Seed coating treatments of sunflower by the systemic insecticide imidacloprid was suspected of affecting honey bees and bumblebees. The hypothesis raised was whether imidacloprid could migrate into nectar and pollen, then modify flower attractiveness, homing behavior, and colony development. Our greenhouse and field experiments with Bombus terrestris L. were aimed at the following: the behavior of workers foraging on treated and control plants blooming in a greenhouse, the homing rate of colonies placed for 9 d in a treated field compared with colonies in a control field, and the development of these 20 colonies under laboratory conditions when removed from the fields. In the greenhouse, workers visited blooming heads of treated and control plants at the same rate and the mean duration of their visits was similar. In field colonies, analysis of pollen in hairs and pellets of workers showed that in both fields 98% of nectar foragers visited exclusively sunflowers, whereas only 25% of pollen gatherers collected sunflower pollen. After 9 d, in the control and treated field, 23 and 33% of the marked foragers, respectively, did not return to hives. In both fields, workers significantly drifted from the center to the sides of colony rows. During the 26-d period under field and laboratory conditions, the population increase rate of the 20 colonies was 3.3 and 3.0 workers/d in hives of the control and treated field, respectively. This difference was not significant. New queens were produced in eight colonies in either field. The mean number of new queens per hive was 17 and 24 in the control and treated field, respectively. Their mating rate was the same. It was concluded that applying imidacloprid at the registered dose, as a seed coating of sunflowers cultivated in greenhouse or in field, did not significantly affect the foraging and homing behavior of B. terestris and its colony development.

On a étudié les effets de la pollinisation du colza (Brassica napus L. var. oleifera Metzger) par un bourdon Pollinisation entomophile, ( Bombus terrestris L .) dans une expérience en cage, en vue de déterminer les conditions les plus favorables à Brassica na p us var . ole i fera , une production de graines homogène par les plantes. Cette homogénéisation est une nécessité pour l'étude Bombus terrestris, 0 ' ' des pertes de rendements dues à un ravageur.Composantes du rendement, La pollinisation entomophile augmente considérablement la production de l'inflorescence principale par Compensation, ' accroissement du nombre de siliques et du nombre de graines par silique. Ceci entraîne au niveau de la plante Essai sous cage.entière, une diminution du nombre d'inflorescences, notamment tertiaires. L'étude des inflorescences de ssal sous cage, même rang suggère l'existence d'une inhibition de l'initiation florale ou du développement des siliques lorsque la production de la hampe principale est importante. Le drainage des métabolites par l'inflorescence principale entraîne une réduction du nombre de graines par silique sur les inflorescences secondaires les plus hautes. Cet effet disparaît pratiquement au niveau de la 4 c inflorescence secondaire. Au niveau de la plante entière la pollinisation a un effet essentiellement qualitatif : elle réduit la variabilité des composantes du rendement et homogénéise la maturation et la production. L'augmentation de 26 p. 100 du rendement des plantes entières pollinisées par rapport aux non pollinisées n'est pas significative. SUMMARYEffects of pollination on rape in a cage experiment Insect pollination,.The effects of pollination of rape (Brassica napus L. var. oleifera Metzger) by a bumble bee (Bombus terrestris Brassica napus var . olcifera , L.) have been studied in a cage experiment. The principal aim was to find out the best conditions for ensuring Bo mbus terrcst ri s , homogeneous yield. This is required for studies on yield losses caused by pests. Pollination greatly increased Yield components, the yield of the main shoot through an increase in the number of pods and number of seeds per pod. This led Compensation, to a reduced number of racemes per plant. The study of racemes at the same level suggests that a high-yieldingCage experiment.main shoot has an inhibitory effect on floral initiation and pod development. The draining of metabolites by the main shoot induces a reduced number of seeds per pod on the highest secondary racemes. This effect practically disappears at the level of the 4th secondary raceme. At the whole plant level insect pollination has an essentially qualitative effect : it reduces variability among yield components so that maturity and yield components are more homogeneous. The 26 % increase in yield in pollinated plants (compared with unpollinated ones) is not statistically significant.

Estimation de l'action du charançon des siliques (Ceuthorrhynchus assimilis Payk.) sur la productivité du colza d'hiver. II. Evaluation des pertes dans des expériences en cages Jacques LERIN d'Eric RIVAULT

Cet article présente quelques problèmes méthodologiques relatifs à la détermination des pertes de rendement du colza dues au charançon des siliques dans des expériences en cage. La pollinisation doit être assurée par Etude méthodologique, l'adjonction d'insectes pollinisateurs malgré le caractère autofertile du colza. Brassica napus L. var. Les variations du nombre de siliques et du nombre de graines par silique masquent l'action du charançon. oleifera Metzger, Afin de pouvoir analyser les résultats dans de bonnes conditions d'application des tests statistiques, la Ceuthorrhynchus assimilis transformation en logarithmes du nombre de siliques et du rendement et en racine carrée du nombre de larves Payk, est nécessaire pour stabiliser les variances. Pollinisation entomophile, La répartition des larves sur les plantes et l'effet du développement de la plante sur l'abondance de la Composantes du rendement, descendance des femelles ont été particulièrement étudiés. Une méthode d'échantillonnage est préconisée Essai sous cage, pour déterminer le niveau d'infestation de lots de plantes. Distribution spatiale, Rapports plante insecte. SUMMARY Assessment of yield loss in winter rape due to seed-pod weevil (Ccuthorrhynchus assimilis Payk.)-I.-Methodological aspects Methodological study, Brassica napus L. var. This paper presents some methodological problems in the determination of yield losses in rape caused by the oleifera Metzger, seed-pod weevil in a cage experiment. Although rape is self-fertile, bumblebees had to be introduced to Ceuthorrhynchus assimilis improve pollination and reduce the variance of the number of pods per plant. Payk, Variation in the number of pods and in the number of seeds per pod tended to conceal the damage caused by Insect pollination, the seed-pod weevil. High numbers of plants had to be assessed to show the impact of the seed-pod weevil on Yield components, yield. Logarithmic transformation of the number of pods and yield per plant and square-root transformation Cage experiment, of the number of larvae per plant were necessary to avoid links between means and variances. Spatial distribution, The distribution of larvae on the plants is described and a sampling method is proposed to determine the level Insect plant relationship. of attack of a plant lot.

Effect on pea production of Acyrthosiphon pisum (Harris) (Horn., Aphididae) infestation during flowering periodThe effect on pea production of aphid populations starting a t early stages and stopped at the beginning or at the end of flowerinn has been studies in uroteaeinous oea fields with artificial infestations under I " small cages. Comparison; between frequency distributions of the number of aphids per plant in these conditions and frequency distributions in open field infestations allow us to consider that the risk relative to a mean number of aphids per plant is maximized in our experiments. It is shown that complex mechanisms are involved in the plant response to the action of A . pisum: for example aphids can stimulate production on young nodes. The interaction between plant response and environmental factors is demonstrated. Anyhow, the weight of seeds per plant or their nitrogen content have never been reduced by any of the observed aphid dynamics in our experiments. The natural local dynamics of this aphid allow us to conclude that production losses (if any) would be of no economic significance in our agrometeorological conditions. ' Collaborateurs techniques.U.S.