Enhancement of Bacillus thuringiensis with monosodium glutamate against larvae of obliquebanded leafroller (Lep.:Tortricidae)

Abstract:  Monosodium glutamate, a taste enhancer widely used in food industry, was tested in the laboratory to determine its phagostimulatory effects on larvae of Choristoneura rosaceana (Harris). Larvae fed apple leaves treated with 50–700  μ g/l monosodium glutamate increased leaf tissue consumption by approximately 40%. The stimulatory effect of monosodium glutamate (at 675  μ g/l concentration) was maintained throughout 10 days of continuous exposure. Adding 675  μ g/l monosodium glutamate to commercial formulation of Bacillus thuringiensis ssp. kurstaki, (DiPel^®2X DF), lowered LC₅₀ from 450 to 150  μ g/l (P < 0.05, Lethal Ratio Significance Test), indicating good potential for monosodium glutamate to enhance B. thuringiensis -based formulations.     

Behavior of codling moth (Lepidoptera: Tortricidae) neonate larvae on surfaces treated with microencapsulated pear ester

Codling moth, Cydia pomonella (L.), larvae cause severe internal feeding damage to apples, pears, and walnuts worldwide. Research has demonstrated that codling moth neonate first instar larvae are attracted to a pear-derived kairomone, ethyl (2E,4Z)-2,4-decadienoate, the pear ester (PE). Reported here are the behavioral activities of neonate codling moth larvae to microencapsulated pear ester (MEC-PE) applied in aqueous solutions to both filter paper and apple leaf surfaces that were evaluated over a period of up to 20 d of aging. In dual-choice tests the MEC-PE treatment elicited attraction to and longer time spent on treated zones of filter papers relative to water-treated control zones for up to 14 d of aging. A higher concentration of MEC-PE caused no preferential response to the treated zone for the first 5 d of aging followed by significant responses through day 20 of aging, suggesting sensory adaptation as an initial concentration factor. Estimated emission levels of PE from treated filter papers were experimentally calculated for the observed behavioral thresholds evident over the aging period. When applied to apple leaves, MEC-PE changed neonate walking behavior by eliciting more frequent and longer time periods of arrestment and affected their ability to find the leaf base and stem or petiole. Effects of MEC-PE on extended walking time and arrestment by codling moth larvae would increase temporal and spatial exposure of neonates while on leaves; thereby potentially disrupting fruit or nut finding and enhancing mortality by increasing the exposure to insecticides, predation, and abiotic factors.     

Uptake of Granulovirus from the Surface of Apples and Leaves by First Instar Larvae of the Codling Moth Cydia pomonella L. (Lepidoptera: Olethreutidae)

Cydia pomonella granulovirus (CpGV) has received considerable attention as a potential microbial insecticide for the control of the codling moth (Cydia pomonella L.) , a worldwide pest of apples. Laboratory experiments were established to investigate virus uptake by first instar larvae, using a novel leaf disc bioassay technique. Virus uptake was found to be independent of active feeding and larvae became infected simply by walking or browsing on sprayed leaf disc surfaces in as little time as 3.5 min. Infection increased as a function of time spent on the leaf disc surface and a linear log time/probit mortality relationship could be fitted. The bioassay technique used has potential for the realistic laboratory testing of virus spray formulations. A field experiment showed that virus infection could be contracted by newly hatched codling moth larvae both from the surface of sprayed leaves and sprayed fruit. The potential for exploiting this knowledge for improving spray formulations is discussed.     

The Role of Formulation Additives in Increasing the Potency of Cydia pomonella Granulovirus for Codling Moth Larvae,in Laboratory and Field Experiments

Studies were undertaken to improve the biological efficacy of the granulovirus (CpGV) of the codling moth, Cydia pomonella , by evaluating the performance of some formulation additives that might improve virus persistence and/or virus uptake by first instar larvae. Laboratory studies, using a leaf disc bioassay, demonstrated that 15% cane molasses incorporated within a formulation of purified CpGV dramatically reduced the median lethal exposure time (LET 50 ) to CpGV for neonate larvae at a CpGV dosage rate of 10 7 occlusion bodies (OBs) ml -1 . Screening of a range of other compounds showed that sucrose, fructose and sorbitol (at 10% concentrations) and extracts of apple flesh and skin also gave significant reductions in the LET 50 of CpGV formulations containing these ingredients. Pectin, malic acid and &#102 -farnesene did not significantly reduce the LET 50 . In a field trial, molasses included at 15% (v/v) in a CpGV formulation, containing a dosage rate of 10 12 OBs ha -1 , gave as good control of codling moth damage as virus formulations containing the 'sticker' 0.2% skimmed milk at higher dosage rates of 10 13 and 10 14 OBs ha -1 . Studies of CpGV persistence on foliage revealed no significant improvement of virus persistence on apple foliage using 10% or 15% molasses formulations. A second field trial demonstrated that 10% molasses, 10% sorbitol or 0.08% &#102 -farnesene significantly reduced codling moth deep damage to fruit when these ingredients were added to formulations of pure CpGV. Substantial sooty-mould growth ( Cladosporium spp.) was observed on apple foliage treated with formulations containing molasses, indicating that this formulation additive has secondary consequences that would need to be taken into account if molasses was to be used in commercial CpGV formulations. Nonetheless, these studies clearly demonstrate that major biological improvements in CpGV performance can be achieved by the incorporation of formulation additives, including molasses and several other compounds, that probably function as attractants and/or feeding stimulants for codling moth larvae.     

Control of diapause in codling moth larvae

Diapause in a New Zealand strain of codling moth (Cydia pomonella Linnaeus [Lepidoptera: Olethreutidae]) was induced in larvae by photoperiods of 15 h or less. Once diapause had been initiated, it could not be terminated by any combination of conditions tested for at least 20 days after cocooning. In diapausing larvae a low rate of pupation occurred at 25 °C under a long day (18 h) photoperiod. A high rate of pupation was achieved under a long day regime when larvae were decocooned, and provided with apple as nourishment. Diapause could be terminated predictably in 94–100% of larvae by 1) conditioning at 15 °C and constant darkness for periods of 40–100 days, then 2) chilling at 2±2 °C and constant darkness for 20–50 days followed by 3) any post-chill condition periods at 25 °C, 18 h photoperiod. Complete diapause termination was achieved when 100 days conditioning was followed by 30 days or 50 days post-chill period. Under these conditions, 76% termination occurred in the post-chill period after 10 days, and 93% after 25 days.To terminate diapause in codling moth larvae, we recommend that a 100 days conditioning followed by 30 days chilling and 50 days post chilling periods be used.     

Avidin expressed in transgenic tobacco leaves confers resistance to two noctuid pests,Helicoverpa armigera and Spodoptera litura

Fertile transgenic tobacco plants with leaves expressing avidin in the vacuole have been produced and shown to halt growth and cause mortality in larvae of two noctuid lepidopterans, Helicoverpa armigera and Spodoptera litura. Late first instar H. armigera larvae and neonate (<12-h-old) S. litura larvae placed on leaves excised from T₀ tobacco expressing avidin at 3.1–4.6M (moles/kg of fresh leaf tissue) had very poor growth over their first 8 days on the leaves, significant numbers had died by days 11 or 12 and all were dead by day 22 (H. armigera) or day 25 (S. litura). Similar results were obtained when late first instar H. armigera larvae were placed on leaves from T₁ plants expressing avidin at six different average concentrations, ranging from 3.7 to 17.3M. Two larvae on the lowest expressing leaves survived to pupation, but there was total mortality among the other groups and no relationship between avidin concentration and the effects on the larvae. Synergistic effects between avidin-expressing tobacco plants and a purified Bt toxin, Cry1Ba, were demonstrated. Late instar H. armigera larvae fed with leaves from T₂ plants expressing avidin at average concentrations of either <5.3 or >12.9M, and painted with Cry1Ba protein at a rate equivalent to an expression level of 0.5% of total leaf protein, died significantly faster than larvae given either of the two treatments alone. Larvae fed with avidin-expressing leaves painted with the protease inhibitor, aprotinin, at a rate equivalent to 1% of total leaf protein had mortality similar to those given avidin-leaves alone. There was no evidence of antagonism between these two proteins.     

Temperature and food quality influences feeding behavior,assimilation efficiency and growth rate of arctic woolly-bear caterpillars

Summary The energy budget for feeding activity and growth of larval Gynaephora groenlandica was investigated on the tundra and in the laboratory. Larvae fed only in June when the buds and young leaves of Salix arctica, its principal host plant, contained the highest concentrations of macro-nutrients and total nonstructural carbohydrates (TNC). The mid-summer hiatus in larval feeding was coincident with an abrupt decline in the TNC content of leaves and a buildup of plant secondary metabolites in the leaves of S. arctica. Following cessation of feeding, the larvae remained concealed from the sun within crevices and vegetation mats. Growth rates of larvae incubated at 15 and 30°C were similar (4.7–5.0 mg/larva/day), but the assimilation efficiency at 15°C was four times greater (40%) than at 30°C. Growth rates were lowest at 5°C (0.22mg/larva/day) as was the assimilation efficiency (6.6%), because of the extended residence time of food in the gut. The high rate of ingestion and excretion at 30°C was caused by elevated maintenance metabolism. Changes in metabolic state influenced oxygen consumption, which was highest for feeding larvae (0.29 ml/g/h) and significantly lower for each, digesting, moving, starved larvae, and lowest for inactive larvae (0.06 ml/g/h). An influence of temperature and leaf quality on digestion rate and maintenance metabolism is the most likely cause of the feeding behavior pattern in G. groenlandica. The larvae may undergo voluntary hypothermia in order to avoid an energy, deficit resulting from high maintenance metabolism during mid-season when the energy content and food quality declines. The restriction of growth and development to a very short period prior to mid-summer may have contributed, to the extended 14-year life cycle of this species.     

Resistance to the pink potato aphid, Macrosiphum euphorbiae, in two accessions of Lycopersicon hirsutum f. glabratum

An integrated programme of pheromone-mediated mating disruption using Isomate-C®, post-harvest removal of fruit, and trapping overwintering larvae with cardboard tree bands, was used to control codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), in four commercial organic apple orchards in Cawston, British Columbia during 1989–1992. One application of 1000 dispensers ^{– 1} on May 1 delivered estimated seasonal totals of 16.6, 16.5 and 19.9 g of E,E-8,10-dodecadien-1-ol [=codlemone] ^{– 1}in 1990, 1991 and 1992, respectively, at median rates of 8.4, 8.3, and 13.3 mg · < ha^–1 · ha^–1 during dusk flight periods of first brood and 5.3, 4.7 and 4.6 mg · ^{– 1}· ha^–1 in second brood, respectively. Over this 3-year period damage from codling moth at harvest ranged from 0.08 to 2.4%, and averaged 60.7% in these four organic orchards, while damage in five conventional orchards receiving sprays of azinphosmethyl ranged from 0.02 to 1.85%, and averaged 0.5%. Damage in an experimental orchard that was banded only, ranged from 43.5 to 56.7%, and averaged 48.9%. Between 1990 and 1992 cumulative male catches in Pherocon 1-CP wing traps baited with 10 mg of codlemone declined by 52% and densities of overwintering codling moth larvae declined an average of 49.5% in all organic orchards. Overwintering populations in the banded experimental orchard showed an increase of 57.7% during this study period. We conclude that an integrated programme of pheromone-mediated mating disruption, post-harvest fruit removal and tree banding, controls codling moth effectively enough to make organic apple production viable in British Columbia.     

Complementary Behaviors of Maternal and Offspring <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>: Oviposition Site Selection and Larval Movement Together Maximize Performance

The selection of oviposition and feeding sites within cotton plants by Spodoptera littoralis was investigated in the field in 2 years, 2007 and 2008. The female moths exhibited significant oviposition preference for young leaves (YL), particularly the 3rd and 4th leaves from top. The larvae originating from egg batches deposited on YL fed mostly in situ for about 5 days, after which they gradually moved their feeding site toward fully expanded or mature leaves on the same individual plant or on neighboring plants. Larvae hatching from batches deposited on fully expanded leaves (FE) fed in situ only for about 2 days, after which they moved toward younger leaves, where they fed for about 3 more days. After the fifth day, however, larvae of the two groups dispersed mainly downward and outward from their hatching site until the end of a 12-day observation. Larvae hatching from eggs deposited on mature or pre-senescent leaves (MP) moved mainly horizontally to other plants after a slight upward shift. The YL and FE larvae grew significantly faster than MP larvae, both in the field and in a laboratory experiment. In the laboratory experiment, the larval period was shorter and the pupal weight was higher when the animals were offered young leaves or young and fully expanded leaves, than when the animals were offered mature and pre-senescent leaves during the first 5 days after hatching. Possible causes and advantages of the exhibited oviposition preference, as well as the apparent ability of larvae to correct for small egg misplacements made by the females, are discussed.     

A proteinase inhibitor from Nicotiana alata inhibits the normal development of light-brown apple moth, Epiphyas postvittana in transgenic apple plants

Insecticidal proteins are a potential resource to enhance resistance to insect pests in transgenic plants. Here, we describe the generation and analysis of the apple cultivar ‘Royal Gala’ transgenic for Nicotiana alata (N. alata) proteinase inhibitor (PI) and the impact of this PI on the growth and development of the Epiphyas postvittiana (light-brown apple moth). A cDNA clone encoding a proteinase inhibitor precursor from N. alata (Na-PI) under the control of either a double 35S promoter or a promoter from a ribulose-1,5-bisphosphate carboxylase small sub-unit gene (rbcS-E9 promoter) was stably incorporated into ‘Royal Gala’ apple using Agrobacterium-mediated transformation. A 40.3 kDa Na-PI precursor protein was expressed and correctly processed into 6-kDa proteinase inhibitors in the leaves of transgenic apple lines. The 6-kDa polypeptides accumulated to levels of 0.05 and 0.1% of the total soluble protein under the control of the rbc-E9 promoter and the double 35S promoter, respectively. Light-brown apple moth larvae fed with apple leaves expressing Na-PI had significantly reduced body weight after 7 days of feeding and female pupae were 19–28% smaller than controls. In addition, morphological changes such as pupal cases attached to the wing, deformed wings, deformed body shape, and pupal cases and curled wings attached to a deformed body were observed in adults that developed from larvae fed with apple leaves expressing Na-PI, when compared to larvae fed with the non-transformed apple leaves.     

Host plant exploitation within a population of a generalist herbivore, Choristoneura rosaceana

Feeding performance of larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harris), was estimated on apple and three alternative hosts in the Okanagan Valley. The obliquebanded leafroller is native to the study area and apple was introduced in the valley at the beginning of the century. Components of insect fitness were measured to help formulate predictions about the evolution of host preference in this generalist herbivore. In the summer, females attained a higher pupal weight on apple than on trembling aspen, wild rose and snowberry. Males performed best on apple and trembling aspen. In the field, females arising from caterpillars fed on apple leaves had a 26% greater mean fecundity than if fed on alternative hosts. The diet also affected development time; females initiated pupation later on trembling aspen than on the other hosts. Finally, no differences were found in larval survival nor in the proportion of larvae diapausing when fed on different hosts. These components of fitness indicate apple as the most suitable host in the summer.In the fall, diet influenced larval propensity to initiate diapause in the second or third instar, the time elapsed from hatching to diapause initiation and the weight of the instars initiating diapause. However, no difference in overwintering survival among larvae fed on different hosts was detected. The rank order of water and nitrogen contents of leaves of the host plants did not match the rank order of larval feeding performance in either season. A high suitability of apple and its abundance in the Okanagan valley are factors that would favor the evolution of an increased utilization of this host by the obliquebanded leafroller.     

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.     

Evaluation ofMicrothrix inconspicuella, [Lepidoptera: Pyralidae], a potential biological control agent forEmex australis in Australia,carried out in apple orchards in South Africa

Host specificity tests carried out in the laboratory in Australia during 1977, showed thatMicrothrix inconspicuella Ragonot could develop on young apple leaves (Harley et al., 1979). Field studies in unsprayed apple orchards in South Africa showed that some feeding occurred, but fewer than 40% of late instar larvae developed to adults when confined in sleeves on apple tree branches. No feeding or survival occurred in large field cages or in the open. Adults which developed from apple fed larvae were smaller, deformed, occasionally mated and laid fertile eggs but their progeny did not feed or develop on apple fruit or leaves. In conclusion,M. inconspicuella larvae did not develop on apple fruit or leaves in the field, damage was mainly limited to apples already injured and feeding on leaves was minimal. Under normal pest control practicesM. inconspicuella populations did not survive on any part of the apple tree or onE. australis growing under the trees.      

The effect of the granulovirus (PapyGV) on larval mortality and feeding behaviour of the Pandemis leafroller,Pandemis pyrusana (Lepidoptera: Tortricidae)

An indigenous betabaculovirus (PapyGV) of the Pandemis leafroller, Pandemis pyrusana (Kearfott), was studied in the laboratory and greenhouse to determine how the virus affected leafroller mortality and foliar damage. Probability of mortality increased with virus concentration as observed after 7 and 10 days of feeding on virus treated diet in neonates and second instar larvae. LC₅₀ estimates for neonates at 7 and 10 days was 2743 and 389 occlusion bodies (OBs)/mm². For second instars, LC₅₀ was 139,487 and 813 OBs/mm² at 7 and 10 days. There was no biologically significant mortality response to increasing virus concentrations by fourth instar larvae; however, when fourth instar larvae were infected with virus on diet and then fed apple leaves, the leaf area consumed declined up to 50% with higher virus concentrations. In a greenhouse study, neonate larvae that fed on seedlings treated with water showed >90% survival and 80% pupation rate of larvae after being transferred to diet. In contrast, larvae that fed on apple seedlings sprayed with 3×10⁶ OBs/ml showed poor survival when transferred to diet after acquiring the virus and failed to reach the pupal stage. This virus shows promise for population regulation and can produce reduction in feeding damage.     

Behaviour of late-instar gypsy moth larvae in high and low density populations

ABSTRACT. 1. Using scaffolding and night-vision equipment, we observed fifth and sixth instars of the gypsy moth, Lymantria dispar (L.), on Quercus velutina Lam. in the field.
2. In low-density populations, larvae fed at night and spent the day resting in sheltered sites away from the canopy. In high-density populations, larvae remained in the canopy throughout the day and night, and the amount of feeding during daylight hours increased with population density.
3. Larvae at all population densities used a similar sequence of behaviours and sampled a number of leaves when selecting feeding sites, but larvae in high-density populations switched feeding sites more frequently and fed continuously for shorter periods.
4. Larvae seldom interfered with each other's feeding in any of the populations.
5. When fifth instars were collected from the field and held for 24 h in an electronic feeding monitor, they maintained feeding rhythms that were characteristic of their source populations. Larvae spent more time crawling and less time feeding when offered foliage from high-density rather than low-density populations.     

Effect of dietary selenium supplementation on resistance to baculovirus infection

We have examined the effects of dietary selenium (Se) supplementation on larval growth and immunocompetence of the lepidopteran pest, the cabbage looper, Trichoplusia ni. Supplementation of the diet of T. ni larvae with 10–20 ppm Se resulted in a 1 day delay in pupation. The effects of the addition and/or removal of dietary Se on total Se bioaccumulation and sequestration were determined by neutron activation analysis of pupae. Early penultimate instar larvae moved from selenium containing diet to basal diet lost total pupal Se content down to the level of those fed basal diet. Conversely, larvae moved from basal diet to diet containing additional Se rapidly attained pupal Se levels comparable to larvae fed Se throughout larval development. Therefore, dietary Se is rapidly accumulated or lost during larval development, but significant amounts are sequestered from diet into pupae. Larvae were reared on diet supplemented with 5 or 10 ppm Se until the onset of the penultimate instar then infected per os with increasing concentrations of the fatal baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Larvae fed Se in the penultimate and ultimate instars were more resistant to viral infection than larvae not fed Se in the final instars. This study indicates that dietary Se levels rapidly impact Se assimilation and sequestration and that tissue Se levels are an important factor in resistance to AcMNPV infection in larval T. ni.     

亚麻荠对小菜蛾幼虫取食和成虫行为反应的影响

亚麻荠是一种很少有害虫危害的油料作物。用室内生测和Y 型嗅觉仪研究了亚麻荠对小菜蛾Plutella xylostella幼虫取食和成虫行 为反应的影响。以甘蓝作对照,用亚麻荠叶片喂养的小菜蛾初孵幼虫3天后校正死亡率为79 .2%,显示了较强的致死作用;喂养小菜蛾3龄幼虫至化蛹,其存活率、化蛹率、蛹重及成 虫寿命都显著降低,表明亚麻荠对小菜蛾幼虫的生长发育有不利影响。在幼虫的取食选择实 验中,有甘蓝叶供选择时,小菜蛾幼虫不取食亚麻荠;在无可选择的情况下,小菜蛾幼虫也 取 食亚麻荠叶片,但取食量很小,与取食甘蓝叶的量相比,差异极显著。行为反应测试表明, 小菜蛾成虫对甘蓝和亚麻荠植株的挥发物都有明显的趋性反应,与对照（净化空气）相比, 差异极显著,而在甘蓝和亚麻荠之间无选择性。说明小菜蛾成虫对亚麻荠植株的挥发物具有 较强的定向反应。     

Leaf quality and insect herbivory in model tropical plant communities after long-term exposure to elevated atmospheric CO2

Results from laboratory feeding experiments have shown that elevated atmospheric carbon dioxide can affect interactions between plants and insect herbivores, primarily through changes in leaf nutritional quality occurring at elevated CO₂. Very few data are available on insect herbivory in plant communities where insects can choose among species and positions in the canopy in which to feed. Our objectives were to determine the extent to which CO₂-induced changes in plant communities and leaf nutritional quality may affect herbivory at the level of the entire canopy. We introduced equivalent populations of fourth instar Spodoptera eridania, a lepidopteran generalist, to complex model ecosystems containing seven species of moist tropical plants maintained under low mineral nutrient supply. Larvae were allowed to feed freely for 14 days, by which time they had reached the seventh instar. Prior to larval introductions, plant communities had been continuously exposed to either 340 l CO₂ l^–1 or to 610 l CO₂ l^–1 for 1.5 years. No major shifts in leaf nutritional quality [concentrations of N, total non-structural carbohydrates (TNC), sugar, and starch; ratios of: C/N, TNC/N, sugar/N, starch/N; leaf toughness] were observed between CO₂ treatments for any of the species. Furthermore, no correlations were observed between these measures of leaf quality and leaf biomass consumption. Total leaf area and biomass of all plant communities were similar when caterpillars were introduced. However, leaf biomass of some species was slightly greater-and for other species slightly less (e.g. Cecropia peltata)-in communities exposed to elevated CO₂. Larvae showed the strongest preference for C. peltata leaves, the plant species that was least abundant in all communites, and fed relatively little on plants species which were more abundant. Thus, our results indicate that leaf tissue quality, as described by these parameters, is not necessarily affected by elevated CO₂ under relatively low nutrient conditions. Hence, the potential importance of CO₂-induced shifts in leaf nutritional quality, as determinants of herbivory, may be overestimated for many plant communities growing on nutrient-poor sites if estimates are based on traditional laboratory feeding studies. Finally, slight shifts in the abundance of leaf tissue of various species occurring under elevated CO₂ will probably not significantly affect herbivory by generalist insects. However, generalist insect herbivores appear to become more dependent on less-preferred plant species in cases where elevated CO₂ results in reduced availability of leaves of a favoured plant species, and this greater dependency may eventually affect insect populations adversely.     

Temperature and food quality effects on growth,consumption and post-ingestive utilization efficiencies of the forest tent caterpillar Malacosoma disstria (Lepidoptera: Lasiocampidae)

Temperature and food quality can both influence growth rates, consumption rates, utilization efficiencies and developmental time of herbivorous insects. Gravimetric analyses were conducted during two consecutive years to assess the effects of temperature and food quality on fourth instar larvae of the forest tent caterpillar Malacosoma disstria Hübner. Larvae were reared in the laboratory at three different temperatures (18, 24 and 30 degrees C) and on two types of diet; leaves of sugar maple trees Acer saccharum Marsh. located at the forest edge (sun-exposed leaves) or within the forest interior (shade-exposed leaves). In general, larvae reared at 18 degrees C had lower growth rates and lower consumption rates than larvae reared at the warmer temperatures (24 and 30 degrees C). Moreover, the duration of the instar decreased significantly with increasing temperatures. Type of diet also affected the growth rates and amount of food ingested by larvae but did not affect the duration of the instar. Larvae fed sun-exposed leaves consumed more food and gained higher biomasses. Values of approximate digestibility and efficiency of conversion of ingested food were also higher when larvae were fed sun-exposed leaves. Higher growth rates with increasing temperatures were primarily the result of the shorter stadium duration. The higher growth rates of larvae fed sun-exposed leaves were possibly the result of stimulatory feeding and consequently greater food intake and also a more efficient use of food ingested. This study suggests that the performance of M. disstria caterpillars could be enhanced by warmer temperatures and higher leaf quality.