A study of poplar resistance to Phratora (= Phyllodecta) vitellinae L. (Col. Chrysomelidae): 2. Field observations

The choice of the phytophagous Chrysomelid Phratora (= Phyllodecta) vitellinae between different Populus clones, previously studied by greenhouse experiments, was estimated by field observations in experimental plots in a nursery. A first series of observations concerned 3 clones: ‘Ghoy’, ‘Columbia River’ and ‘Beaupré’.A second series concerned 8 clones: ‘Ghoy 1’, ‘Ghoy’, ‘Gaver’, ‘Robusta vert’ ‘Fritzy Pauley’, ‘Columbia River’, ‘Unal’ and ‘Beaupré’. Food choice and oviposition site choice were both recorded. Food choice was estimated by counting the number of beetles on each plant. Oviposition preferences were ascertained by counting the number of eggs and larvae.In the second series of experiments, we analysed the temporal fluctuations of the results. The variation from year to year and the modifications within a year were considered.The results were as follows: the order of increasing “resistance” (negative choice by the insects) was: P. trichocarpa X deltoïdes (‘Unal‘ and ‘Beaupré’) and ‘Columbia River’ (P. trichocarpa); P. deltoïdes X nigra (‘Gaver’ and ‘Ghoy’) and ‘Fritzy Pauley’ (P. trichocarpa); P. nigra (‘Ghoy 1‘).The field observation corroborated the high resitance of P. nigra ‘Ghoy 1’ to Ph. vitellinae.There was a significant correlation between the feeding and egg-laying preference.The distribution of the insects may depend considerably on the year of observation. Within a year, the closer the surveys in time, the greater the concordance between the observations made.FLWNA