Combination of generalist predators, Nesidiocoris tenuis and Macrolophus pygmaeus, with a companion plant, Sesamum indicum: What benefit for biological control of Tuta absoluta?

Tuta absoluta is one of the most damaging pests of tomato crops worldwide. Damage due to larvae may cause up to 100% loss of tomato production. Use of natural enemies to control the pest, notably predatory mirids such as Nesidiocoris tenuis and Macrolophus pygmaeus, is increasingly being promoted. However, considering the potential damage caused to tomatoes by these omnivorous predators in the absence of T. absoluta, an alternative solution could be required to reduce tomato damage and improve the predators' performance. The use of companion plants can be an innovative solution to cope with these issues. The present study aimed to determine the influence of companion plants and alternative preys on the predators' performance in controlling T. absoluta and protecting tomato plants. We evaluated the effect of predators (alone or combined) and a companion plant (sesame (Sesamum indicum)) on T. absoluta egg predation and crop damage caused by N. tenuis. The influence of an alternative prey (Ephestia kuehniella eggs) on the spatial distribution of predators was also evaluated by caging them in the prey presence or absence, either on tomato or sesame plants or on both. We found that the presence of sesame did not reduce the efficacy of N. tenuis or M. pygmaeus in consuming T. absoluta eggs; hatched egg proportion decreased when N. tenuis, M. pygmaeus, or both predators were present. More specifically, this proportion was more strongly reduced when both predators were combined. Sesame presence also reduced necrotic rings caused by N. tenuis on tomato plants. Nesidiocoris tenuis preferred sesame over tomato plants (except when food was provided only on the tomato plant) and the upper part of the plants, whereas M. pygmaeus preferred tomato to sesame plants (except when food was provided only on the sesame plant) and had no preference for a plant part. Combination of predators N. tenuis and M. pygmaeus allows for better coverage of cultivated plants in terms of occupation of different plant parts and better regulation of T. absoluta populations. Sesamum indicum is a potential companion plant that can be used to significantly reduce N. tenuis damage to tomatoes.

Effects of restricting movement between root and canopy populations of woolly apple aphid.

Movement of insect pests between spatially subdivided populations can allow them to recolonize areas where local extinction has occurred, increasing pest persistence. Populations of woolly apple aphid (Eriosoma lanigerum [Hausmann]; Hemiptera: Aphididae), a worldwide pest of apple (Malus domestica [Borkhausen]), occur both below- and aboveground. These spatially subdivided subpopulations encounter different abiotic conditions, natural enemies, and control tactics. Restricting movement between them might be an effective management tactic to decrease woolly apple aphid persistence and abundance. We examined this possibility in the field, using sticky barriers to restrict upward woolly apple aphid movement to tree canopies, and in the greenhouse, using mulches and sand amendments to restrict downward movement to roots. In the field, blocking aphid movement up tree trunks did not decrease the number of colonies in tree canopies. Instead, sticky-banded apple trees had higher aphid colony counts late in the study. Earwigs, which are woolly apple aphid predators, were excluded from tree canopies by sticky bands. In the greenhouse, fewer root galls (indicative of aphid feeding) occurred on trees in sandy potting media and on those with mulch (wood chips or paper slurry). Our results suggest that upward movement is less important than other factors that affect aboveground aerial woolly apple aphid population dynamics. In addition, apple orchards planted in sandier soils or with mulches may be partially protected from woolly apple aphid root feeding.

The effect of ozone fumigation on the biogenic volatile organic compounds (BVOCs) emitted from Brassica napus above- and below-ground.

The emissions of BVOCs from oilseed rape (Brassica napus), both when the plant is exposed to clean air and when it is fumigated with ozone at environmentally-relevant mixing ratios (ca. 135 ppbv), were measured under controlled laboratory conditions. Emissions of BVOCs were recorded from combined leaf and root chambers using a recently developed Selective Reagent Ionisation-Time of Flight-Mass Spectrometer (SRI-ToF-MS) enabling BVOC detection with high time and mass resolution, together with the ability to identify certain molecular functionality. Emissions of BVOCs from below-ground were found to be dominated by sulfur compounds including methanethiol, dimethyl disulfide and dimethyl sulfide, and these emissions did not change following fumigation of the plant with ozone. Emissions from above-ground plant organs exposed to clean air were dominated by methanol, monoterpenes, 4-oxopentanal and methanethiol. Ozone fumigation of the plants caused a rapid decrease in monoterpene and sesquiterpene concentrations in the leaf chamber and increased concentrations of ca. 20 oxygenated species, almost doubling the total carbon lost by the plant leaves as volatiles. The drop in sesquiterpenes concentrations was attributed to ozonolysis occurring to a major extent on the leaf surface. The drop in monoterpene concentrations was attributed to gas phase reactions with OH radicals deriving from ozonolysis reactions. As plant-emitted terpenoids have been shown to play a role in plant-plant and plant-insect signalling, the rapid loss of these species in the air surrounding the plants during photochemical pollution episodes may have a significant impact on plant-plant and plant-insect communications.

Nematicidal activity of nonacosane-10-ol and 23a-homostigmast-5-en-3ß-ol isolated from the roots of Fumaria parviflora (Fumariaceae).

Two bioactive nematicidal phytochemicals, viz., nonacosane-10-ol and 23a-homostigmast-5-en-3ß-ol, were isolated from the n-hexane fraction of the roots of Fumaria parviflora through activity-guided isolation. The structures of the compounds were elucidated using ¹³C and ¹H nuclear magnetic resonance. Activity of the two compounds against eggs and juveniles (J2s) of Meloidogyne incognita was evaluated in vitro at the concentrations of 50, 100, 150, and 200 µg mL⁻¹. Over 120 h of incubation, the cumulative percent mortality and hatch inhibition of both of the compounds tested ranged from 20 to 100% and from 15 to 95.0%, respectively. In pot trials with tomato cultivar Riogrande, the two compounds, applied as soil drenches at the concentrations of 100, 200, and 300 mg/kg, significantly decreased the nematodes and plant growth parameters. Nonacosane-10-ol and 23a-homostigmast-5-en-3ß-ol reduced the numbers of galls (42.6 and 60.3), galling index (1.6 and 2.8), females per gram of root (37.3 and 57.0), eggs per gram of root (991.3 and 1273.0), reproduction factor (Rf) (0.1 and 0.2), and fresh root weight (14.33 and 17.0 g) at 300 mg/kg concentration and increased fresh shoot weight (49.0 and 48.4 g), dry shoot weight (28.0 and 25.3 g), and plant height (53.5 and 49.6 cm), respectively. These compounds could provide new insight in the search for novel nematicides against M. incognita.

Aboveground-belowground herbivore interactions: a meta-analysis.

Research investigating interactions between aboveground (AG) and below-ground (BG) herbivores has been central to characterizing AG-BG linkages in terrestrial ecosystems, with many of these interactions forming the basis of complex food webs spanning the two subsystems. Despite the growing literature on the effects of AG and BG herbivores on each other, underlying patterns have been difficult to identify due to a high degree of context dependency. In this study, we present the first quantitative meta-analysis of AG and BG herbivore interactions. Previous global predictions, specifically that BG herbivores normally promoted AG herbivore performance and AG herbivores normally reduced BG herbivore performance, were not supported. Instead, the meta-analysis identified four factors that determined the outcome of AG-BG interactions. (1) Sequence of herbivore arrival on host plants was important, with BG herbivores promoting AG herbivore performance only when introduced to the plant simultaneously, whereas AG herbivores had negative effects on BG herbivores only when introduced first. (2) AG herbivores negatively affected BG herbivore survival but tended to increase population growth rates. (3) AG herbivores negatively affected BG herbivore performance on annual plants, but not on perennials, and these effects were observed more consistently in laboratory than field studies. (4) The type of herbivore was also important, with BG insect herbivores belonging to the order Diptera (i.e., true flies) having the strongest negative effects on AG herbivores. Coleoptera (i.e., beetles) species were the most widely investigated BG herbivores and had positive impacts on AG Homoptera (e.g., aphids), but negative effects on AG Hymenoptera (e.g., sawflies). The strongest negative outcomes for BG herbivores were seen when the AG herbivore was a Coleoptera species. We found no evidence for publication bias in AG-BG herbivore interaction literature and conclude that several biological and experimental factors are important for predicting the outcome of AG-BG herbivore interactions. The sequence of herbivore arrival on the host plant was among the most influential.

Root herbivore effects on aboveground multitrophic interactions: patterns, processes and mechanisms.

In terrestrial food webs, the study of multitrophic interactions traditionally has focused on organisms that share a common domain, mainly above ground. In the last two decades, it has become clear that to further understand multitrophic interactions, the barrier between the belowground and aboveground domains has to be crossed. Belowground organisms that are intimately associated with the roots of terrestrial plants can influence the levels of primary and secondary chemistry and biomass of aboveground plant parts. These changes, in turn, influence the growth, development, and survival of aboveground insect herbivores. The discovery that soil organisms, which are usually out of sight and out of mind, can affect plant-herbivore interactions aboveground raised the question if and how higher trophic level organisms, such as carnivores, could be influenced. At present, the study of above-belowground interactions is evolving from interactions between organisms directly associated with the plant roots and shoots (e.g., root feeders - plant - foliar herbivores) to interactions involving members of higher trophic levels (e.g., parasitoids), as well as non-herbivorous organisms (e.g., decomposers, symbiotic plant mutualists, and pollinators). This multitrophic approach linking above- and belowground food webs aims at addressing interactions between plants, herbivores, and carnivores in a more realistic community setting. The ultimate goal is to understand the ecology and evolution of species in communities and, ultimately how community interactions contribute to the functioning of terrestrial ecosystems. Here, we summarize studies on the effects of root feeders on aboveground insect herbivores and parasitoids and discuss if there are common trends. We discuss the mechanisms that have been reported to mediate these effects, from changes in concentrations of plant nutritional quality and secondary chemistry to defense signaling. Finally, we discuss how the traditional framework of fixed paired combinations of root- and shoot-related organisms feeding on a common plant can be transformed into a more dynamic and realistic framework that incorporates community variation in species, densities, space and time, in order to gain further insight in this exciting and rapidly developing field.

Entomopathogenic nematodes, root weevil larvae, and dynamic interactions among soil texture, plant growth, herbivory, and predation.

Greenhouse experiments were conducted to assess the influence of soil texture on the persistence, efficacy and plant protection ability of entomopathogenic nematodes (EPNs) applied to control larvae of the Diaprepes root weevil (DRW), Diaprepes abbreviatus, infesting potted citrus seedlings. Seedlings were grown in pots containing either coarse sand, fine sand, or sandy loam. Three DRW larvae were added to each of 80 pots of each soil type. 24 h later, 20 pots of each soil type that had received weevil larvae were inoculated with EPN infective juveniles (IJs) of one of the following species: Steinernema diaprepesi, Steinernema riobrave and Heterorhabditis indica. Pots of each soil without EPNs were established as controls with DRW and controls without DRWs. Subsequently, pots with larvae received three additional larvae monthly, and the experiment continued for 9 months. Plant root and top weights at the end of the experiment were affected by both soil (P≤0.0001) and nematodes (P≤0.0001), and nematode species protected plants differently in different soils (interaction P≤0.0001). Soil porosity was inversely related to plant damage by DRW, whether or not EPNs were present; and porosity was directly related to the level of plant protection by EPNs. Mortality of caged sentinel weevil larvae placed in pots near the end of the experiment was highest in pots treated with S. diaprepesi. In a second, similar experiment that included an additional undescribed steinernematid of the Steinernema glaseri-group, soil type affected root damage by DRW and root protection by EPNs in the same manner as in the first experiment. Final numbers of S. diaprepesi and Steinernema sp. as measured by real-time PCR were much greater than those of S. riobrave or H. indica in all soils. Across all treatments, the number of weevil larvae in soil at the end the experiment was inversely related to soil porosity. In all soils, fewer weevil larvae survived in soil treated with S. diaprepesi or Steinernema sp. than in controls with DRW or treatments with S. riobrave or H. indica. The results of these experiments support the hypothesis that EPNs provide greater protection of seedlings against DRW larvae in coarse textured soil than in finer textured soil. However, less vigorous growth of the control without DRW seedlings in the two finer textured soils suggests that unidentified factors that stressed seedlings in those soils also impaired the ability of seedlings to tolerate weevil herbivory.

Attack on all fronts: functional relationships between aerial and root parasitic plants and their woody hosts and consequences for ecosystems.

This review discusses how understanding of functional relationships between parasitic plants and their woody hosts have benefited from a range of approaches to their study. Gross comparisons of nutrient content between infected and uninfected hosts, or parts of hosts, have been widely used to infer basic differences or similarities between hosts and parasites. Coupling of nutrient information with additional evidence of key processes such as transpiration, respiration and photosynthesis has helped elucidate host-parasite relationships and, in some cases, the anatomical nature of their connection and even the physiology of plants in general. For example, detailed analysis of xylem sap from hosts and parasites has increased our understanding of the spatial and temporal movement of solutes within plants. Tracer experiments using natural abundance or enriched application of stable isotopes ((15)N, (13)C, (18)O) have helped us to understand the extent and form of heterotrophy, including the effect of the parasite on growth and functioning of the host (and its converse) as well as environmental effects on the parasite. Nutritional studies of woody hosts and parasites have provided clues to the distribution of parasitic plants and their roles in ecosystems. This review also provides assessment of several corollaries to the host-parasite association.

Exploration of the acarine fauna on coconut palm in Brazil with emphasis on Aceria guerreronis (Acari: Eriophyidae) and its natural enemies.

Coconut is an important crop in tropical and subtropical regions. Among the mites that infest coconut palms, Aceria guerreronis Keifer is economically the most important. We conducted surveys throughout the coconut growing areas of Brazil. Samples were taken from attached coconuts, leaflets, fallen coconuts and inflorescences of coconut palms in 112 localities aiming to determine the occurrence and the distribution of phytophagous mites, particularly A. guerreronis, and associated natural enemies. Aceria guerreronis was the most abundant phytophagous mite followed by Steneotarsonemus concavuscutum Lofego & Gondim Jr. and Steneotarsonemus furcatus De Leon (Tarsonemidae). Infestation by A. guerreronis was recorded in 87% of the visited localities. About 81% of all predatory mites belonged to the family Phytoseiidae, mainly represented by Neoseiulus paspalivorus De Leon, Neoseiulus baraki Athias-Henriot and Amblyseius largoensis Muma; 12% were Ascidae, mainly Proctolaelaps bickleyi Bram, Proctolaelaps sp nov and Lasioseius subterraneus Chant. Neoseiulus paspalivorus and N. baraki were the most abundant predators on attached coconuts. Ascidae were predominant on fallen coconuts, while A. largoensis was predominant on leaflets; no mites were found on branches of inflorescences. Leaflets harboured higher mite diversity than the attached coconuts. Mite diversity was the highest in the state Pará and on palms surrounded by seasonal forests and Amazonian rain-forests. Neoseiulus paspalivorus, N. baraki and P. bickleyi were identified as the most promising predators of A. guerreronis. Analyses of the influence of climatic factors revealed that dry ambient conditions favour the establishment of A. guerreronis. Neoseiulus paspalivorus and N. baraki have differing climatic requirements; the former being more abundant in warm and dry areas, the latter prevailing in moderately tempered and humid areas. We discuss the significance of our findings for natural and biological control of A. guerreronis.

Extrafloral nectaries in aspen (Populus tremuloides): heritable genetic variation and herbivore-induced expression.

BACKGROUND AND AIMS: A wide variety of plants produce extrafloral nectaries (EFNs) that are visited by predatory arthropods. But very few studies have investigated the relationship between plant genetic variation and EFNs. The presence of foliar EFNs is highly variable among different aspen (Populus tremuloides) genotypes and the EFNs are visited by parasitic wasps and predatory flies. The aim here was to determine the heritability of EFNs among aspen genotypes and age classes, possible trade-offs between direct and indirect defences, EFN induction following herbivory, and the relationship between EFNs and predatory insects. METHODS: EFN density was quantified among aspen genotypes in Wisconsin on trees of different ages and broad-sense heritability from common garden trees was calculated. EFNs were also quantified in natural aspen stands in Utah. From the common garden trees foliar defensive chemical levels were quantified to evaluate their relationship with EFN density. A defoliation experiment was performed to determine if EFNs can be induced in response to herbivory. Finally, predatory arthropod abundance among aspen trees was quantified to determine the relationship between arthropod abundance and EFNs. KEY RESULTS: Broad-sense heritability for expression (0.74-0.82) and induction (0.85) of EFNs was high. One-year-old trees had 20% greater EFN density than 4-year-old trees and more than 50% greater EFN density than > or =10-year-old trees. No trade-offs were found between foliar chemical concentrations and EFN density. Predatory fly abundance varied among aspen genotypes, but predatory arthropod abundance and average EFN density were not related. CONCLUSIONS: Aspen extrafloral nectaries are strongly genetically determined and have the potential to respond rapidly to evolutionary forces. The pattern of EFN expression among different age classes of trees appears to follow predictions of optimal defence theory. The relationship between EFNs and predators likely varies in relation to multiple temporal and environmental factors.

Plant defence signalling induced by biotic attacks.

Induced defence responses are elicited when plants are exposed to biotic stresses such as attack by herbivores or pathogens. In nature, plants are often subjected to attack by more than one organism, and defence responses elicited by one organism can thereby be modified by the presence of another. Below-ground attack can influence responses to above-ground attack and vice versa, due to systemic induction of defence metabolism. In some interactions defence is enhanced through prior attack by another organism, whereas in others there are conflicting signals. Recent research has shown how plants integrate these signals to coordinate defence by regulation of key metabolic pathways, although there is still much to be learnt.

[Main evolution lines of plant parasitic nematodes of the order Aphelenchida siddiqi, 1980].

Phylogenic models for each aphelenchid family and phylogeny of the order Aphelenchida as a whole were developed on the base of detailed comparative morphological and bionomical analysis of the order. Bionomical and morphological characters having a phylogenetic significance were selected. Classification proposed by Hunt, 1993 was used as the starting-point of the study. Life cycles and their evolution in Aphelenchida were analyzed on the base of phylogenetic trees. It is concluded, that aphelenchid ancestors combined mycophagy, plant parasitic, and partly predaceous feeding. Relations of the primitive Aphelenchida with their symbionts developed from the spots of the fungal organic matter decomposition in the "nema- tode-fungi" associations, followed by a transition to the temporary endoparasitic habit omitting ectoparasitism. With a complication of the nematodes' life cycles, the insect vector (detritophagous or pollinator) transformed into the real insect host of the parasitic nematode in the 2-host life cycle (with the plant and insect hosts) or in the obligate 1-host entomoparasitic life cycle of the aphelenchid nematodes. Specialization of the aphelenchid life cycles to insect vectors followed two main ways. In the first way, the resistant to unfavorable environmental conditions nematode juveniles, known already for the primitive aphelenchids transformed into dispersal juveniles, and later into parasitic juveniles. In the second evolution line the dispersal function were laid on inseminated but non-gravid (not egg-producing) females. Both above-mentioned trends of parasitic specialization were arisen independently in different phylogenetic lines of the Aphelenchida. In each line of the parasitic development in different nematode families, the highly specialized ectoparasites, as well as endoparasites on insects, were formed. In the evolution of life cycle of parasitic nematodes, a tendency to decrease the body size took place. The function of dispersion shifted to more junior juvenile stage (the first line of specialization), or body sizes of non-gravid females and males copulated with the latter become smaller (second specialization line, till the development of dwarf males and location of the males and small inseminated non-gravid females in the uterus of gravid nematode female). The hypothetic fundamental model of the parasitic cycles' specialization in the order Aphelenchida was developed, basing on the comparison of known life cycles in different phylogenetic lines within aphelenchid families. The conception of the geographic origin and historic dispersal of the order Aphelenchida was proposed. The origin of the superfamily Aphelenchoidoidea and order Aphelenchida as a whole probably took place in eastern areas of Gondwana (parts of which are recently Hindustan, Indo-Malaya, Australia and Antarctica), presumably in the Devonian period. When the Gondwana and Laurasia paleocontinents were joined into Pangea in Carbon period, aphelenchids dispersed in the Laurasian part of Pangea. Endemism of the advanced entomophilic ectoparasitic Acugutturidae indicates on the secondary hotbed of speciation in Caribbean area. Development of the anhydrobiotic adaptations in the Aphelenchida promoted their successful invasion in the cold regions of Holarctic. Another important adaptations was the transformation of the initially resistant nematode life cycle phase into the dispersal phases vectored by insects.

Larval densities and field hosts of Ceratapion basicorne (Coleoptera: Apionidae) and an illustrated key to the adults of Ceratapion spp. that feed on thistles in the eastern Mediterranean and Black Sea regions.

Many members of the tribe Cardueae are invasive weeds, including yellow starthistle (Centaurea solstitialis L.), one of the most important weeds in the Western United States. We examined the root crowns and stems of yellow starthistle and related plants growing in five countries (Armenia, Republic of Georgia, Greece, Russia, and Turkey) where yellow starthistle is native. In its native range, the root crowns and lower stems of yellow starthistle are frequently attacked by the internal feeding larvae of apionid weevils. We present illustrations and a key to the adults of the six apionid species that we reared from yellow starthistle and its relatives: Ceratapion basicorne (Illiger), C. carduorum (Kirby), C. gibbirostre (Gyllenhal), C. onopodri (Kirby), C. orientale (Gerstaecker), and C. penetrans (Germar). The only apionid we reared from yellow starthistle was C. basicorne. In Turkey, where we collected most intensively, 58% of the yellow starthistle at 20 sites had larvae of this weevil, and at sites where C. basicorne was present, there were an average of 1.8 immatures per yellow starthistle plant. This apionid is currently being further researched for its potential as a biological control agent for yellow starthistle.

Sources of variation in the interaction between three cereal aphids (Hemiptera: Aphididae) and wheat (Poaceae).

The relative contributions of host plant, herbivore species and clone to variation in the interaction between cereal aphids and wheat were investigated using five clones each of three species, Rhopalosiphum padi (Linnaeus), Sitobion avenae (Fabricius) and Schizaphis graminum (Rondani), on seedlings of two cultivars of Triticum aestivum L. and one cultivar of Triticum durum Desf. More individuals and biomass of R. padi than of the other two species were produced on seedlings. The three wheat cultivars lost similar amounts of biomass as a result of infestation by aphids, with the amount lost depending on aphid species: S. avenae caused the lowest loss in biomass. Variation in aphid biomass production was due mostly to differences among aphid species (70%), less to the interaction between wheat type and aphid species (7%), and least to aphid clone (1%). The specific impact of the aphids on the plants ranged from 1.7 to 3.7 mg of plant biomass lost per mg of aphid biomass gained, being lowest for R. padi and highest for S. graminum. Variation in plant biomass lost to herbivory was due mostly to unknown sources of error (95%), probably phenotypic differences among individual seedlings, with 3% due to aphid species and none attributable to aphid clone. For these aphid-plant interactions, differences among aphid clones within species contributed little to variation in aphid and plant productivity; therefore, a small sample of clones was adequate for quantifying the interactions. Furthermore, one clone of each species maintained in the laboratory for about 200 parthenogenetic generations was indistinguishable from clones collected recently from the field.

Lygus hesperus feeding and salivary gland extracts induce volatile emissions in plants.

Induction of plant volatiles by leaf-chewing caterpillars is well documented. However, there is much less information about volatile induction by insects with different feeding habits. We studied the induction of plant volatiles by a piercing-sucking insect, the western tarnished plant bug Lygus hesperus Knight. Adults of both genders and nymphs of Lygus induced the local emission of a blend of volatiles from both cotton and maize. Feeding by Lygus also induced the systemic emission of volatiles that was similar but less complex than the blend emitted at the site of feeding. Infestation by mated, mature adult females (>4 days old), but not by nymphs or mature males, caused detectable emission of alpha-pinene, myrcene. and (E)-beta-caryophyllene, compounds that are stored in the glands of cotton tissue. This indicated that damage to glands in the petiole and leaf by the female ovipositor, rather than feeding, contributed significantly to the emission of these volatiles. Girdling the plant stem to disrupt phloem transport markedly decreased the movement of 14C-labeled photosynthetic products to the apex of the plant, and this treatment also markedly reduced the amount of systemically induced volatiles caused by Lygus feeding. Lygus salivary gland extracts were capable of inducing emission of the same volatile blend as measured for plants infested by feeding insects or treated with volicitin. an elicitor isolated from caterpillar regurgitant. The results indicate that L. hesperus is capable of inducing the emission of plant volatiles and that induction is caused by an elicitor that is contained in the insect salivary gland.