Pia Parolin

Secondary plants used in biological control: A review

In crop systems, different types of plant or secondary crop may be grown together with the primary crop for pest management purposes. These additional plants – henceforth called secondary plants – may increase the efficiency and sustainability of biological control of pests by natural enemies. Such plants fall into several categories: companion, repellent, barrier, indicator, trap, insectary, and banker. Despite their effectiveness and accepted function in biological control, to date the full potential of secondary plants in integrated pest management has not been put to good use. This may be partly attributed to a lack of detailed knowledge of the way the secondary plant–crop systems operate, including the effects of the secondary plants on tritrophic interactions. The biggest constraint upon progress, however, has been confusion over definitions and terminology. In this paper, we review the knowledge of the currently employed plant categories and provide clear definitions.

Functional characteristics of secondary plants for increased pest management

Secondary plants may be added to a cropping system for the purpose of improving pest control. In a recent article (Parolin P, Bresch C, Brun R, Bout A, Boll R, Desneux N, Poncet C (2012) Secondary plants used in biological control: a review, International Journal of Pest Management 58, 91–100) we defined different categories of secondary plants used to enhance biological control: companion, repellent, barrier, indicator, trap, insectary, and banker plants are intentionally added to agricultural systems in order to improve pest management through either top-down or bottom-up processes. In the present paper, we focus on the functional characteristics of secondary plants and on the mechanisms which contribute to reducing the presence of pests. If we understand and integrate the effects that such plants have on pests and beneficial arthropods, together with the multitrophic interactions in which these organisms are involved, the application of pesticides in crop systems can be reduced and enhanced productivity in agro-ecosystems achieved. Here, we identify the main characteristics of, and the prerequisites for, plants which can enhance crop protection in agro-ecosystems.

Introducing the term 'Biocontrol Plants' for integrated pest management

Studies of interactions between crops, additional plants, pests and beneficial organisms already exist as well as studies of natural enemy preference, dispersal, and abundance. However, these studies focus on tri-trophic interactions from an arthropod point of view. We think that in order to optimize crop protection methods we need to understand the effects that plant structures have on the various arthropods and on subsequent tri-trophic interactions. Although studies and reviews describing the role of secondary plants in Integrated Pest Management (IPM) exist, to date a general term which encompasses all plants added to a cropping system with the aim of enhancing IPM strategies has yet to be formulated. Therefore, we suggest a new term, biocontrol plants, which we define as plants that are intentionally added to a crop system with the aim of enhancing crop productivity through pest attraction and/or pest regulation; a term that will promote the use of biocontrol services, and can ultimately lead to an increase in the sustainability of cropping systems.

Testing banker plants for biological control of mites on roses

We tested whether plant species used in a banker plant system influence the success of a biological control program with predatory mites. Banker plants (BP) may sustain a reproducing population of predators and provide long-term pest suppression. In an experiment lasting 12xa0weeks, we analyzed the responses of the predatory mite Amblyseius californicus and the pest mite Tetranychus urticae to eight species of potential BP with different morphological structures. Every BP was paired with a rose plant and infested with pest and predatory mites. The measured parameters were vitality and growth of the plants and numbers of predators, pests and their eggs. Reproduction and establishment of the pest and predatory mites differed among plant species as well as plant growth and vitality. Vitis riparia and Viburnum tinus were the most efficient BP in this combination of pest–predator species. Their presence resulted in best health of the rose crops, highest number of predatory mites and lowest number of pests. Both these BP possess domatia which may be responsible for the efficiency in hosting predatory mites. Overall, the species which fulfilled the requirements of a BP best was the local shrub V, tinus, which bore no pests and a very large number of predators and has a compact growth form suited for application in greenhouses. Although our study gives only evidence for an artificial system with a high BP:crop ratio, high numbers of introduced predators and short distances between plants, this study contributes to knowledge of BP systems and to improve the understanding of the criteria for the choice of local plant species to be used as BP for biological control in IPM.

Forest structure of artificial islands in the Tucuruí dam reservoir in northern Brazil: a test core-area model

Construction of hydroelectric dams in tropical regions has been contributing significantly to forest fragmentation. Alterations at edges of forest fragments impact plant communities that suffer increases in tree damage and dead, and decreases in seedling recruitment. This study aimed to test the core-area model in a fragmented landscape caused by construction of a hydroelectric power plant in the Brazilian Amazon. We studied variations in forest structure between the margin and interiors of 17 islands of 8-100 hectares in the Tucurui dam reservoir, in two plots (30 and >100m from the margin) per island. Mean tree density, basal area, seedling density and forest cover did not significantly differ between marginal and interior island plots. Also, no significant differences were found in liana density, dead tree or damage for margin and interior plots. The peculiar topographic conditions associated with the matrix habitat and shapes of the island seem to extend edge effects to the islands centers independently of the island size, giving the interior similar physical microclimatic conditions as at the edges. We propose a protocol for assessing the ecological impacts of edge effects in fragments of natural habitat surrounded by induced (artificial) edges. The protocol involves three steps: (1) identification of focal taxa of particular conservation or management interest, (2) measurement of an edge function that describes the response of these taxa to induced edges, and (3) use of a Core-Area Model to extrapolate edge function parameters to existing or novel situations.

Metabolite Profiling Reveals a Specific Response in Tomato to Predaceous Chrysoperla carnea Larvae and Herbivore(s)-Predator Interactions with the Generalist Pests Tetranychus urticae and Myzus persicae

The spider mite Tetranychus urticae Koch and the aphid Myzus persicae (Sulzer) both infest a number of economically significant crops, including tomato (Solanum lycopersicum). Although used for decades to control pests, the impact of green lacewing larvae Chrysoperla carnea (Stephens) on plant biochemistry was not investigated. Here, we used profiling methods and targeted analyses to explore the impact of the predator and herbivore(s)-predator interactions on tomato biochemistry. Each pest and pest-predator combination induced a characteristic metabolite signature in the leaf and the fruit thus, the plant exhibited a systemic response. The treatments had a stronger impact on non-volatile metabolites including abscisic acid and amino acids in the leaves in comparison with the fruits. In contrast, the various biotic factors had a greater impact on the carotenoids in the fruits. We identified volatiles such as myrcene and α-terpinene which were induced by pest-predator interactions but not by single species, and we demonstrated the involvement of the phytohormone abscisic acid in tritrophic interactions for the first time. More importantly, C. carnea larvae alone impacted the plant metabolome, but the predator did not appear to elicit particular defense pathways on its own. Since the presence of both C. carnea larvae and pest individuals elicited volatiles which were shown to contribute to plant defense, C. carnea larvae could therefore contribute to the reduction of pest infestation, not only by its preying activity, but also by priming responses to generalist herbivores such as T. urticae and M. persicae. On the other hand, the use of C. carnea larvae alone did not impact carotenoids thus, was not prejudicial to the fruit quality. The present piece of research highlights the specific impact of predator and tritrophic interactions with green lacewing larvae, spider mites, and aphids on different components of the tomato primary and secondary metabolism for the first time, and provides cues for further in-depth studies aiming to integrate entomological approaches and plant biochemistry.

Presence of Arthropod pests on eight species of banker plants in a greenhouse

En los cultivos de invernadero, a pesar de las precauciones, a veces es inevitable la instalacion espontanea de especies no deseadas de plagas de artropodos. Para el control biologico, se pueden emplear plantas secundarias que aumenten la proliferacion de los enemigos naturales de dichos artropodos plaga. Sin embargo, estas plantas adicionales tambien pueden atraer plagas que ataquen a los cultivos. El presente estudio tiene que ver con los datos producto del efecto secundario de un experimento a largo plazo que ponia a prueba ocho especies de plantas banco (PB) y su eficacia para la proteccion biologica contra el acaro Tetranychus urticae, empleando al acaro depredador Amblyseius californicus como enemigo natural. La intencion era encontrar las mejores especies de plantas locales adecuadas para ser utilizadas como PB, que mejoren la reproduccion y liberacion continua de los depredadores en un invernadero. A pesar de todas las precauciones, despues de un corto periodo hubo muchas especies exoticas en las PB en el invernadero. En el presente trabajo se documenta la instalacion espontanea de artropodos en ocho especies de BP en un plazo de tres meses, en un invernadero en el sur de Francia. Despues de 4-8 semanas desde el inicio del experimento, los primeros artropodos aparecieron espontaneamente en algunas de las plantas. Despues de tres meses se encontraron 6 especies adicionales de artropodos (moscas blancas Trialeurodes vaporariorum, afidos rosa Rhodobium porosum, moscas hiel Feltiella acarisuga, trips Frankliniella occidentalis, avispas parasitas Encarsia sp. y acaros depredadores Phytoseiulus persimilis). Diferentes especies de plantas atrajeron distintas especies de artropodos, de acuerdo con las propiedades quimicas especificas y los rasgos morfologicos, como hirsutismo foliar, superficies de cera, o la presencia de domatia, tipico de algunas especies de plantas. Estas no se reprodujeron en las plantas disponibles en la fase experimental y por lo tanto no representaron unxa0problema para los cultivos. Esto muestra que la presencia de los artropodos en un invernadero no afecta seriamente el cultivo, siempre que hay una cierta diversidad de especies de plantas presentes. Es posible que las plantas banco actuen como multiplicadores involuntarios para las plagas, pero para las especies aqui elegidas, no hay evidencia de que esto suceda. Nuestro estudio muestra que las plantas banco elegido, en las condiciones dadas, no contribuyeron a una multiplicacion de los artropodos plagas.