Effects of host switching on gypsy moth (Lymantria dispar (L.)) under field conditions

Effects of various single and two species diets on the performance of gypsy moth (Lymantria dispar (L.)) were studied when this insect was reared from hatch to population on intact host trees in the field. The tree species used for this study were red oak (Quercus rubra L.), white oak (Q. alba L.), bigtooth aspen (Populus grandidentata Michaux), and trembling aspen (P. tremuloides Michaux). These are commonly available host trees in the Lake States region. The study spanned two years and was performed at two different field sites in central Michigan. Conclusions drawn from this study include: (1) Large differences in gypsy moth growth and survival can occur even among diet sequences composed of favorable host species. (2) Larvae that spent their first two weeks feeding on red oak performed better during this time period than larvae on all other host species in terms of mean weight, mean relative growth rate (RGR), and mean level of larval development, while larvae on a first host of bigtooth aspen were ranked lowest in terms of mean weight, RGR, and level of larval development. (3) Combination diets do not seem to be inherently better or worse than diets composed of only a single species; rather, insect performance was affected by the types of host species eaten and the time during larval development that these host species were consumed instead of whether larvae ate single species diets or mixed species diets. (4) In diets composed of two host species, measures of gypsy moth performance are affected to different extents in the latter part of the season by the two different hosts; larval weights and development rates show continued effects of the first host fed upon while RGRs, mortality, and pupal weights are affected strongly by the second host type eaten. (5) Of the diets investigated in this study, early feeding on red oak followed by later feeding on an aspen, particularly trembling aspen, is most beneficial to insects in terms of attaining high levels of performance throughout their lives.     

Utilization of primary nutrients by the polyphagous xylophage,Homalodisca coagulata,reared on single host species

Feeding experiments were conducted to assess development of the polyphagous leafhopper, Homalodisca coagulata, on single host species. Insects were reared from eggs on two cultivars of Euonymus japonica, two cultivars of Lagerstroemia indica, and two species of Prunus. Only insects on nonvariegated E. japonica and L. indica cv. Osage survived to maturity, although a substantial proportion of those on P. salicinia developed to the fourth instar. Chemical profiles of food source (xylem fluid), insect excreta and body composition, and consumption rates were used to estimate assimilation efficiencies, daily assimilation rates, and efficiency of conversion of food into biomass for all primary nutrients identified in the xylem fluid. Rates of successful maturation were greatest on the highest nitrogen and carbon source (nonvariegated E. japonica) and were associated with low consumption rates, high assimilation efficiencies, and prolonged instar durations. Developmental period on L. indica was shorter and consumption rates were higher, yet assimilation efficiencies were reduced and young nymphs had lower survivorship. Low consumption rates, coupled with the low nutritional value of P. salicinia, precluded sufficient accumulation of nutrients to complete development. Insects fed on hosts with xylem fluid containing high ratios of amides to total organic compounds (indicative of low carbon to nitrogen ratios) had higher consumption rates but less efficient assimilation of primary nutrients. Carcass analyses of newly enclosed adults suggest that regulation of consumption rates and assimilation efficiencies to provide adequate accumulation of essential amino acids may be pivotal for successful development. © 1996 Wiley-Liss, Inc.     

Differential responses of tiger swallowtail subspecies to secondary metabolites from tulip tree and quaking aspen

Summary Two subspecies of the eastern tiger swallowtail butterfly, Papilio glaucus, exhibit reciprocal inabilities to survive and grow on each other's preferred foodplant. P. g. canadensis R. & J. performs well on quaking aspen (Populus tremuloides Michx.) but not on tulip tree (Liriodendron tulipifera L.); P. g. glaucus L. performs well on tulip tree but not on quaking aspen. This study was designed to test the hypothesis that secondary metabolites in tulip tree and quaking aspen are responsible for these differential utilization abilities. We extracted and fractionated leaf constituents into different chemical classes, applied them to a mutually acceptable diet (black cherry, Prunus serotina, leaves), and bioassayed them against neonate larvae (survival) and penultimate instar larvae (survival, growth, digestibility and conversion efficiencies). For each plant species, one fraction in particular showed activity against the unadapted subspecies. One tulip tree fraction dramatically reduced survival of P. g. canadensis neonates, and reduced consumption rates, growth rates, and ECI's of fourth instar larvae. The tulip tree constituents most likely responsible for these effects are sesquiterpene lactones. One quaking aspen fraction greatly lowered survival of P. g. glaucus neonates, and decreased survival, consumption rates, growth rates and ECD's of fourth instar larvae. The compounds responsible for these results are probably simple phenols or phenolic glycosides. Surprisingly, P. g. glaucus and P. g. canadensis showed slightly poorer performance on the active tulip tree and quaking aspen fractions, respectively, indicating that even adapted insects incur a metabolic cost in the processing of their host's phytochemicals.     

Diurnal and seasonal changes of leaf lamina hydraulic conductance in bur oak (Quercus macrocarpa) and trembling aspen (Populus tremuloides)

The aim of this study was to examine the diurnal and seasonal variations in the sensitivity of leaf lamina (K _lam) hydraulic conductance to irradiance in bur oak (Quercus macrocarpa Michx.) and trembling aspen (Populus tremuloides Michx.), which vary in their responses of K _lam to irradiance. K _lam was determined using the high-pressure method and the measurements were carried out in June, August and September. The irradiance response of K _lam in bur oak was present throughout the day and declined in senescing leaves. In trembling aspen, K _lam declined from morning to late afternoon and drastically decreased before the onset of leaf senescence, but it was not sensitive to irradiance. In both tree species, the capacity of the petioles to supply water to leaf lamina changed during the day in accordance with the ability of the leaf lamina to transport water. Petiole hydraulic conductivity (K _pet) declined during the season in bur oak leaves, while it tended to increase in trembling aspen leaves. There was no correlation between the K _lam values and air temperature or light intensity at the time of leaf collection. For trembling aspen, K _pet was negatively correlated with the air temperature suggesting sensitivity to drought. We conclude that the water transport properties of petioles and leaf lamina in the two studied tree species reflect their ecological adaptations. Trembling aspen leaves have high hydraulic conductivity and high stomatal conductance regardless of the irradiance level, consistent with the rapid growth and high demand for water. In contrast, the increased lamina hydraulic conductivity and stomatal conductance under high irradiance in bur oak trees reflect a water conservation strategy.     

Behavioural and physiological plasticity of gypsy moth larvae to host plant switching

Larvae of the gypsy moth, Lymantria dispar L. (Lepidoptera: Lymantriidae), a generalist species, frequently encounter spatial and temporal variations in diet quality. Such variation favoured the evolution of high behavioural and physiological plasticity which, depending on forest stand composition, enables more or less successful exploitation of the environment. Even in mixed oak stands, a suitable habitat, interspecific and intraspecific host quality variation may provoke significant variation in gypsy moth performance and, consequently, defoliation severity. To elucidate the insufficiently explored relationship between gypsy moth and oaks (Fagaceae), we carried out reciprocal switches between Turkey oaks (Quercus cerris L.) and less nutritious Hungarian oaks (Quercus frainetto Ten.) (TH and HT groups), under controlled laboratory conditions, and compared larval performance between the switched larvae and larvae continuously fed on either Turkey oak (TT) or Hungarian oak (HH). We found that larval traits were most strongly affected by among‐tree variation in oak quality and identity of the host consumed during the fourth instar. Switching from Turkey to Hungarian oak (TH) led to a longer period of feeding, decrease of mass gain, growth, and consumption rate, lower efficiency of food use and nutrient conversion, and increase of protease and amylase activities. Larvae exposed to the reverse switch (HT) attained values of these traits characteristic for TT larvae. It appeared that the lower growth in the TH group than in the TT group was caused by both behavioural (consumption, pre‐ingestive) and metabolic (post‐digestive) effects from consuming oaks. Multivariate analyses of growth, consumption, and efficiency of food use revealed that early diet experience influenced the sensitivity of the most examined traits to less suitable Hungarian oaks, suggesting the development of behavioural and physiological adjustments. Our results indicate that lower risks of defoliation by gypsy moth might be expected in mixed stands with a higher proportion of Hungarian oak.     

Antibiosis/antixenosis in tulip tree and quaking aspen leaves against the polyphagous southern armyworm,Spodoptera eridania

Summary Previous studies have shown leaves of tulip tree, Liriodendron tulipifera L. (of the Magnoliaceae) and of Populus tremuloides Michx. (of the Salicaceae) to be antixenotic/antibiotic to many Lepidoptera, including one of the most polyphagous of all phytophagous insects, the southern armyworm, Spodoptera eridania Cramer (Noctuidae). We investigated the physiological responses to this phytochemical activity on neonate and late instar armyworm larvae in controlled environments with particular emphasis upon the leaf extracts containing condensed tannins and hydrolysable tannins. These tannin-containing extracts of tulip tree leaves and quaking aspen leaves were generally toxic to neonate larvae. For later instars, growth suppression was not due to digestibility-reduction, but instead to suppressed consumption rates and greatly increased metabolic (respiratory) costs as reflected in reduced biomass conversion efficiencies.     

Effect of dietary nitrogen on gypsy moth larval nutritional indices, development and lipid content

Nutritional indices, development rates, percent dry weights and total lipids were determined in gypsy moth larvae (Lymantria dispar L.) reared on a high wheat germ (HWG) diet or diets prepared from lyophilized, ball-milled oak or pine foliage as the only source of dietary nitrogen (N). With regard to both total and proteinaceous N content, HWG diet>oak diet>pine diet. All nutritional indices measured were significantly lower in second instars fed pine diet vs. oak diet. Protein supplementation of pine diet with either casein or ovalbumin to bring total N up to the level present in oak diet resulted in small increased in approximate digestibility (AD) and effciency of conversion of ingested food (ECI), but relative growth rate (RGR) remained unaffected. The low RGR of larvae fed pine diet (unsupplemented or protein supplemented), as compared to those fed HWG or oak diet, was accompanied by significantly lower larval percent dry weight and percent total lipid. In contrast, RGR, larval percent dry weight and total lipid values were comparable in second instars fed HWG or oak diet. Insects reared from the first through the final instar on oak diet exhibited lower pupal weights compared to those reared on HWG. Casein addition to oak diet generally resulted in even more extended larval development times and further reduced pupal weights, but wheat germ addition to oak diet did not alter development rates and caused an increase in pupal weights.     

Increased mortality of gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae) exposed to gypsy moth nuclear polyhedrosis virus in combination with the phenolic gycoside salicin

Second instar gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), larvae suffered significantly greater mortality from aerially applied gypsy moth nuclear polyhedrosis virus (Gypchek) when the virus was consumed on quaking aspen, Populus tremuloides Michx., versus red oak, Quercus spp. L., foliage. Laboratory assays in which various doses of Gypchek and salicin (a phenolic glycoside present in aspen foliage) were tested in combination demonstrated that salicin significantly increased total larval mortality and lowered the LD50 estimates (dose of Gypchek that resulted in 50% population mortality) for the virus, although not significantly. While salicin did not impact larval survival in the absence of Gypcek, it did act to significantly deter feeding when it was present in high concentrations (up to 5.0%) within the treatment formulations. The enhanced activity of Gypchek in the presence of salicin is similar to prior reports of enhanced activity of the bacterial pathogen Bacillus thuringiensis when consumed concurrently with phenolic glycosides commonly present in aspen foliage. The enhancement of viral activity is in contrast to the inhibitory effects on the virus reported for another common group of phenolic compounds, tannins.     

Intraspecific variation in aspen phytochemistry: effects on performance of gypsy moths and forest tent caterpillars

Individual quaking aspen trees vary greatly in foliar chemistry and susceptibility to defoliation by gypsy moths and forest tent caterpillars. To relate performance of these insects to differences in foliar chemistry, we reared larvac from egg hatch to pupation on leaves from different aspen trees and analyzed leaf samples for water, nitrogen, total nonstructural carbohydrates, phenolic glycosides, and condensed tannins. Larval performance varied markedly among trees. Pupal weights of both species were strongly and inversely related to phenolic glycoside concentrations. In addition, gypsy moth performance was positively related to condensed tannin concentrations, whereas forest tent caterpillar pupal weights were positively associated with leaf nitrogen concentrations. A subsequent study with larvae fed aspen leaves supplemented with the phenolic glycoside tremulacin confirmed that the compound reduces larval performance. Larvae exhibited increased stadium durations and decreased relative growth rates and food conversion efficiencies as dietary levels of tremulacin increased. Differences in performance were more pronounced for gypsy moths than for forest tent caterpillars. These results suggest that intraspecific variation in defensive chemistry may strongly mediate interactions between aspen, gypsy moths and forest tent caterpillars in the Great Lakes region, and may account for differential defoliation of aspen by these two insect species.     

Effects of elevated CO2 on feeding preference and performance of the gypsy moth (Lymantria dispar) larvae

Multiple‐choice assays were conducted in the laboratory to examine the effect of CO₂‐induced changes in leaf quality on growth, nutritional indices and preferences of the gypsy moth (Lymantria dispar) larvae. The tested tree species, one‐year‐old aspen (Populus pseudo‐simonii Kitag.), two‐year‐old birch (Betula platyphylla) and three‐year‐old oak (Quercus mongolica Fisch.) were transplanted to open‐top chambers at ambient or elevated CO₂ (650 ppm) concentrations in May 2005. The present study was conducted in 2006. Leaves from the upper and lower crowns of each tree species were sampled and analysed, respectively. On both measurement dates (24 July 2006 and 16 August 2006), there were significant CO₂ effects on levels of condensed tannin, starch, nitrogen and C : N ratio. But only on the latter date, were the concentrations of total phenolics, soluble sugar, carbon and total non‐structural carbohydrates significantly affected by elevated CO₂. Leaf dry weight content and specific leaf weight were almost completely unaffected by CO₂ enrichment. Gypsy moth larvae exhibited a clear selectivity for tested leaf types (leaves from the upper and lower crowns of each tree species) even in their early instar stage, with the upper leaves of P. pseudo‐simonii being the most preferable and the lower leaves of Q. mongolica being the least preferred. The changes in leaf quality significantly reduced larval growth and altered partial indices of insect performance (e.g., relative growth rate and relative consumption rate). However, at least in this short‐term choice feeding assay (13 days), the CO₂‐induced changes in leaf quality had no significant effects on food preference behaviour of the gypsy moth larvae, neither within the limited range of host plants nor within the leaves at different canopy heights of the same tree species.     

Leaf age effects of elevated CO2-grown white oak leaves on spring-feeding lepidopterans

Folivorous insect responses to elevated CO₂-grown tree species may be complicated by phytochemical changes as leaves age. For example, young expanding leaves in tree species may be less affected by enriched CO₂-alterations in leaf phytochemistry than older mature leaves due to shorter exposure times to elevated CO₂ atmospheres. This, in turn, could result in different effects on early vs. late instar larvae of herbivorous insects. To address this, seedlings of white oak (Quercus alba L.), grown in open-top chambers under ambient and elevated CO₂, were fed to two important early spring feeding herbivores; gypsy moth (Lymantria dispar L.), and forest tent caterpillar (Malacosoma disstria Hübner). Young, expanding leaves were presented to early instar larvae, and older fully expanded or mature leaves to late instar larvae. Young leaves had significantly lower leaf nitrogen content and significantly higher total nonstructural carbohydrate:nitrogen ratio as plant CO₂ concentration rose, while nonstructural carbohydrates and total carbon-based phenolics were unaffected by plant CO₂ treatment. These phytochemical changes contributed to a significant reduction in the growth rate of early instar gypsy moth larvae, while growth rates of forest tent caterpillar were unaffected. The differences in insect responses were attributed to an increase in the nitrogen utilization efficiency (NUE) of early instar forest tent caterpillar larvae feeding on elevated CO₂-grown leaves, while early instar gypsy moth larval NUE remained unchanged among the treatments. Later instar larvae of both insect species experienced larger reductions in foliage quality on elevated CO₂-grown leaves than earlier instars, as the carbohydrate:nitrogen ratio of leaves substantially increased. Despite this, neither insect species exhibited changes in growth or consumption rates between CO₂ treatments in the later instar. An increase in NUE was apparently responsible for offsetting reduced foliar nitrogen for the late instar larvae of both species.     

Tri-trophic effects of plant defenses: chickadees consume caterpillars based on host leaf chemistry

Few studies have addressed how plant chemical defenses that directly affect herbivores in turn affect consumption patterns of vertebrates at higher trophic levels. We studied how variable foliar chemistry of trembling aspen ( Populus tremuloides Michx.) affects the diet preferences of an avian insectivore feeding on an introduced herbivore, the gypsy moth ( Lymantria dispar L.).
Black-capped chickadees ( Poecile atricapilla ) were offered paired choices of gypsy moth caterpillars feeding on one of three genotypes of aspen that differed in chemical composition. Chickadees chose to eat caterpillars fed aspen foliage with low levels of both condensed tannins and phenolic glycosides, or caterpillars fed foliage with high levels of tannins and low levels of phenolic glycosides, over caterpillars fed foliage with low levels of condensed tannins and high levels of phenolic glycosides. In addition, diet choices of the birds were affected by their previous experience. These findings are consistent with the "extended phenotype" concept, in that genetically-based chemical traits in an ecologically dominant plant influence the feeding behavior of third trophic level organisms, whose efficacy as regulators of herbivore populations may in turn be modified.     

Cd胁迫对舞毒蛾幼虫食物利用的影响及其Cd的外泌机制

为探明植食性昆虫对受重金属胁迫的寄主植物的生理生态响应机制,本研究用Cd胁迫下银中杨的叶片饲养舞毒蛾幼虫,分析舞毒蛾幼虫对食物的利用情况以及其对Cd的排毒代谢机制.结果表明: 取食Cd胁迫下银中杨的叶片后,舞毒蛾3～6龄幼虫体内的Cd浓度和Cd含量均显著高于对照,但随着幼虫龄期增长,其体内Cd浓度显著降低,而Cd含量有不同程度的提高;舞毒蛾幼虫粪便和虫蜕中的Cd浓度均显著高于对照;舞毒蛾3～5龄幼虫的食物消耗率显著高于对照,而转化率显著低于对照;3～4龄幼虫的食物利用率均与对照差异不显著,但在5龄时显著低于对照.说明在Cd胁迫下,舞毒蛾幼虫能通过有效的排毒代谢途径将体内富集的部分Cd排出体外,且高龄幼虫的排毒代谢能力强于低龄幼虫;舞毒蛾幼虫体质量的增加会对体内的Cd浓度形成一种稀释效应;舞毒蛾幼虫能通过调整食物消耗率和转化率之间的比例,来维持其正常生长发育所需的食物利用率,但超过一定限度后仍会造成食物利用率降低.     

Contributions of insects and droughts to growth decline of trembling aspen mixed boreal forest of western Canada

Insects, diseases, fire and drought and other disturbances associated with global climate change contribute to forest decline and mortality in many parts of the world. Forest decline and mortality related to drought or insect outbreaks have been observed in North American aspen forests. However, little research has been done to partition and estimate their relative contributions to growth declines. In this study, we combined tree‐ring width and basal area increment series from 40 trembling aspen (Populus tremuloides Michx.) sites along a latitudinal gradient (from 52° to 58°N) in western Canada and attempted to investigate the effect of drought and insect outbreaks on growth decline, and simultaneously partition and quantify their relative contributions. Results indicated that the influence of drought on forest decline was stronger than insect outbreaks, although both had significant effects. Furthermore, the influence of drought and insect outbreaks showed spatiotemporal variability. In addition, our data suggest that insect outbreaks could be triggered by warmer early spring temperature instead of drought, implicating that potentially increased insect outbreaks are expected with continued warming springs, which may further exacerbate growth decline and death in North America aspen mixed forests.     

The Role of Microsite Conditions in Restoring Trembling Aspen (Populus tremuloides Michx) from Seed

Encouraging natural regeneration of Populus tremuloides Michx (trembling aspen) from seed is a largely unexplored means for reintroducing the species into reclamation areas. We evaluated the effects of microsite (surface contour and substrate type) on aspen seedling establishment and growth on a reclaimed coal mine. The 4.6 ha study site was divided into six 48 m‐wide strips that had 15 or 40 cm capping material salvaged from a nearby forest floor added to the mine surface. We surveyed 126 m long transects located in the center of each strip for microsite conditions, and the presence and height of aspen seedlings. We found that aspen seedlings generally preferred mineral‐organic substrates and concave microsites. To facilitate the regeneration of aspen by seed, we suggest that land managers increase small‐scale roughness and microtopographic diversity on reclaimed sites .     

Phenology of Parasetigena silvestris (Diptera: Tachinidae), gypsy moth (Lymantria dispar) (Lepidoptera: Lymantriidae) larval parasitoid and its efficiency for parasitisation

Parasetigena silvestris is a univoltine, solitary, larval endoparasitoid which lays its eggs on the surface of gypsy moth larvae. Field collection of the host larvae (2nd through 5th instar) from an artificially established gypsy moth population were made to compare stage specific parasitism between larvae without and with P. silvestris tachinid eggs. The tachinid oviposition rate detected was highest in second instar larvae, and then decreased as larvae developed toward full maturity. The opposite was true for tachinid parasitoid emergence which had no emergence from second through third host instar larvae. Fourth instar gypsy moth larvae, however, experienced significantly higher parasitism by P. silvestris in the larvae with eggs than those without the eggs. The braconid wasp Cotesia melanoscelus caused significantly higher parasitism in early instar larvae with P. silvestris eggs than in those without the eggs. The tachinid prefers to lay more eggs on parasitised larvae by the braconid even though the braconid is a superior competitor to the fly during multiparasitism. Factors influencing parasitism rates by P. silvestris such as host-parasitoid synchronisation and the multiparasitism interaction with C. melanoscelus are discussed.     

Nutrients are assimilated efficiently by Lymantria dispar caterpillars from the mature leaves of trees in the Salicaceae

The efficient aquisition of nutrients from leaves by insect herbivores increases their nutrient assimilation rates and overall fitness. Caterpillars of the gypsy moth (Lymantria dispar L.) have high protein assimilation efficiencies (PAE) from the immature leaves of trees such as red oak (Quercus rubra) and sugar maple (Acer saccharum) (71–81%) but significantly lower PAE from their mature leaves (45–52%). By contrast to this pattern, both PAE and carbohydrate assimilation efficiencies (CAE) remain high for L. dispar larvae on the mature leaves of poplar (Populus alba × Populus tremula) grown in greenhouse conditions. The present study tests two alternative hypotheses: (i) outdoor environmental stresses cause decreased nutrient assimilation efficiencies from mature poplar leaves and (ii) nutrients in the mature leaves of trees in the poplar family (Salicaceae) remain readily available for L. dispar larvae. When poplar trees are grown in ambient outdoor conditions, PAE and CAE remain high (approximately 75% and 78%, respectively) in L. dispar larvae, in contrast to the first hypothesis. When larvae feed on the mature leaves of species in the Salicaceae [aspen (Populus tremuloides), cottonwood (Populus deltoides), willow (Salix nigra) and poplar], PAE and CAE also remain high (68–76% and 72–92%, respectively), consistent with the second hypothesis. Larval growth rates are strongly associated with protein assimilation rates, and more strongly associated with protein assimilation rates than with carbohydrate assimilation rates. It is concluded that tree species in the Salicaceae are relatively high‐quality host plants for L. dispar larvae, in part, because nutrients in their mature leaves remain readily available.     

Host‐associated divergence in the activity of digestive enzymes in two populations of the gypsy moth Lymantria dispar (Lepidoptera: Erebidae)

The gypsy moth is a generalist insect pest with an extremely wide host range. Adaptive responses of digestive enzymes are important for the successful utilization of plant hosts that differ in the contents and ratios of constituent nutrients and allelochemicals. In the present study, we examined the responses of α‐amylase, trypsin, and leucine aminopeptidase to two tree hosts (suitable oak, Quercus cerris, and unsuitable locust tree, Robinia pseudoacacia) in the fourth, fifth, and sixth instars of gypsy moth larvae originating from oak and locust tree forest populations (hereafter assigned as Quercus and Robinia populations, respectively). Gypsy moths from the Robinia forest had been adapting to this unsuitable host for more than 40 generations. To test for population‐level host plant specialization, we applied a two‐population × two‐host experimental design. We compared the levels, developmental patterns, and plasticities of the activities of enzymes. The locust tree diet increased enzyme activity in the fourth instar and reduced activity in advanced instars of the Quercus larvae in comparison to the oak diet. These larvae also exhibited opposite developmental trajectories on the two hosts, i.e. activity increased on the oak diet and decreased on the locust tree diet with the progress of instar. Larvae of the Robinia population were characterized by reduced plasticity of enzyme activity and its developmental trajectories. In addition, elevated trypsin activity in response to an unsuitable host was observed in all instar larvae of the Robinia population, which demonstrated that Robinia larvae had an improved digestive performance than did Quercus larvae.     

Variation in temperature and dietary nitrogen affect performance of the gypsy moth (Lymantria dispar L.)

Abstract. . The independent and interactive effects of temperature and dietary nitrogen content on performance of the gypsy moth (Lymantria dispar L.) were examined. In long-term feeding trials, larvae were reared from egg hatch to pupation on low (1.5%) and high (3.7% dry weight) nitrogen diets, under three temperature regimes. Short-term feeding trials with fourth instars and the same treatments were conducted in order to calculate nutritional indices.
Higher temperatures did not influence larval survival and marginally increased final pupal weights, but strongly decreased long-term development rates. They also accelerated short-term growth and consumption rates, and tended to improve food processing efficiencies. High concentrations of dietary nitrogen increased survival rates and final pupal weights markedly, but decreased long-term development rates only marginally. A high content of dietary nitrogen also accelerated short-term development and growth rates, reduced consumption rates, and improved food digestibility. Insects responded to low nitrogen-content diets primarily by eating faster, rather than by altering efficiency of nitrogen use. In the short-term feeding trials, thermal regime and dietary nitrogen interacted to influence growth rates, overall food processing efficiencies and nitrogen consumption rates. No interactive effects were observed in long-term studies.
This research demonstrates that small changes in thermal regime and ecologically relevant variation in dietary nitrogen content can strongly affect gypsy moth performance. Moreover, various performance parameters are differentially sensitive to the direct and interactive effects of temperature and diet.     

Temptations of weevil: feeding and ovipositional behaviour of Hylobius warreni Wood on host and nonhost bark in laboratory bioassays

• 1 Warren root collar weevil Hylobius warreni Wood (Coleoptera: Curculionidae) is a long‐lived, flightless insect native to coniferous forests across northern North America. Girdling by larval feeding causes significant mortality on young trees. The insect poses considerable challenges to reforestation.
• 2 Adult weevils feed on all life stages of a variety of coniferous hosts prior to oviposition. Their relative feeding preferences, however, have not been quantified. Moreover, it is not known whether host bark influences oviposition behaviour.
• 3 Feeding preferences of adult weevils were tested in both choice and no‐choice laboratory bioassays using small branches from three conifers (lodgepole pine Pinus contorta var. latifolia, interior hybrid spruce Picea glauca×engelmannii, and Douglas‐fir Pseudotsuga menziesii) and one deciduous tree (trembling aspen Populus tremuloides). Measurements included the surface area of bark consumed, rate of consumption, the number of days of feeding, and, in the no‐choice assay, the number of eggs oviposited.
• 4 Bark consumption was greatest on pine and Douglas‐fir, followed by spruce. Little to no feeding occurred on aspen. Consumption did not vary between male versus female insects for any of the feeding metrics quantified.
• 5 The presence of aspen branches did not inhibit feeding on any of the other species in the choice bioassays.
• 6 The number of eggs laid by female insects did not differ significantly among tree species in the no‐choice assay. Eggs were laid indiscriminately in the presence of all four host types.
• 7 Results and opportunities for future research are discussed in the context of formulating new integrated pest management strategies for this insect, which is increasingly important in the period of reforestation subsequent to the mountain pine beetle epidemic in western Canada.