C-2-8

SYSTEMIC RESISTANCE IN COTTON INDUCED BY FEEDING OFSPODOPTERA EXIGUA

Heather J. McAuslane1 and Hans T. Alborn2
1 Dept. of Entomology & Nematology, University of Florida,PO Box 110620, Gainesville, FL 32611-0620, USA;
2 USDA ARS, CMAVE, PO Box 14565, Gainesville, FL 32604-2565,USA.


Feeding by larval beet armyworm, Spodoptera exigua Hübner,on cotton, Gossypium hirsutum L., systemically induces feeding deterrencein undamaged portions of these plants. It is known that pigment glandsin cotton leaves and reproductive tissues contain terpenoid aldehydes,such as gossypol, with toxic and feeding deterrent effects on several lepidopteraninsects. We hypothesized that systemic feeding deterrence may beassociated with pigment glands and conducted experiments to determine thedynamics and chemical nature of inducible feeding deterrents. Feedingchoice tests conducted 1 or 7 d after initial feeding damage revealed thatS. exigua larvae consumed more of the young leaves from controlcotton plants than from plants whose two oldest leaves had been fed onfor 24 hr by S. exigua. Larval preference for leaves fromcontrol plants was significant 1 d after initial damage and highly significant7 d after damage. HPLC analysis revealed significantly greater quantitiesof hemigossypolone, gossypol, and heliocides 1 and 2 (H1 and H2) per glandin undamaged young foliage of damaged plants than control plants 1 d afterinitial injury. By 7 d after initial injury, significantly greaterquantities of all terpenoid aldehydes except H4 were detected in youngfoliage from damaged plants compared to control plants. Concentrationsof H1 increased the most of all terpenoid aldehydes measured (3.4 ´the amount found in control plants). We suggest that systemicallyinduced feeding deterrence to S. exigua in young leaves of cottonwas due to increased quantities of terpenoid aldehydes in pigment glands.