EFFECTS OF CARBON DIOXIDE ENRICHMENT IN REPRODUCTION OF TWOSPOTTED SPIDER MITES ON WHITE CLOVER

Authors: Heagle, Allen; Burns, Joseph; Fisher, Dwight; Miller, Joseph

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2002
Publication Date: 8/1/2002
Citation: N/A

Interpretive Summary: Carbon dioxide (CO2) in the atmosphere is essential for plant photosynthesis and growth. Concentrations of CO2 have been steadily rising and the annual mean concentration is approximately 360 ppm (ppm = parts of CO2 per million parts of air). Carbon dioxide concentrations are expected to reach more than 700 ppm during the 21st century. It is well known that CO2 enrichment increases plant growth, but little is known about how this affects insects or other arthropod pests on plants. We studied the effects of five CO2 concentrations (395, 484, 570, 657 and 748 ppm) on reproduction of twospotted spider mites feeding on white clover. Numbers of mite eggs, larvae, nymphs and adults and clover leaf area and leaf nutritive values were measured 26 days after mites were introduced to the plants. Carbon dioxide enrichment increased plant growth and increased the rate of mite reproduction. Leaf sugars and leaf starch also increased but leaf nitrogen decreased. The increase in spider mite populations was five times greater than the increase in clover leaf area. For example, for each 100 ppm increase in the CO2 concentration, larvae, nymphs and adults increased by approximately 42%, whereas the area of clover leaves increased by only 8%. Increased leaf sugars and starch may be the cause of increased mite populations on white clover. Whether CO2 enrichment can stimulate populations of twospotted spider mites on other crop species is yet to be determined.

Technical Abstract: It is well known that CO2 enrichment increases plant growth, but little is known about how this affects insects or other arthropod pests of plants. Effects of elevated carbon dioxide (CO2) on reproduction of twospotted spider mites (Tetranychus urticae Koch) grown on two clones of white clover (Trifolium repens L.) were measured. The CO2 treatments were applied for 24 hr/day at approximately 395, 484, 570, 657 and 748 microliter per liter starting at 14 days before infestation with adult female mites, and for the next 26-27 days. Eggs, larvae, nymphs and adult mites were removed from leaves and counted 27 to 29 days after infestation. leaf area and weight were measured, and leaves were analyzed to measure N, structural and nonstructural carbohydrates, amino acids and digestibility. Carbon dioxide enrichment caused linear increases in leaf area, leaf weight and leaf nonstructural carbohydrates, but caused linear decreases in N. Carbon dioxide enrichment significantly increased the rate of mite population growth on both clover clones. Linear regression models for the clones combined estimated an 8% increase in leaf area and a 42% increase in motile mites for each 100 microliter per liter CO2 increment as measured 27 to 29 days after infestation. Correlations between mite population increase were significantly positive for foliar nonstructural carbohydrates and significantly negative for foliar N.