Foliage Protection Research Articles

Extrafloral nectar as entrée and elaiosomes as main course for ant visitors to a fireprone, mediterranean-climate shrub.

Thousands of plants produce both extrafloral nectaries (EFNs) on their leaves and nutrient-rich appendages on their diaspores (elaiosomes). Although their individual ecology is well-known, any possible functional link between these structures has almost always been ignored. Here, we recognized their co-presence in the shrub, Adenanthos cygnorum (Proteaceae), and studied their function and interaction. We observed that the same ants frequently visit both structures, seeds are attractive to vertebrate granivores but are released into a leafy cup from where they are harvested by ants and taken to their nests, from which seeds, lacking elaiosomes, germinate after fire. We showed that juvenile plants do not produce EFNs and are not visited by ants. We conclude that EFNs are not just an indirect adaptation to minimize herbivory via aggressive ant visitors (the role of a minority) but specifically enhance reproductive success in two ways: First, by inducing ants to visit the plant as a reliable food source throughout the year. Second, by promoting discovery of the seasonally available, elaiosome-bearing seeds for transport to their nests (the majority of visitors), so avoiding the risk of granivory should seeds instead fall to the ground. Parasitoid wasps play a supporting role in controlling the main insect herbivore whose larvae devour the reproductive apices. Thus, the EFN-elaiosome relationship has three components that enhance species fitness: foliage protection, seed transport, and granivore escape. A similar system has been described only once before (in an unrelated biome) and, consistent with the objectives of ecology as an integrative science, deserves wider study.

Efficacy of insecticide aerial spraying programs to reduce tree mortality during a spruce budworm outbreak (1967–1992) in the province of Quebec

Abstract Spruce budworm (Choristoneura fumiferana) is the most important pest of conifer forests in eastern North America. The main approach for protecting forests against this defoliator is aerial spraying of insecticides. Despite the crucial role of aerial insecticide applications in the global forest protection strategy, little is known about its real effects on tree mortality or the stand characteristics that may affect its long‐term efficacy. We evaluated the efficacy of the protection program that was implemented during the 1967–1992 outbreak in Quebec (Canada) in tree mortality reduction. We established 422 plots in eastern Quebec based upon the following parameters: insecticide application; stand composition; drainage quality; and stand age. Unprotected plots exhibited 18 to 44% greater tree mortality than protected plots. Insecticide efficacy was affected by drainage condition. Protected plots that established on sites with poor quality drainage exhibited 67.53% lower balsam fir (Abies balsamea) mortality than did unprotected plots. Stand age did not affect tree mortality. Insecticide application had no substantial effect on spruce mortality. Our study also found that the return on protection investment in terms of mortality reduction may decline after 7 years of aerial spraying, and that it is not necessary to achieve the target protection goal (50% foliage protection) every year to reduce host tree mortality. Our results may be useful for decision‐makers to decide where and when to apply insecticides during a spruce budworm outbreak and may help to determine the appropriateness of treating the forest on an annual basis depending upon the protection goals.

Spinosad and Mixtures of an Entomopathogenic Fungus and Pyrethrins for Control of Sitona lineatus (Coleoptera: Curculionidae) in Field Peas.

The pea leaf weevil, Sitona lineatus L., is an important pest of field peas and faba beans in most temperate regions. As no information is currently available on efficacy of biopesticides for S. lineatus control, laboratory bioassays were performed to evaluate the impact of biopesticides (spinosad, Beauveria bassiana strain GHA, pyrethrins, B. bassiana GHA + pyrethrins, and B. bassiana GHA + azadirachtin) against adults of this pest. The concentrations used in this bioassay were 0.1, 0.5, 1.0, and 2.0 times the lowest labeled application rate of each product. Results were further verified in cage experiments by assessing biopesticide effects on adult mortality and feeding damage in pea plants. The impact of biopesticides on mortality of larvae of two beneficial species, Chrysoperla carnea and Adalia bipunctata, was also tested in laboratory conditions. We found spinosad to be the most promising candidate, causing 100% adult mortality at high and medium concentrations. Beauveria bassiana and its combination with pyrethrins caused 60-62% adult mortality, but only at the highest concentration. In contrast, B. bassiana + azadirachtin and pyrethrins treatments caused only minimal adult mortality at all concentrations. In cage experiments, spinosad and B. bassiana + pyrethrins had significant effects on adult mortality and provided foliage protection from adult feeding. Conversely, the fungus treatment alone showed inconsistent performance. Beauveria bassiana and spinosad were generally harmless to C. carnea and A. bipunctata larvae, but B. bassiana + pyrethrins was toxic toward beneficial species. These results could help to improve integrated pest management programs intended to control S. lineatus.

A Conceptual Framework for the Spruce Budworm Early Intervention Strategy: Can Outbreaks be Stopped?

The spruce budworm, Choristoneura fumiferana, Clem., is the most significant defoliating pest of boreal balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea sp.) in North America. Historically, spruce budworm outbreaks have been managed via a reactive, foliage protection approach focused on keeping trees alive rather than stopping the outbreak. However, recent theoretical and technical advances have renewed interest in proactive population control to reduce outbreak spread and magnitude, i.e., the Early Intervention Strategy (EIS). In essence, EIS is an area-wide management program premised on detecting and controlling rising spruce budworm populations (hotspots) along the leading edge of an outbreak. In this article, we lay out the conceptual framework for EIS, including all of the core components needed for such a program to be viable. We outline the competing hypotheses of spruce budworm population dynamics and discuss their implications for how we manage outbreaks. We also discuss the practical needs for such a program to be successful (e.g., hotspot monitoring, population control, and cost–benefit analyses), as well as the importance of proactive communications with stakeholders.

Effects of tebufenozide on the assemblage of moths (Lepidoptera) in an operational spruce budworm (Lepidoptera: Tortricidae) suppression programme

AbstractTebufenozide (Mimic) kills Lepidoptera larvae that ingest it. Aerial applications of tebufenozide were made against spruce budworm (Choristoneura fumiferana(Clemens)) (Lepidoptera: Tortricidae) in boreal forest in Manitoba, Canada, in 1999 and 2000. In 2000 and 2001, moths in sprayed and unsprayed plots were sampled with light traps; trapping was supplemented by foliage sampling. Relative to unsprayed plots, catches of spruce budworm moths in plots sprayed in 1999 and 2000 were depressed in 2000, but not in 2001. Host tree defoliation was reduced in 2000 by 1999 and 2000 applications; the 2000 application reduced numbers of spruce budworm larvae in 2000 and 2001. Multivariate analysis revealed negative effects of tebufenozide application on two species of non-target moths in 2000 and no negative effects in 2001. Negatively affected species have larvae feeding in the tree canopy at the time of spray application. Higher catches of non-target species in sprayed treatments were observed for three species in 2000 and two species in 2001. We conclude that tebufenozide can depress the numbers of spruce budworm larvae and provide foliage protection during the year of application and the following year, and that negative effects on non-target species are detectable for about 15 months after application.

Economics of Early Intervention to Suppress a Potential Spruce Budworm Outbreak on Crown Land in New Brunswick, Canada

We investigated the potential economic impacts of future spruce budworm (Choristoneura fumiferana Clem.) (SBW) outbreaks on 2.8 million ha of Crown land in New Brunswick, Canada and compared an early intervention strategy (EIS) with foliage protection approaches. We coupled the Spruce Budworm Decision Support System (SBW DSS) with a Computable General Equilibrium (CGE) model to assess the impacts of EIS and foliage protection on 0%, 5%, 10%, and 20% of susceptible Crown (publicly owned) forest, under moderate and severe SBW outbreak scenarios. Cumulative available harvest supply from 2017 to 2067 was projected to be reduced by 29 to 43 million m3, depending upon SBW outbreak severity, and a successful EIS approach would prevent this loss. These harvest reductions were projected to reduce total economic output by $25 billion (CAD) to $35 billion. Scenarios using biological insecticide foliage protection over 20% of susceptible Crown forest area were projected to reduce losses to 6–17 million m3 and $0.5–4.1 billion. Depending upon SBW outbreak severity, EIS was projected to have benefit/cost ratios of 3.8 to 6.4 and net present values of $186 million to $353 million, both higher than foliage protection strategies. Sensitivity analysis scenarios of ‘what if’ EIS partially works (80% or 90%) showed that these produced superior timber harvest savings than the best foliage protection scenario under severe SBW outbreak conditions and generally superior results under moderate outbreak scenarios. Overall, results support the continued use of EIS as the preferred strategy on economic grounds to protect against SBW outbreaks on Crown land in New Brunswick.

Some effects of copper-based fungicides on plant-feeding terrestrial molluscs: A role for repellents in mollusc management

The effects of three copper-based fungicides on feeding by four terrestrial molluscs (two slugs and two snails) were assessed in laboratory choice and no-choice tests. These products functioned effectively as short-term feeding deterrents. However, a copper hydroxide-based fungicide was more persistent than copper octanate- and copper diammonia diacetate-based fungicides under field conditions. Tests with foliage treated in the field and fed to Leidyula floridana and Lissachatina fulica showed that significant feeding suppression persisted for several days. We also determined that copper hydroxide was repellent, affecting movement of L. floridana slugs independent of food. Further, we assessed copper hydroxide effects with and without iron phosphate molluscicide bait. Copper hydroxide alone significantly suppressed foliage consumption, but did not affect slug survival. Iron phosphate bait alone caused slug mortality, and significantly suppressed feeding, but only after 24 h. Significantly improved foliage protection, relative to iron phosphate bait application alone, was attained when copper hydroxide repellent was used simultaneously with iron phosphate bait. Where terrestrial molluscs are a plant protection issue, it appears that ancillary benefit can be derived from using copper hydroxide fungicides. These data provide evidence for the potential application of the “push–pull” or “stimulo-deterrent” concept relative to mollusc management; plant protection may be enhanced when attractant and repellent treatments are applied simultaneously.

Bacillus thuringiensis efficacy in reducing spruce budworm damage as affected by host tree species

Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana in black spruce (Picea mariana (Mill.) BSP), white spruce (P. glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.) was investigated in Quebec’s Cote-Nord region. As expected, larval mortality was higher in Btk-treated plots (80.26 ± 2.34 %) than in control plots (66.32 ± 2.80 %). There were no differences in larval mortality among the three host tree species tested. Btk was most efficient in reducing spruce budworm defoliation when applied to black spruce and white spruce trees. Black spruce and white spruce exhibited lower final defoliation in Btk-treated plots than balsam fir. Btk applications produced a reduction in defoliation of 36 % in balsam fir, 44 % in white spruce and 41 % in black spruce. Control plots exhibited about 35 % higher amount of current-year foliage destroyed (AFD) and 56 % lower amount of current-year foliage remaining (ARF) than Btk-treated plots, whereas no differences in the amount of current-year foliage produced (AFP) were observed among host tree species. Black spruce trees showed the lowest AFD. Although not statistically significant, black spruce also showed the highest ARF. Our results suggest that Btk application is more efficient in protecting against spruce budworm damage when it is applied to spruce species than it is to balsam fir. It appears that the observed inter-specific differences in host tree foliage protection might be related to interactions between Btk, host tree foliage, and larval feeding behaviour.

Field Note: Emamectin Benzoate Reduces Defoliation by <I>Choristoneura occidentalis</I> Freeman (Lepidoptera: Tortricidae) on Three Host Species

Stem injections of insecticides are generally regarded as a safer and a more environmentally friendly option (compared to foliar sprays) for protecting high-value trees against insects in sensitive areas or near homes. We carried out a three year study to determine the efficacy of trunk injections of emamectin benzoate for protection of foliage of three common host species attacked by the western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera: Tortricidae). Defoliation by C. occidentalis was significantly reduced by nearly half over a 3-year period on treated compared to control grand fir, Douglas-fir, and alpine fir. Reduction of defoliation was comparable to standards used for aerial spraying (e.g., 50%) of conifer feeding budworms in Canada.

Re-examining wood supply in light of future spruce budworm outbreaks: A case study in New Brunswick

Forest protection (spraying of biological insecticide), salvage harvesting, and strategic re-planning are typical mitigation options to reduce wood supply impacts caused by spruce budworm (Choristoneura fumiferana [Clem.]) defoliation. However, all such measures are expensive and difficult to implement, and decisions about if and to what extent such measures should be applied hinge on the magnitude of benefits and associated costs. We used an integrated forest estate pest-impact planning model to quantify harvest impacts for three plausible outbreak scenarios, and the effect of these typical mitigation strategies for 3.0 million ha in New Brunswick. Cumulative harvest reductions, relative to the no defoliation case, reached 18% and 25% by 2052 under moderate and severe defoliation patterns, respectively. We demonstrate that up to 30% to 50% of these projected reductions could be avoided through foliage protection treatments, depending on the outbreak scenario. Salvage and re-planning mitigated harvest losses by up to 20% in the short term (20 to 25 years), but had little benefit over the long run (40+ years). Even with aggressive implementation of all mitigation measures, significant harvest impacts (10% reduction from 2017 to 2042) were unavoidable, regardless of outbreak scenario.

Performance of Dimethomorph + Mancozeb Applied to Seed Potatoes in Early Management of Late Blight (Phytophthora infestans)

Treating seed potatoes with contact fungicides prevents infection of Phytophthora infestans from tuber to tuber during handling but does not prevent field infections in the young plant. Dimethomorph (DMM) 9% + mancozeb 60% (Acrobat MZ, BASF) can cover both aspects due to the contact and systemic action of mancozeb and DMM, respectively. Experiments were performed under greenhouse and field conditions (three seasons and two locations) with cvs Kennebec, Shepody, Spunta, Russet Burbank, and Ranger Russet. Immediately after cutting, seed pieces were treated with Acrobat MZ at doses equivalent to 2, 3, and 4 kg ha−1. At any dose, Acrobat MZ protected healthy seed tubers against P. infestans infections. Acrobat MZ (4 kg ha−1) also protected the foliage of all cultivars against artificial inoculation of P. infestans, assessed by the detached-leaf method. These effects were observed up to 30 days after emergence in greenhouse experiments and up to 28 days after crop emergence under field conditions in two growing seasons. In cv Spunta, significant foliage protection was observed up to 35 days after field emergence whereas in seed tubers of cv Kennebec planted in sandy soils, significant foliage protection persisted longer. Additional evidence for acropetal translocation of Acrobat MZ in field crops was also found. With this strategy, there is no need to apply contact or systemic fungicides early in the season, and spraying costs and environmental risks are also reduced.

Early management of late blight ( Phytophthora infestans) by using systemic fungicides applied to seed-potato tubers

Planting of seed tubers infected with late blight has been reported as a major cause in initiating the disease at field level. Seed treatments with contact fungicides can protect healthy tubers from infection during handling, grading and cutting before planting, but are not effective in protecting the young plant after emergence, when is more susceptible to the disease. Foliar fungicide applications are still required so crop protection early in the season, as a consequence of seed treatments could be an advantage especially in environments conducive to late blight epidemics. The systemic fungicides iprovalicarb+propineb (Melody Duo) and propyl carbamate (Previcur N), from Bayer CropScience, were applied to seed potato tubers (40–50 g) immediately after cutting or at planting to the bottom of the furrow and seed piece in cultivars Kennebec, Shepody, Ranger Russet, Russet Burbank and Spunta, at doses of 0.8 and 1.6 kg ton −1 and 0.4 and 0.8 l ton −1 of seed, respectively. Treated and control seed tubers were planted in pots in a greenhouse. From the time plants had one fully expanded leaf up to 40 days after emergence each treatment was evaluated by the detached-leaf method to assess foliage protection by means of artificial late blight inoculation. For all cultivars a higher level of foliage protection was found in those plants from seed tubers treated with iprovalicarb+propineb, while no effects were observed when the chemical was applied at planting to the bottom of the furrow. Used as described, this fungicide provided a higher protection against late blight than propyl carbamate. Further pre-commercial field trials, carried out during two growing seasons, with iprovalicarb+propineb was effective in protecting the foliage of cultivars Spunta, Kennebec and Shepody up to 4–6 weeks after crop emergence. For the first 4 weeks protection was high and the following two weeks it was satisfactory. This innovative application of iprovalicarb+propineb was only effective when the chemical was applied to cut seed tubers immediately after cutting and before suberization. Due to its effectiveness in controlling late blight this type of treatment should be part of a strategy for integrated late blight management, particularly where late blight epidemics occur early in the season.

<I>Bacillus thuringiensis</I> subsp. <I>kurstaki</I> Aerial Spray Prescriptions for Balsam Fir Stand Protection Against Spruce Budworm (Lepidoptera: Tortricidae)

Although commercial formulations of Bacillus thuringiensis subsp. kurstaki (Btk) are being widely used in forest protection against lepidopteran defoliators, optimal application prescriptions have often yet to be worked out in detail. We conducted field experiments over a 6-yr period (1996-2001) in southwestern Québec to determine application prescriptions for optimal protection of balsam fir, Abies balsamea (L.), healthy stands against the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). At moderate larval densities (<30 larvae per 45-cm branch tip), similar foliage protection was achieved with one or two Btk applications of 30 billion international units per hectare (BIU/ha). When larval densities exceeded 30 larvae per branch tip, two successive applications of 30 BIU/ha significantly increased foliage protection. Whether the second application took place 5 or 10 d after the first spray did not affect treatment efficacy. Increasing the application dosage from 30 to 50 BIU/ha did not lead to better foliage protection against high larval densities, but the current standard dosage of 30 BIU/ha saved more foliage than 15 BIU/ha against moderate populations. The recommended dosage of 30 BIU can be applied in lower application volumes (1.5 liters/ha) by using a high-potency product (20 BIU/liter), because we did not observe a reduction in efficacy compared with the application of a lower potency product (12.7 BIU/liter) in 2.37 liters/ha. We also demonstrated that Btk can be applied much earlier in the season without compromising spray efficacy: there was no difference in treatment efficacy of double applications at 30 BIU/ha when the first spray was timed for early third, peak third, or early fourth instars.

Activity of conventional and reduced‐risk insecticides for protection of grapevines against the rose chafer, Macrodactylus subspinosus (Coleoptera: Scarabaeidae)

Abstract: Bioassays were conducted to compare the residual toxicity and leaf protection activity of conventional broad‐spectrum and reduced‐risk insecticides against the rose chafer, Macrodactylus subspinosus. Insecticides were applied to a Vitis labrusca (F.) vineyard and residues were aged for 1, 3 or 7 days before leaves were collected and exposed to beetles in no‐choice tests. Azinphosmethyl caused rapid knockdown and mortality for up to 1 week after application, with 1‐day‐old residues providing 95.6% protection against feeding, dropping to 51.6% when residues were a week old. Fenpropathrin caused mortality and knockdown after beetles had been exposed to fresh residues for 72 h. Although these effects diminished as residues aged, this compound provided the best protection of leaves against beetle feeding, with 77.9% reduction in feeding compared with the control after 7 days of aging in the vineyard. Of the reduced‐risk insecticides, imidacloprid caused the greatest initial mortality and knockdown of beetles, providing protection against feeding that was equivalent to azinphosmethyl. Exposure to azadirachtin caused a low level of knockdown and mortality when residues were 1‐ and 3‐days old. Protection against feeding was also low, lasting for only 3 days. Beetles were minimally affected by capsaicin and kaolin, with mortality and knockdown seen only when beetles were exposed to 1‐day‐old residues for 72 h. Foliage protection from these compounds was minimal, with between 10 and 15% reduction in feeding injury. Results are discussed in relation to development of semi‐field bioassay methods for evaluating reduced‐risk insecticides, and the management of M. subspinosus within grape pest management programs.

Effects of bud phenology and foliage chemistry of balsam fir and white spruce trees on the efficacy of Bacillus thuringiensis against the spruce budworm, Choristoneura fumiferana

Abstract 1 Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana was investigated in mixed balsam fir‐white spruce stands. Btk treatments were scheduled to coincide with early flaring of balsam fir shoots, and later with flaring of white spruce shoots. Btk efficacy on the two host trees was compared and examined according to the foliar content of nutrients and allelochemicals and the insect developmental stage at the time of spray.2 Larvae fed white spruce foliage were less vulnerable to Btk ingestion than larvae fed balsam fir foliage. Higher larval survival on white spruce, observed 10 days after spray, was related to higher foliage content in tannins and a lower N/tannins ratio, which might have induced inactivation of Btk toxins.3 Larval mortality due to Btk did not depend on spruce budworm larval age.4 Foliage protection of both host trees was similar in plots treated with Btk: larval mortality due to Btk treatment reduced insect grazing pressure on balsam fir trees; meanwhile, suitability of white spruce foliage seemed to decrease very rapidly, which induced high larval mortality among spruce budworm fed on white spruce trees. Nevertheless, following Btk sprays, 50% more foliage remained on white spruce than on balsam fir trees, because of the higher white spruce foliage production.5 Both spray timings achieved similar protection of white spruce trees, but Btk treatments had to be applied as early as possible (i.e. during the flaring of balsam fir shoots to optimally protect balsam fir trees in mixed balsam fir‐white spruce stands).

Leaf ontogeny influences leaf phenolics and the efficacy of genetically expressed Bacillus thuringiensis cry1A(a) d-endotoxin in hybrid poplar against gypsy moth.

We tested the hypothesis that ontogenetic variation in leaf chemistry could affect the efficacy of genetically expressed Bacillus thuringiensis cry1A(a) d-endotoxin, and thus provide spatial variation in (1) foliage protection and (2) selective pressures that could delay the resistance of folivores. Our model consisted of clonal hybrid Populus plants (NC5339). Consumption of foliage and relative growth rates of gypsy moth, Lymantria dispar (L.) increased, and phenolic glycoside concentrations decreased, as leaves from transformed plants containing the cry1A(a) d-endotoxin and nontransformed plants matured from leaf plastochron index (LPI) 1-6. Feeding and growth rates were negatively correlated with phenolic glycosides in both transformed and nontransformed foliage. The presence of the B. thuringiensis d-endotoxin was at most, additive to the effect of the phenolic glycosides. Feeding and growth rates were positively correlated with condensed tannins in transformed foliage, but there was no relationship with condensed tannins in nontransformed foliage. The results indicate that the presence of foliar allelochemicals of poplar can enhance the effectiveness of genetically expressed B. thuringiensis d-endotoxin against gypsy moth larvae. However, the spatial variation in gypsy moth performance in response to the combination of foliar allelochemicals and d-endotoxin was not greater than the effect of ontogenetic variation in foliar allelochemicals alone. These results suggest that for this important pest, foliage protection may be obtained without genetically engineered defenses, and instead, by relying on ontogenetic and clonal variation in allelochemicals. The benefits of combining novel resistance mechanisms with natural ones will depend upon the specific folivore's adaptation to natural resistance mechanisms, such as allelochemicals. Moreover, some of the greatest benefits from transgenic resistance may arise from the need to protect trees from multiple pests, some of which may not be deterred by, or may even prefer, allelochemicals that confer protection from a few species.

Disease Development Following Infection of Tomato and Basil Foliage by Airborne Conidia of the Soilborne Pathogens Fusarium oxysporum f. sp. radicis-lycopersici and F. oxysporum f. sp. basilici

ABSTRACT Fusarium oxysporum f. sp. radicis-lycopersici, the causal agent of Fusarium crown and root rot of tomato, and F. oxysporum f. sp. basilici, the causal agent of Fusarium wilt in basil, are soilborne pathogens capable of producing conspicuous masses of macroconidia along the stem. The role of the airborne propagules in the epidemics of the disease in tomato plants was studied. In the field, airborne propagules of F. oxysporum f. sp. radicis-lycopersici were trapped with a selective medium and their prevalence was determined. Plants grown in both covered and uncovered pots, detached from the field soil, and exposed to natural aerial inoculum developed typical symptoms (82 to 87% diseased plants). The distribution of inoculum in the growth medium in the pots also indicated the occurrence of foliage infection. In greenhouse, foliage and root inoculations were carried out with both tomato and basil and their respective pathogens. Temperature and duration of high relative humidity affected rate of colonization of tomato, but not of basil, by the respective pathogens. Disease incidence in foliage-inoculated plants reached 75 to 100%. In these plants, downward movement of the pathogens from the foliage to the crown and roots was observed. Wounding enhanced pathogen invasion and establishment in the foliage-inoculated plants. The sporulation of the two pathogens on stems, aerial dissemination, and foliage infection raise the need for foliage protection in addition to soil disinfestation, in the framework of an integrated disease management program.

EXPOSING LARVAE OF THE SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) TO SUBLETHAL DOSES OF BACILLUS THURINGIENSIS SUBSP. KURSTAKI DOES NOT AFFECT SURVIVAL DURING THE PUPAL STAGE

A process-oriented model was recently developed to simulate the efficacy of spray products containing Bacillus thuringiensis Berliner subsp. kurstaki (Bacillaceae) against the spruce budworm, Choristoneura fumiferana Clemens (Cooke and Régnière 1996). The model accurately predicted foliage protection and larval population reduction during validation spray trials (Régnière and Cooke 1998; Cooke and Régnière 1999). The impact of treatment on budworm generation survival was generally well mimicked by the model except for a consistent overestimation of survival at the end of immature development in the treated plots. Régnière and Cooke (1998) speculated that residual mortality due to treatment may be occurring during the pupal stage. Carry-over of B. thuringiensis from larvae to pupae has been documented for spruce budworm (Klein and Lewis 1966) and several other Lepidoptera (Legner and Oatman 1962; Angus 1965). Although we recently investigated the response of spruce budworm larvae to ingestion of sublethal doses of B. thuringiensis (Pedersen et al. 1997), effects on pupal survival or adult emergence were not examined. In this note, we report the results of an experiment designed to assess such effects.

Analysis and use of historical patterns of spruce budworm defoliation to forecast outbreak patterns in Quebec

Historical records of defoliation by spruce budworm in Quebec from 1965 to 1992 were analyzed to determine the degree of variability in the spatial and temporal patterns of defoliation. Approximately 80% of the provincial variation in the 28-year record could be described by 25 representative defoliation patterns after first removing the geographic trends in onset year of outbreak. The spatial distribution and probable host impact of these geo-referenced representative defoliation patterns are discussed. These patterns can be used in the context of forest protection and resource management decision-making, especially if they are incorporated into a decision support system with a geo-referenced database of stand characteristics and a stand growth model. Such a system can improve estimates of expected losses due to defoliation by spruce budworm and of the potential benefits of foliage protection. The spatial and temporal patterns of defoliation can be used also to investigate the influence of environmental conditions on the characteristics of budworm outbreaks. They also constitute a basis for the validation of spatial patterns predicted by epidemiological models of the insect's population dynamics.

Deletion of the Lymantria dispar Multicapsid Nucleopolyhedrovirus Ecdysteroid UDP-Glucosyl Transferase Gene Enhances Viral Killing Speed in the Last Instar of the Gypsy Moth

Abstract The Lymantria dispar multicapsid nucleopolyhedrovirus (Ld M NPV) is used on a limited basis as a gypsy moth ( L. dispar ) control agent. In an effort to improve the efficacy (i.e., killing speed) of the Ld M NPV, we generated a recombinant viral strain (vEGT-) that does not produce the enzyme ecdysteroid UDP-glucosyltransferase (EGT). We compared the potency and efficacy of vEGT- to wild-type virus (A21-MPV) and the impact of vEGT- and A21-MPV on larval weight gain. Bioassay of L. dispar 1st, 4th, and 5th instars showed no significant difference in the LC 50 values in larvae infected with vEGT- or A21-MPV. The LT 50 values of 1st and 4th instar larvae infected with either virus were similar, but the LT 50 value of 5th instar larvae infected with vEGT- was significantly lower by ca. 33% compared with larvae infected with A21-MPV. Female 4th and 5th instar larvae infected with vEGT- gained significantly less weight than those infected with A21-MPV, whereas male 4th and 5th instar larvae infected with either virus showed no significant difference in weight gain. Larval weight gain was also used as an indicator of feeding activity through generation of FT 50 values (time when 50% of larvae ceased feeding). Fifth instar larvae infected with vEGT- exhibited a decrease in the FT 50 of ca. 32% compared with A21-MPV-infected larvae. Comparison of the total number of polyhedra produced in vEGT- or A21-MPV infected larvae showed that significantly more polyhedra were produced in 5th instars infected with A21-MPV. Deletion of the Ld M NPV egt gene generated an improved virus strain since the killing speed of vEGT- is significantly faster than wild-type virus in 5th instar L. dispar larvae, and larvae infected with vEGT- stopped gaining weight earlier than larvae infected with wild-type virus. Because the majority of foliage consumption by L. dispar larvae occurs in the 5th instar, the use of vEGT- may offer better foliage protection than wild-type virus in the field.