A laboratory feeding test was conducted on queenless micro-colonies of three bumblebee workers (Bombus terrestris L) to study the effects of low doses of imidacloprid on pollen and syrup consumption, worker survival, brood size and larval development. Two doses were used: D1 = 10 mg AI kg À1 in syrup and 6 mg AI kg À1 in pollen; D2 was 2.5 times higher in syrup and 2.7 higher in pollen. During 85 days 27, 30 and 29 micro-colonies were reared for control, D1 and D2 treatments respectively.Food consumption was not affected by either dose. During the 5-day pre-oviposition period the mean insecticide intake was 4.8 ng per day per worker in treatment D2. Both doses slightly but signi®cantly affected worker survival rate by 10% during the ®rst month, without any dose-effect relationship. Brood production was signi®cantly reduced in D1 treatment and larval ejection by workers was signi®cantly lower in D1 and D2 than in control. No signi®cant effect of D1 and D2 treatments on the duration of larval development was revealed. No residue could be detected in workers still alive after 85 days.It was concluded that the survival rate and reproductive capacity of B terrestris was not likely to be affected by prolonged ingestion of nectar produced by sun¯ower after seed-dressing treatment with imidacloprid (Gaucho), since honey or pollen collected by honeybees foraging treated sun¯ower never revealed concentrations of imidacloprid higher than 10 mg kg À1 .
International audienceThe estimation of Acridid (Orthoptera: Acrididae) density is the goal of a wide variety of conservation studies to monitor the impacts of grassland management or habitat change. The first aim of this paper was to study the influence of surveyors, time of the day and size/form of the box quadrat method on density values of Acridids in grassland habitats in Western France. The main taxa were Calliptamus italicus (L.) and Gomphocerinae sub-family. Surveyor and day-time (early morning vs. mid-day) were not significantly influencing the density values of Acridids produced using a 1 m2 box quadrat. A smaller box quadrat of 0.5 m2, square or rectangular, produced underestimates of Acridid density, such as square 1 m2 box quadrat should be preferred. Population densities change through time. Thus, data-based inferences about density are tied to the time periods during which data are collected. This was the main focus of this paper to provide a description of Acridid density fluctuations from egg hatching to adult's death in grasslands with differing vegetation structures and grasshopper densities. Acridid densities were monitored weekly in 23 grassland plots over three seasons from 2004 to 2006. Weibull formulation was used to model density fluctuations for the two main taxa in each field with the Julian date as time. Phenological parameters of density were quite similar for the two taxa in the three years. This could be explained by similar meteorological conditions in the three years. However, these parameters exhibited a great variability between fields in the same year. Divergences between the fields could be attributable to different field ecological characters and to different grasshopper associations in the case of Gomphocerinae sub-family. This study provided data which may be useful in determining the optimum survey dates
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.
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