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Species Page

alfalfa blotch leafminer

Agromyza frontella
This information is part of a full datasheet available in the Crop Protection Compendium (CPC). Find out more information on how to access the CPC.
©CAB International. Published under a CC-BY-NC-SA 4.0 licence.

Distribution

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Extent
Invasive
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Host plants / species affected

Main hosts

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Medicago sativa (lucerne)

List of symptoms / signs

Leaves - internal feeding

Symptoms

The leaf mine is initially narrow and linear, following the margin of the leaf towards the apex, and then turns back to develop into a blotch mine in the area of the midrib (Spencer, 1973). The mine usually represents approximately 27% of the leaf area (Guppy, 1981).

Prevention and control

Cultural Control

Early harvest has some effect on reducing end-of-season root reserves (Sawyer and Fick, 1987) and early canopy removal eliminated partly-developed larvae and increased mortality of those that had already left the mines and were pupariating in the soil (Therrien and McNeil, 1985). However, Alicandro and Peters (1983) showed that 34% of third-instar larvae could still complete their development following harvest and they questioned the practice of field-curing lucerne hay.

Biological Control

Biological control has been used successfully against A. frontella, primarily using the introduced parasitoid Dacnusa dryas. This species is well established as an effective biocontrol agent in Quebec (Letendre et al., 1991), Ontario (Harcourt et al., 1988) and north-eastern USA (Drea and Hendrickson, 1986).

Host-Plant Resistance

Some work has been performed on the development of resistant lucerne cultivars, for example, Drolet and McNeil (1984) tested four cultivars, but no differences in resistance were recorded.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Impact

A. frontella is not normally a pest in Europe, although Steyskal (1972) did note that an isolated outbreak occurred in Germany in 1955. Drea et al. (1982) noted that in France and Denmark only 0.4% of lucerne leaflets were mined compared to incidences of 25-30% typically found in eastern North America. However, Daley and McNeil (1987) questioned the economic significance of A. frontella infestations as they found that there was little difference in forage accumulation and net photosynthesis between insecticide treated and non-treated plots, although pest numbers were significantly lower in treated plots. Conversely, other workers have considered the reduced photosynthesis caused by mine damage to be significant, for example, Hendrickson and Day (1986) noted that 30 or more large mines per stem constituted an economic threshold at which yields were reduced by 11%. Richard and Guibord (1980) found that occurrence of a pathogen, spring black stem (Phoma medicaginis), was correlated with A. frontella attack.