Asian chestnut gall wasp in Tuscany: gall characteristics,egg distribution and chestnut cultivar susceptibility

• 1 Preliminary investigations were carried out on Dryocosmus kuriphilus Yasumatsu on Castanea sativa Miller in Tuscany to assess variations in gall characteristics in coppice and high forest at two crown heights (height < 2 or 2–6 m), influence of bud size and bud position on oviposition rates and susceptibility of three cultivars.
• 2 Gall size may depend on various factors, including wasp population density. In the present study area, small galls (with one or two cells) were the most numerous in 2008, whereas larger galls (with more than three cells) prevailed in 2009.
• 3 Dryocosmus kuriphilus oviposition occurrence was influenced by both bud size and bud position. Buds with eggs tended to be larger in size compared with bud without eggs, suggesting that D. kuriphilus females prefer to lay eggs in larger buds (approximately 6 mm³) compared with smaller buds (approximately 3 mm³). The mean number of eggs per bud tended to decrease from the apical bud toward the basal bud.
• 4 Three C. sativa cultivars, Carpinese, Fusca and Cesurone, were examined. Fusca grafts had significantly more galls compared with Carpinese and Cesurone, whereas Cesurone grafts had more larvae per bud compared with Carpinese and Fusca. Overall, the Carpinese cultivar may be less susceptible to D. kuriphilus galling compared with the Fusca and Cesurone cultivars.

     

A plant pathogen causes extensive mortality in an invasive insect herbivore

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Invasion windows for a global legume invader are revealed after joint examination of abiotic and biotic filters

• Successful alien plant invasion is influenced by both climate change and plant–plant interactions. We estimate the single and interactive effects of competition and extreme weather events on the performance of the global legume invader Lupinus polyphyllus (Lindl.).
• In three experimental studies we assessed (i) the stress tolerance of seedling and adult L. polyphyllus plants against extreme weather events (drought, fluctuating precipitation, late frost), (ii) the competitive effects of L. polyphyllus on native grassland species and vice versa, and (iii) the interactive effects of extreme weather events and competition on the performance of L. polyphyllus.
• Drought reduced growth and led to early senescence of L. polyphyllus but did not reduce adult survival. Fluctuating precipitation events and late frost reduced the length of inflorescences. Under control conditions, interspecific competition reduced photosynthetic activity and growth of L. polyphyllus. When subjected to competition during drought, L. polyphyllus conserved water while simultaneously maintaining high assimilation rates, demonstrating increased water use efficiency. Meanwhile, native species had reduced performance under drought.
• In summary, the invader gained an advantage under drought conditions through a smaller reduction in performance relative to its native competitors but was competitively inferior under control conditions. This provides evidence for a possible invasion window for this species. While regions of high elevation or latitude with regular severe late frost events might remain inaccessible for L. polyphyllus, further spread across Europe seems probable as the predicted increase in drought events may favour this non‐native legume over native species.

     

No loss of genetic divergence in Torymus sinensis following its release for Dryocosmus kuriphilus control in Europe

1. Arrival, establishment, and further dispersal of non-native natural enemies are considered essential for a successful biological control programme, while among the factors that may determine the success of such a programme, genetic diversity of the introduced population plays an important role in the establishment of a non-native species.
2. The Chinese parasitoid wasp Torymus sinensis Kamijo (Hymenoptera: Torymidae) was initially released in Europe in Italy to control biologically the Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), and reduce the damage induced on sweet chestnut (Castanea sativa Miller). In the following years, T. sinensis was then released in numerous other European countries as a biological control agent of D. kuriphilus. Its presence has also been reported beyond the countries of release due to rapid natural dispersal.
3. To assess the post-release genetic diversity of D. kuriphilus, we screened T. sinensis populations from six European countries and tested the possibility of these populations suffering from frequently observed genetic effects that could threaten its successful establishment in Europe.
4. Our results exhibit that T. sinensis populations have suffered neither from the Allee effect nor from genetic bottleneck after their release and establishment in Europe, something that increases the possibility to effectively control D. kuriphilus in Europe.

     

Cicadomorpha community (Hemiptera: Auchenorrhyncha) in different agroecosystems in the north of Portugal

1. The infraorder Cicadomorpha is a diverse group comprising several species considered important pests of economic crops and species that may act as vectors of plant pathogens. In Europe, the gram-negative bacterium Xylella fastidiosa is one of the most important and severe insect-borne plant pathogens associated with the infraorder Cicadomorpha.
2. Therefore, the knowledge of the abundance and diversity of native Cicadomorpha insect vectors related to the different agroecosystems is essential to design and implementing specific measures to control insect-borne plant pathogens.
3. In this work, in two consecutive years (2018 and 2019), five almond orchards, five vineyards, five olive orchards, and five scrublands distributed in the North of Portugal were sampled in three different periods (early summer, summer and autumn) to investigate species composition, richness, and diversity of the Cicadomorpha community. Also, in 2019, five lemon orchards were sampled.
4. A total of 6056 individuals were collected (2322 in 2018 and 3734 in 2019), belonging to 71 species of three families. Observing several considered pests or vectors of vicious pathogens within these species was possible. The confirmed vectors of X. fastidiosa (Philaenus spumarius (Linnaeus, 1758) and Neophilaenus campestris (Fallen, 1805)) were captured in all agroecosystems and, in general, with more abundance in autumn. The highest abundance, richness, and diversity of Cicadomorpha were observed in vineyards. However, these parameters (abundance, richness and diversity) significantly differed between the agroecosystem and sampling period.
5. Further research on how the composition of the vegetation cover shapes the Cicadomorpha community is essential to implement strategies to reduce the spread of insect-borne pathogens if they are introduced into agroecosystems.

     

Water‐soluble carbohydrates in Patzkea paniculata (L.): a plant strategy to tolerate snowpack reduction and spring drought in subalpine grasslands

• In subalpine grasslands of the central French Alps, cessation of traditional mowing promotes dominance of Patzkea paniculata (L.) G.H.Loos (Poaceae) tussocks, with high biomass but low fodder quality. Mowing limits P. paniculata abundance through the depletion of its water‐soluble carbohydrate (WSC) reserves, which sustain early spring growth initiation. However, the effectiveness of mowing effects is modulated by grassland functional composition, fertilization and climate change, as WSC compounds, and notably fructans, support plant physiological responses to climate stresses such as drought or frost.
• To characterize the mechanisms underpinning the control of P. paniculata under global change, we tested the effects of climate manipulation (combined snow removal and drought) and management (cutting and fertilization) alone or in combination on P. paniculata WSC storage in assembled grassland communities of varying functional composition.
• Management and climate treatments individually decreased seasonal fructan storage, with neither additive nor synergic effects between them, primarily due to the dominance of management over climate effects. Fructan amounts were higher in individuals growing in unmanaged exploitative communities compared to unmanaged conservative communities, regardless of climate treatments, but management overrode these differences.
• Our findings suggest that reduction by combined snow removal and drought of P. paniculata carbon allocation to WSC storage may similarly limit its dominance to that in current mowing practices.

     

Effects of water stress on plant volatile emission and insect oviposition preference in an agroecosystem

1. Drought has become more common and severe in many parts of the world due to climate change. The effect of water stress on insect oviposition preference that is key determinant for their fitness has received less attention.
2. Here, we examined how water stress may affect oviposition selection of Ostrinia furnacalis for maize plants in the greenhouse, and tested difference in volatile compounds emitted from treated maize, and electronantennogram and bioassay responses of O. furnacalis to the volatile profiles in maize plants.
3. Ostrinia furnacalis were more prone to lay eggs on the well-watered maize. Most plant volatile compounds differed significantly among the three water treatments, including increased emissions of β-caryophyllene, (E)-2-hexenal, and linalool, and decreased emission of (Z)-3-hexen-1-ol when subjected to increasing intensity of drought.
4. Varied volatile profiles of maize may drive oviposition decision of O. furnacalis, because O. furnacalis showed a clear oviposition preference for (Z)-3-hexen-1-ol, while not for β-caryophyllene, (E)-2-hexenal, and linalool, at the concentration of 1000 ppm.
5. This study advances understanding of drought effects on plant–insect interactions through volatile profiles. Our finding calls for attention to oviposition selection for insect pest management in agricultural settings, especially in regions under changing precipitation patterns.

     

Investigating the abundance and flight period of bark beetles (Coleoptera: Curculionidae: Scolytinae) over elevational gradients in Sitka spruce forests

1. A warming climate, as predicted under current climate change projections, is likely to influence the population dynamics of many forest insect species. Numerous bark beetle species in both Europe and North America have already responded to a warming climate by significantly expanding their geographical ranges.
2. The aim of the current study was to investigate how populations of bark beetles within stands of Sitka spruce, a widely planted non-native commercial plantation tree species in the U.K., were likely to respond to a warming climate. Experimental plots were established in stands of Sitka spruce over elevational gradients in two commercial forest plantations, and the abundance and emergence times of key bark beetle species were assessed over a 3-year period using flight interception traps. The air temperature difference between the lowest and highest experimental plot in each forest was consistently >1°C throughout the 3-year period.
3. In general, the abundance of the most dominant bark beetle species (e.g. Trypodendron, Dryocoetes, Hylastes spp.) was higher, and emergence times tended to be earlier in the year at the lower elevation plots, where temperatures were higher, although not all bark beetle species responded in the same manner.
4. The results of the study indicated that, under the projected future climate warming scenarios, monoculture Sitka spruce stands at low elevations may potentially be more vulnerable to significant outbreak events from existing or invasive bark beetle species. Hence, consideration of establishing more resilient forests of Sitka spruce by diversifying the species composition and structure of Sitka spruce stands is discussed.

     

Biology and monitoring of Dryocosmus kuriphilus on Castanea sativa in Southern Italy

• 1 The cynipid gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) is an invasive wasp in Europe and is one of the major pests of chestnuts worldwide. An investigation of this cynipid was started in Campania, Southern Italy, in 2008, with the aim of providing guidelines for its sustainable control.
• 2 The number of larvae/gall increased in the second year of colonization relative to the first one but thereafter decreased in the third year of colonization, whereas the volume of the galls after the initial increase in the second year of colonization became stable. Adult emergence generally peaked between the middle of June and July.
• 3 The only reliable method for assessing the presence of the pest at its earliest stage was through dissecting the buds because oviposition scars on the buds tended to disappear during the winter.
• 4 Yellow traps were shown to be an effective method for assessing the emergence of cynipid adults and could potentially be used to time chemical applications in those cases in which this control method is feasible.
• 5 No correlation was recorded between the relative durations of the final stages (pupae, pharate adults and emergence).
• 6 Possible control strategies for this invasive pest are discussed.

     

Tolerance to multiple climate stressors: a case study of Douglas‐fir drought and cold hardiness

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Invasion by the chestnut gall wasp in Italy causes significant yield loss in Castanea sativa nut production

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The effects of drought and herbivory on plant–herbivore interactions across 16 soybean genotypes in a field experiment

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Histological investigation on gall development induced by a worldwide invasive pest,Dryocosmus kuriphilus,on Castanea sativa

The Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae) is one of the most serious pests of chestnut trees worldwide. Wasps lay eggs into chestnut buds from mid Jane to late July, depending on latitude, and galls develop the following spring on new vegetation, reducing photosynthesis and nut production. We observed that modification of tissues surrounding D. kuriphilus eggs, which differentiate to form the larval chamber, started approximately 1 month after oviposition, shortly after eggs hatch. The larval chambers continued to increase slightly in size throughout the autumn months until January. After that, a period of stagnation, which corresponds to the plant's dormancy, occurred, followed by rapid growth from March to May, during the period from bud swelling to bud break. Galls continued to grow during the leaf expansion after bud break and stopped when plant organs achieved their final size. Our results have implications for the management of the pest, providing a better understanding of the critical time periods for the effective control.     

Seasonal flight activity and genetic relatedness of Torymus species in Italy

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Multiple effects of temperature,photoperiod and food quality on the performance of a pine sawfly

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Influence of light,dark, temperature and drought on metabolite and ion composition in nectar and nectaries of an epiphytic bromeliad species (Aechmea fasciata)

• Research into the influence of stress factors, such as drought, different temperatures and/or varied light conditions, on plants due to climate changes is becoming increasingly important. Epiphytes, like many species of the Bromeliaceae, are particularly affected by this, but little is known about impacts on nectar composition and nectary metabolism.
• We investigated the influence of drought, different temperatures and light–dark regimes on nectar and nectaries of the epiphytic bromeliad species, Aechmea fasciata, and also the influence of drought with the terrestrial bromeliad, Billbergia nutans. The content of sugars, amino acids and ions in nectar and nectaries was analysed using HPLC. In addition, the starch content and the activities of different invertases in nectaries were determined.
• Compositions of nectar and nectaries were hardly influenced, neither by light nor dark, nor by different temperatures. In contrast, drought revealed changes in nectar volumes and nectar sugar compositions in the epiphytic bromeliad as well as in the terrestrial bromeliad. In both species, the sucrose‐to‐hexose ratio in nectar decreased considerably during the drought period. These changes in nectar sugar composition do not correlate with changes in the nectaries. The total sugar, amino acid and ion concentrations remained constant in nectar as well as in nectaries during the drought period.
• Changes in nectar composition or in the production of floral pollinator rewards are likely to affect plant–pollinator interactions. It remains questionable how far the adaptations of the bromeliads to drought and diverse light or temperature conditions are still sufficient.

     

Frost fatigue response to simulated frost drought using a centrifuge in Acer mono Maxim

In the coldest part of winter, water uptake is blocked by the frozen soil and frozen stems known as ‘frost drought’ causing severe embolisms in woody plants. Frost drought in stems was simulated in a centrifuge by a synergy between freeze–thaw cycles and the different tensions induced by changing the rotation speed. Frost fatigue was defined as a reduction of embolism resistance after a freeze–thaw cycle and determined from ‘vulnerability curves’, which showed percent losses of conductivity vs tension (positive value) or xylem pressure (negative value). Different tensions combined with a controlled freeze–thaw cycle were induced to investigate the effects on frost resistance over the course of year. During the growing season, Acer mono Maxim. developed significant frost fatigue, and a significant positive correlation was found between frost fatigue response and exogenous tension. During the dormant season, A. mono showed very high embolism resistance to frost drought, even under a tension of 2 MPa. When the exogenous tension was increased to 3 MPa while the stem was frozen, significant frost fatigue occurred. Longer freezing times had more serious effects on frost fatigue in A. mono. A hypothesis was raised that at the same low temperature, the severer the drought (higher tension) when stems were frozen, the higher frost fatigue response would be induced.     

Rearing,release and settlement prospect in Italy of <Emphasis Type="Italic">Torymus sinensis</Emphasis>, the biological control agent of the chestnut gall wasp <Emphasis Type="Italic">Dryocosmus kuriphilus</Emphasis>

Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), is one of the most serious pests attacking chestnut trees. Recently it was incidentally introduced into Northwest Italy and it is now spreading throughout Europe. This pest was successfully controlled in Japan by introducing a parasitoid, Torymus sinensis Kamijo (Hymenoptera: Torymidae), from China’s mainland. Following this successful experience, the parasitoid was introduced into Italy from Japan. One year of preliminary studies led to a successful method of rearing imported galls with a synchronization between the parasitoid’s emergence and the presence of the target galls in the field. In two consecutive years, a total of 2,117 individuals were released in several sites covering most of the infested area. There are encouraging data about the settlement of the parasitoid and its synchrony with the host’s cycle: from about 64,000 host galls collected in the field over 200 T. sinensis were reared. The role of native parasitoids associated with the chestnut gall pest in its Italian distribution range is also discussed.     

Population dynamics of noctuid moths and damage forecasting in sugar beet

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Increased nutrient availability decreases insect resistance in cranberry

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