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.

     

Adaptation of an outbreaking insect defoliator to chronic nutritional stress

During insect outbreaks, the high number of individuals feeding on its host plant causes a depletion of the food source. Reduced availability and decreased quality of nutrients negatively influence life‐history traits of insects driving them to develop adaptive strategies to persist in the environment. In a laboratory experiment with three repetitions, we tested the effect of chronic nutritional stress on spruce budworm performance during three generations to determine the adaptive strategies employed by the insect to deal with a selection pressure produced by low‐quality diet. Our results show that all tested life‐history traits (mortality, developmental time, pupal mass, growth rate and female fecundity) but female fertility were negatively influenced by the low‐quality diet simulating food depletion during outbreak conditions. However, especially females in the third generation under chronic nutritional stress show an adaptive response in life‐history traits when compared to those reared only one generation on low‐quality diet. Larval developmental time significantly decreased and pupal mass, growth rate and fecundity significantly increased. The study demonstrates the capacity of spruce budworm to react to chronic nutritional stress with adaptations that may be caused by epigenetic parental effects. This information can help to understand the course of an outbreak especially at peak densities and during the collapse.     

Legacy effects of low N diets on a vernal folivore: deprivation leads to gluttony

We tested for legacy effects of low-N diets offered to newly emerged second-instar spruce budworm (Choristoneura fumiferana) larvae for a duration of either one or two full instars on their growth and nutritional physiology in the sixth instar. The experimental design evaluated the effects of initial diet, final diet, and sex on energy consumption, assimilation, retention, and growth rates. Legacy effects were apparent after two instars of low-N diet exposure and were manifested by elevated ( approximately 10%) consumption rates (RCRs) coupled to elevated ( approximately 10%) growth rates (RGRs) and elevated ( approximately 3%) body energy densities, i.e., heightened fat deposition. However, initial dietary N levels had no legacy main effects on food assimilation efficiencies (ADs), and gross (ECI) and net (ECD) food conversion efficiencies. RCR and AD were dependent on an initial x final diet interaction (i.e., nonlinear legacy effects). RGR depended on an initial diet x sex interaction but not on an initial x final diet interaction. Therefore, the legacy effects of low-N initial diets on RGR and body energy density were simply additive to final diet effects. Final diet universally affected all indices and interacted with sex. Low-N final diets increased RCR ( approximately 41%) and decreased AD (14-18%) but unexpectedly increased ECD (21-24%) and RGR ( approximately 36%). Females generally had higher performance than males on the low-N diets but often only matched males on the high-N diets. Low-N initial diets extended larval development times ( approximately 7-26%) and lowered growth rates (6-24%) to the sixth instar, depending on duration of diet exposure, but did not affect total growth achieved by the start of the sixth instar.     

Heritability of life‐history traits in the spruce budworm

The heritability of life‐history traits is of particular importance for insects that are very dependent on host conditions. Severe defoliation caused by the spruce budworm negatively impacts its food source, which in turn imposes environmental constraints on the insect. The heritability of those traits can help elucidate this species' evolutionary process. Heritability also helps identify which traits exhibit significant additive variance and can be key to understanding natural selection effects. Individuals were reared under laboratory conditions over three generations on an artificial diet. Heritability was estimated by parent–offspring regression. Fertility and fecundity demonstrated significant heritability followed by larval development, while pupal mass showed minimal heritable variation. These results suggest an important percent of additive variance in life‐history traits. This study contributes to our understanding of the relationship of this forest pest to its environmental conditions. This study also reveals an important genetic architectural structure of life‐history traits in the spruce budworm.     

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.     

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.     

Elevated CO2 and temperature alter development and food utilization of Spodoptera litura fed on resistant soybean

Effects of elevated atmospheric CO₂ (elevated CO₂ vs. ambient CO₂) and temperature (+0.67–0.79°C vs. ambient temperature) on the developmental life cycle of Spodoptera litura and the food utilization of the fourth‐instar larvae fed on soybean (resistant cultivar Lamar vs. susceptible landrace JLNMH) grown in open‐top chambers were studied from 2013 to 2015. The results indicated that: (i) compared with ambient CO₂, elevated CO₂ significantly prolonged the duration of larva and pupa, and adult longevity; significantly decreased the pupation rate, pupal weight, fecundity, the relative growth rate (RGR), efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD); and increased the relative consumption rate (RCR) and approximate digestibility (AD). (ii) Compared with ambient temperature, elevated temperature significantly shortened the duration of larva and pupa; significantly decreased the pupal weight; and increased the RGR, RCR, ECD and ECI. (iii) Compared with the susceptible soybean accession JLNMH, the resistant soybean cultivar Lamar significantly prolonged the duration of larva and pupa; significantly decreased the pupation rate, pupal weight, adult longevity, fecundity and RGR, RCR and AD; and increased the indexes of ECD. (iv) At elevated temperature, S. litura fed on resistant vs. susceptible cultivars showed opposite trends in the RGR, RCR, AD, ECD and ECI. In addition, elevated temperature under elevated CO₂ significantly decreased the RGR (2014), ECD (2013 & 2014) and ECI (2013) and increased the AD (2013 & 2014) compared with other treatment combinations when S. litura fed on Lamar. Future climatic change of temperature and CO₂ concentration would likely affect growth and food utilization of S. litura, with increased food intake, but the reduced fecundity may compensate for the increased food consumption, resulting in no significant reduction in insect‐induced yield loss in soybean production. Nevertheless, use of insect resistant soybean cultivars will aid in ecological management of S. litura and reduce the insecticide load in soybean production.     

Interspecific variation in resistance of two host tree species to spruce budworm

Woody plants regularly sustain biomass losses to herbivorous insects. Consequently, they have developed various resistance mechanisms to cope with insect attack. However, these mechanisms of defense and how they are affected by resource availability are not well understood. The present study aimed at evaluating and comparing the natural resistance (antibiosis and tolerance) of balsam fir (Abies balsamea [L.] Mill.) and white spruce (Picea glauca [Moench) Voss] to spruce budworm, Choristoneura fumiferana (Clem.), and how drainage site quality as a component of resource availability affects the expression of resistance over time (6 years). Our results showed that there are differences in natural resistance between the two tree species to spruce budworm, but it was not significantly affected by drainage quality. Balsam fir exhibited higher foliar toxic secondary compounds concentrations than white spruce in all drainage classes, resulting in lower male pupal mass, survival and longer male developmental time. This, however, did not prevent spruce budworm from consuming more foliage in balsam fir than in white spruce. This response suggests that either natural levels of measured secondary compounds do not provide sufficient toxicity to reduce defoliation, or spruce budworm has developed compensatory mechanisms, which allow it to utilize food resources more efficiently or minimize the toxic effects that are produced by its host's defensive compounds. Larvae exhibited lower pupal mass and higher mortality in rapidly drained and subhygric sites. Drainage class also affected the amount of foliage destroyed but its impact varied over the years and was probably influenced by climatic variables. These results demonstrate the complexity of predicting the effect of resource availability on tree defenses, especially when other confounding environmental factors can affect tree resource allocation and utilization.     

Adaptation of the gypsy moth to an unsuitable host plant

The pattern of adaptation with regard to life history traits and traits thought to be important in feeding habits of caterpillars in two populations of the gypsy moth (Lymantria dispar L.; Lepidoptera: Lymantriidae) originating from the locust tree (Robinia pseudoacacia; Fabaceae) and oak (Quercus petrea; Fagaceae) forests were investigated in the laboratory. The Robinia population has experienced unsuitable locust tree leaves as an exclusive food resource for more than 40 years. Since Quercus species are the principal host plants of the gypsy moth, the specific objectives of this study have been to measure the extent of differentiation between ancestral and derived populations in several life history traits (egg-to-adult viability, duration of larval and pupal stages, and pupal weight) and nutritional indices – relative growth rate (RGR), relative consumption rate (RCR), assimilation efficiency (AD), gross growth efficiency (ECI), and net growth efficiency (ECD). Significant differences between the Quercus and Robinia populations were detected in pupal duration, RGR, RCR, and AD. The presence of a significant population × host interaction in traits such as preadult viability, duration of pupal stage, RGR, and ECI suggests that adaptation of the gypsy moth to the unsuitable host might be ongoing. Using a full-sib design, we screened for genetic variation in life history traits within both populations, and examined the genetic correlations of performance across oak and locust leaves within both populations. The genetic variances for analyzed life history traits were lower under conditions that are commonly encountered in nature. Our data show that positive cross-host genetic correlations preponderate within both populations.     

Nutritional physiology of the eastern spruce budworm,Choristoneura fumiferana,infected with Nosema fumiferanae,and interactions with dietary nitrogen

Summary Female eastern spruce budworm larvae, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), inoculated with a medium lethal spore dosage of the microsporidium Nosema fumiferanae (Thomson) exhibited significant reductions in consumptive index (CI), nitrogen consumptive index (NCI), relative growth rate (RGR), and gross (ECI) and net (ECD) production effeciencies when compared to microsporidian-free larvae. Diseased larvae also exhibited significant increases in approximate digestibility (AD), N utilization efficiency (NUE), and larval moisture content. Both healthy and diseased insects were reared on 2.5% N and 4.5% N diets. Those on the 2.5% N diet showed significant increases in CI, although NCI was still lower than NCI measured for larvae reared on 4.5% N. NUE was also higher on the 2.5% N diet. Diseased cohorts reared on 2.5% N diet had significantly greater mortality than those reared on 4.5% N diet. Pupal weight and development time of infected individuals did not respond to dietary N concentration. However, healthy insects achieved greater pupal weights in a shorter time on the 4.5% N diet than those on the 2.5% N diet. Mortality of healthy insects was unaffected by dietary N.     

Influence of various host plants on the consumption and utilization of food by Pieris brassicae (Linn.)

Pieris brassicae (Linn.) is a destructive cosmopolitan pest of cruciferous crops. It is present wherever its host plants occur, and it is considered to be one of the most widely distributed of all the Lepidoptera. We investigated the affect of various host plants on the food consumption and utilization by P. brassicae. We quantified consumption of food, larval duration, pupal duration and weight on cabbage (Brassica oleracea var. capitata), cauliflower (Brassica oleracea var. botrytis), radish (Raphanus sativus), broccoli (Brassica oleracea var. italica) and mustard (Brassica campestris) under laboratory conditions. Insect-host relationships can be better understood by knowing the rate of food consumption, its digestibility and conversion of food eaten to body tissue. The consumption of food generally increased with the advancement of larval age. In our study we found that consumption of food was highest on radish and lowest on broccoli. The highest consumption of a particular host does not always indicate greater suitability of that host, until and unless other factors like consumption index (CI), relative growth rate (RGR), efficiency of conversion of ingested food (ECI), approximate digestibility (AD) and efficiency of conversion of digested food (ECD) are also considered. In the current investigation, factors like CI, RGR, ECI and ECD were highest on cabbage. Low body weight of pupa is associated with rapid development. On cabbage, the weight of pupa of both sexes was found lowest. Thus, from the present study, it can be concluded that cabbage is a more suitable host for P. brassicae than other host plants evaluated. Hence, on cabbage, the values of Waldbauer indices were highest and P. brassicae developed with a faster rate.     

Evidence of a direct chemical plant defense role for maltol against spruce budworm

This study examines the direct chemical defensive role of maltol, a previously identified secondary metabolite found in balsam fir, Abies balsamea (L.) Mill. (Pinaceae), that was detected during herbivory of spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). Although used extensively in many industries, in addition to being found in multiple plant species, its functional role in plants remains unknown. The objectives of this study were to quantify the amount of free maltol and its potential conjugated form, maltol glucoside, in various foliage age classes and to evaluate whether constitutive foliage levels of maltol have an impact on spruce budworm fitness in maltol supplementation assays. Gas chromatography–mass spectrometry (GC‐MS) analysis of balsam fir foliage showed that maltol is produced in all foliage age classes tested; however, concentrations were significantly higher in older foliage. Liquid chromatography–mass spectrometry–mass spectrometry (LC‐MS‐MS) analysis showed that maltol also exists in balsam fir in its glucosylated form, a unique discovery in conifers. Similar to maltol, maltol glucoside is also present in current and 1‐year‐old balsam fir foliage and in significantly higher concentration in older foliage. We investigated the impact of maltol‐treated diet on spruce budworm fitness. Maltol additions that reflected constitutive foliage concentrations caused a significant reduction in larval development rate and pupal mass, whereas higher concentrations were required to cause significant mortality. These results suggest that maltol may be an important component of a direct defense strategy in balsam fir against spruce budworm herbivory.     

Facultative monophagy as a consequence of prior feeding experience: behavioral and physiological specialization in Colias philodice larvae

Summary Although newly-emerged Colias philodice readily accept Medicago sativa, Melilotus alba, and Coronilla varia, fifth instar larvae reared on any single plant species display a highly significant induced feeding preference for their rearing host. Forced host-switching reveals that fifth instar relative growth rate (RGR) on M. sativa and M. alba is significantly reduced by prior feeding on either alternative host. Moreover, regardless of rearing diet, switching to a novel host during the fifth instar results in reduced RGR, relative consumption rate (RCR), efficiency of conversion of digested food (ECD), and pupal weight. These results support the hypothesis that induction of feeding preference is an adaptive response that predisposes larvae to feed on the plant species they are most capable of utilizing for growth.     

Interactive effects of temperature and concentration of the flavonol rutin on growth, molt and food utilization of Manduca sexta caterpillars

A factorial experiment tested the effects of varying concentrations of the flavonol rutin and daytime temperatures of 20 and 30°C on growth, molting and food utilization efficiencies of third instar tobacco hornworms (Manduca sexta (L.)). Cool temperature prolonged both the growth (=feeding) and non-feeding periods and consequently the relative consumption rates (RCR) and relative growth rates (RGR). Temperature had no impact on the amount of food consumed and the utilization indices of efficiency of conversion of ingested food and efficiency of conversion of digested food to larval biomass. But rutin was more concentrated in the frass of the larvae at the warm temperature. With increasing levels of rutin in the diet, the efficiency of conversion of ingested food tended to decline. Rutin reduced RCR and RGR. At the cool temperature, rutin increased the time spent in the first portion of the non-feeding period disproportionately. Analysis of growth rate intervals within the growth period indicated that at the cool temperature rutin had no discernible impact over the first half of the growth period, during which developmental competence to molt is likely achieved. Overall, these results indicate an overlap in the growth and molting phases and suggest that rutin interferes with physiological processes at the time of molt initiation, with these effects magnified at a cool temperature.     

砂地柏提取物、鬼臼毒素和脱氧鬼臼毒素对粘虫幼虫生长发育和食物利用的影响

采用重量法研究了砂地柏Sabina vulgaris Ant.果实乙醇提取物、鬼臼毒素和脱氧鬼臼毒素等3种植物源拒食性物质在AFC₃₀、AFC₅₀及AFC₈₀剂量处理下对粘虫Mythimna separata幼虫生长发育和食物利用的影响。结果表明,3种供试物质对粘虫幼虫正常的生长发育历期具有明显的延缓作用,可显著延长试虫龄期。2种鬼臼类物质在处理期内均可造成粘虫幼虫相对生长率和相对代谢率的明显降低,并且表现出与剂量的相关性,但停止处理3～5天后,又都能恢复到正常水平;3种物质对粘虫幼虫食物近似消化率没有明显影响。处理期内食物转化率和利用率显著增加,停止处理后,均可恢复到正常水平; 不同物质处理间存在一定差异,同一物质不同处理剂量间差异不明显。     

Carry-over effect of host nutritional quality on performance of spruce budworm progeny

The effect of host nutritional quality on spruce budworm (Choristoneura fumiferana (Clemens)) parental and offspring performance was studied using field and laboratory rearing experiments, and foliar chemical analyses. Foliage of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and black spruce (P. mariana (Mill.) BSP) was used to rear the parental generation in the field, whereas an artificial diet was used to rear the progeny under laboratory conditions. Important differences in the food quality were provided by the three hosts. Black spruce foliage had higher concentrations of certain monoterpene deterrents and total phenolics, together with stronger seasonal declines in nutrients such as N, P and Mg, compared with the other hosts. We hypothesise that this trend may be related to poor performance and survival of the progeny. Laboratory rearing showed that progeny of parents that fed on black spruce exhibited longer developmental times and greater mortality, and had lower pupal mass than progeny of parents fed on the other hosts. Further, artificial food-fed progeny of insects reared on black spruce reached sixth-instar later, with lower mass, and exhibited higher relative growth rate (RGR) than progeny of parents fed on the other hosts. These results suggest nutritionally-based parental effects. These results also confirmed that the quality of food consumed by the parents can influence the fitness of the next generation.     

Bromatological characterization of mulberry cultivars, Morus spp., and determination of nutritional indexes of Bombyx mori L. (Lepidoptera: Bombycidae)

The objective of this work was to assess, through consumption and utilization of natural food measurements, whether mulberry cultivars, Morus spp., could be recommended to rear the silkworm, Bombyx mori L., in a commercial scale. The mulberry cultivars Miura (standard), Korin and Tailandesa and the hybrids FM 3/3, FM 86, SK 1 and SK 4 were tested. Seventy five fifth-instar commercial hybrid larvae were individualized in gerbox? unities and maintained in a rearing room (25 ± 3oC and 80 ± 10% RH).The mulberry leaves of each of the five cultivars used to feed the silkworm larvae were submitted to bromatological analysis. The dry weight of larvae at the beginning and at the end of the fifth instar, the food consumed and the feces eliminated were recorded to determine the following indexes: relative consumption rate (RCR), relative metabolic rate (RMR), relative growth rate (RGR), approximate digestibility (AD), efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), metabolic cost (MC). The bromatological composition analysis of mulberry leaf cultivars revealed that the hybrid SK 4 presented superior nutritional quality compared to the standard cultivar Miura, due to its higher content in crude protein and ethereal extract, and lower detergent fiber content. The hybrid SK 4 was the most adequate food to the silkworm larvae because it was ingested in small amounts, thus providing good digestibility to the larvae, low metabolic cost, good growth rate and one of the highest efficiencies in the conversion of the ingested food and ingested and digested in biomass.     

Interactions among white spruce tannins, Bacillus thuringiensis subsp. kurstaki, and spruce budworm (Lepidoptera: Tortricidae), on larval survival, growth, and development

The interactions among white spruce, Picea glauca (Moench) Voss, purified acetone tannin extracts (hydrolyzable and condensed tannin), Bacillus thuringiensis subsp. kurstaki Cry1A(c) delta-endotoxin strain HD-73 (Btk), and spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) on larval survival, growth, and development were investigated over the whole larval feeding period by using artificial diet supplemented with three concentrations of Btk toxins per milliliter of diet (0, 0.021, and 1.72 microg/ml) and three concentrations of foliar tannin extract (0, 8, and 15% dry mass basis). At high Btk concentration, tannin antagonized Btk potency against spruce budworm by lowering Btk-related larval mortality from 83 to 43%. At moderate Btk concentration tannin did not affect Btk potency. Host tree tannins antagonized not only the lethal effects of Btk toxin but also sublethal Btk-related impacts in terms of larval development, pupal weight, relative consumption rate, and growth rate. When alone in the diet, tannin negatively affected larval survival, growth, and development. Maximum potency of tannins against spruce budworm larvae (60% mortality) was reached at dietary concentrations corresponding to what is found in the plant (8% dry mass). The addition of Btk toxin in food containing tannin reduced percentage of larval mortality by one-third, indicating that Btk toxin can antagonize tannin potency against the insect. Development of Btk transgenic spruce trees should consider the antagonistic effect the toxin may have on the resistance conferred by tannins that have evolved naturally in spruce trees.     

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.     

丽斗蟋翅二型雄虫食物消化能力及消化酶活性比较

【目的】丽斗蟋Velarifictorus ornatus具明显的翅二型现象,为探讨翅型分化对丽斗蟋翅二型雄虫消化能力及中肠内消化酶活性产生的影响,对长翅型与短翅型雄虫食物消化能力及中肠内消化酶活性进行了检测比较。【方法】我们采取重量营养指数测定了羽化后12 d内丽斗蟋两型雄成虫增长量、相对增长率、取食量、食物利用率、近似消化率和食物转化率。为进一步明确丽斗蟋翅二型成虫食物消化能力与中肠内消化酶活性的关系,我们采用4种专用底物测定了中肠内用于分解蛋白质、脂肪和碳水化合物的总蛋白酶、胰蛋白酶、脂肪酶和淀粉酶的活性。【结果】结果表明,丽斗蟋两型雄虫取食量、食物转化率、食物利用率与增长量均无统计差异,但中肠内消化酶活性变化规律不同。成虫羽化后4 d时,长翅型雄虫中肠内总蛋白酶与胰蛋白酶活性显著高于短翅型雄虫,相反,羽化后0 d时,短翅型雄虫中肠内总蛋白酶与胰蛋白酶活性则显著高于长翅型雄虫,而羽化后12 d时,虽然短翅型雄虫总蛋白酶活性高于长翅型雄虫,但胰蛋白酶活性在两型雄虫间并无差异。成虫羽化后0 d时,两型雄虫脂肪酶活性无差异,但无论是羽化后4 或 12 d,长翅型雄虫中肠内脂肪酶活性皆显著大于短翅型雄虫。成虫羽化后4 d时,短翅型雄虫中肠内淀粉酶活性显著高于长翅型雄虫,而羽化后0与12 d时,两型雄虫间无显著差异。【结论】丽斗蟋翅二型雄虫食物消化能力无显著差异,但羽化后不同时间,中肠内消化酶活性存在差异,该差异可能与成虫羽化后不同时期,翅二型雄虫在飞行与繁殖投资中对不同能源物质的需求有关。