Responses of natural enemies to experimentally increased populations of the forest tent caterpillar, Malacosoma disstria

1. The responses of predators and parasitoids to increased forest tent caterpillar populations were studied by introducing eggs to two trembling aspen, Populus tremuloides Michx., forests where natural populations were at very low density.
2. Of five parasitoid species recovered, only the braconid Aleiodes malacosomatos (Mason) and the tachinid Patelloa pachypyga (Aldrich & Webber) exhibited spatially density-dependent responses, in dry upland forest and mesic lowland forest, respectively. Forest type restrictions on the abundance of these species and the weak density-dependent response by A. malacosomatos suggests that parasitoids may not be capable of regulating low-density tent caterpillar populations.
3. Predation of final-instar larvae and pupae by birds, in particular the northern oriole, Icterus galbula (L.), virtually eliminated the experimental populations. Avian predation was widespread and dominated mortality at all densities.
4. Implications for the initiation of outbreaks of cyclic defoliators are discussed.     

Macrogeographic clines in fecundity, reproductive allocation, and offspring size of the forest tent caterpillar Malacosoma disstria

1. The fecundity of the forest tent caterpillar varies considerably across its geographic range. Field data indicate that populations in the southern United States (Gulf States) produce nearly twice as many eggs as females from Canada or the Lake States, with little or no difference in the size of adult females. 2. In controlled rearing experiments, female forest tent caterpillar from the southern United States (Louisiana) had much larger clutch sizes than same sized females from northern populations in Michigan or Manitoba, Canada. Increased fecundity in Louisiana females was achieved through a significant reduction in egg size and a concomitant increase in the allocation of resources to egg production. 3. Comparison of 10 forest tent caterpillar populations spanning a 27° latitudinal gradient, validated the results of detailed comparisons among the three populations above by confirming the strong negative correlation between latitude and clutch size. 4. Neonate forest tent caterpillars from Manitoba were significantly larger than larvae from either Michigan or Louisiana. Michigan larvae were intermediate in size. It is postulated that large neonates are advantageous in thermally limiting environments. More than three times as many degree‐days are available to Louisiana neonates during the first 2 weeks after hatching. A consistently favourable climate during the vulnerable post‐hatching period may have allowed the evolution of larger clutches at the expense of neonate size in southern populations.     

Host locating behaviour of Leschenaultia exul and Patelloa pachypyga: two tachinid parasitoids of the forest tent caterpillar, Malacosoma disstria

Leschenaultia exul (Townsend) and Patelloa pachypyga (Aldrich & Webber) (Diptera: Tachinidae) are the principal larval parasitoids of the forest tent caterpillar (FTC) Malacosoma disstria (Hübner) (Lepidoptera: Lasiocampidae) in Canada. The response of these two fly species to M. disstria differs depending on the tree species on which the host feeds. In wind tunnel experiments, L. exul spent more time on the side of the tunnel containing volatiles from FTC frass and was attracted to the FTC-aspen poplar (Populus tremuloides Michx.) complex preferentially to the FTC-balsam poplar (Populus balsamifera L.) complex. Field bioassays confirmed that this fly species was preferentially attracted to the herbivore-aspen poplar complex as compared to the herbivore-balsam poplar complex. In field bioassays, P. pachypyga was also attracted preferentially to aspen poplar trees containing FTC larvae, compared to balsam poplar trees with host larvae.     

Intermitochondrial bridge junctions in fat body cells of the pre-hatch larvae of the forest tent caterpillar Malacosoma disstria HBN.

An electron microscopic feature of fat body cells of diapausing Malacosoma disstria pre-hatch caterpillars, experimentally held at certain controlled time-and-temperature conditions, is an elaborate bridge junction, between mitochondria, strikingly similar in appearance to the septate junction which has frequently been described as occurring between cells of many invertebrate species. It is suggested that the intermitochondrial unctions may well represent elaborate forms of interaction between organelles in order to enhance metabolic efficiency in times of stress.     

Thermal properties of the tent of early instar colonies of the eastern tent caterpillar, Malacosoma americanum (Lepidoptera: Lasiocampidae)

The extent to which the small tents of the early instars of Malacosoma americanum warmed when irradiated by sunlight was investigated by continuous electronic monitoring of field colonies for 137 colony-days. Tent temperatures exceeded the threshold for larval growth of 15 °C on 88–96% of the study days, exceeding in degree-minutes the ambient excess-over-threshold by a factor of approximately five. In still air, tents constructed by third instar caterpillars achieved greater temperature excesses over ambient than did a model of a tightly sealed glass house, but smaller tents and tents exposed to simulated wind did not perform as well. Tents of M. americanum warmed more rapidly and to a high temperature than silk nests of markedly different design constructed by other species.     

A Continuous Model for Oscillating Outbreaks of the Population of a Phytophagous Moth,the Tent Caterpillar,Malacosoma disstria (Lepidoptera,Lasiocampidae)

Biophysics - Outbreaks of individual species populations are important phenomena in many aspects and are not alike in terms of the theory of multispecies community dynamics. Outbreaks of insect...     

Variation in the susceptibility of the forest tent caterpillar (Lepidoptera: Lasiocampidae) to Bacillus thuringiensis variety kurstaki HD-1: effect of the host plant.

Host-mediated effect on the efficacy of Bacillus thuringiensis Berliner against larvae of the forest tent caterpillar. Malacosoma disstria Hübner, was investigated under controlled conditions. Host plants used in this study were quaking aspen, Populus tremuloides Michx., a preferred host, and sugar maple, Acer saccharum Marsh., a secondary host. Larvae were reared in the laboratory on leaves of these hosts, and upon reaching the third, fourth, and fifth instar, they were fed leaves treated with one of a range of concentrations of B. thuringiensis variety kurstaki HD-1 suspensions. Larvae were tested on the host on which they were feeding before the 4-d bioassays. The estimated LC50s were 100-fold greater on quaking aspen than on sugar maple. Also, there was a decrease in efficacy over the whole ranges of concentrations with larval age on both hosts. LC50s varied approximately two-fold between third and fifth instar. These results indicate that host-mediated effects on B. thuringiensis efficacy warrant more interest. In particular, they strongly indicate that the host plant modifies the interaction between B. thuringiensis and a target insect, and offer the opportunity to investigate the mechanism(s) that may be involved in the enhancement of B. thuringiensis toxicity.     

Interaction of the bacteria Xenorhabdus nematophila (Enterobactericeae) and Bacillus subtilis (Bacillaceae) with the hemocytes of larval Malacosoma disstria (Insecta: Lepidoptera: Lasiocampidae)

Malacosoma disstria larvae are a pest of deciduous trees. Little is known on the interaction of bacteria with the immediate hemocytic antimicrobial responses of these insects. Incubating dead Xenorhabdus nematophila and Bacillus subtilis with a mixture of serum-free granular cells and plasmatocytes in vitro revealed differential bacterial-hemocyte adhesion and differential discharge of lysozyme and phenoloxidase but not total protein. Although active phenoloxidase adhered equally to both bacterial species, X. nematophila limited enzyme activation whereas B. subtilis enhanced activation. Serum with active phenoloxidase (as opposed to tropolone-inhibited phenoloxidase) and purified insect lysozyme increased bacterial-hemocyte adhesion of both bacterial species. An apolipophorin-III-like protein when incubated with hemocytes, limited their responses to glass slides and bacterial adhesion. However, initial binding of the protein to both bacteria increased granular cell levels with bacteria while lowering the plasmatocyte levels with adhering procaryotes. The protein also increased lysozyme and phenoloxidase activities. Although B. subtilis in vivo elicited a nodulation-based decline in total hemocyte counts and did not affect hemocyte viability, dead X. nematophila elevated hemocyte counts and damaged the hemocytes as lipopolysaccharide levels increased and X. nematophila emerged into the hemolymph. Apolipophorin-III-like protein once bound to the bacteria slowed their removal from the hemolymph.     

Chromosomal characterisation of five lepidopteran cell lines of Malacosoma disstria (Lasiocampidae) and Christoneura fumiferana (Tortricidae).

Chromosome number and morphology have been examined in four established cell lines (Md63, Md66, Md108, and Md109) of the forest tent caterpillar, Malacosoma disstria Hübner, and one (Cf124) of the spruce budworm, Choristoneura fumiferana (Clemens). Chromosome number distributions of Md63 (mode = 112) Md108 (mode = 103), Md109 (mode= 103), and Cf124 (mode = 110) overlap sufficiently to prevent identification of individual lines by number alone. However, Md66 is exceptional in possessing a modal number of 157. One large chromosome occurs in cells of all lines. The presence of this chromosome, the lack of any distinct polyploid series among chromosome numbers encountered, and the general inverse relationship between number and size of chromosomes, suggest that the high level of heteroploidy characteristic of these and other lepidopteran cell lines reflects not only a possible polyploid origin but also extensive chromosomal rearrangement and fragmentation. Tolerance for such change is attributed to the holokinetic organisation of lepidopteran chromosomes. A distinct heteropycnotic body is present in about 10% of Cf124 cell nuclei, and can be used as a marker for this line. This body may represent the sex chromatin normally encountered in somatic cells of female C. fumiferana.     

Instar duration, adult consumption, oviposition and nitrogen utilization efficiencies of leafhoppers feeding on different quality food (Auchenorrhyncha: Homoptera)

Abstract. 1. Plant material of Holcus lanatus L. removed from an artificially fertilized trial was used to rear leafhoppers of three feeding types: Dicrano-tropis hamata Boheman and Ebmana sulphurella Zetterstedt, (phloem feeders), Eucelis incisus Kirschbaum (xylem feeder) and Zyginidia scutellaris Herrich-Schaeffer (mesophyll feeder).
2. In the laboratory, leafhopper instar durations, adult consumption rate, oviposition rate, and nitrogen utilization efficiency were influenced by the quality of the food consumed. Adult longevity was unaffected by the level of food quality normally found in plants.
3. Z.scutellanis consumed mesophyll contents equivalent to 72% of its body weight each day but only digested about 30% of its intake. Eincicus had a low dry weight consumption rate (12% body weight/day) but digested its food more efficiently (60%) than the other feeding types. The two phloem feeders consumed mounts equivalent to 25% of their body weight each day and digested 40–50% of their intake.
4. Each species reached maximum nitrogen utilization efficiencies at different plant nitrogen levels. This suggests that leafhopper species may be associated with a particular nitrogen concentration in the grasses.     

Nuclear polyhedrosis virus as a biological control agent for Malacosoma americanum (Lepidoptera: Lasiocampidae)

In addition to damaging trees, the eastern tent caterpillar is implicated in early fetal loss and late‐term abortion in horses. In a field study, we evaluated the potential biological control of the caterpillar using eastern tent caterpillar nuclear polyhedrosis virus (ETNPV), a naturally occurring virus that is nearly species‐specific. Egg masses were hatched and second instar larvae were fed virus‐inoculated foliage to propagate the virus in vivo. Then, a viral pesticide was formulated at concentrations of 10⁴, 10⁶ and 10⁸ polyhedral inclusion bodies per ml. The pesticide was applied to foliage on which second, third and fourth instar caterpillars were feeding. When the majority of surviving larvae reached the sixth instar, colonies were collected and the surviving caterpillars counted. Mean numbers of surviving caterpillars per treatment were compared via 95% bootstrap confidence intervals. The data indicate second instar caterpillars were highly susceptible to the virus, but only at the highest concentration tested. Third instar caterpillars were also somewhat susceptible to high virus concentrations, while fourth instar caterpillars were fairly resistant. Our data provide the strongest evidence to date that ETNPV can be propagated, harvested and refined for formulation as a biological control agent for eastern tent caterpillar. Its use on this insect may be merited in circumstances where landowners and managers need to protect trees and horses.     

Effects of a kaolin-based particle film on oviposition and feeding of gypsy moth (Lep., Lymantriidae) and forest tent caterpillar (Lep., Lasiocampidae) in the laboratory

Abstract:  In the laboratory we investigated a kaolin-based crop protectant, Surround^® WP, that was mixed in a spray carrier (94% water, 2% methanol, 4% Triton X100) and applied as particle film against gypsy moth Lymantria dispar (L.) and forest tent caterpillar Malacosoma disstria Hubner. Paired-choice feeding tests showed that gypsy moth larvae were significantly (P < 0.05) less disposed to feed on red oak Quercus rubrus L. treated with high concentrations (60 and 120 g/l carrier) of kaolin than on untreated foliage. There was no significant difference (P > 0.05) between gypsy moth's consumption of kaolin-treated and untreated red oak when given a single food choice, but the adults were less inclined to oviposit on the kaolin-treated surfaces than on controls. However, no kaolin treatment completely deterred gypsy moth feeding or oviposition. Kaolin particle film did not influence forest tent caterpillar feeding and there were insufficient data to evaluate the effect of kaolin on the species' oviposition. The spray carrier did not increase the efficacy of the kaolin, but as an independent, albeit impractical treatment it constrained feeding by both insect species but did not affect gypsy moth oviposition. These initial laboratory findings suggest that applying kaolin-based particle film to forests would present significant challenges; but if these could be surmounted, the technique might assist in the management of gypsy moth but not likely in that of forest tent caterpillar.     

Effect of pine foliage damage on the incidence of larval diapause in the pine caterpillar Dendrolimus punctatus (Lepidoptera: Lasiocampidae)

The pine caterpillar Dendrolimus punctatus (Walker) with a larval facultative diapause is one of the most destructive insect pests of the pine tree Pinus massoniana in China. The larvae feeding on pine trees with different damage levels were studied to determine the induction of diapause under both laboratory and field conditions. Developmental duration of larvae before the third instar was the longest when fed with 75%–90% damaged needles, followed by 25%–40% damaged needles and intact pine needles, whereas mortalities did not differ among different treatments under the conditions of 25° and critical photoperiod 13.5:10.5 L:D. At 25°, no diapause was induced under 15:9 L:D, whereas 100% diapause occurred under 12:12 L:D regardless of the levels of needle damage. Incidences of larvae entering diapause when they were fed with intact, 25%–40% and 75%–90% damaged pine needles were 51.7%, 70.8% and 81% under 13.5:10.5 L:D, respectively. Similar results were obtained in the field experiment. Incidence of diapause was significantly different among the pine needle damage levels of pine trees when the photoperiod was close to the critical day length, indicating that the effect of host plants on diapause induction was dependent on the range of photoperiod. The content of amino acid and sugar decreased and tannin increased in pine needles after feeding by the pine caterpillars, suggesting that changed levels of nutrients in damaged needles or a particular substance emitted by damaged pine trees was perhaps involved in the diapause induction of the pine caterpillar.     

Cell lines, Md108 and Md66, from the hemocytes of Malacosoma disstria (Lepidoptera) display aspects of plasma-free innate non-self activities

The innate non-self response systems of the deciduous tree pest, the forest tent caterpillar, Malacosoma disstria has been documented by us in terms of in vitro and in vivo reactions towards the Gram-positive nonpathogenic bacterium, Bacillus subtilis and Gram-negative pathogenic microbe, Xenorhabdus nematophila and their respective surface antigens, lipopoteichoic acids (LTA) and lipopolysaccharides (LPS). These studies, often conducted in whole and diluted hemolymph, preclude examination of plasma-free cellular (hemocyte) responses. Plasma-free hemocytes as primary cultures are difficult to obtain. The floating cell line Md66 and attached cell line Md108 from M. disstria hemocytes were examined as a model for plasma-free M. disstria hemocyte non-self responses. Herein, it was established that although both lines differed from each other and from the primary hemocyte cultures of M. disstria in growth parameters, cell composition and sizes both cell lines displayed granular cell-like (GL) cells and plasmatocyte-like (PL) cells according to morphological criteria and to some extent antigenic similarities based on labeling with anti-Chrysodeixis includens hemocyte monoclonal antibodies. Hemocyte-specific neuroglian-like protein was detected on cells of both cell lines and in the primary hemocyte cultures albeit with staining patterns differing according to culture and cell types, confluency levels and cell–cell adhesion. Both cell lines bound B. subtilis and X. nematophila, the reaction extent varying with the cell line and its cell types. LPS damaged both cell types in the two cell lines whereas LTA enhanced the adhesion of Md66 GL cells to flask surfaces followed by PL cell adhesion. PL cells of both lines, like the primary cultures, phagocytosed FITC-labeled B. subtilis; only Md108 GL cells phagocytosed B. subtilis. In either case phagocytosis was always less in frequency and intensity than the primary cultures. Proteins released from the cell lines differed in pattern and magnitude but contained bacterial binding proteins that enhanced differential bacterial adhesion to both cell types in both cell lines: the GL cells both cultures, and those of granular cells in primary cultures, were more involved than the primary plasmatocytes and PL cells. Only Md66 cells possessed lysozyme and both cell types of both lines contained phenoloxidase. Neither enzyme type was released during early phase reaction with the bacteria. LPS inhibited phenoloxidase activity. The similarities and differences between the lines and primary cultures make Md66 and Md108 useful for the systematic examination of plasma-free cellular non-self reactions.     

Tent-based thermoregulation in social caterpillars of Eriogaster lanestris (Lepidoptera: Lasiocampidae): behavioral mechanisms and physical features of the tent

(1) We investigated thermoregulatory behavior of social tent building caterpillars of Eriogaster lanestris.

(2) The silk layers of the tent shield most of the incoming radiation and reduce heat exchange with the surroundings by convective heat loss.

(3) As a consequence its interior provides a wide range of temperatures.

(4) By changing their position inside or on the tent caterpillars are able to stabilize their body temperatures at 30–35°C over a wide range of ambient temperatures as long as solar irradiation is sufficiently strong.

(5) Overall behavioral thermoregulation takes precedence over the tent's physical features.     

Steinernema carpocapsae DD136: metabolites limit the non-self adhesion responses of haemocytes of two lepidopteran larvae, Galleria mellonella (F. Pyralidae) and Malacosoma disstria (F. Lasiocampidae)

Live adult and juvenile entomopathogenic Steinernema carpocapsae DD136 (P. Nematoda) were not subjected to adhesion by haemocytes of lepidopteran insect larvae of Galleria mellonella or Malacosoma disstriain vitro or in vivo. In vitro freeze-killed nematodes exhibited haemocyte attachment, the intensity increasing with time. Accumulation of haemocytes on the dead nematodes was associated with host phenoloxidase activity; live nematodes and their exudates did not activate the enzyme whereas dead nematodes but not their exudate did activate phenoloxidase. Live-nematode exudate inhibited granular cell and some plasmatocyte adhesion to slides, increased granular cell but not plasmatocyte dissociation from preformed haemocyte monolayers and in vivo elevated total haemocyte counts and changed the floating haemocyte types while impairing bacterial removal from the haemolymph. Dead-nematode exudate did not affect these parameters thus immunosuppressant activity by live nematodes may represent the release of inhibitors not associated with their cuticle. The third stage juveniles released the inhibitors.     

Biochemical ecology of the forest tent caterpillar: responses to dietary protein and phenolic glycosides

Summary Interactions between quaking aspen (Populus tremuloides) and the forest tent caterpillar (Malacosoma disstria) are likely to be influenced by leaf protein and phenolic glycoside levels, and insect detoxication activity. We investigated the direct and interactive effects of dietary protein and phenolic glycosides on larval performance and midgut enzyme activity of forest tent caterpillars. We conducted bioassays with six artificial diets, using both first and fourth stadium larvae. Four of the diets comprised a 2×2 factorial design-two levels of protein, each with and without phenolic glycosides. Additionally, we assayed high protein diets containing S,S,S-tributylphosphorotrithioate (DEF, an esterase inhibitor) and DEF plus phenolic glycosides. Enzyme solutions were prepared from midguts of sixth instars and assayed for -glucosidase, esterase and glutathione transferase activities. First instar mortality and development times were higher for larvae on diets low in protein or containing phenolic glycosides. Effects of phenolic glycosides were especially pronounced at low protein levels and when administered with DEF. Fourth instar development times were prolonged, and growth rates reduced, in response to consumption of low protein diets. Effects of phenolic glycosides on growth were less pronounced, although the effect for larvae on the low protein diet was nearly significant. Activity of each of the enzyme systems was reduced in larvae reared on low protein diets, and esterase activity was induced in larvae fed phenolic glycosides. Our results suggest that larval performance may be strongly affected by levels of protein and phenolic glycosides commonly occurring in aspen foliage, and that these factors may play a role in differential defoliation of aspen by forest tent caterpillars.     

柳杉毛虫防治试验研究

用白僵菌、苏云金杆菌、2 4 .5 %全力、2 0 %氰戊菊酯等 4种杀虫剂的不同浓度对柳杉毛虫 (Dendrolimushoui L ajonquiere)进行室内毒力测定和林间防治试验 ,结果表明 ,野外防治柳杉毛虫以氰戊菊酯 6 0 0 0倍液 +苏云金杆菌 1.4× 10 9n/ ml+全力 80 0 0倍液 +白僵菌 1.2× 10 8n/ ml林间喷雾效果最佳 ,杀虫效果达 90 %以上。应用该复合剂大面积防治 2 0 hm2 ,效果达 80 %以上。