Helen Nicol

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.

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.

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.

Selection of nectar plants for use in ecological engineering to promote biological control of rice pests by the predatory bug, Cyrtorhinus lividipennis, (Heteroptera: Miridae).

Ecological engineering for pest management involves the identification of optimal forms of botanical diversity to incorporate into a farming system to suppress pests, by promoting their natural enemies. Whilst this approach has been extensively researched in many temperate crop systems, much less has been done for rice. This paper reports the influence of various plant species on the performance of a key natural enemy of rice planthopper pests, the predatory mirid bug, Cyrtorhinus lividipennis. Survival of adult males and females was increased by the presence of flowering Tagetes erecta, Trida procumbens, Emilia sonchifolia (Compositae), and Sesamum indicum (Pedaliaceae) compared with water or nil controls. All flower treatments resulted in increased consumption of brown plant hopper, Nilaparvata lugens, and for female C. lividipennis, S. indicum was the most favorable. A separate study with a wider range of plant species and varying densities of prey eggs showed that S. indicum most strongly promoted predation by C. lividipennis. Reflecting this, S. indicum gave a relatively high rate of prey search and low prey handling time. On this basis, S. indicum was selected for more detailed studies to check if its potential incorporation into the farming system would not inadvertently benefit Cnaphalocrocis medinalis and Marasmia patnalis, serious Lepidoptera pests of rice. Adult longevity and fecundity of both pests was comparable for S. indicum and water treatments and significantly lower than the honey solution treatment. Findings indicate that S. indicumis well suited for use as an ecological engineering plant in the margins of rice crops. Sesame indicum can be a valuable crop as well as providing benefits to C. lividipennis whilst denying benefit to key pests.

Influence of Botrytis cinerea (Helotiales: Sclerotiniaceae) infected leaves of Vitis vinifera (Vitales: Vitaceae) on the preference of Epiphyas postvittana (Lepidoptera: Tortricidae)

Herbivorous insects use sensory cues to choose their host plants for feeding and/or oviposition by assessing host quality. Olfactory, contact and visual cues of the host mediate such choices. The right‐host choice for oviposition by a lepidopteran is essential for the performance of its progeny. In natural conditions, plants are often and concurrently attacked by both herbivorous insects and pathogenic fungi. In such a three‐way relationship, the interaction between the plant and insect is usually influenced by the fungal population, and such an influence can be either mutualistic or antagonistic. In the present study, we tested the three‐way relationship using the system, Epiphyas postvittana–Vitis vinifera–Botrytis cinerea. We sought answers to the questions: (1) whether the females of E. postvittana prefer to oviposit on V. vinifera leaves infected by B. cinerea; and (2) whether the larvae of E. postvittana prefer to feed on V. vinifera leaves infected by B. cinerea. We found that the host‐seeking gravid females of E. postvittana ‘tested’ the infection status of the host plant using olfactory, visual, and tactile cues; in consequence, they laid significantly fewer eggs on the moderately (30–60%) and intensely (90–100%) infected leaves of V. vinifera. The neonate larvae preferred to feed on mildly (5–10%) and moderately (30–60%) infected leaves, as against the uninfected (control) leaves, and showed no preference for intensely (90–100%) infected leaves. External and internal examination of the larvae established that the larvae fed on B. cinerea‐infected leaf because viable conidia of B. cinerea occurred on the body surface and within the gut of the neonate larvae.

Effects of flowering groundcover vegetation on diversity and activity of wasps in a farm shelterbelt in temperate Australia

Significant worldwide interest in conservation biological control in agricultural systems currently exists but little information is available on the usefulness of this approach in farm forestry. In a field experiment conducted in a native vegetated shelterbelt in central-west New South Wales, we measured the diversity of wasps in plots comprising Eucalyptus blakelyi Maiden (Myrtaceae) trees with and without a groundcover of Lobularia maritima (L.) Desv. (Brassicaceae). Vacuum samples revealed a greater abundance and species richness of parasitic wasps in the plots comprising trees surrounded by the L. maritima groundcover. Cotesia sp. (Hymenoptera: Braconidae), Pteromalus sp. (Hymenoptera: Pteromalidae), Anagyrus sp. (Hymenoptera: Encyrtidae), Entedoninae sp. and Eulophidae sp. 1 (Hymenoptera: Eulophidae) were the most common taxa. These were more abundant also in the trees with the L. maritima groundcover. Ardozyga stratifera (Meyrick) (Lepidoptera: Gelechiidae) larvae, that were naturally infesting the E. blakelyi trees, were significantly more parasitized in the trees with the L. maritima groundcover. Results indicate that parasitic wasps associated with a native-tree shelterbelt in Australia were amenable to manipulation via groundcover vegetation.

Reducing the immigration of suspected leafhopper vectors and severity of Australian lucerne yellows disease

Three newly-sown lucerne stands in the mid Lachlan Valley region of New South Wales, Australia, were sampled, over 50 weeks, for Australian lucerne yellows disease symptom distribution and severity. Leafhopper populations were also monitored. Symptoms developed in all 3 stands within 32 weeks of sowing. There were statistically significant spatial differences in the density of symptomatic plants for 2 dates at this and another site. Two possible insect vectors, Austroagallia torrida and Batracomorphus angustatus were more numerous in some sections of crop margins at 2 sites. These 2 species and a third possible insect vector Orosius argentatus each had a statistically significant spatial and temporal correlation with symptomatic plant numbers for at least 1 site date. Two subsequent border treatment experiments evaluated the effect of crop-margin treatments on leafhopper movement into and from the stand. The second border treatment experiment examined also the treatment effect on Australian lucerne yellows disease symptomatic plant numbers. Treatment with insecticide or herbicide significantly reduced the overall movement of leafhoppers. In addition, the insecticide treatment lowered the incidence of disease expression in adjacent lucerne. Results suggest that there is scope for management of this plant disease by reducing immigration of leafhopper vectors into lucerne from non-crop vegetation.

Survey of fungi and nematodes associated with root and stolon diseases of white clover in the subtropical dairy region of Australia

A survey of 12 white clover-based dairy pastures on the north coast of New South Wales and south-eastern Queensland, Australia, detected 65 species of fungi and 6 nematode species. The fungi included species of Fusarium, Gliocladium, Codinaea, Alternaria, Colletotrichum, Drechslera, Rhizoctonia, Phoma, Pythium, Phytophthora, Penicillium, Rhizopus and Trichoderma from roots and stolons of white clover. Fungal rots of roots and stolons were most severe during the summer months (November and January samples), while root-knot symptoms caused by plant parasitic nematodes were more severe in June. Sedentary endoparasitic nematodes Meloidogyne trifoliophila, Heterodera trifolii and the ectoparasitic nematode Helicotylenchus dihystera were the numerically dominant nematodes in the region. Other nematode species, including Pratylenchus, Xiphinema and Tylenchorhynchus, were present at lower frequencies and principal component analysis indicated that these were less important as white clover pathogens. Meloidogyne trifoliophila was detected for the first time in Australia and was present at all sites. Many of the fungi and nematodes found are common pathogens of white clover. These pathogens are likely to be contributing to the poor seedling performance, growth and persistence of white clover typical in dairy pastures of the subtropical east coast of Australia.

Effect of the clover root-knot nematode (Meloidogyne trifoliophila) on growth of white clover

Root-infecting nematodes are common on white clover ( Trifolium repens ) in dairy pastures on the north coast of New South Wales and southeastern Queensland, Australia, where they are thought to contribute to poor growth and persistence. The nematode responsible for causing root-knot symptoms on white clover was identified as Meloidogyne trifoliophila , a species not previously recorded from Australia. M. trifoliophila failed to reproduce on any of the standard North Carolina hosts used to identify M. javanica , M. hapla , M. arenaria and M. incognita , but caused severe galling and exhibited a high rate of reproduction on white clover. PCR primers for these Meloidogyne species also failed to amplify DNA of M. trifoliophila . Identity was confirmed by morphological measurements and plant symptoms. In a glasshouse test, increasing initial nematode density within the range 0 to 10 000 per 500 ml pot led to reduced shoot and root growth, fewer nodules and more severe root-knot symptoms. A second pot test screened weed species as potential alternative hosts of M. trifoliophila . None of the eight grass species was galled but M. trifoliophila reproduced on two of the eight dicotyledon weeds, spear thistle ( Cirsium vulgare ) and pigweed ( Portulaca oleraceae ).

Populations of soil organisms under continuous set stocked and high intensity‐short duration rotational grazing practices in the central tablelands of New South Wales (Australia)

Abstract Grazing management practices modify soil structure, which, in turn, alters the behaviour and population dynamics of soil‐inhabiting organisms. Monitoring of changes in abundance and richness of soil organisms is vital in determining the sustainability of grazing regimes. In this paper, populations of soil organisms were compared—using abundance and population trends as an indicator of diversity—in two different grazing practices (a) conventional, set stocked (SS) grazing regime and (b) high intensity‐short duration (HI‐SD) grazing regime) and an ungrazed control (C). A thorough sampling of earthworms and arthropods, and an assay of soil microbial biomass and respiration was made in Spring 2004 (September‐November), after a pilot sampling of earthworms and arthropods in Autumn 2004 (March‐May). Earthworm numbers were found to be unaffected by grazing regimes, however, microarthropod abundance at 0–10 cm soil depth was significantly higher in soil of the HI‐SD grazing regime and in the ungrazed control, when compared with set stocking. Microbial biomass and respiration did not differ across treatments. Overall, our results indicate that arthropod abundance reflects the changes impacting on soil structure as a consequence of grazing practice. Evaluation of earthworm populations was not found to be useful in discriminating between the two grazing regimes, because the earthworm numbers were principally affected by rainfall.