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.     

Oviposition behavior in spruce budwormChoristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae)

Epicuticular waxes of balsam fir, Abies balsamea,act as oviposition stimulants for fertilized females of the eastern spruce budworm, Choristoneura fumiferana(Clem.). Those same waxes do not stimulate unfertilized females, nor do the latter respond to nonchemical cues such as leaf texture, shape, etc. Ablation experiments suggest that the chemoreceptors responsible for the perception of waxes are located on the proboscis.     

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.     

Oral exudate as a mediator of behavior in larval eastern and western spruce budworms (Lepidoptera: Tortricidae)

The production of oral exudate by larval eastern and western spruce budworms,Choristoneura fumiferana (Clem.) andChoristoneura occidentalis Free., respectively, was investigated in the laboratory. All larvae except those entering into a molt exhibited aggressive behavior and produced exudate in response to handling or intraspecific encounters. Larvae could be induced to produce exudate up to four times over 2–3 min and produced an average of 1.92±0.04 µl (X ± SE) per induction. Larvae on foliage spent much of their time maintaining their silken feeding tunnel, including spinning and combing silk and removing frass. Exposure to conspecific oral exudate deposited inside the tunnel, or released by agitated larvae inside the tunnel, increased the proportion of larvae that dispersed away from the tunnels and, apparently, increased the larval sensitivity to disturbances. The behavior induced by the oral exudate indicates that it acts as an epideictic (spacing) pheromone.     

Age-related responses from the maxillary sensilla styloconica of Choristoneura fumiferana larvae to foliage extracts from balsam fir hosts

An electrophysiological study of the sensilla styloconica of the galea in Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae) larvae showed a differential response between fourth- and sixth-instars to extracts of balsam fir foliage. Larvae raised on artificial diet were stimulated with the water soluble fraction of needle extracts obtained from terminal and lateral shoots of 30- and 70-yr-old balsam fir trees. An extract-sensitive neuron was found in the lateral styloconic sensillum of both instars. The lateral styloconica in the fourth-instar larvae were more sensitive to extracts from terminal than from lateral shoot foliage of both young and old trees. The lateral styloconica of sixth-instar larvae were more sensitive to lateral shoot foliage of old trees. Results are discussed with respect to their relationship to feeding preferences and feeding rates observed in a previous behavioural study.     

Feeding preferences of eastern spruce budworm larvae in two-choice tests with combinations of host-plant extracts

Three extracts were obtained from each of four host plants: sugars/glycosides; amino acids/bases; and organic acids. The four hosts studied were balsam fir, black spruce, red spruce, and white spuce. The effects of recombined host plant extracts on the feeding behaviour of eastern spruce budworm larvae were examined in two-choice tests. Results compare feeding preferences as well as feeding rates between combinations of extracts. The importance of each class of polar compounds is discussed.

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Préférences des larves de la tordeuse des bourgeons de l'épinette envers extraits combinés de leurs plantes-hôtes

Résumé Trois extraits ont été obtenus de chacune de quatre plantes-hôtes: sucres/glycosides; acides aminées/bases organiques; acides organiques. Les quatre plantes-hôtes étudiées furent le sapin baumier, et les épinettes blanc, noir, et rouge. Le comportement gustatoire des larves a été étudié en raison de l'effet de combinaisons d'extraits de chaque plantehôte. Les résultats comparent la préférence des larves ainsi que leur consommation totale envers ces extraits.

     

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.     

Food consumption and utilization by 6th-instar larvae of spruce budworm, Choristoneura fumiferana: a comparison on three Picea (spruce) species

The effects of tree species, shoot age, and sex of larvae on food consumption and utilization were investigated in a factorial experiment. Diets prepared from lyophilized and powdered current-year shoots, from two age classes (sample dates) of Picea glauca (Moench) Voss, Picea rubra, Sarg., and Picea mariana (Mill.) B.S.P., were evaluated for eight performance criteria. All factors had significant effects on all criteria except for tree species on assimilation efficiency, shoot age on development time, and sex on net growth efficiency. Eight of the possible 24 two-factor interactions and one of the possible eight three-factor interactions were significant. Food utilization efficiencies and relative growth rate were in the low and moderate characterization limits for immature arthropods; relative consumption rates were high. The higher performance values on Picea glauca were related to this species greater vulnerability to spruce budworm. Performance criteria of similar larvae on an artificial diet were compared with those on the foliage-diets.

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Résumé L'auteur a déterminé la quantité d'aliments utilisées, à 22±0,5 °C, par des larves de Tordeuse des bourgeons de l'épinette parvenues à leur sixième stade de développement qui s'étaient nourries d'un régime artificiel et d'aiguilles de l'année en cours lyophilisées et réduites en poudre, prélevées à deux dates différentes, à 10 jours d'intervalle, et provenant d'épinettes blanchés (Picea glauca [Moench] Voss), d'épinettes rouges (Picea rubra Sarg.) et d'épinettes noires (Picea mariana [Mill.] B.S.P.). Les femelles ont invariablement ingéré une quantité significativement plus importante de tous les régimes que les mâles, consommant 24% de plus d'aiguilles d'épinette noire et 73% de plus d'aiguilles d'épinette blanche.Les femelles prenaient en général plus de temps pour parvenir au stade de chrysalide et avaient un taux d'utilisation des aliments significativement plus élevé. L'efficacité nette de la croissance chez les deux sexes ne présentait toutefois aucune différence significative. La performance des larves ayant ingéré des aiguilles provenant de deux classes d'âge différait de façon significative mais non pas uniforme d'un régime à l'autre: les aiguilles d'épinette blanche plus récentes donnaient une performance généralement plus élevée contrairement aux aiguilles plus jeunes d'épinette rouge et d'épinette noire. Les larves ingéraient une quantité significativement plus élevée, avaient un taux de consommation et de croissance supérieur et augmentaient davantage leur biomasse avec des aiguilles d'épinette blanche. L'efficacité d'utilisation des aliments et le taux de croissance relatif étaient de faibles à modérément faibles pour un lépidoptère arboricole phyllophage; la vitesse d'ingestion relative était élevée. La qualité des aiguilles des trois essences d'épinettes était faible. Les aiguilles d'épinette blanche permettaient aux larves d'avoir une performance significativement plus élevée, performance mesurée à partir de plusieurs critères, alors que les aiguilles d'épinette rouge et d'épinette noire donnaient une performance égale. La supériorité des performances obtenues avec l'épinette blanche explique la plus grande vulnérabilité de cette essence à la Tordeuse des bourgeons de l'épinette.

     

Free and bound amino acids of spruce budworm larvae feeding on balsam fir and red and white spruce

Levels of free and to a lesser extent bound amino acids in larvae of the spruce budworm (Choristoneura fumiferana (Clem.)) varied significantly with food source (host species) and date of sampling (instars V and VI). Amino acids most prominent and occurring free were glutamine, glutamic acid, alanine, and proline, whereas those bound and released by acid hydrolysis were mainly aspartic and glutamic acids. Arginine contributed most to the protein N of larvae and in the host species was the main storage form of nitrogen. Percentages of twelve free amino acids including ornithine, glutamic and γ-aminobutyric acid, lysine, valine, leucine, and isoleucine reflected significantly food sources, sampling dates, and their interactions. When feeding stopped (instar VI), levels of most bound amino acids in red spruce and fir larvae increased/unit weight as levels of free amino acids dropped. Although percentages of most bound amino acids were unaffected by diet, significant differences were found with glutamic acid, histidine, and threonine. Compared to white and red spruce, balsam fir, the preferred host in the sampled area, provided larvae with the highest levels of free and bound amino acids and greatest size.     

RearingGlypta fumiferanae [Hym.: Ichneumonidae] on a multivoltine laboratory colony of the western spruce budworm (Choristoneura occidentilis) [Lep.: Tortricidae]

Methods were developed for rearingGlypta fumiferanae Viereck on a nondiapausing laboratory colony of the western spruce budworm,Choristoneura occidentalis Freeman. Both host and parasite are univoltine and undergo diapause in nature. In this study, the parasite's voltinism was synchronized with that of a nondiapausing host.G. fumiferanae mated readily in the laboratory, and 5 consecutive generations were reared with an average generation time of less than 8 weeks-much less than the 23 weeks needed for 1 generation to develop in the field. Developmental times are reported, and some aspects of behavior described.     

Response of the western spruce budworm to temperature and dose of a virus, a growth regulator, and an organophosphate

Pathogenicity of nuclear polyhedrosis virus (NPV) to western spruce budworm larvae, Choristoneura occidentalis Freeman, increased as temperature increased. In constrast, at temperature extremes, mortality increased for a specified dose of malathion or diflubenzuron, while at the optimal temperatures (20–25°C), mortality decreased. Malathion was the fastest acting insecticide, followed by diflubenzuron and then NPV.Simulation results considered temperature dependent developmental rates of the larvae, energy consumption, time to achieve total mortality, and mortality at specified doses of insecticides. Low temperatures provided the greatest reduction in the amount of energy consumed by spruce budworm relative to the energy consumed when no treatment was applied. This was due to both the percent mortality and because total mortality was realized in the larval stage while at the higher temperatures, mortality was not fully realized until the pupal stage.

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Résumé La température modifie la toxicité ou la pathogénie du virus de la polyhédrose nucléaire (NPV), du diflubenzuron, et du malathion consommés par Choristoneura occidentalis Freeman. La pathogénie du NPV augmente avec la température, si bien qu'il y a une relation linéaire entre mortalité et température. Pour le diflubenzuron et le malathion, la température est liée à la mortalité d'une façon gradiatique. Aux températures extrêmes, la mortalité augmente pour une dose donnée de malathion ou de diflubenzuron, tandis qu'aux températures optimales (20 à 25°C), la mortalité diminue. Des modèles multiples ont été utilisés pour évaluer les effets ci-dessus.Le moment de la mortalité finale observée et la mortalité cumulative ont été modifiés par la température, mais non par la dose d'insecticide. L'effet le plus rapide est obtenu avec le malathion, suivi par le diflubenzuron et enfin le NPV.Selon les résultats de simulation,—tenant compte des taux de développement larvaires à différentes températures, de la consommation d'énergie, du temps nécessaire pour obtenir la mortalité totale calculée et de la mortalité calculée, pour une dose donnée d'insecticide à une température particulière —, ce sont les basses températures qui réduisent le plus l'énergie consommée par la population par comparaison avec l'énergie consommée en l'absence de traitement. Ceci est dû au pourcentage de mortalité calculée et au fait que la mortalité est toujours obtenue au stade larvaire, tandis qu'aux températures plus élevées, la mortalité se poursuit jusqu'au stade nymphal.

     

The influence of understory nectar resources on parasitism of the spruce budworm Choristoneura fumiferana in the field

1 Nectar provided by flowering plants has been suggested as an important factor enhancing parasitism rates of herbivorous insects. Artificial nectar has been shown to increase parasitoid longevity and fecundity in laboratory studies. 2 We studied the influence of understory nectar on parasitism of the spruce budworm Choristoneura fumiferana in a field experiment in which we either removed understory flowering herbs or sprayed a sucrose solution on the understory vegetation in 0.25 ha quadrats. 3 Cohorts of laboratory-reared second instars were transferred the field to evaluate parasitism in the quadrats. The larvae were harvested as fifth instars and reared for parasitoids. 4 Parasitoids of early instars caused greater mortality in the supplemental sucrose treatment than in the vegetation-removal treatment or the control. Parasitoids of older larvae did not respond to the treatments. Larger-scale treatments may be necessary to elicit a response by the larger parasitoids that attack older larvae.     

Influence of leaf epicuticular waxes from cerrado species on substrate selection byAtta sexdens rubropilosa

The influence of leaf epicuticular waxes of nine woody species from cerrado (a savanna ecosystem of Brazil) on the foraging behavior of the leaf-cutting antAtta sexdens rubropilosa Forel, 1908 (Formicidae, Attini) was investigated. Some waxes showed neither inhibitory nor attractive effect over a series of tests, while a second group caused a delayed rejection. Waxes of two species were shown to be strongly deterrent to the ants. Since different waxes caused different responses, it is concluded that their chemical composition, rather than hydrophobicity or mechanical constraints, accounts for the observed effects. Plant species with leaves rejected by the ants did not necessarily have repellent waxes. On the other hand, no species with acceptable leaves yielded waxes with deterrent effects.     

Occurrence of Cystosporogenes sp. (Protozoa, Microsporidia) in a multi-species insect production facility and its elimination from a colony of the eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae)

We have isolated a microsporidium from a laboratory colony of the eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae). Light and electron microscopic investigations showed that gross pathology and ultrastructure of our isolate are similar to those described for Cystosporogenes legeri from the European grape vine moth, Lobesia botrana. Comparative phylogenetic analysis of the small subunit rDNA using maximum likelihood, maximum parsimony, and neighbour joining distance methods revealed perfect homology with the C. legeri sequence. The microsporidian was infectious to other Choristoneura species, as well as Malacosoma disstria, Lymantria dispar, and Lambdina fiscellaria. Incubation of infected egg masses at 41 degrees C for 20 min followed by 30 min in 33% formaldehyde did not reduce disease incidence in larval offspring. Exposure of one or two generations to fumagillin at 6000 ppm or higher eliminated infection in adult moths, but also reduced colony fitness. A clean colony was established by conducting individual matings and selecting disease-free offspring.     

Physiology of a sucrose-sensitive cell on the galea of the eastern spruce budworm larva, Choristoneura fumiferana

ABSTRACT The lateral styloconic sensillum on the galea of the eastern spruce budworm larva Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae) contains a cell which responds to sucrose. The electro-physiologial threshold for response is below 0.5 mM sucrose. The K_b for the response is 1.5 mM, and the V_max is 200 impulses/s. The physiological data are interpreted with respect to the sucrose-stimulated feeding behaviour of the larva.     

Incubation period, spore egestion and horizontal transmission of Nosema fumiferanae (Microsporidia: Nosematidae) in spruce budworm (Choristoneura sp., Lepidoptera: Tortricidae): the role of temperature and dose

Various instars of Choristoneura occidentalis were fed with a range of doses of Nosema fumiferanae and reared at 20, 24 and 28 degrees C to determine the influence of temperature and dose on the time to spore egestion and the number of spores egested in the frass. When larvae were fed in the third stadium, as few as 10(2) spores per larva initiated infection, and both onset of spore egestion and the number of spores egested were affected by a complex relationship between temperature and inoculation dose. Onset of spore egestion varied from 11 to 15 days postinoculation. At 20 degrees C, the onset was delayed and spore production decreased with increasing inoculation dose whereas at higher temperatures spores were first egested at the lowest dose and spore production increased with dose. When larvae were fed spores in the fifth and sixth stadium, no spores were egested because pupation occurred before completion of the incubation period. To assess the effect of temperature on horizontal transmission, Choristoneura fumiferana larvae fed with 10(4) N. fumiferanae spores per larva were reared with uninfected larvae at 15, 20 and 25 degrees C. At 15 degrees C, we observed the highest degree of horizontal transmission, defined by the largest change in N. fumiferanae prevalence, even though the density of spores available for horizontal transmission was the lowest. Infected adults eclosed later than uninfected adults and the time to eclosion was also dependent on sex and temperature. We relate our experimental findings to consequences for horizontal and vertical transmission of N. fumiferanae in spruce budworm populations.