Bernard Bodson

Aphidophagous guilds on nettle (Urtica dioica) strips close to fields of green pea, rape and wheat

The common nettle (Urtica dioica L.) is a perennial and cosmopolitan plant species and is known to be the source of food for a great diversity of insects. To understand the importance of the nettle in agro‐ecosystems, a field experiment was carried out in an experimental farm at Gembloux (Belgium) to study the effect of nettle margin strips on aphid and aphidophagous populations in close field crops, namely wheat (Triticum aestivum L.), green pea (Pisum sativum L.) and rape (Brassicae napus L.). The aphids and related beneficial populations were weekly assessed, from March to August 2005, by visual observations in two plots per field crop. A higher abundance of aphidophagous beneficials was collected in nettle strips when compared to the field crops. Particularly, the presence of predatory anthocorids, mirids and green lacewings was observed on nettle only. Nevertheless, the most abundant aphid predatory family, the Coccinellidae, was distributed in both environments, in nettle strips and in crop fields. The field margin supported a significantly higher density of Harmonia axyridis than the field crops. In contrast, the field crops, green pea particularly, supported a higher density of Coccinella septempunctata. The distribution of the aphidophagous species, mainly the ladybirds, was discussed in relation to the host plant and related aphid species and their potential effect on integrated pest management.

Fate of nitrogen fertilizer applied on two main arables crops, winter wheat ( Triticum aestivum ) and sugar beet ( Beta vulgaris ) in the loam region of Belgium

Since 1986, the fate of fertilizer N (NH4NO3 or NaNO3) applied in field conditions on two main arable crops, winter wheat (Triticum aestivum) and sugar beet (Beta vulgaris), has been studied using 15N. Up to a rate of 200 kg ha-1 of N, mean recovery of fertilizer by winter wheat was 70%, provided it had been split applied. Single application (with or without dicyandiamid) was less effective. For sugar beet, in 1990, 1991 and 1992, 40% of fertilizer N was found in the crop at harvest when NH4NO3 had been broadcast at 100 to 160 kg N ha-1 at sowing time. For the same N rate, recovery was 50% when row applied near the seeds and 60% for 80 kg N ha-1. For the two experimental crops, residual fertilizer N in soil was exclusively organic. It ranged from 15 to 30% of applied N and was located in the 30 cm upper layer. Losses were generally lower with winter wheat (12%) than with sugar beet (20–40%) and could be ascribed to volatilization and denitrification. Soil derived N taken up by the plant was site and year dependent.

Evolution and Distribution of Hydrolytic Enzyme Activities during Preharvest Sprouting of Wheat (Triticum aestivum) in the Field

To date, research on preharvest sprouted (PHS) wheat has mostly been conducted on kernels germinated under laboratory conditions, which differ widely from conditions in the field. To obtain detailed knowledge of the evolution of hydrolytic enzyme activities in PHS wheat (Triticum aestivum), a broad collection of samples from three varieties was obtained by harvesting before, at, and after maturity. Delaying harvest time coupled with periods of heavy rainfall caused sprouting in the kernels, observed as a drop in Falling Number and an increase in α-amylase activity. The appearance of α- and β-amylase, peptidase, and endoxylanase activity during field sprouting was independent from each other. Consequently, Falling Number could not be used to predict activity of other hydrolytic enzymes. When differentiating endogenous from kernel-associated microbial enzymes, results showed that α- and β-amylase and peptidase activity of PHS kernels were predominantly of endogenous origin, whereas endoxylanase activity was largely from microbial origin.

Targeted control of the saddle gall midge, Haplodiplosis marginata (von Roser) (Diptera: Cecidomyiidae), and the benefits of good control of this pest to winter wheat yield

BACKGROUND Since 2010 there has been a resurgence of the saddle gall midge, Haplodiplosis marginata (von Roser), in Belgium and several other European countries, with this pest sometimes causing severe damage in cereals. In 2012 and 2013, field trials were conducted in heavily infested fields to assess its impact on winter wheat crops and to determine efficient ways of dealing with severe infestations. RESULTS Crop exposure to H. marginata varied with the different protection methods tried. These methods included 1-4 successive applications of lambda-cyhalothrin. Yield losses were significant, reaching 6% in 2012 and as high as 15% in 2013, and these losses were linearly related to the number of galls on stems. CONCLUSION The trials showed that insecticide applications needed to be synchronised with H. marginata flight peaks and to target the egg hatching period. They also revealed that insecticides applied to coincide with the first flight could, in humid conditions, also reach the larvae close to the soil surface, prior to their pupation.

Associations of Wheat with Pea Can Reduce Aphid Infestations

Increasing plant diversity within crops can be beneficial for pest control. In this field study, the effects of two wheat and pea associations (mixed cropping and strip cropping) on aphid populations were compared with pure stands of both crops by observations on tillers and plants. Pea was more susceptible to infestations than wheat. As expected, the density of aphid colonies was significantly higher in pure stands during the main occurrence periods, compared with associations. Additionally, flying beneficials, such as not only aphidophagous adult ladybirds but also parasitoid, hoverfly and lacewing species that feed on aphids at the larval stage, were monitored using yellow pan traps. At specific times of the sampling season, ladybirds and hoverflies were significantly more abundant in the pure stand of pea and wheat, respectively, compared with associations. Few parasitoids and lacewings were trapped. This study showed that increasing plant diversity within crops by associating cultivated species can reduce aphid infestations, since host plants are more difficult to locate. However, additional methods are needed to attract more efficiently adult beneficials into wheat and pea associations.

Identification of 1-methyloctyl butanoate as the major sex pheromone component from females of the saddle gall midge, Haplodiplosis marginata (Diptera: Cecidomyiidae)

The saddle gall midge, Haplodiplosis marginata (von Roser) (Diptera: Cecidomyiidae), has undergone a resurgence recently as a pest of cereals in Belgium and other European countries. An effective monitoring tool of saddle gall midge flights is needed to understand the enigmatic population dynamics of this pest, and to design an integrated management strategy. Therefore, volatile compounds emitted by females (alkan-2-ols and alk-2-yl butanoates) were identified, and the chirality of the emitted esters was determined to be the R absolute configuration. In field-trapping experiments, racemic non-2-yl butanoate attracted substantial numbers of H.marginata males. Thus, this compound will be useful in baited traps for monitoring seasonal flight patterns, and improving integrated management of the saddle gall midge in agricultural systems.

Temporal Dynamics of Soil Microbial Communities below the Seedbed under Two Contrasting Tillage Regimes

Agricultural productivity relies on a wide range of ecosystem services provided by the soil biota. Plowing is a fundamental component of conventional farming, but long-term detrimental effects such as soil erosion and loss of soil organic matter have been recognized. Moving towards more sustainable management practices such as reduced tillage or crop residue retention can reduce these detrimental effects, but will also influence structure and function of the soil microbiota with direct consequences for the associated ecosystem services. Although there is increasing evidence that different tillage regimes alter the soil microbiome, we have a limited understanding of the temporal dynamics of these effects. Here, we used high-throughput sequencing of bacterial and fungal ribosomal markers to explore changes in soil microbial community structure under two contrasting tillage regimes (conventional and reduced tillage) either with or without crop residue retention. Soil samples were collected over the growing season of two crops (Vicia faba and Triticum aestivum) below the seedbed (15–20 cm). Tillage, crop and growing stage were significant determinants of microbial community structure, but the impact of tillage showed only moderate temporal dependency. Whereas the tillage effect on soil bacteria showed some temporal dependency and became less strong at later growing stages, the tillage effect on soil fungi was more consistent over time. Crop residue retention had only a minor influence on the community. Six years after the conversion from conventional to reduced tillage, soil moisture contents and nutrient levels were significantly lower under reduced than under conventional tillage. These changes in edaphic properties were related to specific shifts in microbial community structure. Notably, bacterial groups featuring copiotrophic lifestyles or potentially carrying the ability to degrade more recalcitrant compounds were favored under conventional tillage, whereas taxa featuring more oligotrophic lifestyles were more abundant under reduced tillage. Our study found that, under the specific edaphic and climatic context of central Belgium, different tillage regimes created different ecological niches that select for different microbial lifestyles with potential consequences for the ecosystem services provided to the plants and their environment.

Assessing and modeling economic and environmental impact of wheat nitrogen management in Belgium

Future progress in wheat yield will rely on identifying genotypes and management practices better adapted to the fluctuating environment. Nitrogen (N) fertilization is probably the most important practice impacting crop growth. However, the adverse environmental impacts of inappropriate N management (e.g., lixiviation) must be considered in the decision-making process. A formal decisional algorithm was developed to tactically optimize the economic and environmental N fertilization in wheat. Climatic uncertainty analysis was performed using stochastic weather time-series (LARS-WG). Crop growth was simulated using STICS model. Experiments were conducted to support the algorithm recommendations: winter wheat was sown between 2008 and 2014 in a classic loamy soil of the Hesbaye Region, Belgium (temperate climate). Results indicated that, most of the time, the third N fertilization applied at flag-leaf stage by farmers could be reduced. Environmental decision criterion is most of the time the limiting factor in comparison to the revenues expected by farmers. The economic and environmental impact of Nitrogen fertilization was evaluated.A complete and generic methodology for tactical N optimization is proposed.Climatic conditions occurring between sowing and flag leaf stage greatly impacts N optimization.Environment?× management interactions have to be considered when optimizing N.Environmental consideration is a more limiting factor than expected revenues for N optimization.

Yield variability linked to climate uncertainty and nitrogen fertilisation

At the parcel scale, crop models such as STICS are powerful tools to study the effects of variable inputs such as management practices (e.g. nitrogen (N) fertilisation). In combination with a weather generator, we built up a general methodology that allows studying the yield variability linked to climate uncertainty, in order to assess the best N practice. Our study highlighted that, applying the Belgian farmer current N practice (60-60-60 kg N/ha), the yield distribution was found to be very asymmetric with a skewness of -1.02 and a difference of 5% between the mean (10.5 t/ha) and the median (11.05 t/ha) of the distribution. This implies that, under such practice, the probability for farmers to achieve decent yields, in comparison to the mean of the distribution, was the highest.

Unusual Occurrence of Cocoons in Population of Haplodiplosis marginata (Diptera: Cecidomyiidae) in Belgium

Abstract The saddle gall midge, Haplodiplosis marginata (von Roser) (Diptera: Cecidomyiidae), is a phytophagous species that develops in saddle-shaped galls on stems of wheat Triticum vulgare , barley Hordeum sativum , rye Secale cereale , and some other species of Poaceae. Only one generation develops per year. Full-grown larvae leave galls and drop onto the soil where they remain up to the springtime of the following year. Larvae do not usually spin cocoons. However, formation of cocoons by larvae was observed in populations developing in western Europe: in England in 1954, in the Netherlands in the 1960s, and in Belgium in 2011. On the basis of our analysis, a part of the larval population forms cocoons as protection against unfavorable weather conditions, especially drought.