Cantharidin content in two Mediterranean species of blister beetles,Lydus trimaculatus and Mylabris variabilis (Coleoptera: Meloidae)

Cantharidin (CA), a toxic terpene produced by blister beetles (Coleoptera: Meloidae), attracts the interest of many researchers for its renowned medical properties. The CA content in blister beetles has been mainly quantified in some Oriental species, due to their use in traditional Chinese medicine, or in few other species of toxicological importance. As CA quantification has been largely ignored in many other members of this family, we aimed at estimating CA content in natural populations of two of the most abundant species in central Italy, Mylabris variabilis and Lydus trimaculatus. Nearly 100 individuals for each species were collected in the field, identified and reared in fauna‐boxes until CA collection. Available protocols were optimized for CA extraction from both dried‐body tissues and exuded hemolymph collected from leg joints using capillary tubes. The CA content was quantified in a gas chromatography system coupled to a mass spectrometer using a calibration curve with diethyl‐ester of norcantharidin as the internal standard. We observed: (i) high variability in CA content among specimens, which was positively related to individual dry‐weight; and (ii) slightly larger (though non‐significant) amount of CA in males than in females for both species. Our data are consistent with the available published reports about CA content, transfer and distribution in blister beetles and suggest a conserved biological role of this terpene in Meloidae.     

Behavioural responses of the Colorado potato beetle to trichomes and leaf surface chemicals of Solanum tarijense

Wild Solanum species constitute a source of resistance to several pests and diseases of potato. Several species of wild tuber‐bearing potato have been identified as resistant to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), including Solanum tarijense Hawkes (Solanaceae). Our objective was to determine the mechanism of resistance of S. tarijense to the Colorado potato beetle and, because the resistance is limited to the adult stage of the insect, to study the host selection behaviour on resistant plants. In the field, Colorado potato beetles demonstrated a unique behaviour when in contact with S. tarijense, abandoning the plant by falling to the ground after a few minutes. The abundant trichomes on the leaves of S. tarijense induced the falling behaviour. However, on S. tarijense feeding remained low even after the trichomes were mechanically removed. Observations demonstrated that the normal sequence of behaviour leading to feeding was interrupted before adult beetles fed on S. tarijense leaves. Feeding experiments using volatile and non‐volatile fractions of leaf surface extracts identified a phagodeterrent effect of the volatile fraction. Our results contrast with a similar evaluation of the mode of resistance of Solanum berthaultii Hawkes, a close relative of S. tarijense, on which some feeding occurred and adults did not show falling behaviour. This study presents information on S. tarijense as a new source of resistance to the Colorado potato beetle that can be used for potato breeding.     

Hylobius abietis L. feeding on the novel host Pinus brutia Ten. increases emission of volatile organic compounds

Plants respond to feeding by herbivorous insects by producing volatile organic chemicals, which mediate interactions between herbivores and plants. Yet, few studies investigated whether such plant responses to herbivory differ between historical host and novel plants. Here, we investigated whether herbivory by the pine weevil Hylobius abietis causes a release of volatile organic chemicals from a novel tree Pinus brutia and compared the relative amounts of volatiles released from herbivore's historical hosts and P. brutia. We collected volatiles emitted from P. brutia seedlings that were either subjected to feeding by H. abietis or no feeding. Our results indicated that feeding increased emission of volatile compounds, composed of monoterpenes and sesquiterpenes, and that the emission was several fold higher in the damaged seedlings than in undamaged seedlings. In particular, emission of monoterpenes and sesquiterpenes increased by 4.4‐and 10‐fold in the damaged plants, respectively. Strikingly, individual monoterpenes and sesquiterpenes showed much greater dissimilarity between damaged and undamaged seedlings. Furthermore, several minor monoterpenes showed negative relationships with the weevil gnawed area. We discussed these results with the results of previous studies focused on historical host plants of H. abietis and hypothesized the ecological relevance and importance of our results pertaining relevance to the plant–herbivory interactions.     

Adult large pine weevils Hylobius abietis feed on silver birch Betula pendula even in the presence of conifer seedlings

1 The feeding preference of the adult pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) for Betula pendula Roth was studied in no‐choice and paired‐choice feeding experiments. 2 In the first no‐choice test, large quantities of silver birch bark in Petri dishes were consumed; on average, the daily consumption of each weevil was 67 mm². 3 In the second no‐choice test, the weevils were offered 1‐year‐old silver birch seedlings for 6 days. Initially, the weevils fed mostly on the stem bases; later, they moved upward to feed on other parts of the stems. In addition to the main shoots, scars caused by gnawing were also found on leaf bases, blades, veins and petioles. Feeding resulted in the death of the main stems in 15% of the seedlings. 4 In the paired‐choice tests, the conifers were preferred to silver birch, even though a large amount of silver birch was also consumed in the presence of conifers. 5 In the paired‐choice tests, equal amounts of Scots pine and Norway spruce were always consumed. When hybrid aspen was offered, only small amounts were gnawed.     

The structure of feeding behavior in a phytophagous insect (Hylobius abietis)

Analysis of the feeding behavior of animals using such a high temporal resolution that meals can be defined may improve our understanding of the mechanisms regulating feeding. Meals can be distinguished in an ethologically meaningful manner by using the ‘meal criterion’, the shortest non‐feeding interval between feeding bouts recognized as meals. However, such a criterion has only been determined for a few insect species. Applying a recent method developed for assessing meal criteria for vertebrates, we determined the meal criterion for Hylobius abietis (L.) (Coleoptera: Curculionidae) based on data from video recordings of single individuals feeding on seedlings of Norway spruce, Picea abies (L.) Karst. (Pinaceae). The pine weevil is an economically important pest insect, because it feeds on the stem bark of planted conifer seedlings. Weevils had 4–5 meals per day. Each meal lasted about 24 min during which about 13 mm² of bark per meal were removed. Females had longer total meal durations and longer non‐feeding intervals within meals than males. Girdling seedlings did not affect the weevils' feeding properties. The size of meals was significantly correlated with the duration of non‐feeding intervals before and after them. This study is one of few describing the feeding behavior of an insect at a temporal resolution that allows individual meals to be distinguished. With more meal‐related data from insects available, differences in meal properties may be interpreted based on phylogeny, ecology, and physiology. Our results may also assist in the setup and interpretation of studies of plant‐insect interactions, and facilitate the evaluation and development of methods to protect plants against herbivores.     

Host‐plant use by two Orthomeria (Phasmida: Aschiphasmatini) species feeding on Macaranga myrmecophytes

Myrmecophytes depend on symbiotic ants (plant‐ants) to defend against herbivores. Although these defensive mechanisms are highly effective, some herbivorous insects can use myrmecophytes as their host‐plants. The feeding habits of these phytophages on myrmecophytes and the impacts of the plant‐ants on their feeding behavior have been poorly studied. We examined two phasmid species, Orthomeria alexis and O. cuprinus, which are known to feed on Macaranga (Euphorbiaceae) myrmecophytes in a Bornean primary forest. Our observations revealed that: (i) each phasmid species relied on two closely‐related myrmecophytic Macaranga species for its host‐plants in spite of their normal plant‐ant symbioses; and (ii) there was little overlap between their host‐plant preferences. More O. cuprinus adults and nymphs were found on new leaves, which were attended by more plant‐ants than mature leaves, while most adults and nymphs of O. alexis tended to avoid new leaves. In a feeding choice experiment under ant‐excluded conditions, O. alexis adults chose a non‐host Macaranga myrmecophyte that was more intensively defended by plant‐ants and was more palatable than their usual host‐plants almost as frequently as their usual host‐plant, suggesting that the host‐plant range of O. alexis was restricted by the presence of plant‐ants on non‐host‐plants. Phasmid behavior that appeared to minimize plant‐ant attacks is described.     

Host feeding experience affects host plant odour preference of the polyphagous leafminer Liriomyza bryoniae

Herbivorous insects use highly specific volatiles or blends of volatiles characteristic to particular plant species to locate their host plants. Thus, data on olfactory preferences can be valuable in developing integrated pest management tools that deal with manipulation of pest insect behaviour. We examined host plant odour preferences of the tomato leafminer, Liriomyza bryoniae (Kaltenbach) (Diptera: Agromyzidae), which is an economically important agricultural pest widespread throughout Europe. The odour preferences of leafminers were tested in dependence of feeding experiences. We ranked host plant odours by their appeal to L. bryoniae based on two‐choice tests using a Y‐tube olfactometer with five host plants: tomato, Solanum lycopersicum Mill.; bittersweet, Solanum dulcamara L.; downy ground‐cherry, Physalis pubescens L. (all Solanaceae); white goosefoot, Chenopodium album L. (Chenopodiaceae); and dead nettle, Lamium album L. (Lamiaceae). The results imply that ranking of host plant odours by their attractiveness to L. bryoniae is complicated due to the influence of larval and adult feeding experiences. Without any feeding experience as an adult, L. bryoniae males showed a preference for the airflow with host plant odour vs. pure air, whereas females did not display a preference. Further tests revealed that adult feeding experience can alter the odour choice of L. bryoniae females. After feeding experience, females showed a preference for host plant odour vs. pure air. Feeding experience in the larval stage influenced the choice by adults of both sexes: for males as well as females reared on bittersweet the odour of that plant was the most attractive. Thus, host feeding experience both in larval and/or adult stage of polyphagous tomato leafminer L. bryoniae influences host plant odour preference by adults.     

Effects of conspecific and heterospecific competitors on feeding and oviposition of a predatory ladybird: a laboratory study

Abstract There are several examples of intraguild interactions among insect predators of aphids, but little is known regarding the effects of interactions on feeding and oviposition of individual competitors in a guild. In the laboratory, we determined the feeding and oviposition responses of a ladybird predator to its conspecific and heterospecific competitors in an aphidophagous guild. Gravid females of Menochilus sexmaculatus (Fabricius) (Coleoptera, Coccinellidae) reduced oviposition, but not feeding, when exposed to immobilised conspecific or Coccinella transversalis (Fabricius) (Coleoptera, Coccinellidae) individuals in the short‐term (3 h) and long‐term (24 h). Feeding and oviposition responses were not affected when M. sexmaculatus females were exposed to larvae or adults of Scymnus pyrocheilus Mulsant (Coleoptera, Coccinellidae) beetles or larvae of the syrphid fly Ischiodon scutellaris (Fabricius) (Diptera: Syrphidae). The ratio of eggs laid to numbers of aphids consumed by M. sexmaculatus females was also affected by the presence of conspecific or C. transversalis larvae. The results suggest that fecundity of this predator may be affected by both conspecific and heterospecific competitors in a patchy resource.     

The gut microbiota of the pine weevil is similar across Europe and resembles that of other conifer‐feeding beetles

The pine weevil (Hylobius abietis, Coleoptera: Curculionidae) is an important pest of conifer seedlings in Europe. Despite its economic importance, little is known about the composition of its gut microbial community and the role it plays in mediating the weevil's ability to utilize conifers as a food source. Here, we characterized the gut bacterial communities of different populations of H. abietis across Europe and compared them to those of other beetles that occupy similar ecological niches. We demonstrate that the microbial community of H. abietis is similar at higher taxonomic levels (family and genus) across locations in Europe, with Wolbachia as the dominant microbe, followed by Enterobacteria and Firmicutes. Despite this similarity, we observed consistent differences between countries and locations, but not sexes. Our meta‐analysis demonstrates that the gut bacterial community of the pine weevil is very similar to that of bark beetles that also exploit conifers as a food source. The Enterobacteriaceae symbionts of both host taxa are especially closely related phylogenetically. Conversely, the microbiota of H. abietis is distinct from that of closely related weevils feeding on nonconifer food sources, suggesting that the microbial community of the pine weevil is determined by the environment and may be relevant to host ecology. Furthermore, several H. abietis‐associated members of the Enterobacteriaceae family are known to contain genes involved in terpenoid degradation. As such, we hypothesize that the gut microbial community is important for the utilization of conifer seedlings as a food source, either through the detoxification of plant secondary metabolites or through the supplementation of essential nutrients.     

The large pine weevil Hylobius abietis (L.) as a potential vector of the pathogenic fungus Diplodia sapinea (Fr.) Fuckel

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Activity of some Nile River aquatic macrophyte extracts against the cyanobacterium Microcystis aeruginosa

The anti-algal activity of five macrophyte extracts on the cyanobacterium Microcystis aeruginosa in Egypt was investigated in 2013. Extract activity varied according to plant type, extracting solvent and its concentration. The highest inhibitory activity was achieved with ethanol extract at a concentration of 80 mg l^?1, followed by chloroformic extracts, at 60 mg l^?1. Methanolic extracts of Eichhornia crassipes and Polygonum tomentosum inhibited growth of Microcystis aeruginosa at all concentrations. Acetonic extracts inhibited algal growth at 60 mg l^?1, except for the extract of Ceratophyllum subdemersum, which showed stimulation of M. aeruginosa growth. Eichhornia crassipes ethanolic extract exerted the most powerful inhibition by more than five-fold, 570.17%, followed by those of P. tomentosum, Saccharum spontaneum, Ceratophyllum demersum and C. subdemersum, 559.48, 553.99, 544.11 and 366.51%, respectively. Phytochemical screening for the tested plant extracts revealed the presence of biologically active substances of different concentrations, with P. tomentosum having the highest polyphenols, 1.95% of dry weight.     

Testing associational resistance against pine weevils mediated by Lasius ants attending conifer seedlings

Natural enemies attracted to plants may provide those plants with protection against herbivores but may also protect neighbouring plants, that is through associational resistance. Ant attendance may be an important mechanism for the occurrence of such effects because ants can reduce the damage caused by a wide variety of herbivorous insects. Ants have been shown, in a previous field experiment, to decrease the damage caused by the pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), a pest species that causes high seedling mortality in forest regeneration areas. In this study, we specifically tested whether seedlings planted close to ant‐attended seedlings experience associational resistance. We did this under laboratory conditions using the ant species Lasius niger (L.) (Hymenoptera: Formicidae). The feeding damage by pine weevils was significantly reduced on seedlings attended by ants. The neighbouring seedlings, however, did not experience associational resistance. Nevertheless, some associational effects were observed as the number of weevils recorded on both ant‐attended and neighbouring seedlings was significantly lower compared with ant‐excluded seedlings.     

Species‐specific positive effects in an annual plant community

Plant facilitation studies commonly test the nurse‐plant hypothesis wherein an adult shrub species enhances the establishment of associated herbaceous species under its canopy. Using field and glasshouse experiments, this hypothesis is extended by testing the following four predictions: (1) nurse‐plant effects can occur between species with similar life‐forms and phenologies (2) positive effects are species specific, (3) the outcome of interactions is life‐stage dependent, and (4) facilitative interactions among annuals are primarily commensal. In the Negev Desert in Israel, the response of an annual plant community to removal of relatively larger annuals, Erodium laciniatum, Erucaria pinnata and Trifolium tomentosum, was tested in the field and in the glasshouse. Removal of these dominants was applied early in the growing season, immediately after germination but before establishment of seedlings, and again mid‐season following establishment and growth to adults. In both the field and glasshouse, the presence of E. laciniatum increased establishment and survival to reproduction of neighbouring plants. These positive effects were life‐stage dependent with more positive effects occurring early in the season, and there was no cost of facilitation to E. laciniatum. This positive effect was species specific in that neither E. pinnata nor T. tomentosum had an effect on the plant community. There was also a cost of association with the nurse E. laciniatum in that biomass of neighbours was reduced. These experiments demonstrate that the positive effects typically detected at larger scales between species of different life‐forms are also occurring at finer spatial scales amongst annuals. This study clearly supports the predictions made in the facilitation literature that effects are species‐specific and highly life‐stage dependent.     

Inter‐tree distribution of the spruce web‐spinning sawfly,Cephalcia abietis,at endemic density

1 The spatial distribution of forest defoliating insects at endemic density is a generally little known aspect of pest biology, which may have some importance in monitoring and prediction of outbreaks. In a natural spruce stand in Northern Italy it was possible to detect the presence of some species of web‐spinning sawflies (Cephalcia spp.) at endemic density. This was done over a 3‐year period by using trapping devices for both adults and larvae, including a trap which intercepted adult females climbing the trunk. Traps were operated on eight sample trees with signs of defoliation of the previous year (focal trees) and on 14 trees lacking signs of larval feeding (neighbour trees). 2 Trunk traps on focal trees caught a higher number of adult females than traps on neighbour trees in each of the 3 years considered. The distribution pattern of catches was not spatially autocorrelated at any of the distance bands considered. Focal trees produced more mature larvae per adult female of C. abietis than neighbour trees, indicating that insect performance was higher on focal trees. 3 The endemic population density of C. abietis was similar to that observed in other forests and the relationships between yellow trap catches and prepupal density fitted adequately with the predictive model validated for C. arvensis. The endemic density of the spruce web‐spinning sawflies seems to he higher than that of pine diprionids, and outbreak‐prone species of Cephalcia seem to be more abundant than non‐outbreak species even at very low population level.     

Herbivory effects of Argopistes tsekooni,a chrysomelid beetle,on container‐grown Chinese privet,Ligustrum sinense

Abstract The impact of Argopistes tsekooni Chen (Coleoptera: Chrysomelidae), a herbivore, on Chinese privet, Ligustrum sinense Lour. (Scrophulariales: Oleaceae), an invasive shrub in the United States, was studied in China. Five densities of adults were inoculated into 3‐year‐old potted Chinese privet plants in cages under field conditions for 1 month. Plants exposed to high densities of adults were severely damaged and the above‐ground portions of some were killed, while the survival rates of adult A. tsekooni were comparatively high. The amount of new growth of the main stem, the number of new leaves, and oven‐dried biomass were significantly reduced by the combined feeding of larvae and adults. Above‐ground plant mortality was 100% when plants were exposed to 24 and 30 adults/plant. In this study A. tsekooni had a significant negative impact on Chinese privet growing in pots, which suggests that it may be a promising candidate for biological control of Chinese privet in the field in North America.     

Measurement of volatile terpene emissions in 70 dominant vascular plant species in Hawaii: aliens emit more than natives

Aim Alien plant invasion is prominent in the Hawaiian Islands. There are many factors involved in invader success. To date, there is a general lack of information about one of them, which we aim to study here: the terpene emission capacity of both Hawaiian native and alien plants. Location Oahu (Hawaii). Methods We screened 35 alien and 35 native dominant plant species on Oahu Island for monoterpene emissions. The emission rates were measured from field‐grown plants under standardized conditions of temperature and quantum flux density in the laboratory. Results The emission rates of total terpenes ranged from 0 µg g^?1 h^?1 to 55 µg g^?1 h^?1, and altogether 15 different terpenes were emitted in detectable amounts by the overall set of species. A phylogenetic signal was observed for total terpene emissions. Total terpene emission rates were higher in aliens than in native species (12.8 ± 2.0 vs. 7.6 ± 1.9 µg g^?1 h^?1, respectively). Main conclusions The greater terpene emission capacity may confer protection against multiple stresses and may partly account for the success of the invasive species, and may make invasive species more competitive in response to new global change‐driven combined stresses. These results are consistent with aliens coming from very diverse ecosystems with generally higher biotic and abiotic stress pressures, and having higher nutrient concentrations. On the contrary, these results are not consistent with the ‘excess carbon’ hypotheses. These results indicate changes in vegetation terpene emissions brought about by alien plant invasions.     

Gut microbiota of the pine weevil degrades conifer diterpenes and increases insect fitness

The pine weevil (Hylobius abietis), a major pest of conifer forests throughout Europe, feeds on the bark and cambium, tissues rich in terpenoid resins that are toxic to many insect herbivores. Here, we report the ability of the pine weevil gut microbiota to degrade the diterpene acids of Norway spruce. The diterpene acid levels present in ingested bark were substantially reduced on passage through the pine weevil gut. This reduction was significantly less upon antibiotic treatment, and supplementing the diet with gut suspensions from untreated insects restored the ability to degrade diterpenes. In addition, cultured bacteria isolated from pine weevil guts were shown to degrade a Norway spruce diterpene acid. In a metagenomic survey of the insect's bacterial community, we were able to annotate several genes of a previously described diterpene degradation (dit) gene cluster. Antibiotic treatment disrupted the core bacterial community of H. abietis guts and eliminated nearly all dit genes concordant with its reduction in diterpene degradation. Pine weevils reared on an artificial diet spiked with diterpenes, but without antibiotics, were found to lay more eggs with a higher hatching rate than weevils raised on diets with antibiotics or without diterpenes. These results suggest that gut symbionts contribute towards host fitness, but not by detoxification of diterpenes, as these compounds do not show toxic effects with or without antibiotics. Rather the ability to thrive in a terpene‐rich environment appears to allow gut microbes to benefit the weevil in other ways, such as increasing the nutritional properties of their diet.     

Relationship between volatile compounds of Picea likiangensis var. linzhiensis cone and host selection of Dioryctria abietella

This study aimed to determine the relationship between volatile compounds of Picea likiangensis var. linzhiensis cone and host selection of Dioryctria abietella. During the infestation of P. likiangensis var. linzhiensis by D. abietella, their cones and branches emitted volatile compounds, which were extracted using CH₂Cl₂ extraction and XAD₂ adsorption methods, and were analyzed using gas chromatography–mass spectrometry. Before and after overwintering, D. abietella larva preferred annually infested cones and their extracts, and adult D. abietella preferred to lay eggs on annually infested cones and healthy cones of the year, and the oviposition rate of adult D. abietella was 72% on branches with healthy cones of the year, and no egg was laid on branches with annually healthy cones or branches without cones. The volatile compounds after infestation, α- and β-pinene, were significantly higher in cones than those in other tissues; however, myrcene in cones was significantly lower than those in other tissues. The annually infested cones produced β-caryophyllene and (1S)-(-)-β-pinene, while the annually healthy cones and branches produced myrcene and 3-carene. The annually infested cones and their extracts attracted D. abietella larvae, while that of healthy cones and annually infested cones attracted the adults, indicating that the terpene compounds: α-pinene, β-pinene, (1S)-(-)-β-pinene, limonene, and β-caryophyllene are attractive to D. abietella, and the terpene compounds—myrcene and 3-carene—from the branch tissues may be repulsive to D. abietella.     

The impact of host plant species on the larval development of the large pine weevil Hylobius abietis L.

• 1 The developmental performance of the large pine weevil Hylobius abietis was studied in the laboratory on four species of conifer, Corsican pine Pinus nigra var. maritima, Sitka spruce Picea sitchensis, Douglas‐fir Pseudotsuga menziesii and Japanese larch Larix kaempferi.
• 2 All species supported development, but, there was considerable variation in larval mortality, development time and weight of adults on emergence between host species.
• 3 Levels of mortality were highest in Japanese larch (77%) and lowest in Corsican pine (8.2%), and the heaviest adults emerged from Corsican pine (130 mg) and the smallest from Douglas‐fir (74 mg).
• 4 A constitutive plant defence chemical, lignin, found to vary within a northern provenance of Sitka spruce, also strongly affected larval development.
• 5 The significance of these findings is discussed in relation to the management of H. abietis.