Investigation of ammonium lactate supplementation on fermentation end products and bacterial assimilation of nitrogen in dual-flow continuous culture.

Supplements investigated throughout the present study are produced by fermenting lactose that is present in whey to lactate, yielding products differing in ammonium relative to lactate concentrations and in physical form (liquid or dry). Trials 1 and 2 investigated Lacto-Whey (LW; Fermented Nutrition Corp., Luxemburg, WI) and GlucoBoost (GB; Fermented Nutrition Corp.), respectively, using dual-flow continuous culture systems (n = 4), each with a 4 × 4 Latin square design. A greater proportion of nonprotein nitrogen was present in GB than in LW. In trial 1, the treatment with LW was isonitrogenously dosed against soybean meal (SBM) as a control (no LW) and factorialized with either a wheat- or corn-based concentrate (55% inclusion rate, dry matter basis). We hypothesized that LW would increase propionate production and that the combination of +LW with wheat would increase bacterial assimilation of NH3-N into cellular N. No differences were observed for total volatile fatty acid (VFA) production per day. However, treatment × time interactions revealed that +LW increased lactate concentration at 0, 0.5, and 1 h and tended to increase molar percentage of propionate at 1 and 1.5 h postfeeding, documenting the immediate availability of lactate converted to propionate in the +LW treatments. The main effect of corn increased the proportion of bacterial N derived from NH3-N. Trial 2 was designed to investigate GB; isonitrogenous treatments included an SBM control, crystal GB, liquid GB (LGB), and LGB with yeast culture, which were dosed twice daily. We hypothesized that GB would increase propionate production and bacterial assimilation of NH3-N; the combination of LGB and yeast culture was expected to have a positive additive effect, yielding the greatest VFA production and bacterial NH3-N assimilation. No differences were observed for total VFA production; however, LGB decreased molar percentage of acetate and increased propionate and butyrate molar percentages. There were no differences in non-NH3-N flow or microbial N flow. Under the conditions of our studies, lactate in LW and GB was fermented extensively to propionate, and microbial protein synthesis in these treatments was comparable with that in SBM controls.

Response of Aphidius colemani to aphid sex pheromone varies depending on plant synergy and prior experience.

A critical stage in the success of a parasitoid is the ability to locate a host within its habitat. It is hypothesized that a series of olfactory cues may be involved in altering the parasitoid's movement patterns at this stage of foraging. This paper focuses specifically on host habitat location and host location and the olfactory stimuli necessary to mediate the transition between these stages. Firstly, we confirm the ability of the parasitoid Aphidius colemani to detect the aphid sex pheromone at an electrophysiological level. Following this we investigate the effect of the sex pheromone component (4aS,7S,7aR)-nepetalactone on the movement patterns of A. colemani and its retention within an area. The key findings of this work are that A. colemani is able to detect the sex pheromone components, that parasitoid retention is increased by a synergy of nepetalactone and other host-associated cues and that foraging patterns are augmented by the presence of nepetalactone or experience associated with nepetalactone.

Food security in a perfect storm: using the ecosystem services framework to increase understanding.

Achieving food security in a 'perfect storm' scenario is a grand challenge for society. Climate change and an expanding global population act in concert to make global food security even more complex and demanding. As achieving food security and the millennium development goal (MDG) to eradicate hunger influences the attainment of other MDGs, it is imperative that we offer solutions which are complementary and do not oppose one another. Sustainable intensification of agriculture has been proposed as a way to address hunger while also minimizing further environmental impact. However, the desire to raise productivity and yields has historically led to a degraded environment, reduced biodiversity and a reduction in ecosystem services (ES), with the greatest impacts affecting the poor. This paper proposes that the ES framework coupled with a policy response framework, for example Driver-Pressure-State-Impact-Response (DPSIR), can allow food security to be delivered alongside healthy ecosystems, which provide many other valuable services to humankind. Too often, agro-ecosystems have been considered as separate from other natural ecosystems and insufficient attention has been paid to the way in which services can flow to and from the agro-ecosystem to surrounding ecosystems. Highlighting recent research in a large multi-disciplinary project (ASSETS), we illustrate the ES approach to food security using a case study from the Zomba district of Malawi.

Olfactory selection of Plantago lanceolata by snails declines with seedling age.

BACKGROUND AND AIMS: Despite recent recognition that (1) plant-herbivore interactions during the establishment phase, (2) ontogenetic shifts in resource allocation and (3) herbivore response to plant volatile release are each pivotal to a comprehensive understanding of plant defence, no study has examined how herbivore olfactory response varies during seedling ontogeny. METHODS: Using a Y-tube olfactometer we examined snail (Helix aspersa) olfactory response to pellets derived from macerated Plantago lanceolata plants harvested at 1, 2, 3, 4, 5, 6 and 8 weeks of age to test the hypothesis that olfactory selection of plants by a generalist herbivore varies with plant age. Plant volatiles were collected for 10 min using solid-phase microextraction technique on 1- and 8-week-old P. lanceolata pellets and analysed by gas chromatography coupled with a mass spectrometer. KEY RESULTS: Selection of P. lanceolata was strongly negatively correlated with increasing age; pellets derived from 1-week-old seedlings were three times more likely to be selected as those from 8-week-old plants. Comparison of plant selection experiments with plant volatile profiles from GC/MS suggests that patterns of olfactory selection may be linked to ontogenetic shifts in concentrations of green leaf volatiles and ethanol (and its hydrolysis derivatives). CONCLUSIONS: Although confirmatory of predictions made by contemporary plant defence theory, this is the first study to elucidate a link between seedling age and olfactory selection by herbivores. As a consequence, this study provides a new perspective on the ontogenetic expression of seedling defence, and the role of seedling herbivores, particularly terrestrial molluscs, as selective agents in temperate plant communities.

The usability of digestate in organic farming.

As organic farming prohibits the use of synthetic fertilisers, animal slurries and manures must be used. Digestate offers an alternative to these and this study reports on three experiments conducted to determine its usability in terms of: (1) the effect on earthworm populations, (2) its fertilising effects on Italian Ryegrass and wild Creeping Thistle, and (3) the suppression effects digestate has on weed emergence. The results for digestate application to field plots were intermediate between slurry and no treatment for earthworm attraction and wild thistle suppression. In glasshouse trials it led to increased ryegrass growth compared with undigested slurry. Analysis showed that the digestate had improved nitrogen availability, leading to increased plant growth, but a reduced organic matter content compared with the slurry, leading to a positive though less beneficial impact on the earthworms. Digestate therefore provides a suitable fertiliser for organic farming. This suitability could be improved by drying or separation to increase the OM content making its properties closer to those of slurry whilst still retaining the higher content of plant available nitrogen.

A meta-analysis of the effects of feeding yeast culture produced by anaerobic fermentation of Saccharomyces cerevisiae on milk production of lactating dairy cows.

The purpose of this study was to use meta-analytic methods to estimate the effect of a commercially available yeast culture product on milk production and other production measures in lactating dairy cows using a meta-analysis of randomized controlled trials. Sixty-one research publications (published journal articles, published abstracts, and technical reports) were identified through a review of literature provided by the manufacturer and a search of published literature using 6 search engines. Thirty-six separate studies with 69 comparisons met the criteria for inclusion in the meta-analysis. The fixed-effect meta-analysis showed substantial heterogeneity for milk yield, energy-corrected milk, 3.5% fat-corrected milk, milk fat yield, and milk protein yield. Sub-group analysis of the data showed much less heterogeneity in peer-reviewed studies versus non-peer-reviewed abstracts and technical reports, and tended to show higher, but not significantly different, treatment effects. A random-effects meta-analysis showed estimated raw mean differences between treated and untreated cattle reported in peer-reviewed publications of 1.18 kg/d [95% confidence interval (CI): 0.55 to 1.81], 1.61 kg/d (95% CI: 0.92 to 2.29), and 1.65 kg/d (95% CI: 0.97 to 2.34) for milk yield, 3.5% fat-corrected milk, and energy-corrected milk, respectively. Milk fat yield and milk protein yield for peer-reviewed studies showed an increase in the raw mean difference of 0.06 kg/d (95% CI: 0.01 to 0.10) and 0.03 kg/d (95% CI: 0.00 to 0.05), respectively. Estimated raw mean dry matter intake of the peer-reviewed studies during early lactation (<70 d in milk) and not-early lactation were 0.62 kg/d (95% CI: 0.21 to 1.02) and a decrease of 0.78 kg/d (95% CI: -1.36 to -0.21), respectively. These findings provide strong evidence that this commercially available yeast culture product provides significant improvement in several important milk production outcomes as evaluated in production settings typical for commercial dairies in North America. Utilizing meta-analytic methods to study the complete breadth of information relating to a specific treatment by studying multiple overcomes of all eligible studies can reduce the uncertainty often seen in small individual studies designed without sufficient power to detect differences in treatments.

Fitness trade-off in peach-potato aphids (Myzus persicae) between insecticide resistance and vulnerability to parasitoid attack at several spatial scales.

Insecticide-resistant clones of the peach-potato aphid, Myzus persicae (Sulzer), have previously been shown to have a reduced response to aphid alarm pheromone compared to susceptible ones. The resulting vulnerability of susceptible and resistant aphids to attack by the primary endoparasitoid, Diaeretiella rapae (McIntosh), was investigated across three spatial scales. These scales ranged from aphids confined on individual leaves exposed to single female parasitoids, to aphids on groups of whole plants exposed to several parasitoids. In all experiments, significantly fewer aphids from insecticide-susceptible clones became parasitised compared to insecticide-resistant aphids. Investigations of aphid movement showed at the largest spatial scale that more susceptible aphids than resistant aphids moved from their inoculation leaves to other leaves on the same plant after exposure to parasitoids. The findings imply that parasitoids, and possibly other natural enemies, can influence the evolution and dynamics of insecticide resistance through pleiotropic effects of resistance genes on important behavioural traits.

Why plant volatile analysis needs bioinformatics--detecting signal from noise in increasingly complex profiles.

Plant volatile analysis may be the oldest form of what now is called plant "metabolomic" analysis. A wide array of volatile organic compounds (VOCs), such as alkanes, alcohols, isoprenoids, and esters, can be collected simultaneously from the plant headspace, either within the laboratory or in the field. Increasingly faster and more sensitive analysis techniques allow detection of an ever-growing number of compounds in decreasing concentrations. However, the myriads of data becoming available from such experiments do not automatically increase our ecological and evolutionary understanding of the roles these VOCs play in plant-insect interactions. Herbivores and parasitoids responding to changes in VOC emissions are able to perceive minute changes within a complex VOC background. Plants modified in genes involved in VOC synthesis may be valuable for the evaluation of changes in plant-animal interactions compared to tests with synthetic compounds, as they allow changes to be made within the context of a more complex profile. We argue that bioinformatics is an essential tool to integrate statistical analysis of plant VOC profiles with insect behavioural data. The implementation of statistical techniques such as multivariate analysis (MVA) and meta-analysis is of the utmost importance to interpreting changes in plant VOC mixtures. MVA focuses on differences in volatile patterns rather than in single compounds. Therefore, it more closely resembles the information processing in insects that base their behavioural decisions on differences in VOC profiles between plants. Meta-analysis of different datasets will reveal general patterns pertaining to the ecological role of VOC in plant-insect interactions. Successful implementation of bioinformatics in VOC research also includes the development of MVA that integrate time-resolved chemical and behavioural analyses, as well as databases that link plant VOCs to their effects on insects.

The influence of different nutrient levels on insect-induced plant volatiles in Bt and conventional oilseed rape plants.

Transgenic Bt (expressing the cry1Ac endotoxin gene) and conventional oilseed rape plants grown in different soils were used to study nutrient uptake and emission of volatiles after herbivore damage. All plants were greenhouse-grown in soils representing low-, medium- and high-nutrient levels. The concentrations of N, P, K, Mg and Zn were significantly affected by the transgene, while the main effect of soil type appeared in N, P, Ca, Mg, B, Mn and Zn concentrations in the plants. Plants with four to five leaves were infested with the third instar larvae of Bt-susceptible Plutella xylostella for 48 h, and samples of volatiles were collected and analysed. In the first experiment, the soil nutrient level had a significant effect on the emissions of (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, hexyl acetate, (E)-4,8-dimethyl-1,3,7-non-atriene (DMNT), beta-elemene, gamma-bisabolene, alpha-bisabolene and (E)-nerolidol. The induction of these volatiles was significantly higher in infested conventional plants grown at a high-soil nutrient level compared to infested conventional plants at a low-soil nutrient level. In the second experiment, the soil nutrient level had a significant effect on the emissions of (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate and beta-elemene and, again, this was significantly higher in infested conventional plants grown at high-soil nutrient levels in comparison with infested plants at a low-soil nutrient level. In both experiments, the transgene effect was significant on the emissions of DMNT and (E,E)-alpha-farnesene. The differences in emissions between the two separate experiments suggest that growth conditions (particularly daylength) and sampling procedure may affect the ratio of compounds detected in the emission blend, even though the response to herbivory, nutrient availability and the transgene were similar.

Mitigation of indirect environmental effects of GM crops.

Currently, the UK has no procedure for the approval of novel agricultural practices that is based on environmental risk management principles. Here, we make a first application of the 'bow-tie' risk management approach in agriculture, for assessment of land use changes, in a case study of the introduction of genetically modified herbicide tolerant (GMHT) sugar beet. There are agronomic and economic benefits, but indirect environmental harm from increased weed control is a hazard. The Farm Scale Evaluation (FSE) trials demonstrated reduced broad-leaved weed biomass and seed production at the field scale. The simplest mitigation measure is to leave a proportion of rows unsprayed in each GMHT crop field. Our calculations, based on FSE data, show that a maximum of 2% of field area left unsprayed is required to mitigate weed seed production and 4% to mitigate weed biomass production. Tilled margin effects could simply be mitigated by increasing the margin width from 0.5 to 1.5 m. Such changes are cheap and simple to implement in farming practices. This case study demonstrates the usefulness of the bow-tie risk management approach and the transparency with which hazards can be addressed. If adopted generally, it would help to enable agriculture to adopt new practices with due environmental precaution.

A Comparison of Semiochemically Mediated Interactions Involving Specialist and Generalist Brassica-feeding Aphids and the Braconid Parasitoid Diaeretiella rapae.

Diaeretiella rapae, a parasitoid that predominately specializes in the parasitism of Brassica-feeding aphids, attacks Lipaphis erysimi, a specialist feeding aphid of the Brassicaceae and other families in the Capparales, at a greater rate than the generalist-feeding aphid, Myzus persicae. In this study, we investigated the orientation behavior of D. rapae to the volatile chemicals produced when these two aphid species feed on turnip (Brassica rapa var rapifera). We showed no significant preference orientation behavior to either aphid/turnip complex over the other. Isothiocyanates are among the compounds emitted by plants of the Brassicaceae in response to insect feeding damage, including by aphids. We assessed parasitoid orientation behavior in response to laboratory-formulated isothiocyanates. We tested two formulations and discovered significant orientation toward 3-butenyl isothiocyanate. We also assessed plant and aphid glucosinolate content, and showed large levels of glucosinolate concentration in L. erysimi, whereas there was little change in plant content in response to aphid feeding. Our results suggest that during the process of host location, similar cues may be utilized for locating L. erysimi and M. persicae, whereas the acceptance of hosts and their suitability may involve aspects of nonvolatile aphid chemistry.

Laboratory studies of the effects of reduced prey choice caused by Bt plants on a predatory insect.

Crops transformed to express Bacillus thuringiensis (Bt) toxins can cause close to 100% mortality of certain target pest species. This study assessed the effect of target pest reduction on the predatory insect Chrysoperla carnea (Stephens) in the presence of alternative prey. Numbers of lacewings recovered from Bt oilseed rape (cultivar Oscar, event O52) did not differ significantly from numbers of lacewings recovered from conventional oilseed rape in cage experiments with the target pest Plutella xylostella (Linnaeus) and the non-target pest Myzus persicae (Sulzer) when aphid densities were high. However, significantly fewer lacewings were recovered from Bt plants as aphid densities were lowered. Lacewing weights were not affected by plant type.

Reduced response of insecticide-resistant aphids and attraction of parasitoids to aphid alarm pheromone; a potential fitness trade-off.

Response to the alarm pheromone, (E)-beta-farnesene, produced by many species of aphids, was assessed in laboratory bioassays using an aphid pest, Myzus persicae (Sulzer), and its primary endoparasitoid, Diaeretiella rapae (McIntosh). This was done in three separate studies, the first investigating responses of a large number of M. persicae clones carrying different combinations of metabolic (carboxylesterase) and target site (kdr) insecticide resistance mechanisms, and the other two investigating the responses of young virgin female adult parasitoids. In M. persicae, both insecticide resistance mechanisms were associated with reduced repellence suggesting that each has a pleiotropic effect on aphid behaviour. In contrast, D. rapae females were attracted to the alarm pheromone source. The implications of this apparent fitness trade-off for the evolution and dynamics of insecticide resistance, and the potential for using beneficial insects to combat resistance development are discussed.

Attack rate and success of the parasitoid Diaeretiella rapae on specialist and generalist feeding aphids.

Lipaphis erysimi (Kaltenbach) is a specialist crucifer feeding aphid and Myzus persicae (Sulzer) is a generalist feeding aphid. The foraging behavior of Diaeretiella rapae (McIntosh), a parasitoid with the ability to parasitize both of these species, was assessed using a series of attack rate and success bioassays, with turnip, Brassica rapa var rapifera, as the host plant. The attack rate of D. rapae was significantly greater on L. erysimi than on M. persicae when aphids were feeding on turnip leaf discs in Petri dishes, irrespective of the aphid species upon which the parasitoids were originally reared. Attack rate bioassays with leaf discs absent, using both satiated and starved aphids, revealed that background chemistry and internal aphid chemistry may have small effects on attack rate. Excision of D. rapae pupae from mummy cases and subsequent use of the fully developed adults in attack rate bioassays showed that cues received by D. rapae at the time of adult emergence provide cues that prime D. rapae to attack L. erysimi at a greater rate than M. persicae. However, the relative success of D. rapae on these two aphid species, in terms of the percentage of attacks resulting in a successful adult parasitoid, was not significantly different.

Plant-to-plant communication mediating in-flight orientation of Aphidius ervi.

Broad bean plants (Viciafaba) infested by the pea aphid, Acyrthosiphonpisum, play akey role in the in-flightorientation of the parasitoidAphidius ervi, by producing host-induced synomones (HIS). These volatiles are herbivore-specific and are systemically released from insect-free parts of an infested plant, suggesting the existence of an elicitor circulating throughout the plant. This study was designed to investigate whether the plant metabolic changes, leading to HIS biosynthesis and emission, can in some way trigger similar responses in neighboring plants through aerial and/or root communication. Uninfested broad bean plants maintained in the same pot together with plants infested by A. pisum became more attractive towards A. ervi females when tested in a wind-tunnel bioassay. This change was not observed when root contact was prevented among plants that had their aerial parts in close proximity, suggesting that an exudate from the roots of the infested plant may cause the induction of the attractive volatiles in uninfested plants. Broad bean plants grown hydroponically also produce pea aphid induced signals that attract A. ervi. When an intact (uninfested) plant was placed in a hydroponic solution previously used to grow a pea aphid-infested plant, it became attractive to parasitoids, while an intact plant placed in a solution previously used to grow an intact plant did not undergo such a change. These results indicate that plant-to-plant signaling in this tritrophic system may occur at the rhizosphere level and is most likely mediated by a systemically translocated elicitor.

Oviposition behaviour and host colony size discrimination in Episyrphus balteatus (Diptera: Syrphidae).

Three bioassays were used to examine the oviposition behaviour of the hoverfly, Episyrphus balteatus (Degeer) in which various stimuli purported to influence host assessment and choice were tested. Episyrphus balteatus failed to exhibit enhanced behavioural responses, in terms of approaches and landings, to artificial leaves with the highest numbers of aphids, suggesting that females are merely responding to the colour of the artificial leaves. A density-dependent oviposition response was reported in a second bioassay using whole bean plants, although there was an asymptotic relationship. Syrphid responses, which were measured by oviposition over a five-day period, were greatest towards those plants with the highest number of aphids. In a final series of trials, gravid female E. balteatus showed a behavioural preference for filter papers treated with the greatest honeydew concentrations (0.26 mg microl(-1) honeydew). More time was spent in the treated areas and syrphids demonstrated more proboscis and ovipositor extensions in these treatments. These bioassays provided an opportunity to isolate some of the individual components of decision-making by female E. balteatus during egg-laying behaviour. A greater understanding of natural enemy behaviour is essential before enhanced control of pest populations in the field can be established.

Population-scale laboratory studies of the effect of transgenic plants on nontarget insects.

Studies of the effects of insect-resistant transgenic plants on beneficial insects have, to date, concentrated mainly on either small-scale "worst case scenario" laboratory experiments or on field trials. We present a laboratory method using large population cages that represent an intermediate experimental scale, allowing the study of ecological and behavioural interactions between transgenic plants, pests and their natural enemies under more controlled conditions than is possible in the field. Previous studies have also concentrated on natural enemies of lepidopteran and coleopteran target pests. However, natural enemies of other pests, which are not controlled by the transgenic plants, are also potentially exposed to the transgene product when feeding on hosts. The reduction in the use of insecticides on transgenic crops could lead to increasing problems with such nontarget pests, normally controlled by sprays, especially if there are any negative effects of the transgenic plant on their natural enemies. This study tested two lines of insect-resistant transgenic oilseed rape (Brassica napus) for side-effects on the hymenopteran parasitoid Diaeretiella rapae and its aphid host, Myzus persicae. One transgenic line expressed the delta-endotoxin Cry1Ac from Bacillus thuringiensis (Bt) and a second expressed the proteinase inhibitor oryzacystatin I (OC-I) from rice. These transgenic plant lines were developed to provide resistance to lepidopteran and coleopteran pests, respectively. No detrimental effects of the transgenic oilseed rape lines on the ability of the parasitoid to control aphid populations were observed. Adult parasitoid emergence and sex ratio were also not consistently altered on the transgenic oilseed rape lines compared with the wild-type lines.