Resistance of Pinus Sibirica clones to insect conobionts in the Yelbashinsky nursery of JSC «Berdsky forestry» in Novosibirsk region

The inter-clonal variability of Siberian cedar in resistance to insect conobionts was studied. The authors revealed that the main pests of cones and seeds are cone moth Dioryctria abietella Schiff and giant cone moth Eupithecia abietaria Goeze in the archives of plus-tree clones of Novosibirsk region (Yelbashinsky Nursery of JSC «Berdsky forestry», Iskitimsky district). The moth’s infestation of buds was 23.4%, and the infestation of buds by the moth was 2.0%. Selection of cedar for resistance to cone moths can be an effective way to increase yield at breeding and seed production facilities of this breed based on the study of inter-clonal variability in the degree of cone moth damage and other traits. Selection for resistance to cone moth disease will not significantly change stem wood produc- tivity due to the absence of a reliable interclonal correlation between the degree of cone damage and tree size. The authors described the result of the findings of the inter-clone correlation, consisting of a significant positive correlation between cone size and «granularity» and stem height and diameter. This result was against the background of the complete absence of any correlation between cone damage by conobionts and tree and cone size. The authors also concluded that selection for stem wood productivity in cedar would be accompanied by an increase in cone size and «granularity» (and vice versa), while selection for resistance to conobionts will not lead to significant changes in other vegetative and generative traits.

Predicting Damage to Hop Cones by Tetranychus urticae (Acari: Tetranychidae)

Twospotted spider mite (Tetranychus urticae Koch) is a cosmopolitan pest of numerous plants, including hop (Humulus lupulus L.). The most costly damage from the pest on hop results from infestation of cones, which are the harvested product, which can render crops unsalable if cones become discolored. We analyzed 14 yr of historical data from 312 individual experimental plots in western Oregon to identify risk factors associated with visual damage to hop cones from T. urticae. Logistic regression models were fit to estimate the probability of cone damage. The most predictive model was based on T. urticae-days during mid-July to harvest, which correctly predicted occurrence and nonoccurrence of cone damage in 91 and 93% of data sets, respectively, based on Youden’s index. A second model based on the ratio of T. urticae to predatory arthropods late in the season correctly predicted cone damage in 92% of data sets and nonoccurrence of damage in 77% of data sets. The model based on T. urticae abundance performed similarly when validated in 23 commercial hop yards, whereas the model based on the predator:prey ratio was relatively conservative and yielded false-positive predictions in 11 of the 23 yards. Antecedents of these risk factors were explored and quantified by structural equation modeling. A simple path diagram was constructed that conceptualizes T. urticae invasion of hop cones as dependent on prior density of the pest on leaves in early spring and summer, which in turn influences the development of predatory arthropods that mediate late-season density of the pest. In summary, the biological insights and models developed here provide guidance to pest managers on the likelihood of visual cone damage from T. urticae that can inform late-season management based on both abundance of the pest and its important predators. This is critically important because a formal economic threshold for T. urticae on hop does not exist and current management efforts may be mistimed to influence the pest when crop damage is most probable. More broadly, this research suggests that current management practices that target T. urticae early in the season may in fact predispose yards to later outbreaks of the pest.

Stem Incorporation of Systemic Insecticides to Protect White Spruce Seed Trees

White spruce trees were injected with a liquid formulation of dicrotophos (0.6 g Al/cm DBH) to evaluate the effect of injection times on cone and seed damage by insects. Injections of liquid formulations of dicrotophos (1.1 g Al/cm DBH) and oxydemetonmethyl (0.7 g Al/cm DBH) (approximately four days after the peak of flowering) were evaluated for control of defoliation and cone and seed damage by insects. Implants of a soluble powder formulation of acephate (0.5 and 1.0 g Al/cm DBH) (approximately two weeks after the peak of flowering) were evaluated for control of cone and seed damage. A single injection of dicrotophos reduced cone damage for up to four weeks after the peak of flowering by insects that oviposit and feed after pollination (seed moth, cone maggot, cone-axis midge, and seed inhabitants) whereas damage by insects that begin feeding before pollination was not reduced by single injections after pollination. Dicrotophos and oxydemetonmethyl reduced defoliation by spruce budworm at upper, middle, and lower crown levels for two seasons following injection. In the treatment year, these injections reduced the proportions of cones damaged by insects that feed after pollination whereas damage by insects that feed before pollination was not reduced; cone seed counts were increased 558% by dicrotophos and 267% by oxydemetonmethyl. In the season after injection the proportion of cones damaged by budworm was reduced by both insecticides while seed inhabitant damage was reduced by dicrotophos. Neither insecticide reduced damage by other insects; nonetheless, cone seed counts were increased 90% by dicrotophos and 115% by oxydemetonmethyl. In the year of treatment, implants of acephate reduced the proportions of cones damaged by seedmoth but not other insects whereas, in the season after implanting, they were effective against coneworm, seed moth, cone maggot, and seed inhabitants.

A Test of Foliar-applied Systemic Insecticides to Prevent Damage to White Spruce Cones by Insects

Cone-bearing portions of white spruce trees were sprayed by means of hydraulic sprayers with 1.0 and 1.5 per cent solutions of dimethoate, methomyl, and acephate in a 12-year-old and a 25-year-old plantation. Cone damage was reduced by insecticides but no differences between the two application rates were detected. In the younger plantation, each insecticide provided highly significant reductions in damage by spruce coneworm, spiral spruce cone maggot, and spruce cone-axis midge, but neither reduced spruce budworm damage; there were no differences among insecticides. In the older plantation, each insecticide provided significant and equal reductions in cone maggot damage; seedmoth and cone-axis midge damage was reduced by dimethoate and methomyl, but not acephate, and no insecticide reduced coneworm damage. Some factors to consider in further testing of these or other insecticides for use against cone-damaging insects on seed trees are discussed.

RELATIONSHIP BETWEEN CONE CROP SIZE AND CONE DAMAGE BY INSECTS IN RED PINE SEED-PRODUCTION AREAS

Annual cone abundance and insect damage to cones are highly variable in red pine seed-production areas. Cone crop size fluctuates almost unpredictably from year to year, but the number of insect-attacked cones tends to increase annually unless limited by cone abundance. Sixty-six per cent of the variation in cone damage can be associated with variations in cone abundance. This information, coupled with the fact that red pine cone insects are almost entirely dependent on red pine cones for food, implies that crop size is highly important in regulating populations of cone insects. Insects will be most devastating in areas where crop size varies little from year to year.