripe entire across base, with four longitudinal, wider lines extending to lower margin. Lower margin yellow.
Tip rounded, dark. Underside yellow.
Similar Species: Toxomerus species do not have longitudinal lines on the abdomen.
Size: 5 to 9 mm long.
Habitat: Meadows, forest edges, urban areas with aphids.
Food: Adults feed only on pollen, nectar, or honeydew produced by aphids, particularly fond of mint. Larvae feed on aphids and plant lice or mealybugs.
Flight Time: April to September.
Life Cycle: Can have 4 to 7 generations a year, with a complete life cycle in as little as 16 days. Eggs are chalky-white, laid on leaves and stems infested with aphids or plant lice. Larvae hatch in 3 to 4 days, maggot-like, mouth with teeth. Brown to green with white areas, about 8 to 9 mm long when mature. They can devour 400 aphids during larva stage. Larvae need some shade. They protect themselves from predators, like ants, by a secretion from their mouth, a glue-like substance that immobilizes the predator.
Parasitized by tiny Ichneumonidae wasps.
Comments: Essex County – Point Pelee National Park, Ojibway Prairies. Kent County – Rondeau Provincial Park. Georgian Bay area to Toronto.
For information on synonyms, references and type specimens see next page