Response of the zoophytophagous predators Macrolophus pygmaeus and Nesidiocoris tenuis to volatiles of uninfested plants and to plants infested by prey or conspecifics

Knowledge about the orientation mechanisms used by two important predaceous mirids (Macrolophus pygmaeus Rambour and Nesidiocoris tenuis (Reuter)) in finding their prey (whitefly Bemisia tabaci (Gennadius) and the tomato borer Tuta absoluta (Meyrick)) is limited. In a Y-tube olfactometer, we tested the behavioral responses of naïve and experienced predators to uninfested plants, herbivore-induced plant volatiles (HIPVs) from plants infested with T. absoluta and/or B. tabaci, the sex pheromone of T. absoluta, and volatiles produced by plants injured by the predators. Nesidiocoris tenuis responds to volatiles produced by uninfested plants only after experience with the plant, whereas naïve and experienced M. pygmaeus show positive chemotaxis. Both predators are attracted to volatiles from prey-infested plants, and we provide the first evidence that experience affects this response in M. pygmaeus. Infestation of the same plant by both prey species elicited similar responses by the two predators as plants infested by either herbivore singly. Neither predator responded to sex pheromones of T. absoluta. Macrolophus pygmaeus avoided plants injured by conspecifics, while N. tenuis females were attracted by such plants. The implications of these results for augmentative biological control are discussed.     

Phloem-feeding herbivory on flowering melon plants enhances attraction of parasitoids by shifting floral to defensive volatiles

Emission of herbivore-induced plant volatiles (HIPVs) can differ according to the type of herbivory and the plant development stage, ultimately affecting recruitment of the natural enemy. Little is known about plant defenses induced at the flowering stage by phloem-feeding insects. We investigated the olfactory preference of Encarsia desantisi parasitoids and the chemical profile of flowering melon plants induced or not by the phloem-feeding of Bemisia tabaci whiteflies. In addition, we tested whether the parasitoids were attracted to synthetic defensive HIPVs, which mimicked whitefly-infested flowering melons. The parasitoids recognized volatiles from undamaged melons but preferred the scent of host-infested melons in olfactometry assays. Amounts of most individual volatiles did not differ between plant treatments; however, only whitefly-induced melons released methyl salicylate and tetradecane, compounds known to attract parasitoids. Interestingly, grouping volatiles by chemical classes revealed that whitefly-infested melon released larger amounts of monoterpenes and smaller amounts of benzenoids than undamaged melons, which might underlying the parasitoid attraction and indicate a possible trade-off between defensive and reproductive defenses at the melon flowering stage. Additionally, E. desantisi preferred the mix of synthetic and defensive HIPVs over hexane (control), opening a new avenue for further investigations in using olfactory lures for B. tabaci biological control. This study is the first report of induced defenses in melon plants and their mediation in a tritrophic interaction, as well as the first record of E. desantisi behavioral preference for HIPVs.     

A mixture of herbivore-induced plant volatiles from multiple host plant species enhances the attraction of a predatory bug under field-cage conditions

Plants respond to herbivore attack by emitting a blend of volatiles called herbivore-induced plant volatiles (HIPVs), which attract arthropod natural enemies. Under natural conditions and multiple cropping agriculture systems, natural enemies are thought to encounter a mixture of HIPVs emanating from multiple plant species. The effect of such a mixture of HIPVs on the responses of natural enemies under field conditions has not been explored. Our study assessed whether a mixture of HIPVs from multiple host plant species influenced predator responses in field-cage conditions. We investigated (1) foraging behaviors of a predatory bug, Orius strigicollis, on cotton bollworm (Helicoverpa armigera) larvae-infested multiple host plant species, and (2) the attractiveness of a mixture of reconstituted HIPVs from multiple plant species to O. strigicollis in outdoor cages. Significantly, greater numbers of predators were attracted to H. armigera-infested multiple plant species. The predators exterminated significantly greater numbers of H. armigera larvae with the multiple versus single plant species treatments. Significantly, greater numbers of O. strigicollis were captured on traps baited with the mixture of reconstituted HIPVs from multiple versus single plant species. The enhanced attractiveness of a mixture of HIPVs from multiple plant species to O. strigicollis might be the result of an additive effect of HIPVs from the three plant species when combined in a mixture.     

Experience of plant infestation by the omnivorous arthropod <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis> affects its subsequent responses to prey-infested plant volatiles

Nesidiocoris tenuis, an omnivorous arthropod, infests plants in either the absence or presence of prey arthropods. We studied whether plant-infestation experience of N. tenuis affected its subsequent prey-finding behavior. We used sesame plants and eggplants as food plants for N. tenuis, and common cutworm (CCW) (Spodoptera litura larvae) as prey. We focused on their olfactory response to CCW-infested sesame plants versus CCW-infested eggplants in a Y-tube olfactometer. When N. tenuis adults experienced the infestation of sesame plants for one day, they preferred volatiles from CCW-infested sesame plants to those from CCW-infested eggplants. By contrast, when N. tenuis experienced the infestation of eggplants for one day, they showed no difference in their preference between the two odor sources. When the duration of the infestation of plants was increased to four days, N. tenuis that had experienced sesame plants showed a reversed response: they preferred CCW-infested eggplant volatiles, while those that had infested eggplants again showed no difference in their preference. Next, we studied the olfactory preference of N. tenuis that had previously infested plants with moth (Ephestia kuehniella) eggs. We found that irrespective of plant species and of duration of experience (either one or four days), N. tenuis adults that had previously experienced one plant species showed a significant preference for volatiles from CCW-infested plants of the same species. The blends of the volatiles emitted from CCW-infested sesame plants and those from CCW-infested eggplants were qualitatively different. Possibility to control the olfactory response of N. tenuis to certain prey-infested plant volatiles by adjusting their feeding history is discussed.     

Responses of a predatory bug to a mixture of herbivore-induced plant volatiles from multiple plant species

The attractiveness of herbivore-induced plant volatiles (HIPVs) from a specific plant species to natural enemies has been well established. However, under natural conditions and polycultural agriculture systems, the interactions among trophic levels are thought to be more complex. For instance, complex mixtures of volatiles emitted from diverse host plant species infested by polyphagous herbivores might affect responses of natural enemies. In this study, we investigated whether a mixture of HIPVs emitted from herbivore-damaged multiple host plant species affect responses of a predatory bug. Therefore, we report (1) olfactory responses of the predatory bug (Orius strigicollis) to volatiles emitted from cotton bollworm (Helicoverpa armigera) first instar larvae-damaged multiple plant species (tomato, French bean and sweet corn), (2) chemical analyses of volatiles emitted from the three plant species exposed to different treatments and (3) olfactory responses of the predators to a reconstituted HIPV blend from multiple plant species based on chemical analyses. O. strigicollis significantly preferred volatiles emanating from H. armigera-damaged multiple plant species to volatiles emanating from a single plant species. In all the three plant species, H. armigera-damaged seedlings emitted significantly a greater amount of volatiles as well as a larger number of volatile compounds than an undamaged or a mechanically injured seedling. The predators preferred the reconstituted HIPVs from multiple plant species to the reconstituted HIPVs from a single plant species. Thus, the mixture of HIPVs from multiple plant species enhanced the attractiveness to the predators.     

What signals do herbivore-induced plant volatiles provide conspecific herbivores?

Herbivore-induced plant volatiles (HIPVs) have been opined as ‘indirect or direct defenses’ of plants and are extensively studied. In contrast, HIPVs may also indicate that plant defenses have been overcome by herbivores infesting the plant; however, studies on this aspect have so far received little attention. Using the interaction of Capsicum annum (Bell pepper) with its pest Scirtothrips dorsalis (Chilli thrips) as a model system, we studied the role of HIPVs in this selected insect–plant interaction. Multiple-choice olfactometer assays with headspace volatiles collected from different growth stages of un-infested C. annum plants represented by pre-flowering (PF), flowering (FL) and fruiting stages (FR) proved FR volatiles to be highly attractive to S. dorsalis. Further, FR plants were infested with S. dorsalis adults and HIPVs released by infested plants were collected and subjected to multiple-choice olfactometer bioassays. Thrips were significantly attracted to HIPVs than to headspace volatiles of un-infested FR plants or thrips body odour. Coupled GC-EAG with S. dorsalis and HIPVs or FR plant volatile revealed specific compounds that elicited an EAG response. Individual EAG-active compounds were less attractive to thrips, however, synthetic blends of EAG-active compounds at the ratio similar to headspace samples were found to be highly attractive. However, when given a choice between synthetic blends of HIPVs and FR, thrips were significantly attracted to synthetic blend of HIPVs. Our study provides empirical data on signals HIPVs may provide to conspecific herbivores and suggests that the role of HIPVs, mostly generalized as defense, may vary based on the interaction and must be studied closely to understand their ecological functions.     

Response of mirid predators to synthetic herbivore‐induced plant volatiles

Zoophytophagous plant bugs feed on plant tissue as a source of water and nutrients, besides feeding on prey. By phytophagy, mirid predators activate plant defense responses through different pathways, resulting, among others, in the release of herbivore‐induced plant volatiles (HIPVs). These compounds could repel herbivores and attract parasitoids and predators, and synthetic versions could potentially be used in biological control. Nevertheless, little is known about the influence of synthetic volatiles on mirid attraction. Using Y‐tube olfactometer trials, we evaluated the responses of Nesidiocoris tenuis (Reuter), Macrolophus pygmaeus (Rambur), and Dicyphus bolivari Lindberg (Hemiptera: Miridae), important natural enemies used to control various greenhouse pests, to 10 synthetic versions of HIPVs released from tomato (Solanum lycopersicum L., Solanaceae) plants induced by N. tenuis and M. pygmaeus. Nesidiocoris tenuis responded to five of the 10 HIPVs, whereas M. pygmaeus and D. bolivari responded to four of the 10 HIPVs. Two green leaf volatiles, (Z)‐3‐hexenyl propanoate and (Z)‐3‐hexenyl acetate, and the ester methyl salicylate (MeSA) were attractive to all three mirid predator species. Our results demonstrate that the volatiles released by tomato plants activated by N. tenuis and M. pygmaeus phytophagy are attractive to their conspecifics and also to D. bolivari. Further studies should evaluate the potential of these compounds to attract predatory mirids in the field.     

An omnivorous arthropod, <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis>, induces gender-specific plant volatiles to which conspecific males and females respond differently

Nesidiocoris tenuis Reuter (Heteroptera: Miridae) is an omnivorous mirid bug that preys on diverse generalist herbivorous arthropods. N. tenuis adults are attracted to volatiles from plants induced by their prey, such as tobacco cutworms (CCW) (Spodoptera litura larvae) and two-spotted spider mites (Tetranychus urticae). N. tenuis adults also induce volatiles when they infest plants. In this study, we focused on olfactory responses of N. tenuis males and females to volatiles from eggplants and sesame plants induced by conspecifics of the same or different gender by using a Y-tube olfactometer. Males were attracted to volatiles from plants of both species induced by either males or females. The male preference was biased to volatiles from plants of both species induced by females, probably because the biased response would facilitate their mate-finding. Females were attracted only to volatiles from plants of both species induced by females. Mating occurs multiple times in this species. Thus, the responses would indirectly affect mating of males and females. Slight but significant qualitative and quantitative differences were detected between the volatiles of plants of both species induced by N. tenuis females and those of the plants induced by conspecific males. N. tenuis might use such differences in their gender-specific responses.     

Invasive insect herbivores as disrupters of chemically-mediated tritrophic interactions: effects of herbivore density and parasitoid learning

Invasive insect herbivores have the potential to interfere with native multitrophic interactions by affecting the chemical cues emitted by plants and disrupting the attraction of natural enemies mediated by herbivore-induced plant volatiles (HIPVs). In a previous study, we found that the presence of the exotic herbivore Spodoptera littoralis on Brassica rapa plants infested by the native herbivore Pieris brassicae makes these dually-infested plants unattractive to the main parasitoid of P. brassicae, the braconid wasp Cotesia glomerata. Here we show that this interference by S. littoralis is strongly dependent on the relative densities of the two herbivores. Parasitoids were only deterred by dually-infested plants when there were more S. littoralis larvae than P. brassicae larvae on a plant. Furthermore, the blend of HIPVs emitted by dually-infested plants differed the most from HIPVs emitted by Pieris-infested plants when S. littoralis density exceeded P. brassicae density. We further found that associative learning by the parasitoid affected its preferences: attraction to dually-infested plants increased after parasitoids were presented a P. brassicae caterpillar (rewarding experience) in presence of the odor of a dually-infested plant, but not when presented a S. littoralis caterpillar (non-rewarding experience). A non-rewarding experience prior to the bioassays resulted in a general decrease in parasitoid motivation to respond to plant odors. We conclude that herbivore density and associative learning may play an important role in the foraging behavior of natural enemies in communities, and such effects should not be overlooked when investigating the ecological impact of exotic species on native food webs.     

The toxic effect of greenhouse insecticides on the predatory bugs <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis> Reuter and <Emphasis Type="Italic">Macrolophus pygmaeus</Emphasis> H.-S. (Heteroptera,Miridae)

The study reports the results of toxicity tests for several insecticides which are allowed to be used on greenhouse plants (Admiral, Mospilan, Spintor, and BT), as applied to different developmental stages of the predatory bugs Nesidiocoris tenuis Reuter and Macrolophus pygmaeus H.-S. (family Miridae), which feed on whiteflies, aphids, thrips, and spider mites. The juvenoid Admiral is found to be the least toxic to these species, whereas the spinosyn Spintor is most toxic. The neonicotinoid Mospilan and a microbiological insecticide BT are intermediate in their effects. The timing of application of insecticides most favorable to the predatory mirids when both pest management methods are used together is discussed.     

Humic Fertilizer and Vermicompost Applied to the Soil Can Positively Affect Population Growth Parameters of <Emphasis Type="Italic">Trichogramma brassicae</Emphasis> (Hymenoptera: Trichogrammatidae) on Eggs of <Emphasis Type="Italic">Tuta absoluta</Emphasis> (Lepidoptera: Gelechiidae)

The tomato leaf miner, Tuta absoluta (Meyrick), is a devastating pest of tomato worldwide. One of the control measures of T. absoluta is the use of biological control agents, such as Trichogramma wasps. Interactions between natural enemies and insect pests may be affected by application of fertilizers, because changes in plant quality through the fertilizer application may therefore affect herbivore characteristics and suitability of them to parasitism. Laboratory tests were carried out to evaluate the life table parameters of Trichogramma brassicae Bezdenko on T. absoluta eggs reared on tomato plants treated either with vermicompost (40%), humic fertilizer (2 g/kg soil), or control (suitable mixture of field soil and sand). Population growth parameters of T. brassicae were affected by fertilizer treatments. Significant differences were found for immature life period and total fecundity of T. brassicae on the treatments. Differences of intrinsic rate of natural increase (r _m), finite rate of increase (λ), net reproductive rate (R ₀), mean generation time (T), and doubling time (DT) of T. brassicae among treatments were also significant. The lowest values of r _m, λ, and R ₀ were recorded for T. brassicae developed on T. absoluta eggs on control treatment, whereas the highest values of these parameters were observed on 2 g/kg humic fertilizer. Furthermore, T. brassicae had the shortest T and DT values on 2 g/kg humic fertilizer and 40% vermicompost treatments. Our results showed that application of humic fertilizer and vermicompost could positively affect population growth parameters of T. brassicae on eggs of T. absoluta fed on tomato plants.     

Host Plant Perception and Selection in the Sibling Species <Emphasis Type="Italic">Macrolophus melanotoma</Emphasis> and <Emphasis Type="Italic">Macrolophus pygmaeus</Emphasis> (Hemiptera: Miridae)

The electroantennogram responses (EAGs) of Macrolophus melanotoma and Macrolophus pygmaeus (Hemiptera: Miridae) exposed to volatile compounds (VOCs) of host and non-host plants were compared. The VOCs were identified by gas chromatography. Hosts and non-hosts eliciting similar EAGs were tested in olfactory assays against plants without a significant EAGs for the two Macrolophus species. No characteristic VOC profile was found for hosts and non-hosts. Terpenes predominated in many hosts and carboxylic acids in non-hosts, but no specific VOCs were characteristic of host plants. Significant EAGs (maximum deflection values in mV) were recorded in plants with very different VOC profiles, both hosts and non-hosts. The EAGs were higher for M. melanotoma than for M. pygmaeus, and were higher for males than for females. In M. melanotoma the EAGs were greater with hosts than with non-hosts, but they were similar in M. pygmaeus. The EAGs were correlated with the concentrations of sesquiterpenes and alcohols in both species. In olfactory assays, M. melanotoma and M. pygmaeus preferred their respective hosts, but they did not discriminate between non-host with and without significant EAGs. According to the results, Macrolophus species are expected to rely on ubiquitous VOCs for the identification of their hosts. The variation in the EAGs between M. melanotoma and M. pygmaeus is attributed to the variation in the proportions of olfactory receptor neurones with different sensitivity to VOCs (e.g. sesquiterpenes). Host plant selection is discussed in the light of the perception of VOCs and the processing of information by the central nervous system.     

Phenolic compounds induced by <Emphasis Type="Italic">Bemisia tabaci</Emphasis> and <Emphasis Type="Italic">Trialeurodes vaporariorum</Emphasis> in <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> L. and their relationship with the salicylic acid signaling pathway

Changes in the levels of secondary compounds can trigger plant defenses. To identify phenolic compounds induced by Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) in tobacco (Nicotiana tobacco L.), the content changes of 11 phenolic compounds in plants infested by B. tabaci MEAM1 or Trialeurodes vaporariorum were compared. The chlorogenic acid, catechin, caffeic acid, p-coumaric acid, rutin, and ferulic acid contents in B. tabaci MEAM1-infested tobacco plants increased significantly, having temporal and spatial effects, compared with uninfested control and T. vaporariorum infested plants. The contents were 4.10, 2.84, 2.25, 3.81, 1.46, and 1.91 times higher, respectively, than those in the control. However, a T. vaporariorum nymphal infestation just caused smaller chlorogenic acid, catechin, caffeic acid, and rutin contents increase, which were 2.33, 2.13, 1.59, and 3.19 times higher, respectively, than those in the control. In B. tabaci MEAM1 third-instar nymph-infested plants, chlorogenic acid, catechin, caffeic acid, and rutin increased more significantly in systemic than in local leaves. Salicylate-deficient plants inhibited the induction of the content of 10 phenolic compounds, but not caffeic acid, after a B. tabaci MEAM1 nymphal infestation. Thus, the elevated levels of phenolic compounds induced by B. tabaci MEAM1 were correlated with the salicylic acid signaling pathway and induced the responses of defense-related phenolic compounds.     

Development,Reproduction, Survival,and Demographic Patterns of <Emphasis Type="Italic">Tuta absoluta</Emphasis> (Meyrick) (Lepidoptera: Gelechiidae) on Different Commercial Tomato Cultivars

The increase in the production of tomato, Solanum lycopersicon Mill. (Solanaceae), has favored the proliferation of pests, especially Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). In this study, the development, reproduction, survival, and demographic parameters of T. absoluta reared on six commercial tomato cultivars (Cherry, Cordilheira, Giuliana, Nemoneta, Paron, and Santa Clara) were evaluated. Tuta absoluta completed its development in all tomato cultivars. Development from newly hatched caterpillar to newly emerged adult varied between 24.8 and 28.2 days. Female fecundity ranged from 126.3 to 166.9 eggs, with fertility from 54.2 to 84.1%. Mortality during egg-adult development varied between 21.4 and 46.4% for insects reared on cultivars Cherry and Giuliana, respectively. The cultivars Cordilheira, Giuliana, and Santa Clara are promising options to tomato producers in order to decrease the attack and proliferation of T. absoluta. However, the development and population growth of T. absoluta is faster on the tomato cultivar Cherry.     

Behavioral responses of <Emphasis Type="Italic">Hyalesthes obsoletus</Emphasis> to host-plant volatiles cues

The polyphagous planthopper Hyalesthes obsoletus Signoret is considered to be the principal vector of stolbur phytoplasma, which is associated with yellow diseases of grapevine. To explore the possibility of developing novel control strategies, the behavioral responses to six synthetic mixtures and nine single compounds, previously identified from the headspace of Vitex agnus-castus L. (chaste tree) and Urtica dioica L. (nettle), were investigated in Y-tube bioassays. Choice tests revealed differences in the behavioral responses of males and females to the volatiles that they were exposed to. Males were attracted to a mixture containing (E)-β-caryophyllene, 1,8-cineole, (E,E)-α-farnesene, (E)-β-farnesene, and methyl salicylate (mixture 2). The addition of methyl benzoate to this five-compound mixture (mixture 3) did not attract males but elicited positive responses in females. Furthermore, females were attracted to a mixture containing (E)-β-caryophyllene, (E,E)-α-farnesene, (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, and benzothiazole (mixture 4), but here addition of methyl salicylate (mixture 5) did not attract females. Neither males nor females showed attractivity or repellency toward the singly tested compounds. This study enhances knowledge on the interaction of insect behaviorally effective constituents in complex plant volatile mixtures. The attractive mixtures of plant volatiles identified suggest the possibility of using them in monitoring and management of H. obsoletus.     

Genetic diversity and reproductive traits in triploid and tetraploid populations of <Emphasis Type="Italic">Gladiolus tenuis</Emphasis> (Iridaceae)

Most perennial herbaceous plants are able to reproduce vegetatively as well as sexually. Sometimes, such plants may lose the capacity for sexual reproduction. We have studied the case of sterility in triploid populations (2n = 3x = 45) of Gladiolus tenuis M.Bieb. in a considerable part of its area of distribution. Initially, we recorded the presence of a large clone of G. tenuis to the east of the Volga River, as a result of isozyme analysis. We also used AFLP fingerprinting to genotype 55 samples from 10 populations of G. tenuis and one population of the closely related G. imbricutus L. This analysis revealed an extremely low genetic diversity in sterile triploid populations of G. tenuis and a rather high genetic diversity in fertile tetraploid populations (2n = 4x = 60) over most of the area of this species. Genetic distances between fertile and sterile populations of G. tenuis were similar to those between different species of gladioli. It appears that a single sterile genotype has spread vegetatively over 800 km, propagating by daughter corms. The study of the reproductive features of G. tenuis suggests that the cause of sterility may be self-incompatibility between individuals of the clone.     

A new species of the pufferfish <Emphasis Type="Italic">Eotetraodon</Emphasis> (Tetraodontiformes,Tetraodontidae) from the Eocene of the Northern Caucasus

The Eocene pufferfish genus Eotetraodon (Tetraodontidae) has previously been known only on the basis of E. pygmaeus (Zigno, 1887) from the lowermost Middle Eocene of Monte Bolca, Italy. To Eotetraodon we now add E. gornylutshensis sp. nov. from the uppermost Middle Eocene of the Kuma Horizon of the northern Caucasus (Gorny Luch locality). E. gornylutshensis sp. nov. differs from E. pygmaeus by having much longer ribs and one less vertebra in the caudal peduncle.     

Centromeric and non-centromeric satellite DNA organisation differs in holocentric <Emphasis Type="Italic">Rhynchospora</Emphasis> species

Satellite DNA repeats (or satDNA) are fast-evolving sequences usually associated with condensed heterochromatin. To test whether the chromosomal organisation of centromeric and non-centromeric satDNA differs in species with holocentric chromosomes, we identified and characterised the major satDNA families in the holocentric Cyperaceae species Rhynchospora ciliata (2n = 10), R. globosa (2n = 50) and R. tenuis (2n = 2x = 4 and 2n = 4x = 8). While conserved centromeric repeats (present in R. ciliata and R. tenuis) revealed linear signals at both chromatids, non-centromeric, species-specific satDNAs formed distinct clusters along the chromosomes. Colocalisation of both repeat types resulted in a ladder-like hybridisation pattern at mitotic chromosomes. In interphase, the centromeric satDNA was dispersed while non-centromeric satDNA clustered and partly colocalised to chromocentres. Despite the banding-like hybridisation patterns of the clustered satDNA, the identification of chromosome pairs was impaired due to the irregular hybridisation patterns of the homologues in R. tenuis and R. ciliata. These differences are probably caused by restricted or impaired meiotic recombination as reported for R. tenuis, or alternatively by complex chromosome rearrangements or unequal condensation of homologous metaphase chromosomes. Thus, holocentricity influences the chromosomal organisation leading to differences in the distribution patterns and condensation dynamics of centromeric and non-centromeric satDNA.