|TWOSPOTTED SPIDER MITES|
|Evidence for Spider Mite (Acari:
Tetranychidae) Injury-Induced Leaf Water Deficits and Osmotic Adjustment in Peppermint¹
JACK D. DEANGELIS, RALPH E. BERRY, AND G. W. KRANTZ
Department of Entomology, Oregon State University, Corvallis, Oregon 97331
© 1983 Entomological Society of America
Environ. Entomol. 12: 336-339 (1983)
Studies were conducted to examine the physiological response of peppermint, Mentha piperita L., to leaf water stress induced by feeding of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Levels of mite injury were estimated by a leaf injury index developed for these studies. Symptoms of water stress in miteinjured leaves were: a significant reduction in leaf fresh weight; reduced leaf specific weight (mg of fresh weight per cm² of leaf area); and accumulation of soluble leaf carbohydrates. Soluble leaf carbohydrates of peppermint are sucrose (ca. 50%) and the galactosyl oligosaccharides raffinose and stachyose. Leaf starch content was unaffected by injury at all injury levels. Accumulation of soluble leaf carbohydrate in water stressed leaves may help mite injured leaves maintain cell turgor pressure through an osmotic adjustment (osmoregulation) mechanism. A new method for in situ starch hydrolysis for quantitative analysis of leaf starch also is presented.