STUDY OF THE EFFECT OF THE HEIGHT OF TRAP PING ON CATCHES OF ALATE APHIDS AT DIFFERENT SITES AND OVER SEVERAL YEARS

The variability in the influence of the height of trapping on the abun dance of catches of alate aphids was studied via comparisons between 2 heights of trapping at 7 different sites operating over 5 yr in succe ssion. All the traps were set in the same cultural environment in orde r to limit the influence of other possible factors of variability. The study was based on catches of nearly 40 000 individuals and 121 taxa. It allowed classification of the 23 more abundant species into 4 grou ps: 6 species whose catches were regularly dependent on the height of trapping, 5 species whose catches were also related to the height of t rapping but less regularly, 6 species for which the height effect was weak or irregular and 6 species showing no effect. Among the 11 first species, 8 were sampled at 0.7 m in a higher number than at 0.0 m and 3 were better sampled at 0.0 m. The main factor of heterogeneity remai ned annual variations which constituted 50% of the total variability o bserved in the data set.