Effects of bud phenology and foliage chemistry of balsam fir and white spruce trees on the efficacy of Bacillus thuringiensis against the spruce budworm, Choristoneura fumiferana

Abstract 1 Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana was investigated in mixed balsam fir‐white spruce stands. Btk treatments were scheduled to coincide with early flaring of balsam fir shoots, and later with flaring of white spruce shoots. Btk efficacy on the two host trees was compared and examined according to the foliar content of nutrients and allelochemicals and the insect developmental stage at the time of spray. 2 Larvae fed white spruce foliage were less vulnerable to Btk ingestion than larvae fed balsam fir foliage. Higher larval survival on white spruce, observed 10 days after spray, was related to higher foliage content in tannins and a lower N/tannins ratio, which might have induced inactivation of Btk toxins. 3 Larval mortality due to Btk did not depend on spruce budworm larval age. 4 Foliage protection of both host trees was similar in plots treated with Btk: larval mortality due to Btk treatment reduced insect grazing pressure on balsam fir trees; meanwhile, suitability of white spruce foliage seemed to decrease very rapidly, which induced high larval mortality among spruce budworm fed on white spruce trees. Nevertheless, following Btk sprays, 50% more foliage remained on white spruce than on balsam fir trees, because of the higher white spruce foliage production. 5 Both spray timings achieved similar protection of white spruce trees, but Btk treatments had to be applied as early as possible (i.e. during the flaring of balsam fir shoots to optimally protect balsam fir trees in mixed balsam fir‐white spruce stands).     

Effects of food nutritive quality and Bacillus thuringiensis onfeeding behaviour, food utilization and larval growth of spruce budworm Choristoneura fumiferana (Clem.) when exposed as fourth- and sixth-instar larvae

Abstract 1 Feeding behaviours, and lethal and sublethal (growth, development and food utilization) effects of Foray 48B, a commercial formulation of Bacillus thuringiensis (kurstaki), were investigated on fourth‐ and sixth‐instar spruce budworm larvae according to food nutritive quality. Nitrogen and soluble sugar content of artificial diets were modified to obtain three different qualities of food, simulating variations in nutritive quality of host tree. 2 Larval development times were longer for Bt‐treated larvae and pupal weights were reduced for sixth‐instar larvae only. Bt‐induced mortality levels were influenced by food quality. Ingested dose of Bt and feeding inhibition times were strongly affected by the Bt treatment, but food quality affected only fourth‐instar larvae. Except for food digestibility, nutritional indices were negatively affected by the Bt treatment and by the reduction in food quality. 3 Contrary to early treated larvae (fourth instar), larvae treated at the beginning of the sixth instar were not able to compensate for Bt injury and were consequently more affected by the Bt‐treatment both in terms of lethal and sublethal effects. 4 Bt efficacy was not directly related to the ingested dose. 5 Increase in larval vulnerability to Bt was more likely a consequence of a general stress induced by a less suitable food than a direct interaction between Bt and food nitrogen or sugar compounds. 6 The application of Bt on late‐instar larvae could be a successful operational strategy at low population levels when field sprays target the insect instead of foliage protection.     

Prevalence,transmission and mortality associated with Nosema fumiferanae infections in field populations of spruce budworm Choristoneura fumiferana

• 1 The prevalence, intensity and transmission of Nosema fumiferanae (Thomson) (Microsporidae) infections and potential impacts on the survival of field populations of spruce budworm Choristoneura fumiferana (Clem.) were examined in three plots in New Brunswick, Canada, from 1983 to 1992.
• 2 The highest prevalence of N. fumiferanae infection in post‐hibernation second‐instar larvae occurred in the plot where prevalence in female pupae was the highest in the previous generation, suggesting higher rates of vertical transmission. There was little change in the prevalence of N. fumiferanae infections between the second and sixth instars in the later generations. In the two other plots, N. fumiferanae prevalence increased by approximately 25% from the second to sixth larval stadia. Coincident with the changes in N. fumiferanae prevalence were substantial declines in the populations of spruce budworms, making it difficult to determine rates of horizontal transfer of the disease.
• 3 In all plots and in all years, there were progressive increases in the intensity of N. fumiferanae infections (spore loads/individual) from the second to sixth instars and pupae.
• 4 Annual spruce budworm mortality associated with N. fumiferanae was ≤15% of all mortality in reared specimens and was positively correlated with but generally less than 30% of annual N. fumiferanae prevalence.

     

Susceptibility of the spruce budworm, Choristoneura fumiferana, and the white-marked tussock moth, Orgyia leucostigmata, to Bacillus thuringiensis: Chemical insecticide combinations

Bacillus thuringiensis mixed with the organophosphate insecticides, fenitrothion (Sumithion), Gardona^®, and Orthene^®, or the synthetic pyrethroid, SBP 1382, was incorporated into synthetic diet and fed larvae of the spruce budworm, Choristoneura fumiferana, and the white-marked tussock moth, Orgyia leucostigma. Mortality was highest when larvae were fed combinations of low concentrations of the insecticides and low to moderate concentrations of the pathogen. The data indicated that applications of a B. thuringiensis dosage expected to produce about 45% mortality of third and fourth instar larvae of the spruce budworm combined with a dosage of fenitrothion causing about 40% mortality or a dosage of Orthene causing from 5 to 25% mortality should result in low budworm survival. With a B. thuringiensis dosage causing 20–60% mortality combined with a fenitrothion dosage causing 15–50% mortality or a sublethal dosage of Gardona, a low survival rate of young white-marked tussock moth larvae may be expected.     

The phenological window for western spruce budworm: seasonal decline in resource quality

• 1 Western spruce budworm Choristoneura occidentalis Free. (Lepidoptera: Tortricidae) emerge in the spring before budburst and then face a rapidly deteriorating host quality each season.
• 2 Measures of fitness, survival and fecundity, were made on cohorts of final‐instar spruce budworms deployed on host trees at several times during the season in four field locations in coastal and interior British Columbia, Canada.
• 3 Survival and fecundity were strongly correlated throughout the season and varied as much as four‐fold from maxima at mid‐season to minima at the end of the season.
• 4 Fitness values overall were greatest in the coastal compared with interior locations. Among interior locations, fitness was greatest at the highest elevation and least at the lowest elevation. Both cohort and sample‐based estimates of survival of wild, final‐instar budworms were relatively high in these outbreak populations.
• 5 The influence of the phenological window and degree of synchrony with the host plant on herbivore abundance often depends on other processes affecting population rates of change.

     

Age‐specific maternal effects interact with larval food supply to modulate life history in Coleomegilla maculata

相似文献   

Larval feeding behaviour affects the impact of staminate flower production on the suitability of balsam fir trees for spruce budworm

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing indicated that the feeding behaviour of the larvae, which is affected by the insect population density, significantly influenced the impact of balsam fir, Abies balsamea, staminate flowering on spruce budworm biology. At low budworm density, the production of pollen in the midcrown of host trees reduced the insect development time by 5 days without affecting pupal weight, fecundity and survival. However, at high budworm density, the small amount of current-year foliage produced by flowering branches forced old larvae (sixth instar) either to feed on 1-year-old foliage (backfeeding) or to move from the midcrown to the lower crown section where staminate flowers are absent and more current-year foliage is available. When old larvae fed on old foliage, they exhibited reduced pupal weight and fecundity without losing the advange in development time that they obtained from feeding on pollen during their early stages of development. On the other hand, when old larvae moved to the lower crown section, they avoided the negative effects of backfeeding but lost the advantage in development time that was gained from feeding on pollen. Results from this study indicated that the production of staminate flowers by balsam fir trees could have opposite effects on spruce budworm population dynamics depending upon the insect population density when flowering occurs.     

Larval experience induces adult aversion to rearing host plants: a novel behaviour contrary to Hopkins' host selection principle

1. Hopkins' host selection principle (HSP) states that insects should prefer foliage from their rearing host plant over that of an alternative host. 2. The current study tested whether eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), that were laid and developed on, respectively, resistant and susceptible white spruce Picea glauca (Moench) Voss, showed differences in their feeding and oviposition preferences for these two hosts. 3. The data revealed that previous experience of spruce budworm on a host tree type does not influence the host acceptance and feeding behaviour of later larval stages. However, adult budworm reared on resistant white spruce needles preferentially selected susceptible white spruce needles as the host for their progeny, whereas those reared on susceptible needles showed no preference. 4. To the authors' knowledge, this is the first report of an insect showing an oviposition preference for the non‐rearing host plant. This would tend to increase mixing between insects from susceptible and resistant trees. The present results thus argue against Hopkins' HSP and suggest that learned aversion to resistant foliage experienced by larvae is carried into the adult stage.     

Spruce budworm growth,development and food utilization on young and old balsam fir trees

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing, gravimetric analyses, a transfer experiment, and foliage chemical analyses at six dates during the period of budworm feeding activity indicated that the age of balsam fir, Abies balsamea, trees (70-year-old mature trees or 30-year-old juvenile trees) affected tree suitability for the spruce budworm via the chemical profile of the foliage. Insects reared on old trees had greater survival and pupal weight, shorter development times, and caused more defoliation than those reared on young trees. Young trees were more suitable for the development of young larvae (instars 2–5), while old trees were more suitable for the development of older, sixth-instar larvae. These results were confirmed by the laboratory transfer experiment. Young larvae fed foliage from young trees had higher relative growth rates (RGR), digestibility (AD), and efficiency of conversion of ingested foliage (ECI) than those fed foliage from old trees. These differences appeared to be related to the high N:tannins ratio, and the high contents of P present in young trees during the development of the young larvae. Old larvae fed foliage from old trees had higher relative growth rates, relative consumption rates (RCR), and digestibility of the foliage than those fed foliage from young trees. The high digestibility of the foliage of old trees was compensated for by a lower efficiency of conversion of digested food (ECD), which in turn resulted in no significant effect of tree age on the efficiency of conversion of ingested foliage by old larvae. The low relative consumption rate of old larvae fed foliage from young trees appeared to be related to the low N:tannins ratio, and the high contents of bornyl acetate, terpinolene, and °-3-carene present in young trees during the budworm sixth instar. Variations in these compounds in relation to tree age may serve as mechanisms of balsam fir resistance to spruce budworm by reducing the feeding rate of sixth instar larvae.     

Does nutrition-related stress carry over to spruce budworm,Choristoneura fumiferana (Lepidoptera: Tortricidae) progeny?

Three different patterns of feeding of sixth-instar spruce budworm, Choristoneura fumiferana Clemens were simulated in the laboratory. Larvae were fed artificial diets whose nitrogen and total soluble sugar contents varied according to levels similar to those found in three types of balsam fir, Abies balsamea (L.) Miller foliage (current-year foliage from middle and lower crown sections and one-year-old foliage). The biological performance of offspring was studied according to the nutrition of their parents. Although food quality had no impact on pupal weight of female parents and individual mean egg weight, progeny fitness was influenced by parental nutrition. Old foliage simulated diet, poor in nitrogen, clearly affected the early larval development of progeny, especially the percent of egg hatch and first-instar survival. Lower crown current-year foliage simulated diet, with low total soluble sugar content, reduced the first-instar survival of the progeny. However, the selective pressure exerted by low food qualities on the parental generation and on the early stages of their progenies resulted in C. fumiferana populations having higher tolerance to starvation and higher survival after the diapause period. These results highlighted the potentially direct and indirect effects of C. fumiferana parental nutrition on the next generation. The patterns of feeding of parental generations would appear to affect the quality and size of subsequent populations through several selections on the different life-history stages of both generations.     

Occurrence and effects of Nosema fumiferanae infections on adult spruce budworm caught above and within the forest canopy

1 Nosema fumiferanae infections in populations of both sexes of spruce budworm Choristoneura fumiferana moths, collected live above the forest canopy (canopy moths), within the tree crown (crown moths) and in drop trays (dead moths), were examined over a 5‐year period in New Brunswick, Canada. 2 The incidence of infection and of moderate–heavy infections in canopy and crown moths of both sexes increased concomitantly with moth eclosion, indicating that N. fumiferanae retards larval/pupal development, with infected moths, particularly those having higher disease loads, emerging later in the season. 3 Infection rates differed among canopy, crown, and dead female, but not male, moths. Canopy (i.e. emigrating) females had a lower incidence of infection, lower incidence of moderate–heavy infections, and had longer forewings and higher dry weights, than crown females. These results suggest that N. fumiferanae infections negatively affect aspects of female, but not male, flight performance. Regardless of infection, forewing length and dry weight of both canopy and crown females declined over the moth flight period, but infected females in both moth types were smaller than their uninfected counterparts. Forewing lengths and dry weights of moderately–heavily infected females were most severely affected. 4 Despite high annual infection rates in parents, only a small percentage of offspring (second‐instar larvae) that established feeding sites each spring were infected, indicating that high rates of horizontal transmission occurred annually throughout the larval period. 5 The present study indicates that whether N. fumiferanae infections are a debilitating sublethal factor in spruce budworm populations depends more on the disease load than on the overall incidence of infection. The potential importance of N. fumiferanae infections on various fitness parameters related to host dispersal is discussed.     

Interguild interactions between a non-native phloem feeder and a native outbreaking defoliator

1. Competitive and synergistic interactions directly or indirectly drive community dynamics of herbivorous insects. Novel interactions between non-native and native insects are unpredictable and not fully understood. 2. We used manipulative experiments on mature red spruce trees to test interactions between a non-native phloem feeding insect, the brown spruce longhorn beetle (BSLB), and an outbreaking native defoliator, the spruce budworm. We subjected treatment trees to defoliation by three densities of spruce budworm larvae. Treatment trees were: stressed by (i) girdling (to mimic beetle feeding) or (ii) girdling + BSLB before spruce budworm larvae were introduced on branches in sleeve cages. Budworm larvae then fed on foliage and developed to pupation. We assessed all branches for budworm performance, defoliation, shoot production and shoot growth. 3. Shoot length did not differ in response to stress from girdling or BSLB infestation. Neither stress from girdling, nor interactions with BSLB feeding affected spruce budworm performance or defoliation. Intraspecific impacts on performance and defoliation in relation to budworm density were stronger than the effects of tree stress. 4. Prior infestation of red spruce by BSLB in our experimental set-up did not influence spruce budworm performance. BSLB is a successful invader that has blended into its novel ecological niche because of ecological and phylogenetic similarities with a native congener, Tetropium cinnamopterum. 5. Outbreaks by BSLB will not likely impede or facilitate spruce budworm outbreaks if they co-occur. It would be useful to evaluate the reverse scenario of BSLB success after defoliation stress by spruce budworm.     

Synergistic interaction between sublethal doses of <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> and <Emphasis Type="Italic">Campoletis chlorideae</Emphasis> in managing <Emphasis Type="Italic">Helicoverpa armigera</Emphasis>

Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) is an important solitary larval endoparasitoid of the tomato fruit borer Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in India. The interaction between Bacillus thuringiensis subspecies kurstaki (Btk) HD-1 and C. chlorideae was studied under laboratory condition to explore their compatibility in managing H. armigera. The results had indicated that the growth and development of H. armigera was affected in a dose-dependent manner upon feeding on sublethal doses of Btk HD-1-treated diets. There were no larval survivors in lethal doses of Btk HD-1 (LC₇₀ and LC₉₀). The growth and survival of the parasitoid were normal when the host larvae were fed with sublethal doses or subjected to short time exposure to lethal doses of Btk HD-1. However, the parasitoid offsprings developed slowly and pupal as well as adult period, adult weight and adult emergence rate were reduced significantly if the parasitoid was developing inside a severely Bt intoxicated host larvae. There were no evident differences in longevity of parasitoid adults that were fed on honey solution containing different concentrations of Btk HD-1 as compared to adults fed only on honey solution. This indicates no direct adverse effect of Btk HD-1 on C. chlorideae. Further, the gravid female parasitoid did not discriminate Btk HD-1 intoxicated and normal H. armigera larvae for oviposition. The result implies that spore crystal formulation of Btk HD-1 can be effectively used in a synergistic manner along with existing natural or prereleased population of C. chlorideae in organic farming or as components in biointensive IPM module for managing H. armigera.     

Influence of host size on oviposition behaviour and fitness of Elachertus cacoeciae attacking a low-density population of spruce budworm Choristoneura fumiferana larvae

1. Oviposition behaviour and host size ? fitness relationships of a gregarious, idiobiont ectoparasitoid, Elachertus cacoeciae (Howard) (Hymenoptera: Eulophidae), were studied by implanting one fourth‐, fifth‐, and sixth‐instar spruce budworm Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) larva per tree in a stand where the density of the wild C. fumiferana population was low. 2. Development time of E. cacoeciae larvae was quickest on fifth‐instar C. fumiferana larvae, which were the preferred hosts for oviposition. 3. Brood sex ratio (proportion of females) was related positively to increasing C. fumiferana instar, indicating that more females were laid on larger hosts. 4. Parasitoid offspring size increased with increasing C. fumiferana instar and decreased with increasing brood size on smaller hosts. Female but not male size was related positively to increasing brood sex ratio (proportion of females). 5. Under laboratory conditions, parasitoid longevity was related positively to parasitoid size and realised lifetime fecundity, and clutch size was related positively to host size. 6. These results suggest that selection of intermediate‐sized C. fumiferana larvae may be adaptive for E. cacoeciae.     

Effects of tree age and stand thinning related variations in balsam fir secondary compounds on spruce budworm Choristoneura fumiferana development,growth and food utilization

• 1 The effect of tannins and monoterpenes on the development, mortality and food utilization of spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) was investigated under laboratory conditions using an artificial diet. Tannins were extracted from balsam fir foliage of thinned and unthinned stands to reproduce stand thinning related variations in tannins. A mixture of synthetic monoterpenes was utilized to simulate the concentration found in young and old balsam fir trees.
• 2 Longer development time and lower pupal weight were observed for insects fed on diets with a lower nitrogen concentration and a higher tannin concentration (unthinned treatment). Tannins induced higher insect mortality at a low nitrogen concentration compared with the diet with a higher nitrogen concentration.
• 3 Approximate digestibility was higher for larvae fed on diets with high concentrations of nitrogen at both low and high concentrations of tannins. Efficiency of conversion of digested food (ECD) decreased with an increase in tannin concentration. Tannins reduced both the relative consumption and growth rate (RCR and RGR).
• 4 Monoterpenes increased spruce budworm mortality and this mortality reached almost 50% under concentrations of monoterpene typical of the young trees compared with 20% under monoterpene concentrations found in old trees.
• 5 A higher digestibility was observed for larvae fed on diet with a higher concentration of monoterpenes, whereas efficiency of conversion of ingested food (ECI), ECD, RCR, and RGR decreased with an increase in monoterpenes in the diet.
• 6 The results obtained in the present study are consistent with the defensive role of secondary compounds such as tannins and monoterpenes in the spruce budworm–balsam fir system.

     

Novel strategies for the biocontrol of noctuid pests (Lepidoptera) based on improving ascovirus infectivity using Bacillus thuringiensis

Identifying novel biocontrol agents and developing new strategies are urgent goals in insect pest biocontrol. Ascoviruses are potential competent insect viruses that may be developed into bioinsecticides, but this aim is impeded by their poor oral infectivity. To improve the per os infectivity of ascovirus, Bacillus thuringiensis kurstaki (Btk) was employed as a helper to damage the midgut of lepidopteran larvae (Helicoverpa armigera, Mythimna separata, Spodoptera frugiperda, and S. litura) in formulations with Heliothis virescens ascovirus isolates (HvAV-3h and HvAV-3j). Btk and ascovirus mixtures (Btk/HvAV-3h and Btk/HvAV-3j) were fed to insect larvae (3rd instar). With the exception of S. frugiperda larvae, which exhibited low mortality after ingesting Btk, the larvae of the other tested species showed three types of response to feeding on the formulas: type I, the tested larvae (H. armigera) were killed by Btk infection so quickly that insufficient time and resources remained for ascoviral invasion; type II, both Btk and the ascovirus were depleted by their competition, such that neither was successfully released or colonized the tissue; type III, Btk was eliminated by the ascovirus, and the ascovirus achieved systemic infection in the tested larvae. The feeding of Btk/ascovirus formulas led to a great reduction in larval diet consumption and resulted in a significant decrease in the emergence rate of H. armigera, M. separata, and S. litura larvae, which suggested that the formulas exerted marked oral control effects on both the contemporary individuals and the next generation of these tested pest species.     

Spruce budworm impact, abundance and parasitism rate in a patchy landscape

The hypothesis that vegetational diversity may lessen the impact of forest insect pests by favoring natural enemies is appealing to those who seek ecologically sound solutions to pest problems. We investigated the effect of forest diversity on the impact of the spruce budworm Choristoneurafumiferana following the last outbreak, as well as the budworm's current abundance and parasitism rate, in the boreal forest of northwestern Québec. Mortality of balsam fir caused by the budworm was greater in extensive conifer stands than either in “habitat islands” of fir surrounded by deciduous forest or on true islands in the middle of a lake. Adult spruce budworm abundance, assessed by pheromone traps, did not differ significantly between the three types of sites. Larval and pupal parasitism rates were examined by transferring cohorts of laboratory-reared larvae and pupae to trees in the three site types and later collecting and rearing them. The tachinid Actiainterrupta, a parasitoid of fifth and sixth instar larvae, as well as the ichneumonid pupal parasitoids Itoplectesconquisitor, Ephialtesontario and Phaeogenesmaculicornis, caused higher mortality in the habitat islands than on true islands or in extensive stands. Exochusnigripalpistectulum, an ichneumonid that attacks the larvae and emerges from the pupae, caused greater mortality in the extensive stands of conifers. Received: 17 March 1997 / Accepted: 18 November 1997     

High temperature tolerance and thermal plasticity in emerald ash borer Agrilus planipennis

• 1 The emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae) (EAB), an invasive wood‐boring beetle, has recently caused significant losses of native ash (Fraxinus spp.) trees in North America. Movement of wood products has facilitated EAB spread, and heat sanitation of wooden materials according to International Standards for Phytosanitary Measures No. 15 (ISPM 15) is used to prevent this.
• 2 In the present study, we assessed the thermal conditions experienced during a typical heat‐treatment at a facility using protocols for pallet wood treatment under policy PI‐07, as implemented in Canada. The basal high temperature tolerance of EAB larvae and pupae was determined, and the observed heating rates were used to investigate whether the heat shock response and expression of heat shock proteins occurred in fourth‐instar larvae.
• 3 The temperature regime during heat treatment greatly exceeded the ISPM 15 requirements of 56 °C for 30 min. Emerald ash borer larvae were highly tolerant of elevated temperatures, with some instars surviving exposure to 53 °C without any heat pre‐treatments. High temperature survival was increased by either slow warming or pre‐exposure to elevated temperatures and a recovery regime that was accompanied by up‐regulated hsp70 expression under some of these conditions.
• 4 Because EAB is highly heat tolerant and exhibits a fully functional heat shock response, we conclude that greater survival than measured in vitro is possible under industry treatment conditions (with the larvae still embedded in the wood). We propose that the phenotypic plasticity of EAB may lead to high temperature tolerance very close to conditions experienced in an ISPM 15 standard treatment.

     

Impact of balsam fir flowering on pollen and foliage biochemistry in relation to spruce budworm growth, development and food utilization

The impact of balsam fir (Abies balsamea (L.) Miller) flowering on nutritional and allelochemical quality of pollen, current-year and one-year-old foliage is studied in relation to spruce budworm (Choristoneura fumiferana Clem.) (Lepidoptera: Tortricidae) growth, development and utilization of food and nitrogen. In the laboratory, using fresh food from the field, we simulated conditions of low larval population density, in which there is no current-year foliage depletion during the spruce budworm feeding period. Similarly, we simulated conditions of high larval population density when current-year foliage depletion occurs.Because of the high nutritive value of pollen (high amounts of amino acids and minerals, especially nitrogen; low monoterpene content), insects from flowering trees reached the fifth instar five days earlier than those from non-flowering trees, and had heavier dry- and nitrogen-weights at the beginning of the fifth instar. At budbreak, switching from pollen to current-year foliage negatively affected conversion efficiencies and digestibilities of food and nitrogen (AD; ADN; ECDN; ECI; ECIN). The switch from pollen to new foliage had a detrimental impact on fifth-instar survival and on newly-moulted sixth-instar dry- and nitrogen-weights. Moreover, during the fifth instar, balsam fir flowering reduced the nutritive value of current-year foliage, which in turn, might have contributed to the reduced larval growth. Nevertheless, during the sixth instar, balsam fir flowering affected the biochemistry of current-year foliage in ways that enabled larvae to compensate for their low fifth-instar biological performance; larvae also managed to reach pupal dry weight similar to larvae reared on non-flowering trees. Current-year foliage from flowering trees contained less nitrogen, total soluble sugars and total monoterpenes. Those foliar characteristics enabled larvae to increase food and nitrogen consumption rates (RCR; RNCR), because of lower repellency and/or post-ingestional feedback from monoterpenes.As for current-year foliage, balsam fir flowering reduced nitrogen, total soluble sugar and total monoterpene contents in one-year-old foliage during the sixth-instar feeding period. These characteristics enabled sixth-instar larvae, fed on old foliage from flowering trees, to have high relative food and nitrogen consumption rates (RCR; RNCR). Larvae were also able to reach higher relative growth rates (RGR) and relative nitrogen accumulation rates (RNAR) compared to larvae reared on one-year-old foliage from non-flowering trees. Finally, larvae on flowering trees had pupal dry weight similar to those from non-flowering trees, but reached the adult stage nine days earlier.Regardless the foliage type consumed by spruce budworm larvae during the sixth instar, pollen consumption during early larval stages reduced total development time, and thus exposure time to natural enemies. This phenomenon might increase larval survival. Balsam fir flowering changed the biochemistry of one-year-old and current-year foliages, but did not affect pupal dry weights of larvae reared on flowering trees compared to those reared on non-flowering trees. Thus, at low population density, spruce budworm populations in balsam fir flowering stands might be favoured over those in balsam fir non-flowering stands. In addition, when larvae consumed one-year-old foliage during the entire sixth instar, those on flowering trees are probably favoured over those on non-flowering trees. However, because flowering trees produce less new foliage than non-flowering trees, current-year foliage depletion may occur earlier on flowering trees than on non-flowering trees. Thus, at similar larval population density, larvae on flowering trees might have to feed on one-year-old foliage earlier than those on non-flowering trees. In that case, spruce budworm populations on non-flowering stands would be favoured over those on flowering stands.     

The effect of temperature on the development and life cycle regulation of the pine weevil Hylobius abietis and the potential impacts of climate change

• 1 The pine weevil Hylobius abietis is widely distributed in the Palaearctic region where it is a major pest. Although predominantly semi‐voltine, with a 2‐year life cycle, the generation time across its range can vary from 1 to 4 years. The duration of the life cycle and the seasonal timing of weevil activity affect the economic impact and management of this pest, all of which are likely to change in a warming climate.
• 2 To determine the effect of temperature and tree species on weevil growth and development, laboratory experiments were performed with eggs, larvae, prepupae, pupae and adults, using, as appropriate, the host species Scots pine Pinus sylvestris L. and Sitka spruce Picea sitchensis (Bong.) Carr. under constant or alternating temperatures.
• 3 The development rate was linearly related to temperature, with developmental thresholds for eggs, larvae and pupae of 8, 4.5 and 7.3 °C, respectively. Day‐degrees were estimated for each life stage. Larval development was affected by tree species, being slower on Sitka spruce than on Scots pine, and was faster under alternating than constant temperatures.
• 4 The development time for prepupae was highly variable, with an apparent facultative prepupal diapause initiated by temperature. The temperature range 20–17.5 °C marked the transition between median prepupal development times of approximately 25 and 90 days. The prepupal stage may serve to minimize the risk of overwintering mortality in the pupal stage and help to synchronize the life cycle.
• 5 Larval and adult mass was positively related to developmental temperature, demonstrating an inverse temperature size rule, and weevils were heavier when developing on Scots pine than Sitka spruce. Development in alternating temperatures reduced weevil mass on Scots pine. The influence of temperature on weevil mass is likely to have a positive effect on fecundity and overwintering survival. The effects of climate change on development, voltinism and weevil mass are discussed.