Bionomics of the alfalfa blotch leafminer, Agromyza frontella (Diptera: Agromyzidae), in eastern Ontario.
In studies on lucerne in the field and laboratory in eastern Ontario in 1977-80, Agromyza frontella (Rond.) typically had 3 complete generations a year. It overwintered as a partially developed pupa that completed its development in mid-May. Three distinct adult flight-periods occurred: mid-May to mid-June, late June to late July, and early to late August. Eggs were deposited singly in lucerne leaflets beneath the lower epidermis, and on hatching the larvae moved towards the upper surface of the leaflet where they fed on the mesophyll and developed through 3 instars to form blotch mines, each representing about 27% of the leaf area. The fully grown larvae emerged from the mines to form light-brown puparia, mainly in the top 2.5 cm of the soil. The duration of each stage decreased with rise in temperature up to 25 deg C, but none of the stages survived at 30 deg C. Development rates plotted against temperature gave highly correlated linear relationships for all stages. The theoretical thresholds for the egg, larva and pupa were 7, 3 and 4 deg C, respectively, and the corresponding thermal requirements were 55, 123 and 333 day-degrees C. Survival of the larvae was higher in leaflets with solitary mines than in those with multiple mines; only 25% of the leaflets with 2 mines gave rise to 2 fully grown larvae. Three larvae seldom survived in a single leaflet.