Doppler radar detection of exceptional mass-migration of aphids into Finland

Our objective was to detect mass migrations of insects of economic signific ance by insect traps and a Doppler weather radar. Migrants were sampled by suction traps, tow nets and light traps in the Helsinki region. We used rad ar to observe the migrating insects, and trajectories to backtrack mass mig rations of aphids (Homoptera, Aphididae) in spring 1988. The aphid migratio ns were clearly observed in trap catches and by radar. The first migration, mainly involving Euceraphis betulae. occurred on 18 May and was tracked ba ck to northern Poland. The second migration, mainly of Rhopalosiphum padi ( a serious pest of small-grain cereals), occurred 3 days later and was track ed back to a large area covering Latvia and western Russia south of St Pete rsburg. The third migration included both E. betulae and R. padi, and took place on 30 May. It originated from Estonia. Neither trap nor radar data pr ovide exact quantitative information on migrations. Trapping efficiency dep ends strongly on wind speed and insect size. Radar echo intensity is very s trongly related to the sizes of insects in the large volume of air measured , and the sizes are not known accurately. Weather datal especially temperat ure, can be used in predicting the development of apbids, and air-parcel tr ajectories in estimating the source areas of migrants. These methods for fo recasting aphid migrations, combined with radar observations, are useful fo r warning purposes and to intensify insect trapping. This would contribute to more efficient agricultural pest management.