A climate-adapted push-pull system effectively controls fall armyworm, Spodoptera frugiperda (J E Smith), in maize in East Africa

Fall armyworm, Spodoptera frugiperda (J E Smith), an economically important pest native to tropical and subtropical America has recently invaded Africa, causing substantial damage to maize and other crops. We evaluated functionality of a companion cropping system, ‘climate-adapted push-pull’, developed for control of cereal stemborers in drier agro-ecologies, as an added tool for the management of fall armyworm. The technology comprises intercropping maize with drought-tolerant greenleaf desmodium, Desmodium intortum (Mill.) Urb., and planting Brachiaria cv Mulato II as a border crop around this intercrop. Protection to maize is provided by semiochemicals that are emitted by the intercrop that repel (push) stemborer moths while those released by the border crop attract (pull) them. 250 farmers who had adopted the technology in drier areas of Kenya, Uganda and Tanzania were randomly selected for the study during the long rainy season (March-August) of 2017. Each farmer had a set of two plots, a climate-adapted push–pull and a maize monocrop. Data were collected in each plot on the number of fall armyworm larvae on maize, percentage of maize plants damaged by the larvae and maize grain yields. Similarly, farmers' perceptions of the impact of the technology on the pest were assessed using a semi-structured questionnaire. Reductions of 82.7% in average number of larvae per plant and 86.7% in plant damage per plot were observed in climate-adapted push-pull compared to maize monocrop plots. Similarly, maize grain yields were significantly higher, 2.7 times, in the climate-adapted push-pull plots. Farmers rated the technology significantly superior in reducing fall armyworm infestation and plant damage rates. These results demonstrate that the technology is effective in controlling fall armyworm with concomitant maize grain yield increases, and represent the first documentation of a technology that can be immediately deployed for management of the pest in East Africa and beyond

Changes in concentration of isoflavonoids after cis-jasmone spraying in the leaves of two soybean cultivars.

cis-jasmone is a naturally-occurring compound in plants that activates direct and indirect defence in model and crop plants'". Exogenous application of cis-jasmone increases flavonoid concentrations in soybean and affects negatively Anticarsia gemmatalis weight gain. Here, foliar isoflavonoid concentrations were evaluated after cis-jasmone spraying on soybean cultivars BRS l34 and lAC 100, grown at Embrapa Soybean greenhouse facilities. At V) development stage, plants were sprayed with water, Tween 20 + water or cis-jasmone + tween 20 + water. For flavonoid extraction, leaves were collected 12, 24, 48, 96, and 120h after spraying, and immediately frozen in liquid nitrogen, ground in a mortar and extracted in MeOH 90% or EtOH 80% + HCI (0.001 M). Isoflavonoid concentrations were estimated by HPLC analysis. The extracts obtained from leaves of both genotypes of 24 h cis-jasmone treated plants presented higher quantities of daidzin, malonyl-daidzin, glycitin, malonyl-glycitin, glycitein and genistin, when compared to water and Tween 20 + water treated plants. Daidzein was present in hígh concentration, in both cultivars, 24 h and 48 h after cis-jasmone spraying, but no longer detected in samples collected 120 h after treatment. Coumesterol was detected, but only from samples collected 48 h after spraying. It is possible that such increases may be related to the decrease in daidzein concentration, considering that this compound is involved in coumesterol synthesis. Comparing solvent efficiencies, EtOH 80% + HCI (0.001 M) presented higher extraction capacity than MeOH 90%; coumestrol concentration in ethanolic extracts was approximately twice as high as in methanolic extracts. Our results indicated that cis-jasmone induces the production of non-volatile compounds in soybean such as isoflavonoids, and that EtOH 80% + HCI (O.OOIM)extraction is more efficient when compared to MeOH 90%

Insect oviposition in herbaceous plants attracts egg parasitoids despite fungal phytopathogen infection

Egg parasitoids are important natural enemies of several insect pests. The ability to kill the pest before it can inflict damage to the plant makes egg parasitoids ideal candidates for biological control. Several studies have shown that egg parasitoids exploit oviposition-induced plant volatiles (OIPVs) to locate host eggs laid on plant organs. Yet such studies have often overlooked that, in nature, plants frequently suffer concurrent attack by insect herbivores and phytopathogens. These dual attacks can modify the emission of induced plant volatiles, which may potentially interfere with the host location abilities of egg parasitoids. We investigated this research question using the following study organisms: the broad bean Vicia faba, the plant pathogen Stemphylium sp., the southern green stink bug Nezara viridula and its associated egg parasitoid Trissolcus basalis. We showed that T. basalis is able to exploit OPIVs in order to locate N. viridula egg masses even when V. faba plants were previously infected by Stemphylium sp. Chemical analyses indicate that the egg parasitoid ability to exploit OIPVs persists despite significant alterations of the volatile blends emitted by plants suffering multiple biotic stresses. This study highlights the importance of incorporating the complexity of multiple biotic stresses when studying parasitoid foraging behavior, in order to comprehend how to enhance the effectiveness of natural enemies in crop protection

Climate-adapted companion cropping increases agricultural productivity in East Africa

AbstractProduction of cereals, the main staple and cash crops for millions of farmers in sub-Saharan Africa (SSA) is severely constrained by parasitic striga weed Striga hermonthica, stemborers and poor soil fertility. A companion cropping system known as ‘push–pull’ overcomes these constraints while providing additional soil fertility and forage grass benefits to smallholder farmers. To ensure the technology's long-term sustainability in view of the current and further potential aridification as a consequence of climate change, drought-tolerant crops, Brachiaria cv mulato (border crop) and greenleaf desmodium (intercrop), have been identified and incorporated into a ‘climate-adapted push–pull’. The aims of the current study were to evaluate effectiveness of the new system (i) in integrated control of striga and stemborer pests and (ii) in improving maize grain yields, and to evaluate farmers’ perceptions of the technology to assess potential for further adoption. 395 farmers who had adopted the technology in drier areas of Kenya, Uganda and Tanzania were randomly selected for the study. Each farmer had a set of two plots, a climate-adapted push–pull and a maize monocrop. Seasonal data were collected in each plot on the number of emerged striga plants, percentage of maize plants damaged by stemborers, plant height and grain yields. Similarly, farmers’ perceptions of the benefits of the technology were assessed using a semi-structured questionnaire. There were highly significant reductions in striga and stemborer damage to maize plants in the climate-adapted push–pull compared to the maize monocrop plots: striga levels were 18 times lower and stemborer levels were 6 times lower. Similarly, maize plant height and grain yields were significantly higher. Mean yields were 2.5 times higher in companion planting plots. Farmers rated the climate-adapted push–pull significantly superior in reducing striga infestation and stemborer damage rates, and in improving soil fertility and maize grain yields. These results demonstrate that the technology is effective in controlling both weeds and pests with concomitant yield increases under farmers’ conditions. It thus provides an opportunity to improve food security, stimulate economic growth, and alleviate poverty in the region while making agriculture more resilient to climate change

Expression of lima bean terpene synthases in rice enhances recruitment of a beneficial enemy of a major rice pest

Volatile terpenoids play a key role in plant defence against herbivory by attracting parasitic wasps. We identified seven terpene synthase genes from lima bean, Phaseolus lunatus L. following treatment with either the elicitor alamethicin or spider mites, Tetranychus cinnabarinus. Four of the genes (Pltps2, Pltps3, Pltps4 and Pltps5) were up-regulated with their derived proteins phylogenetically clustered in the TPS-g subfamily and PlTPS3 positioned at the base of this cluster. Recombinant PlTPS3 was able to convert geranyl diphosphate and farnesyl diphosphate to linalool and (E)-nerolidol, the latter being precursor of the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT). Recombinant PlTPS4 showed a different substrate specificity and produced linalool and (E)-nerolidol, as well as (E,E)-geranyllinalool from geranylgeranyl diphosphate. Transgenic rice expressing Pltps3 emitted significantly more (S)-linalool and DMNT than wild-type plants, whereas transgenic rice expressing Pltps4 produced (S)-linalool, DMNT and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). In laboratory bioassays, female Cotesia chilonis, the natural enemy of the striped rice stemborer, Chilo suppressalis, were significantly attracted to the transgenic plants and their volatiles. We further confirmed this with synthetic blends mimicking natural rice volatile composition. Our study demonstrates that the transformation of rice to produce volatile terpenoids has the potential to enhance plant indirect defence through natural enemy recruitment

Behavioural and electrophysiological responses of female Anopheles gambiae mosquitoes to volatiles from a mango bait

Attractive Toxic Sugar Baits (ATSB) are used in a “lure-and-kill” approach for management of the malaria vector Anopheles gambiae, but the active chemicals were previously unknown. Here we collected volatiles from a mango, Mangifera indica, juice bait which is used in ATSBs in Tanzania and tested mosquito responses. In a Y-tube olfactometer, female mosquitoes were attracted to the mango volatiles collected 24–48 h, 48–72 h and 72–96 h after preparing the bait but volatiles collected at 96–120 h were no longer attractive. Volatile analysis revealed emission of 23 compounds in different chemical classes including alcohols, aldehydes, alkanes, benzenoids, monoterpenes, sesquiterpenes and oxygenated terpenes. Coupled GC-electroantennogram (GCEAG) recordings from the antennae of An. gambiae showed robust responses to 4 compounds: humulene, (E)-caryophyllene, terpinolene and myrcene. In olfactometer bioassays, mosquitoes were attracted to humulene and terpinolene. (E)-caryophyllene was marginally attractive while myrcene elicited an avoidance response with female mosquitoes. A blend of humulene, (E)- caryophyllene and terpinolene was highly attractive to females (P < 0.001) when tested against a solvent blank. Furthermore, there was no preference when this synthetic blend was offered as a choice against the natural sample. Our study has identified the key compounds from mango juice baits that attract An. gambiae and this information may help to improve the ATSBs currently used against malaria vectors

Plant Mediated Effects on Tritrophic Interactions in the Solanaceae-Hornworm System

Top-down pressure from parasites is thought to be a key driver in herbivore diet breath, but studies investigating the evolution of food plant shifts as a defense against natural enemies in the environment are still lacking in the literature. I examined how plants alter insect-enemy interactions for a specialist herbivore utilizing solanaceous food plants, Manduca sexta (the tobacco hornworm) and the parasitoid wasp, Cotesia congregata, as a model. In this study, I documented parasite infections in a field population of M. sexta, and then investigated from an eco-immunological perspective how plant toxins influence susceptibility to parasites in order to explain food plant choice. My research demonstrates that M. sexta exhibits a negative preference-performance relationship with plants in the Solanaceae. This is likely to gain protection from parasitoid attack via direct and indirect effects from plants on herbivore physiology. I show that herbivores are unpalatable and toxic to natural enemies when they consume more noxious host plants, but also provide a subsequent explanation for the adaptive value and maintenance of this interaction; specific plant secondary metabolites alter herbivore immune activity, where for M. sexta nicotine demonstrates immunotherapeutic properties by enhancing this insect’s phenoloxidase activity. I also examined phenotypic plasticity in caterpillar immune responses to nonlethal cues from natural enemies. Upon studying non-consumptive effects of natural enemies on M. sexta in the presence of C. congregata and the spined soldier bug, Podisus maculiventris, my work suggests that M. sexta generally accelerates their development in the presence of natural enemies at the cost of some immune defenses, implying a resource allocation tradeoff to physiological development and immunity. Placed within a community level context, M. sexta can mitigate the consumptive and nonconsumptive effects parasitoids have on this herbivore’s physiology by utilizing a food resource in parasite burdened habitats that increases direct resistance to parasites and also improves immune activity, even at the cost of development. Following this, I investigated the consequences of crop domestication on plant-insect-parasitoid interaction via changes in plant traits for direct defense against herbivores and altered plant volatile signaling of natural enemies. I demonstrated that domesticated chili peppers showed no loss of plant direct defenses to M. sexta compared to wild peppers and that crop peppers had increased attraction and efficiency of parasitoids. This highlighted the context-dependent nature domestication has on trophic interactions and emphasizes the need for dedicated investigation in each unique crop system

Ecological management of cereal stemborers in African smallholder agriculture through behavioural manipulation

1. Africa faces serious challenges in feeding its rapidly growing human population owing to the poor productivity of maize and sorghum, the most important staple crops formillions of smallholder farmers in the continent,with yields being among the lowest in the world. 2. A complex of lepidopterous stemborers attack cereals in Africa. However, their effective control is difficult, largely as a result of the cryptic and nocturnal habits of moths, and protection provided by host stem for immature pest stages.Moreover, current control measures are uneconomical and impractical for resource-poor farmers. 3. An ecological approach, based on companion planting, known as ‘push–pull’, provides effective management of these pests, and involves combined use of inter- and trap cropping systems where stemborers are attracted and trapped on trap plants with added economic value (‘pull’), and are driven away from the cereal crop by antagonistic intercrops (‘push’). 4. Novel defence strategies inducible by stemborer oviposition have recently been discovered, leading to the attraction of egg and larval parasitoids, in locally adapted maize lines but not in elite hybrids. We also established that landscape complexity did not improve the ecosystem service of biological control, but rather provided a disservice by acting as a ‘source’ of stemborer pests colonising the crop. 5. Here we review and provide new data on the direct and indirect effects of the push–pull approach on stemborers and their natural enemies, including the mechanisms involved, and highlight opportunities for exploiting intrinsic plant defences and natural ecosystem services in pest management in smallholder farming systems in Africa