Generalist insects behave in a jasmonate-dependent manner on their host plants,leaving induced areas quickly and staying longer on distant parts

Plants are sessile, so have evolved sensitive ways to detect attacking herbivores and sophisticated strategies to effectively defend themselves. Insect herbivory induces synthesis of the phytohormone jasmonic acid which activates downstream metabolic pathways for various chemical defences such as toxins and digestion inhibitors. Insects are also sophisticated animals, and many have coevolved physiological adaptations that negate this induced plant defence. Insect behaviour has rarely been studied in the context of induced plant defence, although behavioural adaptation to induced plant chemistry may allow insects to bypass the host''s defence system. By visualizing jasmonate-responsive gene expression within whole plants, we uncovered spatial and temporal limits to the systemic spread of plant chemical defence following herbivory. By carefully tracking insect movement, we found induced changes in plant chemistry were detected by generalist Helicoverpa armigera insects which then modified their behaviour in response, moving away from induced parts and staying longer on uninduced parts of the same plant. This study reveals that there are plant-wide signals rapidly generated following herbivory that allow insects to detect the heterogeneity of plant chemical defences. Some insects use these signals to move around the plant, avoiding localized sites of induction and staying ahead of induced toxic metabolites.     

The green peach aphid,Myzus persicae,acquires a LIPOXYGENASE5-derived oxylipin from Arabidopsis thaliana,which promotes colonization of the host plant

Oxylipins derived from lipoxygenase (LOX) activity play important roles in plant growth, development and stress response. In a recent study, we provided evidence that infestation of Arabidopsis thaliana foliage by the green peach aphid (GPA; Myzus persicae), a phloem sap-consuming insect, was promoted by plant LOX5-derived oxylipins. In comparison to the wild-type (WT) plant, GPA population was smaller on the Arabidopsis lox5 mutant. The insect spent less time feeding from the sieve element and xylem of the lox5 mutant compared with the WT plant. In addition, compared with insects feeding on the WT plant, when on the lox5 mutant, the GPA was unable to suppress an antibiotic activity that is present in Arabidopsis vascular sap. Roots are the critical source of a LOX5-derived oxylipin(s) that promotes colonization of the foliage by GPA. Here we show that the 9-hydoxy-10E, 12Z-octadecadienoic acid (9-HOD), a LOX5-derived oxylipin, accumulated in GPA that were reared on the WT, but not the lox5 mutant plant. However, 9-HOD accumulated in insects reared on lox5 mutant plants that were irrigated with 9-HOD, thus indicating that the insect ingests oxylipins from the host plant. We further demonstrate that the host plant requires LOX5 function to promote expression of the defense regulatory gene PHYTOALEXIN-DEFICIENT4 in the foliage. Taken together, our previous observations and results presented here indicate that while the host plant utilizes LOX5-dependent factors for promoting defense mechanisms, GPA has evolved to utilize plant 9-LOX-derived oxylipins as cues to facilitate infestation, thus suggesting a complex involvement of oxylipins in Arabidopsis interaction with GPA.     

Effects of the virus satellite gene βC1 on host plant defense signaling and volatile emission

Tomato Yellow Leaf Curl China virus spreads together with its invasive vector, the silverleaf whitefly B biotype, which exhibits higher growth rates on infected plants. Previous studies indicate that the virus satellite gene βC1 accounts for the visible symptoms of infection and inhibits the constitutive expression of jasmonic acid (JA)—a phytohormone involved in plant defense against whiteflies—and of some JA-regulated genes. Here we present new details of the effects of on plant signaling and defense, obtained with (non-host) transgenic Arabidopsis thaliana and Nicotiana benthamiana plants. We found that JA induction in response to wounding was reduced in plants expressing βC1. This result implies that βC1 acts on conserved plant regulation mechanisms and might impair the entire JA defense pathway. Furthermore, transformed N. benthamiana plants exhibited elevated emissions of the volatile compound linalool, suggesting that βC1 also influences plant-derived olfactory cues available to vector and non-vector insects.     

Facilitation and inhibition: changes in plant nitrogen and secondary metabolites mediate interactions between above-ground and below-ground herbivores

To date, it remains unclear how herbivore-induced changes in plant primary and secondary metabolites impact above-ground and below-ground herbivore interactions. Here, we report effects of above-ground (adult) and below-ground (larval) feeding by Bikasha collaris on nitrogen and secondary chemicals in shoots and roots of Triadica sebifera to explain reciprocal above-ground and below-ground insect interactions. Plants increased root tannins with below-ground herbivory, but above-ground herbivory prevented this increase and larval survival doubled. Above-ground herbivory elevated root nitrogen, probably contributing to increased larval survival. However, plants increased foliar tannins with above-ground herbivory and below-ground herbivory amplified this increase, and adult survival decreased. As either foliar or root tannins increased, foliar flavonoids decreased, suggesting a trade-off between these chemicals. Together, these results show that plant chemicals mediate contrasting effects of conspecific larval and adult insects, whereas insects may take advantage of plant responses to facilitate their offspring performance, which may influence population dynamics.     

Review of the Parasa undulata (Cai, 1983) species group with the first conifer-feeding larva for Limacodidae and descriptions of two new species from China and Taiwan (Lepidoptera,Limacodidae)

Although the caterpillars are well-known for the stings and magnificent coloration, the systematics of Limacodidae is historically neglected and chaotic due to the difficulty in matching the larval with adult stages as well as the very conservative and convergent adult morphology. One of the biggest taxonomic problems surrounds a collective group from Southeastern Asia, termed the “green limacodid moths”, which harbours at least 90 species placed in the genus Parasa Walker, 1859 and 14 “subunits”. The P. undulata group was previously composed of 3 species from China and Taiwan, and characterized only by wing pattern. This species group is extensively studied herein with two new species described, i.e. P. viridiflamma sp. n. (Taiwan) and P. minwangi sp. n. (S. China), and discovery of female genitalia of three species, presenting new phylogenetic insights in this potentially paraphyletic genus. In addition, one limacodid larva was found to be feeding exclusively on Picea (Pinaceae) in Taiwan. Its identity, Parasa pygmy Solovyev, 2010 in P. undulata group, is confirmed through matching its COI sequence to the adult. This discovery is also biologically significant because the previous known host breadth of Parasa was of polyphagy on various angiosperm plant families. This case, therefore, represents the first record of conifer-feeding behavior in this family as well as the first of specialized herbivory in the genus. Meanwhile, the background match between Picea leaves and larval coloration is shared with other Picea-feeding insects. This phenomenon is worth of further investigation in the aspect of convergent evolution of crypsis associated with a particular plant.     

Detection of Foodborne Bacterial Pathogens from Individual Filth Flies

There is unanimous consensus that insects are important vectors of foodborne pathogens. However, linking insects as vectors of the pathogen causing a particular foodborne illness outbreak has been challenging. This is because insects are not being aseptically collected as part of an environmental sampling program during foodborne outbreak investigations and because there is not a standardized method to detect foodborne bacteria from individual insects. To take a step towards solving this problem, we adapted a protocol from a commercially available PCR-based system that detects foodborne pathogens from food and environmental samples, to detect foodborne pathogens from individual flies.Using this standardized protocol, we surveyed 100 wild-caught flies for the presence of Cronobacter spp., Salmonella enterica, and Listeria monocytogenes and demonstrated that it was possible to detect and further isolate these pathogens from the body surface and the alimentary canal of a single fly. Twenty-two percent of the alimentary canals and 8% of the body surfaces from collected wild flies were positive for at least one of the three foodborne pathogens. The prevalence of Cronobacter spp. on either body part of the flies was statistically higher (19%) than the prevalence of S. enterica (7%) and L.monocytogenes (4%). No false positives were observed when detecting S. enterica and L. monocytogenes using this PCR-based system because pure bacterial cultures were obtained from all PCR-positive results. However, pure Cronobacter colonies were not obtained from about 50% of PCR-positive samples, suggesting that the PCR-based detection system for this pathogen cross-reacts with other Enterobacteriaceae present among the highly complex microbiota carried by wild flies. The standardized protocol presented here will allow laboratories to detect bacterial foodborne pathogens from aseptically collected insects, thereby giving public health officials another line of evidence to find out how the food was contaminated when performing foodborne outbreak investigations.     

Trap diversity and evolution in the family Droseraceae

We review trapping mechanisms in the carnivorous flowering plant family Droseraceae (order Caryophyllales). Its members are generally known to attract, capture, retain and digest prey animals (mainly arthropods) with active snap-traps (Aldrovanda, Dionaea) or with active sticky flypaper traps (Drosera) and to absorb the resulting nutrients. Recent investigations revealed how the snap-traps of Aldrovanda vesiculosa (waterwheel plant) and Dionaea muscipula (Venus’ flytrap) work mechanically and how these apparently similar devices differ as to their functional morphology and shutting mechanics. The Sundews (Drosera spp.) are generally known to possess leaves covered with glue-tentacles that both can bend toward and around stuck prey. Recently, it was shown that there exists in this genus a higher diversity of different tentacle types and trap configurations than previously known which presumably reflect adaptations to different prey spectra. Based on these recent findings, we finally comment on possible ways for intrafamiliar trap evolution.     

Insects, birds and lizards as pollinators of the largest-flowered Scrophularia of Europe and Macaronesia

Background and Aims

It has traditionally been considered that the flowers of Scrophularia are mainly pollinated by wasps. We studied the pollination system of four species which stand out for their large and showy flowers: S. sambucifolia and S. grandiflora (endemics of the western Mediterranean region), S. trifoliata (an endemic of the Tyrrhenian islands) and S. calliantha (an endemic of the Canary Islands). Our principal aim was to test whether these species were pollinated by birds or showed a mixed pollination system between insects and birds.

Methods

Censuses and captures of insects and birds were performed to obtain pollen load transported and deposited on the stigmas. Also, a qualitative and quantitative analysis of the flowers and inflorescences was carried out.

Key Results

Flowers were visited by Hymenoptera and by passerine birds. The Canarian species was the most visited by birds, especially by Phylloscopus canariensis, and its flowers were also accessed by juveniles of the lizard Gallotia stehlini. The most important birds in the other three species were Sylvia melanocephala and S. atricapilla. The most important insect-functional groups in the mixed pollination system were: honey-bees and wasps in S. sambucifolia; bumble-bees and wasps in S. grandiflora; wasps in S. trifoliata; and a small bee in S. calliantha.

Conclusions

The species studied show a mixed pollination system between insects and passerine birds. In S. calliantha there is, in addition, a third agent (juveniles of Gallotia stehlini). The participation of birds in this mixed pollination system presents varying degrees of importance because, while in S. calliantha they are the main pollinators, in the other species they interact to complement the insects which are the main pollinators. A review of different florae showed that the large showy floral morphotypes of Scrophularia are concentrated in the western and central Mediterranean region, Macaronesia and USA (New Mexico).     

Ecological Trade-offs between Migration and Reproduction Are Mediated by the Nutrition-Sensitive Insulin-Signaling Pathway

Crowding and changes in food availability are two critical environmental conditions that impact an animal''s trajectory toward either migration or reproduction. Many insects facing this challenge have evolved wing polyphenisms. When conditions favor reproduction, wing polyphenic species produce adults that either have no wings or short, non-functional wings. Facultative wing growth reflects a physiological and evolutionary trade-off between migration and reproduction, triggered by environmental conditions. How environmental cues are transduced to produce these alternative forms, and their associated ecological shift from migration to reproduction, remains an important unsolved problem in evolutionary ecology. The brown planthopper, a wing polymorphic insect exhibiting strong trade-offs in investment between migration and reproduction, is one of the most serious rice pests in Asia. In this study, we investigated the function of four genes in the insulin-signaling pathway known to couple nutrition with growth, PI3 Kinase (PI3K), PDK1, Akt (Protein Kinase B), and the forkhead gene FOXO. Using a combination of RNA interference and pharmacological inhibitor treatment, we show that all four genes contribute to tissue level regulation of wing polymorphic development in this insect. As predicted, silencing of the NlPI3K, NlAkt and NlPDK1 through dsRNA and with the pharmacological inhibitor Perifosine resulted in short-winged brown planthoppers, whereas knockdown of NlFOXO resulted in long-winged planthoppers. Morphometric analyses confirm that phenotypes from our manipulations mimic what would be found in nature, i.e., major parameters such as bristle number, wing area and body weight are not significantly different from non-experimental animals. Taken together, these data implicate the insulin-signaling pathway in the transduction of environmental factors into condition-dependent patterns of wing growth in insects.     

Steinernema feltiae (DD-136) and S. glaseri: Persistence in Soil and Bark Compost and Their Influence on Native Nematodes

Infective juveniles (J3) of the entomogenous nematodes Steinernema feltiae DD-136 (ca. 10,000 J3/100 ml) and S. glaseri (ca. 2,500 J3/100 ml) were incubated in steam-sterilized and nonsterilized sandy soil and bark compost for 8 weeks at 25 C. The nematodes were recovered by a two-step extraction procedure at 1-week intervals, and their infectivity to lepidopterous larvae (Spodoptera litura and Galleria mellonella) and their effect on the population and community of native nematodes in soil were determined. Survival of inoculated nematodes and mortality of insects were enhanced in sterilized media. Nonsterilized bark compost proved to be equally as suitable a medium as sterilized compost. In nonsterilized soil, the survival curve of S.feltiae declined more rapidly than that or S. glaseri which was less infective to insects despite its greater persistence even in nonsterilized soil. Soon after the addition of steinernematids to soil, the population of native nematodes showed a fluctuation with an increase in rhabditids and a decrease in other kinds of nematodes.     

Are carbon and nitrogen exchange between fungi and the orchid Goodyera repens affected by irradiance?

Background and Aims The green orchid Goodyera repens has been shown to transfer carbon to its mycorrhizal partner, and this flux may therefore be affected by light availability. This study aimed to test whether the C and N exchange between plant and fungus is dependent on light availability, and in addition addressed the question of whether flowering and/or fruiting individuals of G. repens compensate for changes in leaf chlorophyll concentration with changes in C and N flows from fungus to plant.Methods The natural abundances of stable isotopes of plant C and N were used to infer changes in fluxes between orchid and fungus across natural gradients of irradiance at five sites. Mycorrhizal fungi in the roots of G. repens were identified by molecular analyses. Chlorophyll concentrations in the leaves of the orchid and of reference plants were measured directly in the field.Key Results Leaf δ¹³C values of G. repens responded to changes in light availability in a similar manner to autotrophic reference plants, and different mycorrhizal fungal associations also did not affect the isotope abundance patterns of the orchid. Flowering/fruiting individuals had lower leaf total N and chlorophyll concentrations, which is most probably explained by N investments to form flowers, seeds and shoot.Conclusions The results indicate that mycorrhizal physiology is relatively fixed in G. repens, and changes in the amount and direction of C flow between plant and fungus were not observed to depend on light availability. The orchid may instead react to low-light sites through increased clonal growth. The orchid does not compensate for low leaf total N and chlorophyll concentrations by using a ¹³C- and ¹⁵N-enriched fungal source.     

Novel adaptation to hawkmoth pollinators in Clarkia reduces efficiency,not attraction of diurnal visitors

Background and Aims

Plant populations experiencing divergent pollination environments may be under selection to modify floral traits in ways that increase both attractiveness to and efficiency of novel pollinators. These changes may come at the cost of reducing overall effectiveness of other pollinators. The goal of this study was to examine differences in attractiveness and efficiency between Clarkia concinna and C. breweri, sister species of annual plants with parapatric distributions.

Methods

An assessment was made as to whether observed differences in visitors between natural populations are driven by differences in floral traits or differences in the local pollination environment. Differences in floral attractiveness were quantified by setting out arrays of both species in the geographical range of each species and exposing both species to nocturnal hawkmoths (Hyles lineata) in flight cages. Differences in visitor efficiency were estimated by measuring stigma–visitor contact frequency and pollen loads for diurnal visitors, and pollen deposition on stigmas for hawkmoths.

Key Results

The composition of visitors to arrayed plants was similar between plant species at any particular site, but highly divergent among sites, and reflected differences in visitors to natural populations. Diurnal insects visited both species, but were more common at C. concinna populations. Hummingbirds and hawkmoths were only observed visiting within the range of C. breweri. Despite attracting similar species when artificially presented together, C. concinna and C. breweri showed large differences in pollinator efficiency. All visitors except hawkmoths pollinated C. concinna more efficiently.

Conclusions

Differences in the available pollinator community may play a larger role than differences in floral traits in determining visitors to natural populations of C. concinna and C. breweri. However, floral traits mediate differences in pollinator efficiency. Increased effectiveness of the novel hawkmoth pollinator on C. breweri comes at relatively little cost in attractiveness to other visitors, but at large cost in their efficiency as pollinators.     

Mapping of the Interaction Between Agrobacterium tumefaciens and Vanda Kasem’s Delight Orchid Protocorm-Like Bodies

Physical contact between A. tumefaciens and the target plant cell walls is essential to transfer and integrate the transgene to introduce a novel trait. Chemotaxis response and attachment of Agrobacterium towards Vanda Kasem’s Delight (VKD) protocorm-like bodies (PLBs) were studied to analyse the interaction between Agrobacterium and PLB during the transformation event. The study shows that initially A. tumefaciens reversibly attached to PLB surface via polar and lateral mode of adherence followed by the irreversible attachment which involved the production of cellulosic fibril by A. tumefaciens. Cellulosic fibril allows formation of biofilm at the tip of trichome. Contrarily, attachment mutant Escherichia coli strain DH5α was significantly deficient in the attachment process. Spectrophotometric GUS assay showed the mean value of attachment by A. tumefaciens was 8.72 % compared to the negative control E. coli strain DH5α that produced 0.16 %. A. tumefaciens swarmed with sharper and brighter edge when severe wounding was applied to the PLBs producing the highest swarming ratio of 1.46 demonstrating the positive effect of the plant exudates on bacterial movement. The study shows that VKD’s PLBs are the suitable explants for Agrobacterium-mediated transformation since the bacteria expressed higher competency rate.

Electronic supplementary material

The online version of this article (doi:10.1007/s12088-015-0519-7) contains supplementary material, which is available to authorized users.     

Endozoochory by beetles: a novel seed dispersal mechanism

Background and Aims

Due in part to biophysical sized-related constraints, insects unlike vertebrates are seldom expected to act as primary seed dispersers via ingestion of fruits and seeds (endozoochory). The Mediterranean parasitic plant Cytinus hypocistis, however, possesses some characteristics that may facilitate endozoochory by beetles. By combining a long-term field study with experimental manipulation, we tested whether C. hypocistis seeds are endozoochorously dispersed by beetles.

Methods

Field studies were carried out over 4 years on six populations in southern Spain. We recorded the rate of natural fruit consumption by beetles, the extent of beetle movement, beetle behaviour and the relative importance of C. hypocistis fruits in beetle diet.

Key Results

The tenebrionid beetle Pimelia costata was an important disperser of C. hypocistis seeds, consuming up to 17·5 % of fruits per population. Forty-six per cent of beetles captured in the field consumed C. hypocistis fruits, with up to 31 seeds found in individual beetle frass. An assessment of seeds following passage through the gut of beetles indicated that seeds remained intact and viable and that the proportion of viable seeds from beetle frass was not significantly different from that of seeds collected directly from fruits.

Conclusions

A novel plant–animal interaction is revealed; endozoochory by beetles may facilitate the dispersal of viable seeds after passage through the gut away from the parent plant to potentially favourable underground sites offering a high probability of germination and establishment success. Such an ecological role has until now been attributed only to vertebrates. Future studies should consider more widely the putative role of fruit and seed ingestion by invertebrates as a dispersal mechanism, particularly for those plant species that possess small seeds.     

Molecular Transfer of Nematode Resistance Genes

Recombinant DNA techniques have been used to introduce agronomically valuable traits, including resistance to viruses, herbicides, and insects, into crop plants. Introduction of these genes into plants frequently involves Agrobacterium-mediated gene transfer. The potential exists for applying this technology to nematode control by introducing genes conferring resistance to nematodes. Transferred genes could include those encoding products detrimental to nematode development or reproduction as well as cloned host resistance genes. Host genes that confer resistance to cyst or root-knot nematode species have been identified in many plants. The best characterized is Mi, a gene that confers resistance to root-knot nematodes in tomato. A map-based cloning approach is being used to isolate the gene. For development of a detailed map of the region of the genome surrounding Mi, DNA markers genetically linked to Mi have been identified and analyzed in tomato lines that have undergone a recombination event near Mi. The molecular map will be used to identify DNA corresponding to Mi. We estimate that a clone of Mi will be obtained in 2-5 years. An exciting prospect is that introduction of this gene will confer resistance in plant species without currently available sources of resistance.     

Meloidogyne partityla on Pecan Isozyme Phenotypes and Other Host

Meloidogyne sp. from five pecan (Carya illinoensis) orchards in Texas were distinctive in host range and iszoyme profiles from common species of Meloidogyne but were morphologically congruent with Meloidogyne partityla Kleynhans, a species previously known only in South Africa. In addition to pecan, species of walnut (Juglans hindsii and J. regia) and hickory (C. ovata) also were hosts. No reproduction was observed on 15 other plant species from nine families, including several common hosts of other Meloidogyne spp. Three esterase phenotypes and two malate dehydrogenase phenotypes of M. partityla were identified by polyacrylamide gel electrophoresis. Each of these isozyme phenotypes was distinct from those of the more common species M. arenaria, M. hapla, M. incognita, and M. javanica.     

Superparasitism in Cotesia glomerata does not benefit the host plant by reduction of herbivory caused by Pieris brassicae

Superparasitism occurs in Cotesia glomerata L. (Hymenoptera: Braconidae), a gregarious endoparasitoid of Pieris spp. (Lepidoptera: Pieridae). The responses of Pieris brassicae L. larvae to superparasitism were examined in order to elucidate the ecological significance of this behaviour. Models of tritrophic interactions often imply that attraction of herbivore natural enemies by the plant constitutes a defence. Parasitoid attack on herbivores is assumed to result in a reduction in herbivory and or an increase in plant fitness. Coupled with the active involvement of the plant in producing signals, this can be seen as an indirect mediation of wound induced defence. The results show that superparasitism of P. brassicae by the parasitoid C. glomerata reduced survivorship but increased food consumption and weight growth in P. brassicae larvae. The duration of host larval development was found prolonged as the number of oviposition increased and superparasitized larvae (three to five time parasitized) grew slower than unparasitized larvae or larvae parasitized one or two times.     

Association of Criconemella xenoplax and Fusarium spp. with Root Necrosis and Growth of Peach

Criconemella xenoplax, Fusarium solani, and F. oxysporum caused necrosis of Nemaguard peach feeder roots in greenhouse tests. Root necrosis was more extensive in the presence of either fungus than wtih C. xenoplax alone. Shoot growth and plant height were less for plants inoculated with F. oxysporum or F. solani than for plants inoculated with the fungi plus C. xenoplax. Neither synergistic nor additive effects on root necrosis or plant growth occurred between C. xenoplax and the fungal pathogens.