Qing-He Zhang

A successful case of pheromone mass trapping of the bark beetle Ips duplicatus in a forest island, analysed by 20-year time-series data

The experimental testing of the hypothesis of population reduction by mass trapping with the establishment of treatment/control areas is a logistic problem on landscape scale. We suggest a possible test based on time-series analysis of tree-mortality data. Our example is helped by: an island effect, a 20-year tree-mortality record, and a very competitive synthetic aggregation pheromone. The successful development of synthetic pheromone (ipsdienol and E-myrcenol) dispensers, and the dose-response of wick-dispensers is briefly described. In the 2000 ha of spruce (Picea mongolica) forest reserve at Baiyinaobao, surrounded by grassland, 80 traps were employed for 3 years, catching 0.5–1.7 million beetles/year. In spite of intensive conventional management since 1982 (17 years), the long-term tree mortality had been oscillating around 600. During the first three years of mass trapping, tree mortality was down to 118, 100, and 88, respectively. Neither natural population cycles nor weather conditions could explain the 3-year mortality drop. Cycles did not drive the drop, as auto-correlation function (ACF) and partial ACF plots do not show any clear periodicity, only a weak 5-year cycle is visible. Weather did not explain the drop, as the 3 years of mass trapping had average rainfall and higher than average temperatures. Climate data show negative correlations of tree mortality and temperatures on year basis and a 20-year trend of increased monthly averages, especially for July temperature. The increased temperature (global warming) will increase stress on trees, but mass trapping may have counterbalanced this new threat to the forest.

Peripheral modulation of pheromone response by inhibitory host compound in a beetle

SUMMARY We identified several compounds, by gas chromatographic–electroantennographic detection (GC–EAD), that were antennally active in the bark beetle Ips typographus and also abundant in beetle-attacked spruce trees. One of them, 1,8-cineole (Ci), strongly inhibited the attraction to pheromone in the field. Single-sensillum recordings (SSRs) previously showed olfactory receptor neurons (ORNs) on I. typographus antennae selectively responding to Ci. All Ci neurons were found within sensilla co-inhabited by a pheromone neuron responding to cis-verbenol (cV); however, in other sensilla, the cV neuron was paired with a neuron not responding to any test odorant. We hypothesized that the colocalization of ORNs had a functional and ecological relevance. We show by SSR that Ci inhibited spontaneous activity of the cV neuron only in sensilla in which the Ci neuron was also present. Using mixtures of cV and Ci, we further show that responses to low doses (1–10 ng) of cV were significantly reduced when the colocalized Ci neuron simultaneously responded to high doses (1–10 μg) of Ci. This indicated that the response of the Ci neuron, rather than ligand–receptor interactions in the cV neuron, caused the inhibition. Moreover, cV neurons paired with Ci neurons were more sensitive to cV alone than the ones paired with the non-responding ORN. Our observations question the traditional view that ORNs within a sensillum function as independent units. The colocalization of ORNs might sharpen adaptive responses to blends of semiochemicals with different ecological significance in the olfactory landscape.

A Model for Peak and Width of Signaling Windows: Ips duplicatus and Chilo partellus Pheromone Component Proportions--Does Response have a Wider Window than Production?

Pheromone communication systems have a reliable signal with a restricted window of amounts and ratios released and perceived. We propose a model based on a Gaussian response profile that allows a quantification of the response peak (location of optimum) and a measure of the peak width (response window). Interpreting the Gaussian curve, fitted by nonlinear regression (NLR), as a standard normal distribution, the peak location equals the mean (μ) and the window width equals 2× the standard deviation (2σ). The NLR procedure can provide an objective measure for both peak location and width for a wide range of data sets. Four empirical data sets as well as 10 literature data sets were analyzed. The double-spined spruce engraver, Ips duplicatus, was field tested in four populations to find the optimum proportion for attraction to the two male aggregation pheromone components, ipsdienol (Id) and (E)-myrcenol (EM), ranging from 0 to 100% of Id. Tests in Norway and the Czech Republic confirmed the preference of western populations for a blend between 50 and 90% Id. A population in Inner Mongolia showed a preference for traps with the 10 and 50% Id baits. The NLR fitted values for response peak and width (μ; 2σ) were: Norway 0.64, 0.73; Czech Republic 0.53, 0.73; NE China 0.77, 0.29; and Inner Mongolia 0.33, 0.50. The signal produced by Norwegian field-collected males had a narrower window width (2σ = 0.12). Males of the maize stem borer, Chilo partellus, were tested in a flight tunnel for their response to variation in the two major female sex pheromone gland components, (Z)-11-hexadecenal and the corresponding alcohol (OH). Variation of the alcohol in seven levels from 2 to 29% OH showed the highest male response for 17% OH. For all behavioral steps, the peak of male response was near μ = 0.14, while the window width fell from 2σ = 0.5 to 0.2 for eight sequential behavioral steps from take-off to copulation. Female production had a similar peak location (μ = 0.13) but a narrower width, 2σ = 0.14. Literature data from other moth species showed similar patterns, with a wider male response relative to the female production windows. Literature data on response to enantiomer ratios in a hymenopteran and to pheromone amounts in a dipteran were also described by our model. In a bark beetle population (Ips pini), with two hybridizing enantiomeric strains, the production peaks were narrower (0.1) than the response peaks (0.5). Thus, it in general, seems that in the pheromone systems analyzed, the width of the response window (2σ = 0.1 to 0.8) is larger than that of the production window (2σ = 0.03 to 0.14), irrespective of the sex of the sender.

High recaptures and long sampling range of pheromone traps for fall web worm mothHyphantria cunea (Lepidoptera: Arctiidae) males.

Newly emerged males ofHyphantria cunea (Drury) (Lepidoptera: Arctiidae), marked with different fluorescent colors, were recaptured by pheromone trapping. Three Uni-traps, baited with (3Z,6Z)9,10-epoxyheneicosadiene, (9Z,12Z,15Z)octadecatrienal, and (3Z,6Z)9,10-epoxyheneicosa-triene in a 1:10:1 ratio, total 6 mg/dispenser, were placed in a line 15 m apart, perpendicular to the dominant wind direction, and checked after 12, 36, and 60 hr. At dusk, releases of 10–25 males were made over distances from 30 to 250 m, during 4 periods over a soybean field (nonhost plant). Recapture rates were high; of a total of 176 males released, 115 were recaptured with 88% of these within 12 hours. Between 40 and 100% of males were recovered over shorter distances (30–150 m), and between 10–24% at longer distances (200 and 250 m). No other species or unmarked males were captured. The trapping period showed little effect on recaptures. The central trap of the three traps had somewhat higher catches, but the slope of the regression of recapture over distance did not differ among traps. There was a significant decline of recapture over distance (r=−0.56) for catches of individual traps but a large scatter. Summed recaptures per distance gave less scatter and hadr=−0.86, allowing calculation of the maximum sampling range (Rs) after 60 hr as 340 m with a 95% confidence interval of 190–710 m (regression of arcsin √p and √R). The area of sampling, found by integrating the probability function of recapture over distance, from the source to maximumR, was 7 ha. The high recapture rates and the longR,. compared to those in the literature for other taxa, indicate that pheromone traps are highly efficient sampling devices in this species.

Catching Ips duplicatus (Sahlberg) (Coleoptera: Scolytidae) with pheromone-baited traps: optimal trap type, colour, height and distance to infestation.

BACKGROUND Field trapping experiments were carried out to evaluate effective trap characteristics for maximising Ips duplicatus (Sahlberg) catches in pheromone-baited traps in China. RESULTS Window-slot and cross-barrier traps had significantly higher catches than multiple-funnel traps. The colour of window-slot traps showed a significant effect on catches, with dark colours (black and red) being more effective than light colours, especially white and yellow. Window-slot traps at a 1.5-2.0 m level caught more beetles than those at either ground level (0-0.5 m) or at 3.5-4.0 m. Ips duplicatus can be attracted to pheromone-baited traps over a distance of > 100 m from the forest edge in an open grassy field. There was a strong diurnal pattern of flight activity, with catches on window-slot traps occurring during the daytime with one broad peak at mid- to late afternoon. The seasonal flight activity of I. duplicatus as monitored by pheromone-baited window-slot traps during 2007-2008 indicated that three major flight peaks occurred in early June, late June-early July and late July respectively, suggesting the existence of a potential second generation. CONCLUSION The optimal trap characteristics will improve the performance of pheromone-baited traps as a critical monitoring or mass-trapping tool to combat outbreaks of this pest species.

Chemical Ecology of Bark Beetles in Regard to Search and Selection of Host Trees

Bark beetles (Coleoptera: Scolytidae), especially pests in the genera Dendroctonus, Ips, Scolytus, Trypodendron, Tomicus, and Pityogenes of the Northern hemisphere are reviewed regarding aspects of their chemical ecology during host finding and selection. Most of the species covered here feed on conifers, primarily pines (Pinus) in the Northern hemisphere and Norway spruce (Picea abies) of Europe and Asia. Bark beetles use a variety of olfactory strategies to discriminate suitable host trees from among less suitable, overcolonized, or decaying hosts as well as nonhosts. Bark beetles also use olfactory strategies to find mates and select attack sites. These strategies have implications for coevolution of trees and bark beetles. Knowledge of the chemical ecology of insect-insect and insect-plant relationships is necessary to develop improved methods for monitoring and controlling bark beetles that are predators of trees.

Attraction of the tea aphid, Toxoptera aurantii, to combinations of volatiles and colors related to tea plants

The tea aphid, Toxoptera aurantii Boyer (Hemiptera: Aphididae), is a major pest of the tea plant, Camellia sinensis (L.) O. Kuntze (Theaceae). The attraction of the aphids to different colors and volatile compounds from tea shoots was investigated. Fourteen compounds were identified using gas chromatography‐mass spectrometry from headspace samples of intact tea shoot volatiles (ITSV). Electrophysiological and behavioral responses of winged tea aphids to ITSV as well as to the full blend of 14 synthetic compounds, to a partial mixture of green leaf volatiles (GLV) included in the 14 compounds, and to individual synthetic compounds were studied by using electroantennography (EAG) and a Y‐tube olfactometer. The various tea volatiles and blends were strongly active, with ITSV being the strongest. In the greenhouse and in tea plantations, sticky boards of six different colors strongly attracted tea aphids in flight, with ‘rape‐flower yellow’ and ‘Chinese olive‐yellow‐green’ being the most attractive. Furthermore, these two boards in combination with ITSV attracted winged tea aphids more strongly than their corresponding colored sticky boards alone. In the greenhouse, plastic models of tea seedlings baited with (Z)‐3‐hexen‐1‐ol or the GLV mixture significantly attracted winged tea aphids in flight. This study demonstrates that green leaf volatiles from tea shoots are attractive to the tea aphid. The combination of these volatiles with the color light yellow or green, and the shape of tender tea shoots result in orientation flight and landing of winged tea aphids on host tea shoots.

Olfactory and visual responses of the longlegged chafer Hoplia spectabilis Medvedev (Coleoptera: Scarabaeidae) in Qinghai Province, China

BACKGROUND Monitoring traps and control methods are needed for the long-legged chafer, Hoplia spectabilis Medvedev, which has recently reached outbreak numbers in pastureland of Qinghai Province, China. RESULTS Field trapping experiments, using cross-pane funnel (barrier) traps, showed that H. spectabilis adults were not significantly attracted to branches of the host plant Dasiphora fructicosa (L.) Rydb. However, beetles were slightly attracted to similar host plant branches infested by conspecific beetles, possibly owing to weakly attractive volatiles, primarily (Z)-3-hexenyl acetate, released from beetle-damaged host leaves. This compound was weakly attractive when released from traps. However, H. spectabilis beetles showed strong visual responses to yellow- or white-painted trap panes, with weaker responses to blue, red or green panes, and least response to black panes. Black traps at 0.2-1.5 m above ground intercepted significantly more beetles than traps at 2.5 m. The mean flight height based on trap catches was 0.88 m (SD = 0.76), yielding an effective flight layer of 1.9 m. Flight response of beetles to colored barrier traps occurred between 10:00 and 18:00, and peaked between 12:00-14:00, when daily temperatures reached their maximum. CONCLUSION Unbaited yellow or white cross-pane funnel traps are recommended for both monitoring and mass-trapping programs against this economically and ecologically important scarab beetle.

Aggregation Pheromone of the Qinghai Spruce Bark Beetle, Ips nitidus Eggers

Volatiles from hindgut extracts of males of the Qinghai spruce bark beetle, Ips nitidus, from different attack phases (phase 1: unpaired males and phases 2–4: males joined with one to three females) and hindgut extracts of mated females were analyzed by gas chromatography–mass spectrometry (GC–MS)/flame ionization detection (FID) with both polar and enantioselective columns. The GC–MS/FID analyses demonstrated that unpaired males from attack phase 1 (nuptial chamber constructed) produced 2-methyl-3-buten-2-ol, approx. 74%-(−)-ipsdienol, and (−)-cis-verbenol as major hindgut components, and (−)-trans-verbenol, (−)-ipsenol, (−)-verbenone, myrtenol, and 2-phenylethanol as minor or trace components. The quantities of 2-methyl-3-buten-2-ol and especially ipsdienol decreased after mating during phases 2–4, whereas the quantities of (−)-cis- and (−)-trans-verbenol did not change. In contrast, the quantity of (−)-ipsenol seemed to increase as mating activity progressed. After mating with three females (harem size = 3; phase 4), only trace to small amounts of male-specific compounds were detected from I. nitidus male hindguts. Chemical analysis of the hindgut extracts of mated females showed only trace amounts of semiochemicals. A field-trapping bioassay in Qinghai, China showed that the four-component “full blend” containing the three major components, 2-methyl-3-buten-2-ol, (±)-ipsdienol, and (−)-cis-verbenol, plus a minor component, (−)-trans-verbenol, caught significantly more I. nitidus (♂/♀ = 1:2.2) than did the unbaited control and two binary blends. The replacement of (±)-ipsdienol with nearly enantiomerically pure (−)-ipsdienol in the “full blend” significantly reduced trap catches, which suggests that both enantiomers are needed for attraction. On the other hand, removal of (−)-trans-verbenol from the active “full blend” had no significant effect on trap catches. Our results suggest that the three major components, 2-methyl-3-buten-2-ol, 74%-(−)-ipsdienol, and (−)-cis-verbenol (at 7:2:1), produced by unpaired fed males, are likely the aggregation pheromone components of I. nitidus, thus representing the first characterization of an aggregation pheromone system of a bark beetle native solely to China.

2-methyl-3-buten-2-ol: A Pheromone Component of Conifer Bark Beetles Found in the Bark of Nonhost Deciduous Trees

Volatiles from bark of aspen,Populus tremulaL. and two species of birch: silver birch (Betula pendulaRoth.) and common birch (B. pubescensEhrh.), were collected by direct solvent extraction and aeration of both newly cut bark chips and undamaged stems in June 1998 and subjected to GC-MS analysis. The results showed the presence of 2-methyl-3-buten-2-ol (MB), one of the two principal aggregation pheromone components of the spruce bark beetle,Ips typographus, in bark extraction samples of all the three deciduous tree species tested. In addition, one more oxygenated hemiterpene, 3-methyl-3-buten-2-one, and (E)-3-penten-2-ol were also found in the bark extracts. Only trace amounts of MB were detected in some aeration samples of the fresh bark chips, and no MB was found from the aeration samples of undamaged stems at detectable levels. The occurrence of this compound was also confirmed in the bark of four exotic birch species:B. albosinensisSchneid.,B. ermaniiCham.,B. jacquemontiiSpach, andB. maximowiczianaRegel, but not yet in the European pines/spruces and the common yeasts. Our results raise major questions regarding the evolution, the tropospheric chemistry, and the ecological role of this hemiterpene alcohol. They also suggest that comparative studies on the biosynthetic pathways for MB in different sources would be of considerably evolutionary interest.