SYSTEMIC INDUCTION OF TERPENOID ALDEHYDES IN COTTON PIGMENT GLANDS BYFEEDING OF LARVAL SPODOPTERA-EXIGUA

Pigment glands in cotton contain terpenoid aldehydes that are toxic an d deterrent to feeding of several generalist lepidopteran insects. We hypothesized that previously observed systemically induced feeding det errence may be associated with pigment glands. We conducted experiment s to determine the dynamics and chemical nature of inducible feeding d eterrents in leaves of cotton, Gossypium hirsutum L, to larvae of the beet armyworm, Spodoptera exigua. Production and/or filling of pigment glands was influenced by physiological age of Deltapine 90 cotton pla nts. In undamaged plants, successively formed leaves contained more pi gment glands, up to the seventh or eighth true-leaf developmental stag e. Feeding choice tests conducted one or seven days after initial feed ing damage revealed that third instars of S. exigua consumed more of t he two youngest leaves from control cotton plants than from plants who se two oldest leaves had been fed on previously for 24 hr by S. exigua . The preference for leaves from control plants was significant one da y after initial damage and highly significant seven days after damage. Consumption of mature foliage (leaf immediately above initially damag ed leaves) from control plants and damaged plants did not differ. More pigment glands were counted on the youngest leaf of damaged plants th an on the youngest leaf of control plants one day after initial damage . HPLC analysis revealed greater amounts of hemigossypolone, heliocide s 1 and 2 (H-1 and H-2), and total terpenoid aldehydes per gland in yo ung foliage of damaged plants than control plants one day after initia l injury. By seven days after initial injury, greater quantities of he migossypolone and all heliocides except H-4 were detected in young fol iage from damaged plants compared to control plants. Concentrations of H-1 per gland in young leaves from damaged plants increased the most of all terpenoid aldehydes measured (3.4x the amount found in leaves f rom control plants). Mature leaves from damaged plants did not contain more terpenoid aldehydes than mature leaves from control plants. We s uggest that systemically induced feeding deterrence to S. exigua in yo ung leaves of glanded cotton was due to increased amounts of terpenoid aldehydes in pigment glands.