Winter Oilseed Rape Fields Research Articles

Mitigation of greenhouse gas emissions in the French winter oilseed rape in order to produce sustainable biodiesel

The objectives of the study were (1) to evaluate the possibility for the French winter oilseed rape to achieve the 50% greenhouse gas (GHG) saving criteria of the European Directive on the promotion of renewable energy (2009/28/EC), and (2) to investigate mitigation options. The agricultural GHG emissions were calculated with the actual seed yields and cultural operations of more than 5000 winter oilseed rape fields producing seeds collected by 27 grain storage companies (GSC), while the same values of GHG emissions for transport and biodiesel processing were used for all GSC. The study clearly showed that the 50% GHG saving criteria could not be achieved each year, by each of the grain storage company, without improvements of crop management. The possibility to reduce the GHG emissions by improving the efficiency of mineral N fertilization was demonstrated. Improving seed yields without increasing the amount of N application on the fields would also decrease GHG emissions. On the contrary, the application of organic matter appeared to be largely ineffective because of the way N2O emissions were calculated in the study (tier 1 method of International Panel on Climate Change).

Landscape structure affects activity density, body size and fecundity of Pardosa wolf spiders (Araneae: Lycosidae) in winter oilseed rape

In large parts of Europe Pardosa spp. (Lycosidae) are among the most abundant wolf spiders in arable fields and potentially important natural control agents of pests. We studied the influence of landscape factors on activity density, adult body size and fecundity of P. agrestis in 29 winter oilseed rape fields (Brassica napus L.) in Eastern Austria using pitfall traps. Landscape data were obtained for eight circular landscape sections around each field (radii 250-2000 m). Multivariate regression models were used to analyze the data. Activity density was highest when the length of strips of grassy road-sides in the surroundings was highest and distance to the next grassy fallow lowest. Body size was negatively related to activity density and to the length of road-side strips and positively to woody areas in the vicinity of the fields. Clutch size was unrelated to any of the landscape factors tested but was positively correlated with female body size. Woody areas and grassy fallow in the close vicinity of the fields had a positive influence on number of offspring per female and total number of offspring. These results indicate that various non-crop components in the landscape surrounding oilseed rape fields can specifically influence the activity density and fitness-related traits of P. agrestis in crops. The possible role of Pardosa spp. in natural pest control is discussed.

Pollen beetles are consumed by ground- and foliage-dwelling spiders in winter oilseed rape

Pollen beetles, Meligethes aeneus (Fabricius) (Coleoptera: Nitidulidae), are major pests in oilseed rape (OSR), Brassica napus L. (Brassicaceae). Among the predator species in the generalist predator complex present in OSR fields, wolf spiders (Araneae: Lycosidae) are found on the ground and cobweb spiders (Araneae: Theridiidae) build webs in the foliage. Here we study the incidence of predation of pollen beetles by these two spider groups using DNA-based molecular analysis. Wolf spiders of the genus Pardosa and the cobweb spider, Theridion impressum L. Koch, were each collected in three winter OSR fields over a period of about 3 weeks. Pollen beetle densities as well as the occurrence of predators and alternative prey were monitored. In total, 13.8% of the collected Pardosa spp. tested positive for pollen beetle DNA in the PCR analyses, whereas 51.7%T. impressum were positive. The likelihood of detecting pollen beetle DNA in the gut contents of both spider groups was positively related to pollen beetle larval density. The implications of these results for conservation biological control and future studies of food webs in OSR are discussed.

Mortality factors affecting the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), in its area of origin: A life table analysis

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a widely distributed invasive pest of cruciferous crops in North America. Control measures rely mostly on the application of insecticides but alternative control strategies such as classical biological control are under evaluation. To investigate the impact of parasitoids and other mortality factors on C. obstrictus populations, life table studies were conducted between 2005 and 2007 in 13 winter oilseed rape fields in Switzerland, part of the native range. Under field conditions females only realized approximately 50% of their potential lifetime fecundity, varying between 96 and 631 eggs per individual. Total generational mortality was higher than 99.6% in each year. Overwintering mortality of adults was the major population limiting factor, contributing approximately 50% to the overall generational mortality of C. obstrictus, whereas factors acting on the immature stages were responsible for the remaining 50%. Among the mortality factors of the immature stages, egg, larval and pupal mortality contributed 9–12%, 25–28% and 4–6% to the generational mortality, respectively. Larval ecto-parasitism on its own accounted for 7–15% of the generational mortality. Comparison of life table data presented here with that from North America will be invaluable for elucidating the mortality factors that regulate C. obstrictus populations in Europe, the region of origin.

Parasitism of stem weevils and pollen beetles in winter oilseed rape is differentially affected by crop management and landscape characteristics

We examined the influence of crop management (crop density, nitrogen fertilization level) and landscape parameters [areal proportion of oilseed rape (OSR), Brassica napus L. var. oleifera Metzg. (Brassicaceae), and proportions, lengths and distances of various non-crop habitats] on the parasitism of stem weevils (Ceutorhynchus spp.; Coleoptera: Curculionidae) and pollen beetles (Meligethes spp.; Coleoptera: Nitidulidae) by parasitic wasps (Hymenoptera: Ichneumonidae). Larvae of host insects were sampled in 29 winter OSR fields located in landscapes ranging from structurally simple to complex. Spatial scales of landscape effects were considered at eight radii (250–2,000 m) centered in the studied OSR fields. Stem weevil parasitism was unaffected by crop management variables but negatively related to roadside strip length at radius 250 m and grassy fallow area at a radius of 500 m. Pollen beetle parasitism was positively related to the crop density and to lengths of roadside strips and hedges within a radius of 250 m. Thousand kernel mass of OSR was positively related to pollen beetle parasitism but unrelated to stem weevil parasitism.

Ground-dwelling predators can affect within-field pest insect emergence in winter oilseed rape fields

We investigated, (i) whether the emergence from pupation of two coleopteran pest insect groups in oilseed rape (OSR, Brassica napus L.)—pollen beetles (Meligethes spp. F., Nitidulidae) and stem weevils (Ceutorhynchus pallidactylus Marsh and C. napi Gyll., Curculionidae)—is affected by the exclusion of ground-dwelling predatory arthropods, and (ii) the role for pest control of the widely abundant carabid beetles Anchomenus dorsalis Pontop. and Poecilus cupreus L. Densities of ground-dwelling arthropods were manipulated using enclosures; emerging pest adults were assessed using emergence traps. Where arthropods had been excluded, between two (June sampling) and tenfold (August sampling) more stem weevils emerged than where predators had free access. The addition of 25 adult A. dorsalis m−2 to formerly predator-free enclosures showed similar stem weevil emergence than plots where predators had free access; the addition of 25 adult P. cupreus m−2 did not reduce stem weevil emergence. In August, both A. dorsalis and P. cupreus additions marginally significantly reduced pollen beetle emergence.

Spider assemblages in winter oilseed rape affected by landscape and site factors

Spiders are an abundant and diverse group of generalist predators in arable fields. Knowledge on what landscape and site factors affect this group can be valuable for efforts to reduce biodiversity loss in agricultural landscapes and can have implications for natural pest control. We investigated the impact of landscape and site factors on epigeic spiders in 29 winter oilseed rape fields (Brassica napus, OSR) embedded in differently structured landscapes in an agricultural region east of Vienna (Austria). Landscape factors included proportions of non‐crop areas, woody areas and fallows, lengths of road‐side strips and hedges, and landscape diversity at different spatial scales (r=250–2000 m). Site factors included OSR stand density, soil index, soil cultivation intensity, nitrogen fertilisation level, OSR vegetation cover in late autumn, and insecticide applications. Data were analysed using regression, ordination, and variation partitioning. Different characteristics of spider assemblages responded to different landscape factors at different spatial scales. Observed species richness showed the strongest positive reponse to proportions of woody areas at rather small scale (radius 500 m), but the relation remained significant up to the 1250 m radius. Standardised species richness was positively related to non‐crop area at the smallest scale (radius 250 m). Activity density was positively related to length of road‐side strips with maximum effects at large scale (radius 1750 m) and non‐crop area (radius 750 m). Site characteristics (stand density, insecticide applications, and late autumn ground cover) and landscape factors (woody areas and fallows at radius 500 m) were similarly important for explaining species composition. We interpret the scale‐dependency of relations as the result of differences in dispersal power of the studied spider species. These results demonstrate the important, scale dependent influence of natural and semi‐natural habitats on spider assemblages in arable fields.