Geoff M. Gurr

Multi-function agricultural biodiversity: pest management and other benefits

Abstract This paper reviews two aspects of agricultural biodiversity. 1. The ways in which agricultural biodiversity may be increased to favour pest management are examined. At the simplest level, the structure within a monoculture may be altered by changing management practices to benefit natural enemies. At the other extreme, annual and perennial non-crop vegetation may be integrated with cropping, and biodiversity increased at the landscape level. 2. The existence of a hierarchy for the types of benefits of increased biodiversity is discussed. Vegetational diversity can lead to suppression of pests via ‘top-down’ enhancement of natural enemy populations and by resource concentration and other ‘bottom-up’ effects acting directly on pests. Whilst such low-input pest management mechanisms are attractive in their own right, other (non-pest management related) benefits may simultaneously apply. These range from short-term benefits in crop yield or quality, longer term benefits for sustainability of the farming system and, ultimately, broad societal benefits including aesthetics, recreation and the conservation of flora and fauna. Examples are given of such multi-function agricultural biodiversity. Diese Arbeit betrachtet zwei Aspekte landwirtschaftlicher Biodiversitat. 1. Die Moglichkeiten, landwirtschaftliche Biodiversitat zur Unterstutzung eines Schadlingsmanagements zu erhohen, werden untersucht. Im einfachsten Fall kann die Struktur innerhalb einer Monokultur durch veranderte Managementpraktiken geandert werden, so dass naturliche Gegenspieler davon profitieren. Im anderen Extrem konnen einjahrige und mehrjahrige Nichtnutzpflanzen in die Kultur integriert werden und die Biodiversitat steigt auf Landschaftsebene an. 2. Das Vorhandensein einer Hierarchie der verschiedenen Typen von Vorteilen einer erhohten Biodiversitat wird diskutiert. Pflanzliche Diversitat kann durch top-down Forderung von Populationen naturlicher Gegenspieler, durch Ressourcenkonzentration und durch andere bottom-up Effekte, die direkt auf Schadlinge einwirken, zu einer Unterdruckung von Schadlingen fuhren. Wahrend solche low-input Mechanismen des Schadlingsmanagements durch sich selbst attraktiv sind, ergeben sich gleichzeitig auch andere Vorteile, die nicht mit dem Schadlingsmanagement zusammenhangen. Diese reichen von kurzfristigen Vorteilen bei Ertrag oder Qualitat der Nutzpflanzen uber mittelfristige Vorteile bei der Nachhaltigkeit des Bewirtschaftungssystems bis hin zu breiten, gesellschaftlichen Vorteilen, welche asthetische Aspekte, Erholung und Schutz von Flora und Fauna einbeziehen. Beispiele fur solche multifunktionelle landwirtschaftliche Biodiversitat werden vorgestellt.

A heterozygous moth genome provides insights into herbivory and detoxification

How an insect evolves to become a successful herbivore is of profound biological and practical importance. Herbivores are often adapted to feed on a specific group of evolutionarily and biochemically related host plants, but the genetic and molecular bases for adaptation to plant defense compounds remain poorly understood. We report the first whole-genome sequence of a basal lepidopteran species, Plutella xylostella, which contains 18,071 protein-coding and 1,412 unique genes with an expansion of gene families associated with perception and the detoxification of plant defense compounds. A recent expansion of retrotransposons near detoxification-related genes and a wider system used in the metabolism of plant defense compounds are shown to also be involved in the development of insecticide resistance. This work shows the genetic and molecular bases for the evolutionary success of this worldwide herbivore and offers wider insights into insect adaptation to plant feeding, as well as opening avenues for more sustainable pest management.

Flowers in tri-trophic systems: mechanisms allowing selective exploitation by insect natural enemies for conservation biological control

Many insects have coevolved with certain angiosperm taxa to act as pollinators. However, the nectar and pollen from such flowers is also widely fed upon by other insects, including entomophagous species. Conservation biological control seeks to maximise the impact of these natural enemies on crop pests by enhancing availability of nectar and pollen‐rich plants in agroecosystems. A risk with this approach is that pests may also benefit from the food resource. We show that the flowers of some plants (viz., buckwheat, Fagopyron esculentum Moench and dill, Anethum graveolens L.), and the extrafloral nectaries of faba bean (Vicia faba L.) benefit both Copidosoma koehleri Blanchard (Hymenoptera: Encyrtidae) and its host, the potato pest, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae). In contrast, phacelia (Phacelia tanacetifolia Benth) and nasturtium (Tropaeoleum majus L.) benefited only the parasitoid. When adult moths of P. operculella were caged with flowers of phacelia or nasturtium, longevity of males and females, egg laying life, fecundity, average oviposition rate, and number of eggs in ovaries at death were no greater than in the control treatment with access to shoots without flowers plus water. All the foregoing measures were increased compared to the control when the moths were allowed access to dill, buckwheat or faba bean extrafloral nectaries. Such ‘selectivity’ has the potential to make the use of floral resources in conservation biological control more strategic. We present morphometric and observational evidence to illustrate how such mechanisms may operate.

Habitat manipulation and natural enemy efficiency: Implications for the control of pests

Publisher Summary The chapter examines the approach to a theoretical understanding of the ecological principles that determine the success of habitat manipulation. It tempers theory with some practical considerations relating to how habitat manipulation research may be undertaken and translated into practical guidance to farmers. The scale over which habitat manipulation can lead to a redistribution of natural enemies has important implications. If redistribution occurs on a relatively large scale, extending over many fields and farms, those growers practicing the technique are expected to derive benefit at the expense of more conservative neighbors, whose natural enemies may emigrate to where food plants (or other features such as overwintering habitat) are available. These natural enemies may then be disinclined to distribute away from such features and so concentrate their predation/parasitism on pests in adjacent crops. One of the greatest challenges faced by those seeking to implement habitat manipulation into Western agricultural systems is the tendency for these to employ heavy rates of pesticides. Although habitat manipulation may provide refugia for natural enemies from pesticide-treated areas, toxic residues left within the crop may repel or disrupt subsequent activity.

Multi-country evidence that crop diversification promotes ecological intensification of agriculture

Global food security requires increased crop productivity to meet escalating demand1–3. Current food production systems are heavily dependent on synthetic inputs that threaten the environment and human well-being2,4,5. Biodiversity, for instance, is key to the provision of ecosystem services such as pest control6,7, but is eroded in conventional agricultural systems. Yet the conservation and reinstatement of biodiversity is challenging5,8,9, and it remains unclear whether the promotion of biodiversity can reduce reliance on inputs without penalizing yields on a regional scale. Here we present results from multi-site field studies replicated in Thailand, China and Vietnam over a period of four years, in which we grew nectar-producing plants around rice fields, and monitored levels of pest infestation, insecticide use and yields. Compiling the data from all sites, we report that this inexpensive intervention significantly reduced populations of two key pests, reduced insecticide applications by 70%, increased grain yields by 5% and delivered an economic advantage of 7.5%. Additional field studies showed that predators and parasitoids of the main rice pests, together with detritivores, were more abundant in the presence of nectar-producing plants. We conclude that a simple diversification approach, in this case the growth of nectar-producing plants, can contribute to the ecological intensification of agricultural systems.

Ecological restoration of farmland: progress and prospects.

Sustainable agricultural practices in conjunction with ecological restoration methods can reduce the detrimental effects of agriculture. The Society for Ecological Restoration International has produced generic guidelines for conceiving, organizing, conducting and assessing ecological restoration projects. Additionally, there are now good conceptual frameworks, guidelines and practical methods for developing ecological restoration programmes that are based on sound ecological principles and supported by empirical evidence and modelling approaches. Restoration methods must also be technically achievable and socially acceptable and spread over a range of locations. It is important to reconcile differences between methods that favour conservation and those that favour economic returns, to ensure that conservation efforts are beneficial for both landowners and biodiversity. One option for this type of mutual benefit is the use of agri-environmental schemes to provide financial incentives to landholders in exchange for providing conservation services and other benefits. However, further work is required to define and measure the effectiveness of agri-environmental schemes. The broader potential for ecological restoration to improve the sustainability of agricultural production while conserving biodiversity in farmscapes and reducing external costs is high, but there is still much to learn, particularly for the most efficient use of agri-environmental schemes to change land use practice.

Mechanisms for flowering plants to benefit arthropod natural enemies of insect pests: Prospects for enhanced use in agriculture

Reduction of noncrop habitats, intensive use of pesticides and high levels of disturbance associated with intensive crop production simplify the farming landscape and bring about a sharp decline of biodiversity. This, in turn, weakens the biological control ecosystem service provided by arthropod natural enemies. Strategic use of flowering plants to enhance plant biodiversity in a well‐targeted manner can provide natural enemies with food sources and shelter to improve biological control and reduce dependence on chemical pesticides. This article reviews the nutritional value of various types of plant‐derived food for natural enemies, possible adverse effects on pest management, and the practical application of flowering plants in orchards, vegetables and field crops, agricultural systems where most research has taken place. Prospects for more effective use of flowering plants to maximize biological control of insect pests in agroecosystem are good but depend up on selection of optimal plant species based on information on the ecological mechanisms by which natural enemies are selectively favored over pest species.

Insect attraction to synthetic herbivore-induced plant volatile-treated field crops

1 Plants produce natural enemy‐attracting semiochemicals known as herbivore‐induced plant volatiles (HIPV) in response to herbivore damage. Deployment of synthetic HIPV in crops could enhance the biological control of pests. To test this, six HIPV [methyl salicylate (MeSA), methyl anthranilate (MeA), methyl jasmonate (MeJA), benzaldehyde (Be), cis‐3‐hexenyl acetate (HA), cis‐hexen‐1‐ol (He)] in three concentrations (0.5%, 1.0% and 2.0% v/v) mixed with a vegetable oil adjuvant, Synertrol® (Organic Crop Protectants Pty Ltd, Australia), were sprayed onto winegrape, broccoli and sweet corn plants. 2 The relative abundance of insects within treated plots was assessed with non‐attracting, transparent sticky traps at varying time intervals up to 22 days after spraying. 3 In the vineyard experiment, Trichogrammatidae responded to Be and MeA (0.5%) and Be (1.0%); Encyrtidae and Bethylidae responded to MeA (1.0%); Scelionidae responded to all compounds at 1.0% and 2.0%; and predatory insects responded to MeA. In sweet corn, parasitoids as a group and Encyrtidae responded to MeA (0.5%); Braconidae responded to all compounds at 0.5% and Synertrol‐only; thrips responded to all compounds at 0.5% and 1.0%; while all parasitoids responded to all compounds at 0.5% and 1.0% and Synertrol‐only. In broccoli, parasitoids as a group and Scelionidae responded to Be, HA, He and Synertrol‐only; Trichogrammatidae responded to Be (0.5%), He (0.5% and 1.0%), MeJA (1.0%) and MeSA (0.5%); and thrips responded to all compounds at to 0.5% and 1.0%. 4 Significant attraction of insects occurred up to 6 days after the HIPV application, suggesting that plants may have been induced to produce endogenous volatiles that attracted insects over an extended period. 5 The results obtained are discussed in relation to the potential utility of synthetic HIPV to enhance the biological control of pests.

DNA sequencing reveals the midgut microbiota of diamondback moth, Plutella xylostella (L.) and a possible relationship with insecticide resistance.

Background Insect midgut microbiota is important in host nutrition, development and immune response. Recent studies indicate possible links between insect gut microbiota and resistance to biological and chemical toxins. Studies of this phenomenon and symbionts in general have been hampered by difficulties in culture-based approach. In the present study, DNA sequencing was used to examine the midgut microbiota of diamondback moth (DBM), Plutella xylostella (L.), a destructive pest that attacks cruciferous crops worldwide. Its ability to develop resistance to many types of synthetic insecticide and even Bacillus thuringiensis toxins makes it an important species to study. Methodology/Principal Findings Bacteria of the DBM larval midgut in a susceptible and two insecticide (chlorpyrifos and fipronil) resistant lines were examined by Illumina sequencing sampled from an insect generation that was not exposed to insecticide. This revealed that more than 97% of the bacteria were from three orders: Enterobacteriales, Vibrionales and Lactobacillales. Both insecticide-resistant lines had more Lactobacillales and the much scarcer taxa Pseudomonadales and Xanthomonadales with fewer Enterobacteriales compared with the susceptible strain. Consistent with this, a second study observed an increase in the proportion of Lactobacillales in the midgut of DBM individuals from a generation treated with insecticides. Conclusions/Significance This is the first report of high-throughput DNA sequencing of the entire microbiota of DBM. It reveals differences related to inter- and intra-generational exposure to insecticides. Differences in the midgut microbiota among susceptible and insecticide-resistant lines are independent of insecticide exposure in the sampled generations. While this is consistent with the hypothesis that Lactobacillales or other scarcer taxa play a role in conferring DBM insecticide resistance, further studies are necessary to rule out other possibilities. Findings constitute the basis for future molecular work on the functions of insect midgut microbiota taxa and their possible role in conferring host resistance to toxins.

Tri-Trophic Insecticidal Effects of African Plants against Cabbage Pests

Botanical insecticides are increasingly attracting research attention as they offer novel modes of action that may provide effective control of pests that have already developed resistance to conventional insecticides. They potentially offer cost-effective pest control to smallholder farmers in developing countries if highly active extracts can be prepared simply from readily available plants. Field cage and open field experiments were conducted to evaluate the insecticidal potential of nine common Ghanaian plants: goat weed, Ageratum conyzoides (Asteraceae), Siam weed, Chromolaena odorata (Asteraceae), Cinderella weed, Synedrella nodiflora (Asteraceae), chili pepper, Capsicum frutescens (Solanaceae), tobacco, Nicotiana tabacum (Solanaceae) cassia, Cassia sophera (Leguminosae), physic nut, Jatropha curcas (Euphorbiaceae), castor oil plant, Ricinus communis (Euphorbiaceae) and basil, Ocimum gratissimum (Lamiaceae). In field cage experiments, simple detergent and water extracts of all botanical treatments gave control of cabbage aphid, Brevicoryne brassicae and diamondback moth, Plutella xylostella, equivalent to the synthetic insecticide Attack® (emamectin benzoate) and superior to water or detergent solution. In open field experiments in the major and minor rainy seasons using a sub-set of plant extracts (A. conyzoides, C. odorata, S. nodiflora, N. tabacum and R. communis), all controlled B. brassicae and P. xylostella more effectively than water control and comparably with or better than Attack®. Botanical and water control treatments were more benign to third trophic level predators than Attack®. Effects cascaded to the first trophic level with all botanical treatments giving cabbage head weights, comparable to Attack® in the minor season. In the major season, R. communis and A conyzoides treatment gave lower head yields than Attack® but the remaining botanicals were equivalent or superior to this synthetic insecticide. Simply-prepared extracts from readily-available Ghanaian plants give beneficial, tri-trophic benefits and merit further research as an inexpensive plant protection strategy for smallholder farmers in West Africa.