Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Life history and impact of seed and cone insect species found on Pinus ponderosa Dougl. ex Laws. in southeastern Nebraska
Abstract
Procurement of viable seeds of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) in the Great Plains is hindered by insects that feed on reproductive structures. Dioryctria auranticella (Grote) feeds on flowers and second-year cones. Conelets can be killed by Rhyacionia spp., Retinia metallica (Busck), and Zelleria haimbachi Busck. Dioryctria disclusa Heinrich, Eucosma ponderosa Powell, and Asynapta hopkinsi Felt occasionally infest second-year cones. Leptoglossus occidentalis Heidemann feeds on ovules and seeds, causing conelet mortality and reducing seed yield. Rhyacionia spp. and R. metallica annually killed an average of 8.2 $\pm$ 3.0% and 5.6 $\pm$ 4.9%, respectively, of conelets on tagged branches. Abortion and disappearance of conelets caused by L. occidentalis or physiological dysfunction averaged 65.7 $\pm$ 8.2%, and was reduced by 13% when conelets were protected with screen cages. Survival of conelets after one year of development averaged 18.7 $\pm$ 10.2%. Dioryctria spp. annually damaged an average of 14.2 $\pm$ 7.2% of second-year cones. Mean annual seed potentials ranged from 77.4 to 127.1 seeds per cone, but mean annual seed yields ranged from only 0.4 to 8.1 filled seeds per cone. Caging cones to exclude L. occidentalis increased seed yield and efficiency and decreased damaged and empty seed. Feeding by L. occidentalis damaged an estimated 41% of initial ovules in cones harvested in 1985. D. auranticella is a univoltine insect that infests ponderosa and Austrian pines (Pinus nigra Arnold). First-instar larvae apparently overwinter in hibernaculae. Second- and third-instar larvae feed in male and female flowers during early May. Fourth- and fifth-instar larvae tunnel in second-year cones between mid-May and mid-June. Larvae pupate within cones during June and adults fly from mid-June to late July. Eggs hatch in 6-9 days. Insects can significantly reduce cone production and seed yield of ponderosa pine in southeastern Nebraska. Information on the relative importance, life cycle, and seasonal occurrence of damaging species can be used to develop pest management strategies to increase seed production.
Subject Area
Entomology
Recommended Citation
Pasek, Judith Eleanor, "Life history and impact of seed and cone insect species found on Pinus ponderosa Dougl. ex Laws. in southeastern Nebraska" (1987). ETD collection for University of Nebraska-Lincoln. AAI8803766.
https://digitalcommons.unl.edu/dissertations/AAI8803766