Field response of the pine sawfly Neodiprion sertifer to the pheromone (2S,3S,7S)-diprionyl acetate and its stereoisomers

All eight optical isomers of 3,7-dimethyl-2-pentadecanyl acetate (diprionyl acetate), of high optical purity (> 97.4%), were tested for a behavioural activity on male pine sawflies, Neodiprion sertifer (Geoffr.) (Hymenoptera: Diprionidae), in northern Europe. Males were strongly attracted to (2S,3S,7S)-diprionyl acetate. Addition of more than 0.1% of the (2S,3R,7R)-isomer reduced the catch and above 2% the attraction was completely inhibited. Contrary to what has been reported for North American and Japanese populations, so significant synergistic effect of small amounts of the (2S,3R,7R)-isomer could be demonstrated. The effects of addition of the other six optical isomers alone or in combinations, were also studied, but none was found to be a synergist. The (2S,3R,7S)-isomer had a weak inhibitory effect, and completely inhibited the attraction to the (2S,3S,7S)-isomer when applied in about equal amounts as the attractant. In some cases a reduction in catch was noted when other isomers were tested, but this could be attributed to the very small amounts of the inhibitory (2S,3R,7R)-isomer present in these isomers.     

Geographic variation in the field response of male European pine sawflies, Neodiprion sertifer, to different pheromone stereoisomers and esters

The European pine sawfly, Neodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae), is a widespread and economically important forest insect. The sex pheromone communication system of this species has been previously investigated in North America, Japan and Europe, with the acetate or propionate of the alcohol (2S,3S,7S)-3,7-dimethyl-2-pentadecanol (diprionol) shown to be the main pheromone component. In some locations, male attraction either increased or decreased by the addition of the (2S,3R,7R)-diprionyl acetate isomer. However, these studies were made with different batches of synthetic pheromones, with different types of traps and according to different procedures, so the observed differences might not reflect true geographic variation. Here we investigate the geographic pattern of male sawfly response by using identical chemicals, traps and experimental procedures at eight field sites ranging from Japan in the east to Canada in the west. We found an increased inhibitory effect of the (2S,3R,7R)-isomer from Japan and Siberia to Europe. At the eastern sites, increasing amounts of the (2S,3R,7R)-isomer up to and equal to the amount of the (2S,3S,7S )-isomer, did not influence the trap catch, whereas at sites in Europe, as little as 1% of the (2S,3R,7R)-isomer almost completely inhibited the attraction. The response of the North American population was intermediate. The only site in which the (2S,3R,7R)-isomer was essential for the attraction of males was in Siberia. A similar pattern was found for the (2S,3R,7S)-isomer. Both the acetate and the propionate form of the (2S,3S,7S)-isomer were attractive by themselves in Japan, Europe and North America, and neither the (2S,3R,7S)-isomer nor the (2S,3R,7R)-isomer alone were attractive, in the acetate or propionate form. We discuss the significance of our findings for the development of more efficient monitoring schemes and for the causes of population divergence and speciation in the European pine sawfly.     

Mating disruption of the pine sawfly Neodiprion sertifer (Hymenoptera: Diprionidae) in isolated pine stands

• 1 Previous applications of the mating disruption technique to Neodiprion sertifer resulted in decreased numbers of males caught in the treated area but no effect on sex ratio or overall population density.
• 2 The present study assessed the efficacy of mating disruption against N. sertifer outbreaks in pine stands surrounded by agricultural areas or pasture, and therefore isolated from other infested areas.
• 3 Pine stands were treated by placing dispensers with an erythro‐mixture of the acetate ester of 3,7‐dimethyl‐2‐pentadecanol every 10 m in a grid.
• 4 The efficacy of this technique was evaluated by comparing the number of males caught in sticky traps baited with synthetic pheromone, and by comparing the sex ratio and the population density of the sawfly in the subsequent generation between treated and control pine stands.
• 5 The number of males caught within treated areas was significantly lower than in the control area.
• 6 In the treated pine stands 46% of the egg clusters resulted in male cocoons only, compared to 3% of the clusters in the control stand.
• 7 A significant reduction of the sawfly population was observed in the treated pine stands. The results contrast to the earlier mating disruption attempts with N. sertifer and can probably be ascribed to the isolation of the experimental stands.

     

Monitoring the European pine sawfly with pheromone traps in maturing Scots pine stands

Abstract

• 1 During 1989–93, field studies were conducted in Finland to develop a method based on pheromone traps to monitor and forecast population levels of the European pine sawfly (Neodiprion sertifer Geoffr.) and tree defoliation.
• 2 Three traps per site were baited with 100 µg of the N. sertifer sex pheromone, the acetate ester of (2S,3S,7S)‐3,7‐dimethyl‐2‐pentadecanol (diprionol), in maturing pine stands in southern and central Finland. In addition, three different dosages (1, 10 and 100 µg) of the pheromone were tested in 1991–92.
• 3 The highest number of males was observed in traps baited with the highest dose. On average, there was a 10‐fold increase in trap catch between lure doses.
• 4 Density of overwintering eggs was used to evaluate the effectiveness of pheromone traps in predicting sawfly populations. The proportion of healthy overwintering eggs was determined each year. A model based on the number of current shoots on sample trees, diameter at breast height and tree height was formulated to estimate eggs per hectare.
• 5 Linear regression analysis produced high coefficients of determination between number of males in traps and density of total eggs in the subsequent generation, when populations were at peak densities. The relationships were not significant for low population densities. The results indicate a risk of moderate defoliation when the seasonal trap catch is 800–1000 males per trap or higher.

     

First use of pheromones to detect phenology patterns and density relationships of pine sawflies in German forests

1 Monitoring studies of pine sawflies with pheromone traps were performed for the first time in Germany. Pheromone traps baited with species‐specific pheromone substances were installed in pine forests at different locations in Bavaria, Brandenburg and Lower Saxony during two years. 2 It was possible to track the flight phenology of Diprion pini, Gilpinia pallida and Neodiprion sertifer reliably and to get information about the number of generations of these species in 1997 and 1998. 3 A clear relationship between trap catch and population density could not be detected, but qualitative changes in trap catch caused by different density levels were observed. 4 For D. pini, trap catches were different among endemic populations of different forest types. Furthermore, catches of males reflected the results from the regular cocoon collections by foresters during the previous winter. 5 For N. sertifer, trap catches in endemic populations were well separated from trap catches on sites with higher sawfly densities. However, no significant correlation between trap catch and sawfly density or defoliation level could be found. These results suggest that the efficacy of the pheromone traps probably varied with biological features (sex ratio, density level, immigration) of the particular population.     

Cocoon predation on diprionid sawflies: the effect of forest fertility

Predation by small mammals is thought to be one of the main regulators of outbreaking sawfly species. It has been suggested that predation may be lower in poor and dryish forests, and this is the reason why outbreaks often begin from this type of environment. We studied experimentally how fertility of the forest site affects cocoon predation experienced by two sawfly species, the common pine sawfly Diprion pini (Linnaeus) and the European pine sawfly Neodiprion sertifer (Geoffroy). We applied a fertilization treatment to selected pine-dominated barren forest sites in Finland, and 2–4 years later monitored predation on the sawfly cocoons in fertilized and control areas. The results did not support the idea that forest fertility was related to cocoon predation. We also could not verify that small mammal abundance was related to fertility of the forest. The most obvious pattern we observed was that the two sawfly species differed dramatically in predation experienced. N. sertifer has its cocoon phase in mid-summer and experienced only moderate predation (37%) whereas D. pini, with its cocoon phase in autumn, suffered from very heavy predation (96%). Our observations suggest that if predation is important in controlling the population dynamics of the species, its impact depends more on the sawfly species and season than on the fertility of the forest site. Received: 1 March 1998 / Accepted: 25 May 1998     

Identification and behavioral evaluation of sex pheromone components of the Chinese pine caterpillar moth, Dendrolimus tabulaeformis

Background

The Chinese pine caterpillar moth, Dendrolimus tabulaeformis Tsai and Liu (Lepidoptera: Lasiocampidae) is the most important defoliator of coniferous trees in northern China. Outbreaks occur over enormous areas and often lead to the death of forests during 2–3 successive years of defoliation. The sex pheromone of D. tabulaeformis was investigated to define its chemistry and behavioral activity.

Methodology/Principal Findings

Sex pheromone was collected from calling female D. tabulaeformis by headspace solid phase microextraction (SPME) and by solvent extraction of pheromone glands. Extracts were analyzed by coupled gas chromatography/mass spectrometry (GC-MS) and coupled GC-electroantennographic detection (GC-EAD), using antennae from male moths. Five components from the extracts elicited antennal responses. These compounds were identified by a combination of retention indices, electron impact mass spectral matches, and derivatization as (Z)-5-dodecenyl acetate (Z5-12:OAc), (Z)-5-dodecenyl alcohol (Z5-12:OH), (5Z,7E)-5,7-dodecadien-1-yl acetate (Z5,E7-12:OAc), (5Z,7E)-5,7-dodecadien-1-yl propionate (Z5,E7-12:OPr), and (5Z,7E)-5,7-dodecadien-1-ol (Z5,E7-12:OH). Behavioral assays showed that male D. tabulaeformis strongly discriminated against incomplete and aberrant blend ratios. The correct ratio of Z5,E7-12:OAc, Z5,E7-12:OH, and Z5,E7-12:OPr was essential for optimal upwind flight and source contact. The two monoenes, Z5-12:OAc and Z5-12:OH, alone or binary mixtures, had no effect on behavioral responses when added to the optimal three-component blend.

Conclusions/Significance

The fact that deviations from the optimal ratio of 100∶100∶4.5 of Z5,E7-12:OAc, Z5,EZ7-12:OH, and Z5,E7-12:OPr resulted in marked decreases in male responses suggests that biosynthesis of the pheromone components is precisely controlled. The optimal blend of the sex pheromone components of D. tabulaeformis worked out in this study should find immediate use in monitoring this pest in Chinese forests.     

Development of mating disruption for control of pine sawfly populations

Mating disruption of the pine sawflyNeodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae) was strongly indicated by reduced male trap catches in pine plantations permeated with the sex phermone, (2S, 3S, 7S)-diprionly acetate. The trap catch reduction was 95 to near 100% when dispensers every 10 m were used, giving a total release of about 3 mg per hectare and day. Two mg of pheromone per cotton roll dispenser maintained low catches for the whole season (about 2 months) without any renewal of disruption dispensers. Anerythro-mixture was as effective as the pure pheromone isomer. The effects of the experiments on population density and sex ratio were not possible to investigate, due to a general collapse of the population, also outside experimental plots, the year after the experiments.     

Influence of wind conditions and intertrap spacing on pheromone trap catches of male european pine sawfly,Neodiprion sertifer

The spatial distribution of catches of male European pine sawfly,Neodiprion sertifer (Geoffr.) (Hymenoptera, Diprionidae), was studied using different pheromone trap arrays. In hexagonal trap groups, trap interference was evident by reduced catch in the central of seven traps spaced 10 to 40 m apart. When the trap spacings were either 5 or 80 m no significant reduction could be shown. The interaction was more pronounced for strong (100 μg) pheromone ([2S, 3S, 7S]-3,7-dimethyl-2-pentadecanyl acetate) lures than for weak ones (10 μg). Similarly, the inner traps caught less than the outer traps in grids of 6×6 traps spaced 20 or 50 m apart. Mark-release-recapture experiments in the grid array confirmed that a majority of the males originated from outside the trap group and were caught in the first trap they encountered. There were no differences between catches in downwind, crosswind and upwind traps. Thus, no ‘overshooting’ was evident during average conditions, i.e. the sawflies did not divert from the trap initially attracting them by flying to the upwind trap. However, the proportion caught in the upwind traps increased with increasing wind velocity, suggesting more overlapping pheromone plumes at higher wind speeds. Also, the recapture rate of released males increased with increasing wind velocity up to a daily average of 3.1 m/s at 2m, indicating that sawflies more easily find the pheromone source, probably due to a more stable pheromone puff trajectory during higher wind velocities. The application of pheromone traps in e.g. monitoring studies is discussed and a distance of at least 50 m between the traps with strong lures used in the present study is recommended to avoid trap interaction.     

Effects of group size and pine defence chemicals on Diprionid sawfly survival against ant predation

The defence chemicals and behavioural adaptations (gregariousness and active defensive behaviour) of pine sawfly larvae may be effective against ant predation. However, previous studies have tested their defences against very few species of ants, and few experiments have explored ant predation in nature. We studied how larval group size (groups of 5 and 20 in Neodiprion sertifer and 10, 20 and 40 in Diprion pini) and variation in levels of defence chemicals in the host tree (Scots pine, Pinus sylvestris) affect the survival of sawfly larvae. Food preference experiments showed that ants do eat sawfly larvae, although they are not their most preferred food item. According to our results, ant predation significantly increases the mortality rate of sawfly larvae. Larval mortality was minor on pine tree branches where ant traffic was excluded. We also found that a high resin acid concentration in the host tree significantly decreased the mortality of D. pini larvae when ants were present. However, there was no such relationship between the chemical concentrations of the host tree and larval mortality for N. sertifer. Surprisingly, grouping did not help sawfly larvae against ant predation. Mortality risk was the same for all group sizes. The results of the study seemingly contradict previous understanding of the effectiveness of defence mechanisms of pine sawfly against ant predation, and suggest that ants (Formica exsecta in particular) are effective predators of sawfly larvae.An erratum to this article can be found at     

Relationship between sex pheromone elicited behaviour and response of single olfactory receptor neurones in a wind tunnel

Responses from pheromone‐specific receptor neurones in male Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae) were recorded in a laboratory wind tunnel. Stimuli were: (1) rubber septum dispensers loaded with single components or a four‐component pheromone blend, (2) excised glands from female A. segetum, (3) constrained A. segetum females with extruded glands. Dose–response curves for three neurone‐types with different specificity were established. The neurones were specifically tuned to respond to either one of the two pheromone components (Z)‐5‐decenyl acetate and (Z)‐7‐dodecenyl acetate, or to the behavioural antagonist (Z)‐5‐decenol. In parallel, a behavioural dose–response curve with males flying upwind to a four‐component pheromone blend was established. There was a clear correlation between behavioural arrestment of upwind flight and maximum spiking activity in Z5–10:OAc‐specific neurones. The pheromone release rates of individual females and synthetic dispensers were compared. A load of 50–200 ng of Z5–10:OAc on a rubber septum elicited approximately the same neural response as one female gland.     

High consumption rate by Neodiprion sertifer?—A comment on a paper by Larsson and Tenow

Summary In a recently published food utilization study of larvae of the European pine sawfly, Neodiprion sertifer (Larsson and Tenow, Oecologia (Berl) 43 (1979) 157–172), it was concluded that a high consumption rate was part of a suite of presumed adaptations exhibited by these larvae for feeding on a food with a low nitrogen content. In this note it is shown that larvae of N. sertifer exhibit a relative consumption rate which is comparable to that of other sawflies and intermediate in comparison to other herbivorous insects.     

Electrophysiological and behavioural evidence for a fourth sex pheromone component in the turnip moth, Agrotis segetum

Abstract. In addition to the pheromone components (Z)-5-decenyl, (Z)-7-dodecenyl and (Z)-9-tetradecenyl acetate (Z5-10:OAc, Z7-12:OAc and Z9-14:OAc), it has previously been shown that the sex pheromone gland of the turnip moth, Agrotis segetum (Lepidoptera: Noctuidae Schiff) contains 10:OAc, 12:OAc, Z5-12:OAc, Z9-12:OAc, 11–12:OAc, Z5-14:OAc, Z7-14:OAc and Z11-16:OAc. To find out whether any of these additional compounds is involved in the sex pheromone communication in A. segetum, a comprehensive electro-physiological and behavioural investigation was conducted. Single-sensillum recordings on male antennae revealed three subtypes of sensilla among the previously so-called Z5-10:OAc sensilla. One subtype was identified having one receptor neurone (A) that responded to Z5-10:OAc with a large spike amplitude and another neurone (B) that responded to (Z)-5-decenol (Z5-10:OH) with a small spike amplitude. In another subtype the B neurone responded to Z5-12:OAc and sometimes also to 27-12:OAc and 10:OAc, in addition to responding to Z5-10:OH. In a third subtype the A neurone responded to all acetates identified from the female pheromone gland, whereas the small spike amplitude neurone was tuned to Z5-10:OH. A flight tunnel assay showed that blends composed of nine, eight or seven compounds were equivalent to the previously identified three-component pheromone blend in eliciting male behavioural responses. In field trapping tests, blends of eleven, nine or seven compounds did, however, catch significantly more moths than the three-component blend. Further assays showed that only 25- 12:OAc could significantly increase the catch numbers when added to the three-component blend, and thus qualified as a fourth pheromone component in A. segerum. The behavioural significance of additional female-produced acetates — for which males possess antennal receptors — is suggested, but may be impossible to confirm because of ‘diminishing returns’ when trying to refine a multicomponent pheromone further.     

Antennal sensitivity to female sex pheromone compounds of Spodoptera frugiperda males (Lepidoptera: Noctuidae) and associated field behaviour

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is one of the most important insect pests of corn, sorghum, rice, and grasses. The sex pheromone produced by S. frugiperda is composed of a mixture of esters. In this study, I determined the antennal responses of FAW males from 22 populations in Mexico to the components of the sex pheromone of this species: (Z)-7-dodecenyl acetate (Z7-12:OAc), (Z)-9-tetradecenyl acetate (Z9-14:OAc), and (Z)-11-hexadecenyl acetate (Z11-16:OAc) at four doses (0.01, 0.1, 1, and 10 μg). In addition, I evaluated the behavioural activity of single compounds in the field. The largest antennal responses of FAW males from all the sampled regions were elicited by Z9-14:OAc (all doses evaluated) and Z7-12:OAc (0.01, 0.1, and 1 μg). The male antennal responses evoked by Z11-16:OAc were smaller but similar to responses to Z7-12:OAc at lower doses (0.01 and 0.1 μg). In the field test, Z9-14:OAc produced significantly higher captures of S. frugiperda males compared to Z7-12:AOc and Z11-16:OAc. Antennal responses were related to captures obtained in the field, supported by the positive correlation of these variables [electroantennography (EAG) response and behaviour], with the exception of Z7-12:OAc, which elicited relatively large EAG responses but did not produce high captures of S. frugiperda. These results are of importance to agriculture, enabling the implementation of better methods of monitoring and controlling this pest, and support the suggestion that a mixture of Z9-14:OAc and Z7-12:OAc could represent an effective attractant for all evaluated populations of S. frugiperda in Mexico.     

No inhibitory effect on receptor neurone activity by sulphur analogues of the sex pheromone component (Z)-5-decenyl acetate in the turnip moth, Agrofis segetum (Lepidoptera: Noctuidae)

Abstract. Olfactory responses from the entire antenna and from single antennal sensilla of the male turnip moth, Agrotis segetum (Lepidoptea: Noctuidae Schiff.), were recorded after stimulation of the antenna with the sex pheromone component, (Z)-5-decenyl acetate (Z5-10:OAc), and three sulphur analogues of this compound. Adaptation of olfactory receptor neurones tuned to Z5-10:OAc was investigated after pre-exposure of these receptor neurones to the key stimulus and to the three sulphur analogues. Both electro-antennographic and single sensillum recordings revealed that the sulphur analogues had a significantly decreased effect compared to the natural stimulus. The pre-exposure experiments demonstrated that no further inhibition of neural activity was observed than could be expected from receptor neurone adaptation. Earlier reports, describing sulphur analogues as possible hyperagonists acting on moth pheromone receptor neurones, are not supported by the present study.     

Acidic precipitation increases egg survival in Neodiprion sertifer

The effects of simulated acidic precipitation on the egg viability of the European pine sawfly, Neodiprion sertifer Geoffroy (Hymenoptera: Diprionidae) were studied by spraying egg clusters with a mixture of sulphuric and nitric acid (1:1, pH 2, 3, 4, 5, 6, distilled water, natural precipitation) for a month in April–May. Egg viability analyses showed that the proportion of hatched first instar larvae increased with increasing acidity. The better survival of sawfly eggs in pine needles in more acidic conditions may be partly due to changes in needle physiology affecting egg mortality. However, when the eggs were reared without needles in Petri-dishes, the proportion of successfully hatched larvae likewise increased with increasing acidity indicating direct acid-induced changes in the eggs themselves. Acidic precipitation as a stress factor of the host plant apparently changes population dynamics of pine sawflies and may be an important factor in triggering outbreaks.     

Effect of forest stand type on host plant quality and direct and indirect effects on pine sawfly performance

1. Observed lower levels of herbivory in mixed compared with monoculture stands have been hypothesized to depend on top-down forces, through higher predation pressure by natural enemies or through bottom-up mechanisms through plant quality effects on herbivore performance.
2. In this study, we compared the performance measured as host plant induced mortality, cocoon weight, and predation mortality of the European pine sawfly Neodiprion sertifer (Geoffroy) (Hymenoptera, Diprionidae) in mixed and monoculture forest stands.
3. We did not observe a difference in host plant induced mortality, cocoon weight, or predation mortality between mixed and monoculture forest stands. We did find an effect of local conditions around each experimental tree on pine sawfly performance. For example, the nitrogen content of pine needles is negatively affected by the proportion of pine around the experimental tree, which in turn increases the survival of sawfly larvae.
4. The results suggest that local conditions around individual trees are more important for the performance of the European pine sawfly than stand type, i.e. mixed or monoculture plant stands.
5. We conclude that the ongoing trend for diversification within commercial forestry calls for more research where the effects of both bottom-up and top-down effects are studied at several spatial scales.

     

Notes on New Zealand mammals 10. Effect of observer position on group size and level of aggression of mating brown hares

Abstract

The sex pheromones of two endemic New Zealand tortricid species were investigated. Females of the first species, Cnephasia jactatana, a pest of kiwifruit, were found to produce (Z)-11-tetradecenyl acetate (Z11-14:OAc) in their sex pheromone gland. When tested in the field, this compound on its own elicited significant catches of male C. jactatana. However, the addition of even very small amounts (0.3%) of the geometric isomer, (E)-11-tetradecenyl acetate (E11-14:OAc), to Z 11-14:OAc virtually suppressed trap catches. The sex pheromone of the second species, Merophyas leucaniana, was found to consist of a mixture of Z11-14:OAc, E11-14:OAc, tetradecyl acetate, and (Z)-11-tetradecenol. This species is morphologically very similar to the congeneric species, M. divulsana, the Australian lucerne leafroller. The sex pheromone of M. leucaniana is also very similar to that of the so-called “Z-type” of M. divulsana, which is now found in New Zealand. The pheromone components of C. jactatana and M. leucaniana are discussed in relation to those found in other tortricids.     

Trait‐mediated indirect interactions: Moose browsing increases sawfly fecundity through plant‐induced responses

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Geographic variation in winter freezing susceptibility in the eggs of the European pine sawfly (Neodiprion sertifer)

Abstract 1 The European pine sawfly, Neodiprion sertifer (Geoffroy) (Hymenoptera, Diprionidae), frequently defoliates Scots pine (Pinus sylvestris L.) forests in northern Europe. It overwinters as an egg. It has been proposed that the high egg mortality caused by low winter temperatures limits the occurrence of outbreaks to the southern part of Fennoscandia. 2 In this study, variation in freezing avoidance by egg supercooling between four Finnish populations (originating between latitudes 60°N and 69°N) of N. sertifer was tested by differential thermal analysis. Offspring of 20 females within each population were selected for the study. The freezing avoidance of parasitized eggs was also examined. 3 The northernmost Inari population was found to be the cold hardiest, and the southernmost (Hanko) was the least hardy population. The within‐population variation between females was greatest in the population from Inari, and the next greatest in the one from Hanko. The inland populations in Eastern Finland had the smallest within‐population variation in freezing avoidance. 4 The high variation in freezing avoidance of eggs will enable N. sertifer to adapt to the predicted climate change and to spread its distribution northwards. This may also change the risk for outbreaks in this area. Parasitized eggs froze at higher temperature than healthy eggs. This observation indicates that N. sertifer may experience reduced egg parasitism in certain winter climate conditions.