Neodiprion Abietis Research Articles

Aerial application of nucleopolyhedrovirus induces decline in increasing and peaking populations of Neodiprion abietis

The potential role of diseases in generating population cycles has often been advocated but has received little experimental support from the Weld. We introduced a nucleopolyhedrovirus (NeabNPV) into Weld populations of Neodiprion abietis (Harris), the balsam Wr sawXy, to determine its role in the collapse of outbreaks and examine its potential for biological control. This was accomplished through the use of aerial applications of NeabNPV on increasing, peaking, and declining populations of its host. Results indicate that N. abietis densities were distinctly lower in the generation following an aerial application of NeabNPV, but only when treatments were directed against increasing or peaking populations. When directed against declining populations, NeabNPV applications apparently did not inXuence the natural collapse of outbreaks. Although the artiWcial introduction of NeabNPV did not consistently aVect densities of the treated generation, it had an eVect on host biology in the weeks following the treatment as the incidence of NeabNPV infection increased and frass production (concomitant with larval feeding) decreased in treated areas. This study supports the hypothesis that NeabNPV epizootics initiate the decline of N. abietis populations. Our results also indicate that NeabNPV may provide an eVective tactic to suppress increasing or peaking population outbreaks of N. abietis through the use of aerial applications of NeabNPV at rates as low as 1£ 10 9 polyhedral occlusion bodies per hectare.

Relationship between balsam fir sawfly density and defoliation in balsam fir

Field studies were carried out to examine the relationships between balsam fir sawfly, Neodiprion abietis (Harris), density and resultant defoliation on young balsam fir, Abies balsamea (L.) Mill., in western Newfoundland. Densities of early- and late-instar larvae explained 57 and 70% of variation in defoliation in a sleeve-cage study. Densities of both early- and late-instar larvae were significantly related to defoliation on 1 to 5-year-old, but not always on 6 and 7-year-old foliage, due to the preference of larvae for young, but not current-year, foliage. Defoliation was strongly related to the densities of eggs and larvae in field surveys. Sawfly density and whether or not a population had increased or decreased in density during the previous year explained 77% (eggs), 64% (early-instar larvae) and 83% (mid-instar larvae) of the annual variation in defoliation. Our results suggest that establishment of robust density–damage relationships are possible for N. abietis on balsam fir, using egg densities to estimate defoliation and previously established relationships to predict both the amount of foliage remaining and growth loss.

Notes on larval instars and adult antennae of Neodiprion abietis (Hymenoptera: Diprionidae)

The native balsam fir sawfly, Neodiprion abietis (Harris) (Hymenoptera: Diprionidae), occurs throughout Canada, Alaska, and the northern United States of America (Rose et al. 1994; Drooz 1985). This sawfly was originally described as Lophyrus abietis (Hymenoptera: Diprionidae) (Harris 1841), then transferred to the genus Diprion (Hymenoptera: Diprionidae) (MacGillivray 1916). Rohwer (1918) established the genus Neodiprion for Nearctic species of the genera Lophyrus and Diprion. Based on differences in size, color, and female genitalic characters between adults reared from the genera Abies, Picea, Pseudotsuga, and Tsuga (Pinaceae), Ross (1955) considered N. abietis as a complex. After a thorough morphological and physiological study, Knerer and Atwood (1972) concluded that there were five strains of N. abietis in North America: one western and four eastern.

New synonymy and new sawfly host records for Cirrospilus vittatus (Hymenoptera: Eulophidae) in North America

AbstractCirrospilus flavoviridis Crawford, syn. nov., is synonymized under C. vittatus Walker. It is newly recorded as a solitary egg parasitoid from eggs of Neodiprion abietis Harris (Hymenoptera: Diprionidae) on balsam fir, Abies balsamea (L.) Mill. (Pinaceace), in New Brunswick and Newfoundland and from eggs of Neodiprion nanulus nanulus Schedl in Wisconsin.

Impact of old foliage removal, simulating defoliation by the balsam fir sawfly, on balsam fir tree growth and photosynthesis of current-year shoots

To investigate the effect of defoliation by the balsam fir sawfly ( Neodiprion abietis) on current-year growth and photosynthesis, all 1-year-old and older foliage were removed by manual clipping before the start of the growing season from balsam fir seedlings cultivated at two levels of fertilization. Measurements carried out late in the same growing season showed that both defoliation and withholding fertilizer reduced current-year foliar dry weight, shoot length, needle size, and stem xylem radial width, as well as total foliar dry weight, and root dry weight. Defoliation increased the projected area to weight ratio, nitrogen concentration, net photosynthetic rate per unit of dry weight, and ratio of photosynthesis to internal CO 2 concentration in current-year needles. In contrast, withholding fertilizer did not alter the projected area to weight ratio and decreased the nitrogen concentration, net photosynthetic rate per unit of dry weight, and ratio of photosynthesis to internal CO 2 concentration. Both defoliation and withholding fertilizer also decreased the number of current-year needles produced in the growing season following treatment. The results indicate that (1) the reduction in total photosynthesizing biomass caused by removing old foliage is much greater than the biomass of old foliage removed due to decreased production of current-year foliage, and (2) old foliage removal stimulates net photosynthesis in current-year shoots, probably by improving foliar nitrogen relations. Removing old foliage reduced the total photosynthesizing biomass more, and stimulated net photosynthesis of remaining foliage less, than the removal of current-year foliage measured in earlier studies, which helps explain why tree recovery is slower following defoliation by the balsam fir sawfly than after spruce budworm ( Choristoneura fumiferana) attack.

Temporal patterns of balsam fir sawfly defoliation and growth loss in young balsam fir

A 2-year field study was carried out with the balsam fir sawfly, Neodiprion abietis (Harris), on balsam fir, Abies balsamea (L.) Mill., to determine: (1) the temporal patterns of defoliation and foliage weight loss associated with early- and late-larval instars; (2) the losses in branch and tree stem volume growth as a result of defoliation by larvae; and (3) to determine the extent to which individual branches are autonomous, and their utility for predicting stem growth losses due to defoliation. In addition, this study also permitted us to determine the relationships between defoliation or foliage weight and branch and tree stem volume growth. Defoliation, foliage weight loss and larval development occurred more quickly in the first year due to warmer temperatures, but final levels of defoliation and foliage weight loss were similar in both years. Cumulative defoliation levels increased from <5% at the beginning of the study to 35 and 63%, respectively, in fall 1999 and 2000. Defoliation was greatest on 1-year-old foliage in both years and most defoliation and foliage weight loss occurred after the initiation of third-instar. Based upon individual year–volume increment relationships for each branch and tree, mean volume increment loss in 1999 and 2000, respectively, was 20 and 42% for observation branches and 12 and 35% for tree stems. Similar growth loss estimates of 12 and 46%, respectively, for 1999 and 2000, were obtained when comparing the mean specific volume increment for control and observation branches. Foliage weight after sawfly attack was related to branch and stem volume growth, but defoliation was only related to branch volume loss. Although branch and tree stem growth were strongly related, growth losses in a branch were not related to those in a tree stem. Branch removal and measurement is a practical alternative to cutting trees to estimate stem volume growth in balsam fir.

Advantages of a mixed diet: feeding on several foliar age classes increases the performance of a specialist insect herbivore.

Two field studies were carried out to determine the influence of Abies balsamea foliage age on the preference and performance of larvae of Neodiprion abietis, a specialist Diprionid sawfly. Preference was determined by examining N. abietis defoliation on all age classes of foliage. Performance was estimated using larval survival, cocoon weights and the percentage of adults that were females. Neodiprion abietis preference for, and performance on, current-year foliage was very low, peaked on 2 or 3-year-old foliage, and declined on older foliage. Thus, sawfly feeding preference was adaptive. However, survival and cocoon weight were highest when sawflies were allowed to feed on all age classes of foliage, demonstrating that an insect specialist may perform better when feeding on several age classes of foliage from a single host plant species. These results indicate that either different larval instars have different nutritional requirements, or that food mixing provides the best diet, permitting the herbivore to obtain needed nutrients while avoiding ingestion of toxic doses of secondary metabolites. In addition, our results suggest that limited availability of varied foliage has more negative consequences for N. abietis females than for males, as the percentage of survivors that were females decreased when juvenile mortality was high. Our results emphasize the importance of considering non-linear changes in foliar quality as leaves age on herbivore preference and performance, and demonstrate how a herbivore can use this variability to maximize its fitness.

Lethal and sublethal effects of a neem-based insecticide on balsam fir sawfly (Hymenoptera: Diprionidae).

Lethal and sublethal effects of Neemix 4.5 EC, a commercial neem preparation, on balsam fir sawfly, Neodiprion abietis (Harris), were determined in the laboratory. Larval mortality of N. abietis increased in a concentration-dependent manner, and lethal time decreased with increasing Neemix 4.5 EC concentration. Fifty percent of the larvae died after 4.6 d at a concentration of 90 ppm azadirachtin (AZA) and 12.3 d at a concentration of 0.08 ppm. Neemix 4.5 EC showed some deterrent effects to feeding site selection on N. abietis larvae at high concentrations, but not at low concentrations. Strong reduction of food intake by N. abietis larvae after exposure to Neemix 4.5 EC was demonstrated by significant reduction of frass production. Larvae fed on Neemix 4.5 EC-treated foliage at 90 ppm AZA produced only 16% as much frass as that produced by larvae fed on control foliage (0 ppm). Neemix 4.5 EC at a concentration of 0.08 ppm AZA retarded larval and pupal development. Sublethal doses significantly reduced pupal weight and adult emergence, although the sex ratio of N. abietis adults was not affected. Results indicate that sublethal effects of Neemix 4.5 EC on N. abietis may contribute greatly to the overall field efficacy.

Seasonal changes in intra-tree distribution of immature balsam fir sawfly (Hymenoptera: Diprionidae)

AbstractA field study was carried out to determine the intracrown distribution of the balsam fir sawfly, Neodiprion abietis Harris (Hymenoptera: Diprionidae), throughout the season on balsam fir, Abies balsamea L. (Pinaceae), during the first 2 years of an outbreak in western Newfoundland. Eggs were usually laid one per needle on current-year shoots, and the following year, newly emerged larvae usually initiated feeding on the same shoots. Balsam fir sawfly larvae were gregarious on needle and shoot levels in the early instars but gradually became solitary as larvae developed. The process of becoming solitary was not due to the increased physical area required for the growing larvae as some older individuals, in mainly solitary stages, were seen feeding together. Unlike the continuous change from gregarious to solitary at the needle and shoot levels, the seasonal variation in larval density among whorls varied in an inconsistent manner. The majority of early-instar larvae were found in the middle crown, but on at least one date in both years the majority of late instars were in the lower crown. Seventy-five percent of crawling larvae trapped within the crown were third and fourth instars, suggesting that changes in the intra-tree distribution are due to larval movement.

Growth loss and recovery following defoliation by the balsam fir sawfly in young, spaced balsam fir stands

AbstractTwo stands of intensively managed balsam fir [Abies balsamea (L.) Mill. (Pinaceae)] in western Newfoundland, located within an area infested by the balsam fir sawfly, Neodiprion abietis (Harr.) (Hymenoptera: Diprionidae) complex, were selected to study growth loss and recovery following severe defoliation by the balsam fir sawfly in the early 1990s. Four years after the start of the outbreak, volume increments were reduced by 78–81%. The decreased volume increment and recovery coincided well with the balsam fir sawfly outbreak and decline. The growth recovery rates following severe balsam fir sawfly defoliation were slow due to the absence of bud destruction, which triggers the release of suppressed buds, and thus increases foliage production. It is imperative that the severe losses in volume growth caused by balsam fir sawfly defoliation are incorporated into wood supply analyses so that future annual allowable cuts may be adjusted. In addition, to ensure maximum recovery rates at the end of an outbreak, future populations must be kept at a minimum to avoid additional foliage loss.

Artificial inoculation with Armillaria ostoyae in established conifers stressed by defoliation, planting, and thinning in Newfoundland

Armillaria ostoyae (Romagnesi) Herink causes root disease in conifers of the northern hemisphere. Pathogenicity tests of established conifer trees with A. ostoyae, has never been done in the boreal forest. Seven forest plots were selected in Newfoundland; a black spruce (Picea mariana (Mill.) BSP) plantation, a naturally regenerated black spruce stand, a balsam fir (Abies balsamea (L.) Mill.) stand with hemlock looper (Lambdina fiscellaria (Guen.)) defoliation, two balsam woolly adelgid (Adelges piceae (Ratz.)) infested balsam fir stands (thinned and unthinned sites), a balsam fir sawfly (Neodiprion abietis Harris) defoliated balsam fir stand, and an artificially defoliated black spruce stand. Roots of fir and spruce trees were inoculated with two isolates of A. ostoyae and re-examined after 2 years. The purpose of this study was to compare differences in root infection within plots for different types of host stress to examine the response of trees to controlled inoculations of A. ostoyae. There was a statistically significant difference in number of infected roots between the two isolates used as inoculum. There was significantly more root response with severity of infection within all sites except both adelgid plots. A marginally significant relationship between tree health and root infection was present in the balsam fir sawfly plot. There was a significantly larger number of infected roots associated with rhizomorphs in the naturally regenerated black spruce stand and the artificially defoliated balsam fir stand. These results suggest that stress prediposes the host tree to root infection by A. ostoyae.

Chromosome fission associated with growth of ribosomal DNA in Neodiprion abietis (Hymenoptera: Diprionidae).

The haploid complement consists of seven metacentric chromosomes in most diprionid species but has evolved to n = 8 by fission in Neodiprion abietis. This fission generated a small telocentric chromosome and a large pseudoacrocentric chromosome with a short arm carrying a satellite. In situ hybridization indicated that the location of the rRNA gene cluster corresponds to the whole short arm. This suggests that (i) the breaking point was located close to an rRNA gene cluster, and (ii) fission was associated with growth of rDNA. These results suggest rDNA as a preferential breaking point but with a role in the healing of naked chromosome ends.

ACCUMULATION AND PERSISTENCE OF FENITROTHION IN NEEDLES OF BALSAM FIR AND POSSIBLE EFFECTS ON ABUNDANCE OF NEODIPRION ABIETIS (HARRIS) (HYMENOPTERA: DIPRIONIDAE)

AbstractFenitrothion accumulates in foliage tissue of balsam fir, Abies balsamea (L.) Mill., in the forest, but only until about 1.5 μg/g is reached. The balsam fir sawfly, Neodiprion abietis (Harris), which belongs to the family of forest insects known to be most sensitive to fenitrothion, has become rare but persists in New Brunswick in spite of the use of fenitrothion for control of spruce bud worm, Choristoneura fumerifana (Clemens).

Bionomics ofNeodiprionspecies on white fir in northeastern California

Two sawfly species that feed on white fir were studied in Modoc County, California: Neodiprion near deleoni Ross and N. abietis complex. Neodiprion near deleoni comprised 91 percent of the field Neodiprion populations and spun opaque brown cocoons in the litter or soil. Neodiprion abietis accounted for 9 percent of the field population and spun translucent cocoons that appear green and are attached to foliage. Full-grown larvae, pupae, and adults of the two strains were morophologically distinct, though eggs and young larvae were not. Differences in morphology, phenology, physiology, and behavior are described for the two species. Mortality factors are identified, primarily for N. near deleoni. Parasitoids emerged from eggs and cocoons; many parasitoids that emerge from cocoons attack larvae. Larval predation was observed only rarely, except for predation by theridiid spiders. Sampled cocoons showed: 16 to 21 percent parasitized, 21 to 22 percent attacked by predators, 24 to 37 percent unknown mortality, and 25 to 34 percent sawfly emerged. Encapsulated ichneumonid eggs were found in 10 to 41 percent of emerging sawflies.

Photoperiodism in the early balsam strain of the Neodiprion abietis complex (Hymenoptera: Diprionidae).

The early balsam strain of the Neodiprion abietis complex does not have a photoperiodically controlled, prepupal diapause occurring during the summer in its normal, univoltine life cycle. This is the first instance we have found in laboratory tests of 15 species and subspecies of diprionid sawflies in which photophase does not regulate the course of prepupal development in a normal life cycle. Daylength, however, does influence the induction of an intense, or prolonged, prepupal diapause that in nature would result in at least a 2-year life cycle for individuals with the intense diapause.The duration and variability of larval development are both affected by daylength.

Evolutionary Trends in the Subsocial Sawflies Belonging to theNeodiprion abietisComplex (Hymenoptera: Tenthredinoidea)

Populations of the Neodiprion abietis complex occur on firs and spruces in North America. A distinct western population on white fir differs greatly in appearance from the four eastern strains, of which two feed on balsam fir and one each on black and white spruce respectively. Differences in developmental rates, larval survival on the various food plants, and host selection by the females supply the isolating mechanisms between the strains in the field. All populations cross-mated freely in the laboratory, and the resulting hybrids indicate the transmission of Several morphological and physiological characters. It is speculated that the ancestral line of the complex fed on pine before a jump to spruce and then to balsam was made.

Small Mammals as Predators of Sawflies

The greatest predatory effect of small mammals is exerted upon insects that spend a portion of their life cycle on the ground or in the soil. Sawflies afford ample opportunity for mammalian predation, since they drop to the ground as mature larvae and spin cocoons in the soil. Such sawflies as Neodiprion abietis Harr., which remain within the cocoon for about three weeks, undergo only moderate risk of being preyed upon by small mammal. However, Pristiphora erichsonii (Htg.) remains within the cocoon from about mid-August until the following June, or even over more than one year, thus greatly extending the vulnerable period. Earlier investigations suggest that small mammals may comprise the largest single biological control agent acting against this insect (Graham 1928, Lejeune 1951), but the exact role of mammalian predators of forest insects has yet to be established.