Alkaloid concentration of the invasive plant species Ulex europaeus in relation to geographic origin and herbivory

In the study of plant defense evolution, invasive plant species can be very insightful because they are often introduced without their enemies, and traits linked to defense can be released from selective pressures and evolve. Further, studying plant defense evolution in invasive species is important for biological control and use of these species. In this study, we investigated the evolution of the defensive chemicals quinolizidine alkaloids (QAs) in the invasive species gorse, Ulex europaeus. Using a common garden experiment, our goals were to characterize the role of QAs relative to specialist enemies of gorse and to investigate if QA concentration evolved in invaded regions, where gorse was introduced without these enemies. Our results showed that pod infestation rate by the seed predator Exapion ulicis and infestation by the rust pathogen Uromyces genistae-tinctoriae were negatively correlated to concentration of the QA lupanine. Quinolizidine alkaloid concentration was very variable between individuals, both within and among populations, but it was not different between native and invaded regions, suggesting that no evolution of decreased resistance occurred after gorse lost its enemies. Our study also suggests that QA concentrations are traits integrated into seed predation avoidance strategies of gorse, with plants that mass-fruit in spring but do not escape pod infestation in time being richer in QAs.     

Development of a generalist predator,Podisus maculiventris,on glucosinolate sequestering and nonsequestering prey

Insect herbivores exhibit various strategies to counter the toxic effects of plant chemical defenses. These strategies include the detoxification, excretion, and sequestration of plant secondary metabolites. The latter strategy is often considered to provide an additional benefit in that it provides herbivores with protection against natural enemies such as predators. Profiles of sequestered chemicals are influenced by the food plants from which these chemicals are derived. We compared the effects of sequestration and nonsequestration of plant secondary metabolites in two specialist herbivores on the development of a generalist predator, Podisus maculiventris. Profiles of glucosinolates, secondary metabolites characteristic for the Brassicaceae, are known to differ considerably both inter- and intraspecifically. Throughout their immature (=nymphal) development, the predator was fed on larval stages of either sequestering (turnip sawfly, Athalia rosae) or nonsequestering (small cabbage white butterfly, Pieris rapae) prey that in turn had been feeding on plants originating from three wild cabbage (Brassica oleracea) populations that have previously been shown to differ in their glucosinolate profiles. We compared survival, development time, and adult body mass as parameters for bug performance. Our results show that sequestration of glucosinolates by A. rosae only marginally affected the development of P. maculiventris. The effects of plant population on predator performance were variable. We suggest that sequestration of glucosinolates by A. rosae functions not only as a defensive mechanism against some predators, but may also be an alternative way of harmlessly dealing with plant allelochemicals.     

Potential for biological control of field bindweed in California's coastal vineyards

The possibility of using biological control against field bindweed, Convolvulus arvensis L., was studied in four vineyards along the California coast. Field bindweed is a dominant member of the weed community and the principal plant pest in these vineyards. There is considerable insect and mite damage to its foliage during late summer and autumn, but the stress this places on the weed is unknown. The most significant natural enemies of field bindweed are defoliating caterpillars, Bedellia somnulentella Zeller, Chaetocnema confinis Crotch, and spider mites. Non of the natural enemies present appeared to be suitable as biological control agents. However, some arthropods, such as Noctuelia floralis (Huebner), associated with field bindweed in Mediterranean Europe and Pakistan, could be useful in the California grape agroecosystem, once cleared for importation and release in North America. Others, unsuitable to release in California because of feeding on closely related native plants, may be of value in other parts of the world where no such conflicts of interest exist. It would be feasible to use biological control against field bindweed in California's coastal vineyards and, perhaps, also in orchards under present systems of cultivation. Its effectiveness could be enhanced by certain changes in growing practices, particularly the acceptance of some weed growth, and by changes in existing pest controls. Biological control of field bindweed should be considered in the development of pest management programs for such crops in California and wherever this plant is a serious pest.     

Occurrence of phytophagous insects on wild Vigna sp. and cultivated cowpea: comparing the relative importance of host-plant resistance and millet intercropping

The effects of host-plant resistance on cowpea phytophagous insects and their natural enemies under pure and mixed crop conditions was evaluated at Minjibir, Kano State, Nigeria, in 1992–1994 crop seasons. Cowpea Vigna unguiculata cv ‘IT86D-715' (susceptible to insect pests) and a wild Vigna line Vigna vexillata ‘TVnu 72' (resistant to most insect species) were planted alone and in mixtures with millet (Pennisetum glaucum) in plots of 25×25 m.Mixed cropping had limited effect on major insects and natural enemies. Colonies of Aphis craccivora were significantly smaller and there were more adults of Maruca vitrata in crop mixtures than in monocultures. However, flower and raceme infestation by larval M. vitrata, Megalurothrips sjostedti, and Sericothrips sp. were similar in crop mixtures and monocultures. Empoasca sp. populations and seedling infestation by beanfly Ophiomyia phaseoli were also similar in mixtures and monocultures as well as pod damage by M. vitrata and populations of Clavigralla tomentosicollis. Parasitization rates of M. vitrata, C. tomentosicollis and O. phaseoli and predator–prey ratios of spiders and Orius sp. were similar across cropping systems. Host-plant resistance in TVnu 72 drastically reduced insect populations and damage. Grain yield per hill was high in cowpea IT86D-715 and was not affected by intercropping with millet. Grain yield of TVnu 72 was poor and reflected the low yield potential of this accession.Host-plant resistance is an effective means of controlling insect pest damage in cowpea and there is no evidence that high levels of resistance reduced natural biological control.     

Enzymatic natural dyeing of cotton and silk fabrics without metal mordants

Two step ultrasonic dyeing of cotton and silk fabrics with natural dyes, Terminalia arjuna, Punica granatum, and Rheum emodi have been developed in which an enzyme is complexed with tannic acid first as a pretreatment. This was found to be comparable with one step simultaneous dyeing. The effectiveness of three enzymes—protease-amylase, diasterase and lipase was determined. The enzymatic treatment gave cotton and silk fabrics rapid dye adsorption kinetics and total higher adsorption than untreated samples for all the three dyes. The CIELab values also showed improvement by enzymatic treatment. The tannic acid-enzyme-dye combination method offers an environmentally benign alternative, ‘soft chemistry’ to the metal mordanted natural dyeing.     

Geographical variation in parasitism shapes larval immune function in a phytophagous insect

Two of the central goals of immunoecology are to understand natural variation in the immune system among populations and to identify those selection pressures that shape immune traits. Maintenance of the immune system can be costly, and both food quality and parasitism selection pressure are factors potentially driving immunocompetence. In tritrophic interactions involving phytophagous insects, host plants, and natural enemies, the immunocompetence of phytophagous insects is constrained by selective forces from both the host plants and the natural enemies. Here, we assessed the roles of host plants and natural enemies as selective pressures on immune variation among natural populations of Lobesia botrana. Our results showed marked geographical variation in immune defenses and parasitism among different natural populations. Larval immune functions were dependent of the host plant quality and were positively correlated to parasitism, suggesting that parasitoids select for greater investment into immunity in moth. Furthermore, investment in immune defense was negatively correlated with body size, suggesting that it is metabolically expensive. The findings emphasize the roles of host plants and parasitoids as selective forces shaping host immune functions in natural conditions. We argue that kinds of study are central to understanding natural variations in immune functions, and the selective forces beyond.     

Impact of variable nitrogen fertilisation on arthropods in cotton in Georgia, USA

Reducing fertiliser applications can reduce production costs for cotton (Gossypium hirsutum L.) growers, as well as nitrogen (N) leaching into the soil and contamination of surface and ground water. But altered N fertilisation may also affect pests and their natural enemies. In this study, plots with four different levels of fertiliser input (0, 45, 90 and 135 kg ha⁻¹ N) were used to investigate the influence of N on cotton pest and beneficial arthropod populations, and on cotton yield in Tifton, GA, USA. We predicted that (1) N fertilisation will correlate positively with cotton plant growth; (2) increased N fertilisation will increase pest populations because plants with more N will be more nutritious for and attractive to herbivores; (3) populations of beneficial arthropods and predation of pests will decline with increased N fertilisation because of reduced plant signaling; (4) increased N fertilisation will increase pest mortality due to parasitoids because of increased host quality. Cotton plant growth was enhanced by N fertilisation but yield was unaffected. N fertilisation significantly affected some pest arthropods but inconsistently. Mirids were most abundant in the high N treatment in 1 year of the study and cotton aphids were most abundant in the highest N treatment in the other year of the study. Arthropod predators were generally more abundant in the high N treatment but only spiders and Geocoris spp. were significantly affected by N treatment, with highest numbers present in the highest N treatment but the significant differences were each only in a single year. The greatest mortality of sentinel pest eggs (Spodoptera exigua) due to predation occurred under low N conditions. N fertilisation had no significant effects on parasitism of feral or sentinel caterpillars.     

Biological control of gizzard shad impingement at a nuclear power plant

Biological control of gizzard shad (Dorosoma cepedianum) using predator fish species was managed to reduce impingement on cooling water intake screens at Coffey County Lake (CCL), Kansas. Long term shad and predator proportional stock densities (PSD) and body conditions (Wr) were used to characterize this fishery. Comparisons were completed between the lake’s primary productivity (mg/m³ chlorophyll-a), catch-per-unit-effort (CPUE) of young-of-year (YOY) and adult gizzard shad, and body conditions of predator species. No relationships were found between the lake’s productivity and gizzard shad densities indicating that other mechanisms control shad numbers, likely predation. Body conditions of the prevalent predator species in CCL were positively compared with the previous year’s production during a short-lived increase in shad densities. It is well documented that shad are an important food source for most predator species present in the lake. It is believed that the predator species present played a significant role in reducing YOY shad densities each year. Body conditions of predators did not indicate a surplus of a primary prey species. High shad growth rates and PSD indices promote survival of sufficient shad to adults, thus making this fishery nearly self-sustaining, and beneficial for plant operation.     

Unexpected phenotypes of malformations induced in Xenopus tropicalis embryos by combined exposure to triphenyltin and 9-cis-retinoic acid

Xenopus tropicalis embryos were exposed for 48 hr to the mixtures of 5 g Sn/L triphenyltin(TPT), which is a well-known endocrine disruptor, and 0.25–5 g/L 9-cis retinoic acid(9c-RA), which is the natural ligand of retinoid X receptor. The phenotypes induced by combined exposure were more variable than those resulting from single exposure to either TPT or 9c-RA. The prominent phenotypes included underdeveloped head structures, abnormal eyes, narrow fins, enlarged proctodaeum, etc. Especially, combined exposure induced unexpected notochord malformations, which ranged from small swellings of the surface of the tails to the extension and extrusion of notochord out of the posterior tails. Compared with the 5 g Sn/L TPT-treated group, the index of fin deficiency was not affected, and the index of axis deficiency was significantly increased with increasing RA concentrations in the mixtures. Our results suggest that combined exposure to TPT and 9c-RA induced not only more variable phenotypes of malformations than exposure to single compound but also some new and unexpected phenotypes.     

From repulsion to attraction: species- and spatial context-dependent threat sensitive response of the spider mite Tetranychus urticae to predatory mite cues

Prey perceiving predation risk commonly change their behavior to avoid predation. However, antipredator strategies are costly. Therefore, according to the threat-sensitive predator avoidance hypothesis, prey should match the intensity of their antipredator behaviors to the degree of threat, which may depend on the predator species and the spatial context. We assessed threat sensitivity of the two-spotted spider mite, Tetranychus urticae, to the cues of three predatory mites, Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius andersoni, posing different degrees of risk in two spatial contexts. We first conducted a no-choice test measuring oviposition and activity of T. urticae exposed to chemical traces of predators or traces plus predator eggs. Then, we tested the site preference of T. urticae in choice tests, using artificial cages and leaves. In the no-choice test, T. urticae deposited their first egg later in the presence of cues of P. persimilis than of the other two predators and cue absence, indicating interspecific threat-sensitivity. T. urticae laid also fewer eggs in the presence of cues of P. persimilis and A. andersoni than of N. californicus and cue absence. In the artificial cage test, the spider mites preferred the site with predator traces, whereas in the leaf test, they preferentially resided on leaves without traces. We argue that in a nonplant environment, chemical predator traces do not indicate a risk for T. urticae, and instead, these traces function as indirect habitat cues. The spider mites were attracted to these cues because they associated them with the existence of a nearby host plant.     

Indirect interactions between a phytopathogenic and an entomopathogenic fungus

Slow growth in herbivores may lead to higher mortality, due to prolonged exposure to natural enemies. A number of studies has tested the 'slow-growth, high-mortality' hypothesis using predators or parasitoids as natural enemies of the herbivore, but the possible role of pathogens is poorly documented. We provide evidence that phytopathogenic infection of a plant enhances the susceptibility of herbivore larvae to a generalist entomopathogen. Larvae of the mustard leaf beetle Phaedon cochleariae grow more slowly when feeding on Chinese cabbage leaves infected by the phytopathogenic fungus Alternaria brassicae than larvae feeding on healthy leaves. Treatment of such larvae feeding on diseased plants with an LD₅₀ of the entomopathogenic fungus Metarhizium anisopliae resulted in 100% mortality, compared with a mortality rate of 54% in the control larvae feeding on uninfected leaves. This is the first demonstration of an interaction between a phyto- and an entomopathogenic fungus.     

Survey of current crop management practices in a mixed-ricefield landscape,Mekong Delta,Vietnam — potential of habitat manipulation for improved control of citrus leafminer and citrus red mite

In the Mekong Delta, Vietnam, the citrus leafminer Phyllocnistis citrella (CLM) and the citrus red mite Panonychus citri are major pests in both sweet orange (Citrus sinensis) and Tieu mandarin (C. reticulata). Survey data indicate that these pest problems might be aggravated after farmers have completely destroyed the weed flora in their orchard. As citrus farmers only perceive the larger predators such as the weaver ant Oecophylla smaragdina and spiders, and have no idea about the existence of predatory mites or parasitoids, they do not know about potential positive attributes of weeds in pest management which sustain populations of natural enemies and their alternative food. IPM training programmes could use the weaver ant as an introduction to educating farmers about predatory mites and parasitoids, and should likewise emphasise the importance of beneficial asteraceous weeds such as Ageratum conyzoides. Non-crop trees such as Spondias dulcis, Mangifera indica, Eucalyptus tereticornis and Ceiba pentandra are commonly known to offer good refuge for the weaver ant. These trees should be further studied for their temporal contribution as food resource for other natural enemies of CLM and mites. Small adjustments of current weed management techniques are suggested to improve availability of pollen and nectar for beneficials at crucial moments in the cropping season, with due respect to implications at the landscape level.     

Influence of hedgerow and grassy field borders on ground beetle (Coleoptera: Carabidae) activity in fields of corn

Agricultural landscapes may be manipulated in ways that benefit predatory invertebrates by providing alternate food sources, overwintering sites, and refuge from farming activities. Ecological theory predicts that complex plant communities should support a richer community of natural enemies of pest insects than a simple plant community. A study was conducted in Iowa, USA to investigate the influence of the vegetative diversity of field boarders on the activity, species richness, and community similarities of predatory beetles occurring in corn fields.Ground beetle (Coleoptera: Carabidae) populations were compared among corn fields bounded by either complex hedges or simple grass edges. Directional pitfall traps were used to investigate activity patterns of beetles between border types and their adjacent corn fields. Beetles were trapped during four seasonal periods, based on the growth stage of corn. During corn emergence (May–June) when fields are barren, carabids were more active and species richness was higher in the corn fields bordered by woody hedges. The carabid species Scarites quadriceps, Scarites subterraneus, and Harpalus pensylvanicus, were more dominant in hedge sites as compared to grass sites at this time. Following corn–canopy closure, carabids were now more active in fields bordered by grassy edges, but beetle activity also remained high in the fields adjacent to woody hedges. Further analysis of the carabid communities by Bray–Curtis Similarity Index showed no difference among field edge types at any time of the season. Results indicate that both complex and simple field border habitats support abundant and diverse populations of carabids during most of the growing season. However, during the early growing season hedges appear to be more important than grass edges in supplying carabid beetles to corn fields. Woody hedges may serve as very important overwintering sites and as an early season refuge for predatory beetles in corn.     

What’s the buzz? Ultrasonic and sonic warning signals in caterpillars of the great peacock moth (Saturnia pyri)

Caterpillars have many natural enemies and, therefore, have evolved a diversity of antipredator strategies. Most research focuses on those strategies (crypsis, countershading, and warning coloration) targeting visually guided predators. In contrast, defensive sounds, although documented for more than a century, have been poorly studied. We report on a novel form of sound production—chirping—in caterpillars of the common European Great Peacock moth (Saturnia pyri). Chirps are broadband, with dominant peaks ranging between the sonic (3.7 kHz) and ultrasonic (55.1 kHz) and are generated by a rapid succession of mandibular “tooth strikes.” Chirp trains are induced by simulated predator attacks and precede or accompany the secretion of a defensive chemical from integumental bristles, supporting our hypothesis that these sounds function in acoustic aposematism. We propose that these caterpillars generate multimodal warning signals (visual, chemical, and acoustic) to target the dominant sensory modalities of different predators, including birds, bats, and invertebrates. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Defensive responses by a social caterpillar are tailored to different predators and change with larval instar and group size

Gregariousness in animals is widely accepted as a behavioral adaptation for protection from predation. However, predation risk and the effectiveness of a prey's defense can be a function of several other factors, including predator species and prey size or age. The objective of this study was to determine if the gregarious habit of Malacosoma disstria caterpillars is advantageous against invertebrate natural enemies, and whether it is through dilution or cooperative defenses. We also examined the effects of larval growth and group size on the rate and success of attacks. Caterpillars of M. disstria responded with predator-specific behaviors, which led to increased survival. Evasive behaviors were used against stinkbugs, while thrashing by fourth instar caterpillars and holding on to the silk mat by second instar caterpillars was most efficient against spider attacks. Collective head flicking and biting by groups of both second and fourth instar caterpillars were observed when attacked by parasitoids. Increased larval size decreased the average number of attacks by spiders but increased the number of attacks by both stinkbugs and parasitoids. However, increased body size decreased the success rate of attacks by all three natural enemies and increased handling time for both predators. Larger group sizes did not influence the number of attacks from predators but increased the number of attacks and the number of successful attacks from parasitoids. In all cases, individual risk was lower in larger groups. Caterpillars showed collective defenses against parasitoids but not against the walking predators. These results show that caterpillars use different tactics against different natural enemies. Overall, these tactics are both more diverse and more effective in fourth instar than in second instar caterpillars, confirming that growth reduces predation risk. We also show that grouping benefits caterpillars through dilution of risk, and, in the case of parasitoids, through group defenses. The decreased tendency to aggregate in the last larval instar may therefore be linked to decreasing predation risk.     

Plant surface wax affects parasitoid’s response to host footprints

The plant surface is the substrate upon which herbivorous insects and natural enemies meet and thus represents the stage for interactions between the three trophic levels. Plant surfaces are covered by an epicuticular wax layer which is highly variable depending on species, cultivar or plant part. Differences in wax chemistry may modulate ecological interactions. We explored whether caterpillars of Spodoptera frugiperda, when walking over a plant surface, leave a chemical trail (kairomones) that can be detected by the parasitoid Cotesia marginiventris. Chemistry and micromorphology of cuticular waxes of two barley eceriferum wax mutants (cer-za.126, cer-yp.949) and wild-type cv. Bonus (wt) were assessed. The plants were then used to investigate potential surface effects on the detectability of caterpillar kairomones. Here we provide evidence that C. marginiventris responds to chemical footprints of its host. Parasitoids were able to detect the kairomone on wild-type plants and on both cer mutants but the response to cer-yp.949 (reduced wax, high aldehyde fraction) was less pronounced. Experiments with caterpillar-treated wt and mutant leaves offered simultaneously, confirmed this observation: no difference in wasp response was found when wt was tested against cer-za.126 (reduced wax, wt-like chemical composition) but wt was significantly more attractive than cer-yp.949. This demonstrates for the first time that the wax layer can modulate the detectability of host kairomones.     

The ‘I see you’ prey–predator signal of Apis cerana is innate

An ‘I see you’ (ISY) prey–predator signal can co-evolve when such a signal benefits both prey and predator. The prey benefits if, by producing the signal, the predator is likely to break off an attack. The predator benefits if it is informed by the signal that the prey is aware of its presence and can break off what is likely to be an unsuccessful and potentially costly hunt. Because the signal and response co-evolve in two species, the behaviour underlying an ISY signal is expected to have a strong genetic component and cannot be entirely learned. An example of an ISY signal is the ‘shimmering’ behaviour performed by Asian hive bee workers in the presence of their predator Vespa velutina. To test the prediction that bee–hornet signalling is heritable, we let honey bee workers of two species emerge in an incubator so that they had never been exposed to V. velutina. In Apis cerana, the shimmering response developed 48 h post-emergence, was strong after 72 h and increased further over 2 weeks. In contrast, A. mellifera, which has evolved in the absence of Asian hornets, did not produce the shimmering signal. In control tests, A. cerana workers exposed to a non-threatening butterfly did not respond with the shimmering signal.     

Inaction levels for the red imported fire ant, Solenopsis invicta (hym.: formicidae): A predator of the boll weevil, Anthonomus grandis (col.: curculionidae)

The density of red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), necessary to limit boll weevil abundance, Anthonomus grandis Boheman (Coleoptera: Curculionidae), below the action level was determined. An inaction level of 0.4 fire ants per shake bucket sample (i.e., four ants per 10 plant terminals) will provide boll weevil control approximately 90% of the time. A dynamic inaction level is also provided. Total mortality of boll weevil developmental stages including eggs through teneral adults averaged 97.9%. Of 100 boll weevil eggs deposited in cotton squares (flower buds), an average of two adults survive of which about half are female. Thus, the net replacement rate per generation (R_o is 1.0 which, in this case, indicates a stable boll weevil population.     

Extraction and quantification of "condensed tannins" as a measure of plant anti-herbivore defence? Revisiting an old problem

Contents of phenolic compounds in leaf extracts often serve as a measure of plant anti-herbivore defence. This method suffers from the multifunctionality of phenolics and from problems with their colorimetric quantification. Here we present further evidence for the pertinence of these problems. Contents of condensed tannins (CCT) were spectrophotometrically quantified in leaf extracts of 11 closely related mimosoid species, and Spodoptera littoralis caterpillars were reared on artificial diet containing these extracts. The relationship of CCT with caterpillar growth differed considerably among plant species, since both positive and negative correlations were detected. There was, however, a negative correlation of CCT with fungal spore germination, indicating a role of these compounds in resistance to fungi. Detailed knowledge on the structure and biological function of defensive compounds and on the overall composition of leaves is required to estimate a plant's defensive efficacy against a particular group of enemies.