Considerations When Sampling Spruce Budworm Egg Masses on Balsam Fir in the Lake States: Low to Extreme Population Levels

Nineteen balsam fir trees, Abies balsamea, from five spruce-fir stands in Michigan\u27s Upper Peninsula, were used to study egg mass densities and distributions. Ten were used to study the effects of branch size on mass density estimates. The foliage surface area and the number of new egg masses spruce budworm, Choristoneura fumiferana, were determined for each branch, and the top of each tree and (or) the branch segment of interest. We determined the effects of the bias and the variance of the estimator, of sampling different parts of the tree, and of sampling different size branches. Points that should be considered when estimating spruce budworm egg mass densities on balsam fir were identified. Generally, sampling whole branches from the mid-crown gave the most precise and accurate estimates of tree egg mass density

Spruce Budworm Egg Mass Density on Balsam Fir: Low to Extreme Population Levels (Lepidoptera: Tortricidae)

A study was initiated in Michigan\u27s Upper Peninsula to develop improved foliage sampling methods for spruce budworm, Choristoneura fumiferana (Clemens), egg masses. Four balsam fir, Abies balsamea, trees were chosen from each of four stands in 1979, and four balsam fir trees were chosen from one stand in 1980. The number of new egg masses, foliage surface area, and crown and quadrant classes of each branch were determined for all trees. Egg mass density for each part of the tree was determined by dividing total number of egg masses by total surfaee area. The 20 trees were divided into five groups with forecasted budworm damage varying from low to extreme. On the average the egg mass density (egg mass/lOOO cm2) of the lower-crown was 58% lower than the egg mass density of the entire tree; the mid-crown had 18% higher cgg mass density than the entire tree, the upper-crown had 63% higher density than the entire tree, and the tree top had 69% higher density than the entire tree. There was no strong trend to the small absolute differences in density among the four quadrants. Sampling at mid-crown may lead to over- or underestimation of tree egg mass density. The seriousness of such errors would depend on the bias and where the sample is taken vertically in the mid-crown

Regression Equations and Table for Estimating Numbers of Eggs in Jack Pine Budworm (Lepidoptera: Tortricidae) Egg Masses in Michigan

Three simple linear regression equations were developed to estimate the numbers of eggs in jack pine budworm, Choristoneura pinus pinus, egg masses in Michigan. One equation was developed for each of 2-row, 2-row +, and 3-row egg masses. A table of estimated numbers of eggs per egg mass is given for each of the three row types for egg mass lengths from 1 to 25 nun

Considerations When Sampling Spruce Budworm Egg Masses on Balsam Fir and White Spruce in the Lake States: Low Population Levels

One cluster each of balsam fir, Abies balsamea, and white spruce, Picea glauca, trees was chosen from each of five stands of spruce-fir in Michigan\u27s Upper Peninsula. The foliage surface area and the number of new egg masses of the spruce budworm, Choristoneura fumiferana, were determined for each branch and the top of each tree. The effects, in terms of the bias and the variance of the estimator, of sampling in different parts of the tree and with various size branches were determined. Factors that the sampler should consider in developing sampling plans to estimate spruce bud worm egg mass densities in mixed spruce-fir stands were identified. Egg mass density and its per branch variance may be considerably higher in white spruce than in balsam fir. Sampling whole feasible branches at mid-crown yielded, in general, the most precise and accurate estimates of tree egg mass density

Spruce Budworm Egg Mass Density on Balsam Fir and White Spruce: Low Population Levels (Lepidoptera: Tortricidae)

As part of a study to develop improved foliage sampling methods for spruce budworm, Choristoneura fumiferana (Clemens), egg masses, two balsam fir (four in one stand), Abies balsamea, and two white spruce, Picea glauca, trees were chosen from each of five spruce- fir stands in Michigan\u27s Upper Peninsula in 1980. All stands had very low to low population densities. Each tree was completely enumerated so that the number of new egg masses, foliage surface area, and egg mass density could be determined for the entire tree, three crown classes, four quadrants, and the tree top. Results indicated (1) considerable tree-to- tree and stand-to-stand variation; (2) no meaningful or consistent differences among quad- rants within or between species; (3) the average density in white spruce trees was 3.2 times larger than that in balsam fir trees; (4) the tree-la-tree variation of density in white spruce trees was 8.4 times larger than that in balsam fir trees; (5) densities in the mid-crown, upper-crown, and tree top are considerably higher than that in the lower-crown for both species; the relative differences for balsam fir are about twice that of white spruce; and (6) on the average, density at mid-crown was close to that of the entire tree for balsam fir, but density at mid-crown was 17.9% lower than that of the entire tree for white spruce. These results have important implications to the development of sampling plans for estimating egg mass density in spruce-fir stands

Bibliography of Sequential Sampling Plans in Insect Pest Management Based on Wald\u27s Sequential Probability Ratio Test

This paper contains 65 references dealing with the development of sequential sampling plans in insect pest management based on Wald\u27s Sequential Probability Ratio Test (SPRT), 25 in forest entomology and 40 in agriculture entomology. The insect(s) sampled, whether the decision procedure was based on one or two SPRTs, and the mathematical distribution and probabilities of Type I and Type II errors used to develop the SPRTs are also given for each sequential sampling plan

Regression Equations and Table for Estimating Numbers of Eggs in Jack Pine Budworm (Lepidoptera: Tortricidae) Egg Masses in Michigan

Three simple linear regression equations were developed to estimate the numbers of eggs in spruce budworm, Choristoneura fumiferana, egg masses in Michigan. One equation was developed for each of 2-row, 2- row + , and 3-row egg masses. A table of estimated numbers of eggs per egg mass is given for each of the three row types for egg mass lengths from 1 to 13 mm

Accuracy and Precision of Insect Density and Impact Estimates

In estimating insect density and impact, entomologists are understandably interested in accuracy of estimation, but they almost always are dealing with precision because of bias due to an invalid estimator, probability sampling, or nonsampling errors. Definitions related to statistical estimation are reviewed and the concepts of accuracy and precision examined. Interval estimation and optimum sample size determination related to accuracy and precision, using the concept of allowable error, are examined. Criteria for selecting the best estimator in tenns of accuracy and precision are presented, and the distortion of probability statements due to bias is discussed. Accuracy and precision are compared and contrasted using two examples: (I) estimating insect density and (2) estimating insect impact. Adjusted and more accurate estimators can be obtained if the bias of an estimator can be estimated from a preliminary sample

Development of Empirical Models to Rate Spruce-Fir Stands in Michigan\u27s Upper Peninsula for Hazard From the Spruce Budworm (Lepidoptera: Tortricidae): A Case History

The procedure used to develop empirical models which estimate potential spruce budworm impact to spruce-fir stands in Michigan\u27s Upper Peninsula is reviewed. Criteria used to select independent variables, to select the best of alternative multiple linear regression models. and to validate final models are discussed. Preliminary, intermediate, and final results demonstrate a cyclic pattern to the development procedure. Validation is emphasized as an important step in the procedure. Implications of using the hazard-rating system as a pest management tool in the stand management process are discussed

Regression Equations and Table for Estimating Numbers of Eggs in Jack Pine Budworm (Lepidoptera: Tortricidae) Egg Masses in Michigan

Three simple linear regression equations were developed to estimate the numbers of eggs in spruce budworm, Choristoneura fumiferana, egg masses in Michigan. One equation was developed for each of 2-row, 2- row + , and 3-row egg masses. A table of estimated numbers of eggs per egg mass is given for each of the three row types for egg mass lengths from 1 to 13 mm