Insecticide resistant peach-potato aphid
1994
Hansen, L.M.
In the period 1986-93 peach potato aphids (Myzus persicae) were collected in different beet (Beta vulgaris) areas with a view to mapping the resistance level. The method of determining a resistance level is a biochemical test measuring the content of the enzyme E4. The six different resistance levels have here been reduced to three as the three highest levels are called strongly resistant and the two medium levels weakly resistant. 5 aphids from each population are tested. The sensitive part makes up about 20-30 % of the populations throughout the entire period. The weakly resistant part however has decreased significantly to about 33 % whereas the strongly resistant part has increased significantly to reach the same level as the other two groups. The percentage of strongly resistant aphids dropped in the period from 1992 to 1993. This can be explained by a poor overwintering success which is due to a colder winter in 1993 - particularly the month of March. A comparison of results between sugar beet and fodder beet shows that the high occurrence of resistance is not seen in the fodder beet. A probable explanation is that spraying against aphids is far less widespread in fodder beet than in sugar beet. Therefore it can be concluded that the only way to diminish the occurrence of resistant peach-potato aphids is to reduce the spraying frequency
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