Bean Seed Fly

Adult bean seed fly

This insect, scientifically known as Delia platura, is a highly polyphagous pest whose larvae feed on the seeds or seedlings of many agricultural crops such as various types of beans, chickpeas, lentils, fava beans, mung beans, cabbage, sugar beet, corn, cotton, cucumber, melon, watermelon, wheat, rice, turnip, clover, oats, potatoes, tobacco, cauliflower, rutabaga, peanuts, and onions, destroying seeds, newly emerged sprouts, or weak seedlings. This fly was first reported in Iran by Farhbakhsh in 1961 (1340), and then Kamali studied the species in 1966 (1345) as one of the important pests of legumes and especially beans. Kamali also proposed the name "bean plant-feeding fly" for this pest.

Distribution areas:

The bean seed fly is widely distributed worldwide. In Iran, the distribution areas of this pest have been reported in the northern provinces, Borazjan and Kazeroon, Qazvin, Tehran, Isfahan, and East and West Azerbaijan.

Morphology:

Adult insect

The adult insect is almost similar to the housefly, but is slightly smaller, measuring 4-6 mm in length. The male fly is described as gray with several darker longitudinal stripes on the thorax and a median stripe on the abdomen. However, the female fly appears lighter in color and the stripes on her thorax have disappeared or merged. The fly's capsule head is grayish-brown. In the male, the eyes are close together, but in females, they are separated by a silvery band. The thorax is convex and narrower than the head capsule.
Egg

The eggs are white, cylindrical, and curved. One end of the eggs is rounded and the other end is pointed. The approximate length of the eggs is 1 mm and their width is 0.25 mm.

Larva

The last instar larvae are white, cylindrical, and have a narrow head. The last abdominal segment has protrusions in the middle, which appear as 5 pairs of small papillae, with three pairs located in the center. The length of the last instar larvae is 5-7 mm.

Pupa

It is brown and 5 mm in length.

Damage

The larvae of this fly feed on any type of organic matter, both plant and animal, dead or alive. In addition, seeds and other underground parts of living plants are also attacked by the larvae of this fly. This pest has a host preference for certain plants. The extent of damage and host selection depend on two factors: the level of fly activity and environmental conditions. For example, in France, damage to cereal roots has been reported, which is different from Iran. The larvae of this pest destroy seeds before germination in the soil, or damage them to the extent that the plant becomes weakened. Sometimes, the damage to the larvae extends to the underground stem or young roots of the plant, in which case the plant wilts and dries out. The damage caused by this fly is usually extensive; in a study on legumes in 1346, the damage caused by this insect in fields was estimated at about 40%.

Biology

This pest overwinters as pupae in the soil, in manure, or inside contaminated roots. Under the climatic conditions of Karaj, adult insects appear in late Farvardin (late March/early April) and fly over plants near the ground surface. Female insects lay eggs in groups in decaying materials or in the soil near freshly sown seeds. As the young seedlings emerge or sprouts come out of the seed shells, the eggs also hatch. The embryonic development period is very short. This period has been reported as one day at 27-28°C, three days at 16-19°C, and eight days at 5-7°C. The female fly lays a maximum of 10-12 eggs daily and about 97 eggs during her lifetime. After hatching, young larvae go into the soil where they first feed on organic matter, but after a few days, they attack the cotyledons and feed on them. This moth has three larval stages, and the larval development period lasts 20-28 days at 10-12°C and 8-11 days at 24-25°C. After completing their development, larvae transform into pupae at a depth of 5-6 cm in the soil. The pupal period lasts 10 days at 20°C and 18 days at 17°C. The lifespan of the male fly is 29 days and that of the female is 34 days. The second generation of the pest appears in mid Khordad (mid June), and the insects of this generation lay eggs on autumn cereals after summering. First-instar larvae, after hatching, bore into young seedlings and complete their feeding before the onset of cold, then transform into pupae and spend the entire winter in the pupal stage. Depending on environmental conditions, this insect produces 1-5 generations per year.