| | Alfalfa Blotch Leafminer was discovered in the Brooks area in the summer of 2005. In North America it was originally discovered in 1968 in Maine, USA. Since that time it has been moving slowly westward and northward, arriving in Quebec in 1972 and eastern Ontario in 1974. ABLM arrived in Manitoba in the mid 1990’s and was found in Regina in 2005. The discovery at Brooks represents a jump in the distribution rather than the slow but steady progression westward.
The adult is a very small, black, hump-backed fly. The larvae are small, pale yellow maggots found within tunnels in the leaf tissue
Small pinhole punctures are left in the leaves when the adult feeds and lays its eggs. The developing maggots feed inside the leaflet, creating tunnels or mines between the top and bottom layers of the leaf. These tunnels usually begin at the base of the leaflet and widen towards the leaf apex, creating a "blotch" appearance. Feeding damage primarily decreases forage quality and seldom causes yield loss. Severe damage (several tunnels per leaflet) can cause leaflets to drop. There is no information on the impact of ABLM on alfalfa seed yields.
In the summer of 2006 weekly sweep net samples were taken from 6 fields in the Brooks area. Sampling started in fields 1 to 4 on May 12 and two more fields starting on June 2. All fields were sampled weekly until August 25 with the exception of the hay fields in the weeks they were harvested. Samples were placed in alcohol and stored until they could be sorted. When sorted the number of flies, lygus and hymenoptera (potential parasitoids) were recorded.
In total nearly 10,000 ABLM flies were recorded, along with nearly 2,000 lygus and lygus nymphs and almost 700 potential parasitoids. There appears to be 3 generations of the flies. The sampling ended as the third generation was emerging (August 25). It is therefore difficult to determine if the third generation is a partial or complete generation. It is likely that a portion of both generations overwinter as pupa on or near the soil surface as this is what happens in Ontario. The first ABLM adult generation appeared around 370 Base 5 growing degree days, the second generation 615 Base 5 GDD later and the third generation 540 GDD after that. More years of collection will be needed in order to be certain that this will be similar year to year. This information will be important when managing any spraying operations around emergence of beneficial organisms. |
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