Jean Fitzgerald

Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review

Natural organic biomass burning creates black carbon which forms a considerable proportion of the soil’s organic carbon. Due to black carbon’s aromatic structure it is recalcitrant and has the potential for long-term carbon sequestration in soil. Soils within the Amazon-basin contain numerous sites where the ‘dark earth of the Indians’ (Terra preta de Indio, or Amazonian Dark Earths (ADE)) exist and are composed of variable quantities of highly stable organic black carbon waste (‘biochar’). The apparent high agronomic fertility of these sites, relative to tropical soils in general, has attracted interest. Biochars can be produced by ‘baking’ organic matter under low oxygen (‘pyrolysis’). The quantities of key mineral elements within these biochars can be directly related to the levels of these components in the feedstock prior to burning. Their incorporation in soils influences soil structure, texture, porosity, particle size distribution and density. The molecular structure of biochars shows a high degree of chemical and microbial stability. A key physical feature of most biochars is their highly porous structure and large surface area. This structure can provide refugia for beneficial soil micro-organisms such as mycorrhizae and bacteria, and influences the binding of important nutritive cations and anions. This binding can enhance the availability of macro-nutrients such as N and P. Other biochar soil changes include alkalisation of soil pH and increases in electrical conductivity (EC) and cation exchange capacity (CEC). Ammonium leaching has been shown to be reduced, along with N2O soil emissions. There may also be reductions in soil mechanical impedance. Terra preta soils contain a higher number of ‘operational taxonomic units’ and have highly distinctive microbial communities relative to neighbouring soils. The potential importance of biochar soil incorporation on mycorrhizal fungi has also been noted with biochar providing a physical niche devoid of fungal grazers. Improvements in soil field capacity have been recorded upon biochar additions. Evidence shows that bioavailability and plant uptake of key nutrients increases in response to biochar application, particularly when in the presence of added nutrients. Depending on the quantity of biochar added to soil significant improvements in plant productivity have been achieved, but these reports derive predominantly from studies in the tropics. As yet there is limited critical analysis of possible agricultural impacts of biochar application in temperate regions, nor on the likelihood of utilising such soils as long-term sites for carbon sequestration. This review aims to determine the extent to which inferences of experience mostly from tropical regions could be extrapolated to temperate soils and to suggest areas requiring study.

Biological control of strawberry tarsonemid mite Phytonemus pallidus and two-spotted spider mite Tetranychus urticae on strawberry in the UK using species of Neoseiulus (Amblyseius) (Acari: Phytoseiidae)

Two species of Neoseiulus, N. californicus and N. cucumeris, showed potential for biocontrol of phytophagous mites on strawberry. N. californicus controlled Tetranychus urticae on potted strawberry plants in a gauze-sided glasshouse at temperatures comparableto early summer in the UK (8–20°C). Both species of phytoseiid reducednumbers of the tarsonemid Phytonemus pallidus on potted strawberry plants under glasshouse conditions (15–23°C). In several experiments reductions in the range of 71–81% in numbers of tarsonemid active stages and eggs, compared to non-release plants, were obtained. The importance of establishing a suitable predator: prey ratio at an earlystage was demonstrated in an experiment where an initial ratio of 1 N. cucumeris: 10 P. pallidus gave a greater degree of controlthan 1:20 or 1:40.

Mite-management programmes based on organophosphate-resistant Typhlodromus pyri in UK apple orchards

Abstract In a 4-year trial in apple orchards, the effectiveness of the predatory mite Typhlodromus pyri as a biological control agent against the fruit tree red spider mite, Panonychus ulmi, and the apple rust mite, Aculus schlechtendali, was examined under different pesticide regimes. T. pyri survived insecticide programmes based on organophosphates or carbaryl and, in the third and fourth year of the OP programme and the fourth year of the carbaryl programme, regulated phytophagous mite populations to such an extent that no acaricides were necessary. In plots treated with a synthetic pyrethroid insecticide programme, few T. pyri were found and acaricide treatments were required in each year. A pest-management system that integrates this biological control of phytophagous mites with chemical treatment for other pests is described.

The effect of ant attendance on the success of rosy apple aphid populations, natural enemy abundance and apple damage in orchards

1 The rosy apple aphid, Dysaphis plantaginea, is the most serious pest of apple in Europe and, although conventionally controlled by insecticides, alternative management measures are being sought. Colonies of D. plantaginea are commonly attended by ants, yet the effects of this relationship have received little attention.

Control of the pear psyllid, Cacopsylla pyricola, in South East England by predators and pesticides

Abstract The pear psyllid, Cacopsylla pyricola, is an important pest on pear in England. In orchard trials in Kent, Anthocoris nemoralis usually prevented the psyllid from increasing to high densities, provided that the pesticides applied were not damaging to the predator. Only small numbers of A. nemoralis appeared to overwinter on the pear trees, and synthetic pyrethroid insecticides used at the ‘bud burst’ stage, before colonization by the predators, did not disrupt regulation of the psyllid by A. nemoralis, and were very effective at reducing psyllid numbers. These broad-spectrum pesticides were very damaging to predator populations if used later in the season, generally resulting in an upsurge of psyllid populations. Of the more selective materials tested for post-blossom use, amitraz was the most effective against psyllids, and was not damaging to predatory anthocorids. Diflubenzuron was also effective against psyllids, although slower acting, and caused only slight reduction in anthocorid density. Chemical control of scab and, when necessary, of mite, aphid and lepidopterous pests, can be compatible with the preservation of A. nemoralis; this is the basis of integrated pest management on pear.

Structure, ratios and patterns of release in the sex pheromone of an aphid, Dysaphis plantaginea.

SUMMARY Insect communication is primarily via chemicals. In Aphidinae aphids, the structure and ratio of iridoid (monoterpenoid) chemicals are known to be important components of the sex pheromone. However, for enhanced species specificity, it has been suggested that release of sex pheromone might be restricted to a narrow time period within the diel cycle. Here, we determine the structure, ratios and release patterns of iridoid chemicals produced by a serious global pest, the rosy apple aphid, Dysaphis plantaginea. Volatiles were collected from batches of oviparae (sexual females) and chemicals identified by gas chromatography, mass-spectrometry and microscale NMR spectroscopy. (1R,4aS,7S,7aR)-Nepetalactol and (4aS,7S,7aR)-nepetalactone were detected in a 3.7:1 ratio. To investigate timing of release, we constructed a sequential sampling device that allowed volatile chemicals to be captured hourly from 95 same-aged oviparae over 20 consecutive days. Release patterns of the two sex pheromone components show that D. plantaginea oviparae release high levels of the two components during photophase and low levels during scotophase. Release of the two components increased significantly during the first 3 h of photophase and thereafter remained at a high level until the onset of scotophase. The ratio of (1R,4aS,7S,7aR)-nepetalactol to (4aS,7S,7aR)-nepetalactone released did not change significantly between days two to 14 of the adult stadium, but from the 15th day onward there was a significant decrease in the relative amount of (1R,4aS,7S,7aR)-nepetalactol. Pheromone release was greatest on the eighth day of the adult stadium, with up to 8.4 ng of pheromone released per ovipara per hour. This is the first report on the full structural identification and ratios of volatile iridoid components collected from D. plantaginea oviparae and is also the most detailed temporal study on sex pheromone release from any aphid species. The lack of a temporally narrow and distinct period of very high sex pheromone release suggests that alternative mechanisms or factors for species recognition and isolation may be important. Findings are discussed broadly in relation to the biology of the aphid.

Interactions among phytophagous mites, and introduced and naturally occurring predatory mites, on strawberry in the UK.

In choice test experiments on strawberry leaf disc arenas the phytoseiid mites Neoseiulus californicus and N. cucumeris were more effective than Typhlodromus pyri as predators of the phytophagous mites Tetranychus urticae and Phytonemus pallidus. There were no preferences shown for either prey by any of these predators. In multiple predator leaf disc experiments both Phytoseiulus persimilis and N. cucumeris significantly reduced numbers of T. urticae eggs and active stages; this effect was seen when the two species were present alone or in combination with other predator species. Neoseiulus californicus was less effective at reducing T. urticae numbers, and T. pyri was not effective; no interaction between predator species was detected in these experiments. When T. urticae alone was present as prey on potted plants, P. persimilis and N. californicus were the only phytoseiids to significantly reduce T. urticae numbers. These two predator species provided effective control of T. urticae when P. pallidus was also present; however, none of the predators reduced numbers of P. pallidus. There were no significant negative interactions when different species of predators were present together on these potted plants. In field experiments, releases of both P. persimilis and N. cucumeris significantly reduced T. urticae numbers. However, there was a significant interaction between these predator species, leading to poorer control of T. urticae when both species were released together. These results show the importance of conducting predator/prey feeding tests at different spatial scales.

Dolichodial: a new aphid sex pheromone component?

The sex pheromones of many aphid species from the subfamily Aphididae comprise a mixture of the iridoids (cyclopentanoids) (1R,4aS,7S,7aR)-nepetalactol and (4aS,7S,7aR)-nepetalactone. In this paper, we investigate whether other chemicals, in addition to nepetalactol and nepetalactone, are released from Dysaphis plantaginea (rosy apple aphid) oviparae as part of their sex pheromone. Four compounds present in an air entrainment sample collected from D. plantaginea oviparae feeding on apple (Malus silvestris c.v. Braburn) elicited electrophysiological responses from male D. plantaginea. Active peaks were tentatively identified by gas chromatography (GC) coupled with mass spectrometry, with identification confirmed by peak enhancement with authentic compounds on GC columns of different polarities. The electroantennography-active chemicals were (1R,4aS,7S,7aR)-nepetalactol, (4aS,7S,7aR)-nepetalactone, (1S,2R,3S)-dolichodial, and phenylacetonitrile. (1S,2R,3S)-Dolichodial elicited a behavioral response from male D. plantaginea and naïve-mated female parasitoids, Aphidius ervi. This is the first report of electrophysiological and behavioral responses from any aphid morph to (1S,2R,3S)-dolichodial. Whether or not (1S,2R,3S)-dolichodial is a third component of the aphid sex pheromone is discussed.

Suppression of aphids on strawberry by augmentative releases of larvae of the lacewing Chrysoperla carnea (Stephens)

Abstract In laboratory feeding experiments, larvae of Chrysoperla carnea consumed up to 790 Chaetosiphon fragaefolii during their development. In gauzehouse experiments, releases of C. carnea larvae significantly reduced numbers of C. fragaefolii on potted strawberry plants. In open field experiments numbers of C. fragaefolii were significantly reduced at release rates of eight chrysopid larvae per plant, but a release experiment on larger strawberry plants grown under protection did not give a significant reduction in aphid numbers, even at a release rate of 25 larvae per plant.

Implications of alternative prey on biocontrol of pests by arthropod predators in strawberry

Abstract A range of naturally occurring predator species or commercially produced predators can be used in biocontrol strategies for pests. However, multiple potential prey species or other alternative food sources are often present for predatory insects at any one time. The availability of this ‘alternative’ prey may affect specific pest control by predators and thus influence the release rates of predators required for economic pest control. Strawberry aphid (Chaetosiphon fragaefolii), western flower thrips (Frankliniella occidentalis) and European tarnished plant bug (Lygus rugulipennis) are important and damaging pests in strawberry. In this study, laboratory, glasshouse and field experiments were undertaken to assess the effects of the availability of multiple prey species on biocontrol of specific pests. Results indicated that two of the predators tested showed preferences for prey species such that biocontrol of a particular pest was often less effective when a combination of pest species was present than would have been expected from results of experiments with single prey species alone. The experiments indicated that Orius laevigatus preferred C. fragaefolii to F. occidentalis or to L. rugulipennis, and preferred L. rugulipennis to F. occidentalis. Chrysoperla carnea was shown to prefer C. fragaefolii to L. rugulipennis, and C. fragaefolii over F. occidentalis. Therefore, it is important to consider the effects of alternative prey on suppression of pest species when deciding on management strategies and release rates of predators.