LAB 93603

INVESTIGATOR: Goyer, R. A.

PERFORMING INSTITUTION:
ENTOMOLOGY
LOUISIANA STATE UNIVERSITY
BATON ROUGE, LOUISIANA 70893

INTERACTIONS OF INSECTS AND ENVIRONMENTAL MODIFICATIONS WITH THE HEALTH OF LOUISIANA'S FORESTED WETLANDS

NON-TECHNICAL SUMMARY: Forested wetlands are in declining health and productivity because of a variety of biological and environmental stresses. Our goal is to evaluate the interactions of insect herbivory (defoliation) with fertility and salt water inputs in baldcypress and tupelo dominated swamps.

OBJECTIVES: This project will evaluate: 1. the interactive effects of insect herbivory and multiple stress agents on productivity of second growth timber stands of baldcypress and tupelo in southern Louisiana. 2. the host tree response to insect herbivory and combined abiotic stresses (varying hydrology, salinity and fertility) in a controlled greenhouse environment 3. insect larval growth, development rate and potential population growth when fed leaves of host trees subjected to environmental manipulations (fertility inputs, stand density modifications, genotype variation (in baldcypress) and differing hydrological and salinity levels.

APPROACH: Both field and greenhouse experiments are designed to measure radial growth response of tupelo and baldcypress trees and/or saplings with varying levels of site fertility (through artificial fertilization at levels approximating planned Mississippi River diversions), salinity and insect herbivory. Secondarily, the feedback mechanisms of insect herbivore response to these environmental modifications will be determined by bioassays of treatment foliage and developmental rates and size of baldcypress leafrollers and forest tent caterpillars. Further, height and radial growth of five baldcypress genotypes will be compared in fertilized, thinned and untreated check plots at two field sites. Laboratory bioassays with foliage from these same genotypes and treatment combinations will be utilized to evaluate treatment effects on growth and development of baldcypress leafroller caterpillars.

PROGRESS: 2004/01 TO 2004/12
We studied the effects of nutrient enhancement into degraded forested wetlands in both greenhouse and field experiments. Greenhouse studies evaluated the response of foliar nitrogen and phenolics (a measure of plant defenses to insects) to salinity, nutrient regime, hydrology and mechanical defoliation to baldcypress and tupelo gum. For both tree species, foliar nitrogen (%) was significantly increased with fertilization compared to nonfertilized saplings. Defoliated saplings had significantly higher nitrogen levels than undefoliated saplings. Salt-stressed saplings (3 ppt) displayed increased foliar nitrogen when compared to fresh-water treated saplings. Hydrology alone was not influential in determining nitrogen levels, but the flooded-aerated hydrology treatment significantly increased nitrogen levels in the fertilized, salinated saplings. In all instances, cypress saplings had a lower total phenolic level than tupelo (measured in catechin reagent equivalent, CRE%). For both tree species, fertilized saplings had a lower CRE% than nonfertilized saplings. Mechanical defoliation did not induce the expected increase in phenolics one week after defoliation. Salt-stressed saplings also had a lower CRE% than saplings subjected to freshwater condition. Flooding increased CRE% levels in both of these tree species in freshwater environments, but not in saltwater environments. A significant negative correlation was observed between foliar nitrogen and CRE%. Tupelo CRE% levels were not correlated to N%, whereas cypress responded in a significantly negative manner. It appears that cypress metabolic functions were being sustained better than tupelo, and that cypress may be better able to adapt to multiple stressors than tupelo. A greater allocation to relative below-ground biomass was seen for the nutrient-deprived saplings, but not for salt-stressed saplings. Although plant resources seem to be allocated differently, depending on stress type or severity, insect bioassays revealed that insect defoliators did not respond to phenolic increases. In the field, the 2 degraded sites continued to respond to nutrient inputs 1 year after the inputs were halted (after 3 years of inputs). There was no significant growth increase at the healthiest of the 3 field sites.

IMPACT: 2004/01 TO 2004/12
Increases in nitrogen as a result of increased nutrient inputs have the potential to increase defoliator populations in freshwater environments. An increase in plant chemical defenses in response to stress did not influence insect development. Field studies demonstrated that 3 years on nutrient input, simulating a high level river diversion, resulted in significant tree growth, and at degraded sites there was a 1-year carryover effect after inputs were halted.

PUBLICATIONS: 2004/01 TO 2004/12
Parry, D. and R.A. Goyer 2004. Variation in the suitability of host tree species for geographically discrete populations of forest tent caterpillar. Environ. Entomol. 33:1488-1496.

PROJECT CONTACT:

Name: Goyer, R. A.
Phone: 225-578-1827
Fax: 225-578-1643
E-mail: rgoyer@lsu.edu