Susceptibility of the spruce budworm, Choristoneura fumiferana, and the white-marked tussock moth, Orgyia leucostigmata, to Bacillus thuringiensis: Chemical insecticide combinations

Bacillus thuringiensis mixed with the organophosphate insecticides, fenitrothion (Sumithion), Gardona^®, and Orthene^®, or the synthetic pyrethroid, SBP 1382, was incorporated into synthetic diet and fed larvae of the spruce budworm, Choristoneura fumiferana, and the white-marked tussock moth, Orgyia leucostigma. Mortality was highest when larvae were fed combinations of low concentrations of the insecticides and low to moderate concentrations of the pathogen. The data indicated that applications of a B. thuringiensis dosage expected to produce about 45% mortality of third and fourth instar larvae of the spruce budworm combined with a dosage of fenitrothion causing about 40% mortality or a dosage of Orthene causing from 5 to 25% mortality should result in low budworm survival. With a B. thuringiensis dosage causing 20–60% mortality combined with a fenitrothion dosage causing 15–50% mortality or a sublethal dosage of Gardona, a low survival rate of young white-marked tussock moth larvae may be expected.     

Assessment ofTrichogramma species for biological control of forest lepidopteran defoliators

In a laboratory study, we determined the potential of threeTrichogramma (Hymenoptera: Trichogrammatidae) species,T. brassicae Bezdenko,T. minutum Riley andT. nr.sibiricum Sorokina, for biological control against six species of forest lepidopteran pests, black army cutworm, hemlock looper, eastern spruce budworm, western spruce budworm, white-marked tussock moth, and gypsy moth. Females of each parasitoid species were offered eggs from each of the six host species. Parasitization and the effect of the host species on the emerging progeny were examined and recorded.Trichogramma minutum had the broadest host range and successfully parasitized four host species out of the six offered.Trichogramma nr.sibiricum had the narrowest host range and parasitized only two species of hosts. Of the six host species, black army cutworm was the most preferred by all threeTrichogramma species; white-marked tussock moth and gypsy moth were not parasitized by any parasitoids. There was a positive correlation between the size of female offspring and their corresponding egg complement in all three parasitoid species. The developmental time of parasitoids from egg to adult was influenced by both the parasitoid and host species. Our results suggest thatT. minutum has the greatest potential for biological control against various forest lepidopteran pests and that the black army cutworm may be the best target candidate for further study.     

Some Effects of Douglas Fir Terpenes on Certain Microorganisms

The Douglas fir terpene α-pinene was shown to inhibit the growth of a variety of bacteria and a yeast. Other terpenes of the Douglas fir, including limonene, camphene, and isobornyl acetate, were also inhibitory to Bacillus thuringiensis. All terpenes were inhibitory at concentrations normally present in the fir needle diet of Douglas fir tussock moth larvae. The presence of such terpenes in the diet of these insects was found to strongly influence the infectivity of B. thuringiensis spores for the Douglas fir tussock moth larvae. The terpene α-pinene destroyed the cellular integrity and modified mitochondrial activity in certain microorganisms.     

Action of Douglas Fir Tussock Moth Larvae and Their Microflora on Dietary Terpenes

A single type of bacterium, tentatively identified as a member of the genus Bacillus, was isolated from 2 of 20 midguts of Douglas fir tussock moth larvae being fed a diet of fir needles. No bacteria could be isolated from most midguts. Although spherically shaped bodies were present in the food bolus, these bodies, if microorganisms, could not be distinguished from spherical bodies associated with the plant tissue. The Douglas fir tussock moth dietary terpenes were altered during their passage through the insects, with two new terpenes being detected in the feces. One of these was identified as isoborneol. The relative significance of the insect and gut microflora with respect to terpene modification is unresolved. The well-established toxicity of terpenes may account for the near absence of common gut microflora in the insects.     

Potential of Margosan-O, an azadirachtin-containing formulation from neem seed extract, as a control agent for spruce budworm, Choristoneura fumiferana

The effects on spruce budworm larvae, Choristoneura fumiferana (Clem.), produced by ingestion of Margosan-O, a commercially available neem seed extract formulation containing 0.3% azadirachtin, were investigated. Bioassays with the test material were conducted using various instars of spruce budworm larvae, with either artificial diet, cut branches of balsam fir, Abies balsamea (L.) Mill., or small growing balsam fir trees as substrates. The dose-response data on feeding reduction, developmental retardation, and mortality (LC50, LC95, and LD50) suggest that Margosan-O has promise as a control agent for spruce budworm in an integrated pest management program.     

Impact of aerially appliedBacillus thuringiensis and carbaryl on gypsy moth [Lep.: Lymantriidae] and adult parasites

In 1973, Dipel^® (Bacillus thuringiensis Berliner) and Sevin^® 4 oil (carbaryl) were applied aerially on a dense population of gypsy moths,Lymantria dispar (L.), to evaluate the effect of these biological and chemical insecticides on gypsy moth larvae and adult parasites. Both insecticides provided excellent protection of foliage (29 % average defoliation) and gypsy moth population reduction (99 %). Significantly fewerBrachymeria intermedia (Nees), andApanteles melanoscelus (Ratzeburg),Parasetigena silvestris (Robineau-Desvoidy) andCompsilura concinnata (Meigen) adult parasites were captured in the blocks treated with Sevin 4 oil or Dipel than in the control block during the treatment year and in 1974, respectively.     

Silver fir and Douglas fir are more tolerant to extreme droughts than Norway spruce in south‐western Germany

Improving our understanding of the potential of forest adaptation is an urgent task in the light of predicted climate change. Long‐term alternatives for susceptible yet economically important tree species such as Norway spruce (Picea abies) are required, if the frequency and intensity of summer droughts will continue to increase. Although Silver fir (Abies alba) and Douglas fir (Pseudotsuga menziesii) have both been described as drought‐tolerant species, our understanding of their growth responses to drought extremes is still limited. Here, we use a dendroecological approach to assess the resistance, resilience, and recovery of these important central Europe to conifer species the exceptional droughts in 1976 and 2003. A total of 270 trees per species were sampled in 18 managed mixed‐species stands along an altitudinal gradient (400–1200 m a.s.l.) at the western slopes of the southern and central Black Forest in southwest Germany. While radial growth in all species responded similarly to the 1976 drought, Norway spruce was least resistant and resilient to the 2003 summer drought. Silver fir showed the overall highest resistance to drought, similarly to Douglas fir, which exhibited the widest growth rings. Silver fir trees from lower elevations were more drought prone than trees at higher elevations. Douglas fir and Norway spruce, however, revealed lower drought resilience at higher altitudes. Although the 1976 and 2003 drought extremes were quite different, Douglas fir maintained consistently the highest radial growth. Although our study did not examine population‐level responses, it clearly indicates that Silver fir and Douglas fir are generally more resistant and resilient to previous drought extremes and are therefore suitable alternatives to Norway spruce; Silver fir more so at higher altitudes. Cultivating these species instead of Norway spruce will contribute to maintaining a high level of productivity across many Central European mountain forests under future climate change.     

Incidence of mesoscale convergence lines as input to spruce budworm control strategies

On occasion Greenbank et al. (1980) in their 1973 to 1976 study on spruce budworm moth dispersal in New Brunswick, Canada, detected intense line concentrations of airborne moths crossing special radar observing sites located about 100 km inland from both the Bay of Fundy and the Northumberland Straits. Line concentrations of insects reflect the presence of atmospheric convergence lines. Data from a surface mesonetwork and wind and temperature soundings up to 2 km collected in New Brunswick from 1976 to 1978 around the period of spruce budworm moth activity has revealed sea breeze fronts to be the meteorological origin for the line concentrations of moths. Analysis has shown sea breeze fronts penetrating 80 to 100 km inland in New Brunswick can be expected once or twice each year during the moth dispersal period. An equation for maximum inland penetration was developed which gave a correlation coefficient of 0.78 between predicted and observed inland penetrations with a standard error of 17.5 km. Predicted sea-breeze frontal penetrations of 100 km or more were considered likely to produce a line concentration of moths observable at the radar sited. Using this criteria the prediction scheme delineated four out of the five nights when line concentrations of moths were observed and only over-predicted on one occasion. Thus meteorological data can be used to predict the appearance of line concentrations of spruce budworm moths and so provide input into population redistribution studies and into the development of control strategies directed at the adult budworm.Presented at Eighth International Congress in Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Interpopulation quality in gypsy moths with implications for success of two pupal parasitoids: Brachymeria intermedia (Nees) and Coccygomimus turionellae (L.)*

Abstract.

• 1 Gypsy moth egg masses were collected from innocuous, release and outbreak populations and reared in the laboratory on synthetic diet under identical conditions.
• 2 Outbreak population gypsy moths hatched sooner, were smaller and less fecund than innocuous or release gypsy moths, but had a higher concentration of total carbohydrates in their haemolymph.
• 3 Pupae from each population source were submitted to parasitization by two pupal parasitoids. Emerging B.intermedia, an established parasitoid of the gypsy moth associated with outbreak populations, were largest on outbreak source gypsy moths. C. turionellae, not a usual parasitoid of the gypsy moth, were largest when emerging from innocuous or release population gypsy moths. Implications for population dynamics of the gypsy moth are discussed.

     

Quantitative studies on the pathogenicity of Nosema carpocapsae,a microsporidian pathogen of the codling moth,Cydia pomonella,in New Zealand

The pathogenicity of Nosema carpocapsae for codling moth was studied using dose-infectivity experiments. The IC₅₀ (median infective concentration) was similar for the five larval instars (range 4.0 × 10³ to 6.7 × 10⁴ spores/ml). Spore loads in moths ranged from 6.0 × 10⁶ to 7.1 × 10⁷ spores per moth and varied with dose and with larval age at infection. The infection does not cause mortality but does reduce the fecundity and fertility of infected moths. Nosema carpocapsae is transmitted transovarially as well as horizontally. Infected eggs were not produced by healthy females mated with infected males, although such pairs generally produced fewer eggs than healthy pairs.     

Lepidoptera‐specific insecticide used to suppress gypsy moth outbreaks may benefit non‐target forest Lepidoptera

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Comparative toxicity of the HD-1 and NRD-12 strains of Bacillus thuringiensis subsp. kurstaki to defoliating forest Lepidoptera.

Insecticidal activities of sporulated cultures of the HD-1 and NRD-12 strains of Bacillus thuringiensis subsp. kurstaki were compared against four species of defoliating forest lepidopterans in diet-incorporation assays. There was no difference in LC50 between the two strains to larvae of spruce budworm (Choristoneura fumiferana), gypsy moth (Lymantria dispar), eastern hemlock looper (Lambdina fiscellaria fiscellaria), and whitemarked tussock moth (Orgyia leucostigma), whether expressed as total alkaline soluble protein, activated toxin protein, or International Units as determined by bioassay against Trichoplusia ni. Both strains were consistently more toxic than HD-1-S-1980 when compared on the basis of alkali-soluble protein, but not on the basis of activated toxin or International Units. Hybridization of genomic DNA after restriction with HindIII revealed the presence of all three cryIA toxin genes in each of the isolates used in this study, including HD-1-S-1980, which was previously reported to have lost the cryIA(b) gene.     

Evidence for short-range sonic communication in lymantriine moths

Sexual communication of nun moth, Lymantria monacha (L.), pink gypsy moth, Lymantria mathura Moore, and fumida tussock moth, Lymantria fumida Butler (all Lepidoptera: Noctuidae: Lymantriinae), is known to be mediated by pheromones. We now show that males are attracted by the sounds of conspecific females over short distances and that wing fanning male and female L. monacha, L. mathura and L. fumida produce species- and sex-specific wing beat and associated click sounds that could contribute to reproductive isolation. Evidence for short-range communication in these lymantriines includes (i) scanning electron micrographs revealing metathoracic tympanate ears, (ii) laser interferometry showing particular sensitivity of tympana tuned to frequency components of sound signals from conspecifics, and (iii) phonotaxis of male L. monacha and L. fumida to speakers playing back sound signals from conspecific females. We conclude that tympanate ears of these moths have evolved in response not only to bat predation, but also for short-range mate finding and possibly recognition.     

Competition between the gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis: interactions mediated by host plant chemistry, pathogens, and parasitoids

The gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis, overlap geographically as well as in their host ranges. Adult female swallowtails are incapable of distinguishing between damaged and undamaged leaves, and the opportunities for competition between these two species are numerous. We designed field and laboratory experiments to look for evidence of indirect competition between P. canadensis and L. dispar larvae. Swallowtail caterpillars were reared in the laboratory on leaves from gypsy-moth-defoliated and undefoliated trees to explore host-plant effects. We tested for pathogen-mediated interactions by rearing swallowtail larvae on both sterilized and unsterilized leaves from defoliated and undefoliated sources. In addition, we measured the effects of known gypsy moth pathogens, as well as gypsy moth body fluids, on the growth and survival of swallowtail larvae. Field experiments were designed to detect the presence of parasitoid-mediated competition, as well: we recorded parasitism of swallowtail caterpillars placed in the field either where there were no gypsy moth larvae present, or where we had artificially created dense gypsy moth populations. We found evidence that swallowtails were negatively affected by gypsy moths in several ways: defoliation by gypsy moths depressed swallowtail growth rate and survival, whether leaves were sterilized or not; sterilization significantly reduced the effect of defoliation, and gypsy moth body fluids proved lethal; and swallowtail caterpillars suffered significantly increased rates of parasitism when they were placed in the field near gypsy moth infestations.     

How does synchrony with host plant affect the performance of an outbreaking insect defoliator?

Phenological mismatch has been proposed as a key mechanism by which climate change can increase the severity of insect outbreaks. Spruce budworm (Choristoneura fumiferana) is a serious defoliator of North American conifers that feeds on buds in the early spring. Black spruce (Picea mariana) has traditionally been considered a poor-quality host plant since its buds open later than those of the preferred host, balsam fir (Abies balsamea). We hypothesize that advancing black spruce budbreak phenology under a warmer climate would improve its phenological synchrony with budworm and hence increase both its suitability as a host plant and resulting defoliation damage. We evaluated the relationship between tree phenology and both budworm performance and tree defoliation by placing seven cohorts of budworm larvae on black spruce and balsam fir branches at different lags with tree budburst. Our results show that on both host plants, spruce budworm survival and pupal mass decrease sharply when budbreak occurs prior to larval emergence. By contrast, emergence before budbreak decreases survival, but does not negatively impact growth or reproductive output. We also document phytochemical changes that occur as needles mature and define a window of opportunity for the budworm. Finally, larvae that emerged in synchrony with budbreak had the greatest defoliating effect on black spruce. Our results suggest that in the event of advanced black spruce phenology due to climate warming, this host species will support better budworm survival and suffer increased defoliation.     

Occurrence and effects of Nosema fumiferanae infections on adult spruce budworm caught above and within the forest canopy

1 Nosema fumiferanae infections in populations of both sexes of spruce budworm Choristoneura fumiferana moths, collected live above the forest canopy (canopy moths), within the tree crown (crown moths) and in drop trays (dead moths), were examined over a 5‐year period in New Brunswick, Canada. 2 The incidence of infection and of moderate–heavy infections in canopy and crown moths of both sexes increased concomitantly with moth eclosion, indicating that N. fumiferanae retards larval/pupal development, with infected moths, particularly those having higher disease loads, emerging later in the season. 3 Infection rates differed among canopy, crown, and dead female, but not male, moths. Canopy (i.e. emigrating) females had a lower incidence of infection, lower incidence of moderate–heavy infections, and had longer forewings and higher dry weights, than crown females. These results suggest that N. fumiferanae infections negatively affect aspects of female, but not male, flight performance. Regardless of infection, forewing length and dry weight of both canopy and crown females declined over the moth flight period, but infected females in both moth types were smaller than their uninfected counterparts. Forewing lengths and dry weights of moderately–heavily infected females were most severely affected. 4 Despite high annual infection rates in parents, only a small percentage of offspring (second‐instar larvae) that established feeding sites each spring were infected, indicating that high rates of horizontal transmission occurred annually throughout the larval period. 5 The present study indicates that whether N. fumiferanae infections are a debilitating sublethal factor in spruce budworm populations depends more on the disease load than on the overall incidence of infection. The potential importance of N. fumiferanae infections on various fitness parameters related to host dispersal is discussed.     

Specificity of Developmental Resistance in Gypsy Moth （Lymantria dispar） to two DNA-Insect Viruses

Gypsy moth (Lymantria dispar) larvae displayed marked developmental resistance within an instar to L. dispar M nucleopolyhedrovirus (LdMNPV) regardless of the route of infection (oral or intrahemocoelic) in a previous study, indicating that in gypsy moth, this resistance has a systemic component. In this study, gypsy moth larvae challenged with the Amsacta moorei entomopoxvirus (AMEV) showed developmental resistance within the fourth instar to oral, but not intrahemocoelic, inoculation. In general, gypsy moth is considered refractory to oral challenge with AMEV, but in this study, 43% mortality occurred in newly molted fourth instars fed a dose of 5×10⁶ large spheroids of AMEV; large spheroids were found to be more infectious than small spheroids when separated by a sucrose gradient. Developmental resistance within the fourth instar was reflected by a 2-fold reduction in mortality (18%–21%) with 5×10⁶ large spheroids in larvae orally challenged at 24, 48 or 72 h post-molt. Fourth instars were highly sensitive to intrahemocoelic challenge with AMEV; 1PFU produced approximately 80% mortality regardless of age within the instar. These results indicate that in gypsy moth, systemic developmental resistance may be specific to LdMNPV, reflecting a co-evolutionary relationship between the baculovirus and its host.     

Mechanical thinning to restore oak savanna promoted predator assemblages of gypsy moth pupae in Michigan

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Anthropogenic drivers of gypsy moth spread

The gypsy moth, Lymantria dispar (L.), is a polyphagous defoliator introduced to Medford, Massachusetts in 1869. It has spread to over 860,000 km² in North America, but this still only represents ¼ of its susceptible host range in the United States. To delay defoliation in the remaining susceptible host range, the government maintains a barrier zone and a quarantine, reflecting a presumption that anthropogenic factors are important in the spread of gypsy moth. We develop a model framework that relates these factors along with biophysical characteristics to a county’s susceptibility to gypsy moth invasion. We then compile a dataset for counties within 200 km of the infested area and use trap catch data from 1999 to 2007 to estimate the probability of gypsy moth presence. As expected, gypsy moth is more likely to be found close to the population front and to traps that recorded moths in the previous year. However, when controlling for these factors, our most robust finding is that the use of wood for home heating and energy is consistently positively correlated with the presence of gypsy moth. In contrast, the movement of wood products by industry, which is actively regulated by state and federal governments, is rarely correlated with the presence of gypsy moth. This is consistent with effective regulation of the movement of goods by industry, but not by the public. Our findings provide empirical support for the importance and challenge of firewood as a vector for non-native forest insects.     

A protein complex from Choristoneura fumiferana gut-juice involved in the precipitation of δ-endotoxin from Bacillus thuringiensis subsp, sotto

A 75 kDa protein from spruce budworm (Choristoneura fumiferana) gut-juice has been isolated and shown to cause a specific precipitation of the δ-endotoxin from Bacillus thuringiensis subsp. sotto. This 75 kDa protein, separated by either column chromatography or SDS-PAGE, caused precipitation of the sotto toxin in both agarose diffusion gels and the PAGE gels. The precipitation event leads to limited proteolysis of the toxin and loss of larval toxicity. SDSPAGE analysis of the precipitated toxin indicates that proteolysis of the toxin is not a prerequisite for precipitation. The protein responsible for precipitation, exhibits elastase-like activity and appears to be a complex which partially dissociates during boiling in SDS-PAGE sample buffer. Gut-juice from gypsy moth, forest tent caterpillar and white mark tussock moth also precipitated δ-endotoxin, but silkworm gut-juice gave a much weaker response. These results provide further evidence that, in the larval gut, differential processing of δ-endotoxin may play a role in the expression of activity towards various insect larvae.