Journal of Chemical Ecology, Vol. 23, No. 4, 1997ROLES OF OXALIC AND MALIC ACIDS IN CHICKPEATRICHOME EXUDATE IN HOST-PLANT RESISTANCETO Helicoverpa armigeraMITSURU YOSHIDA,* SUSAN E. COWGILL, andJOHN A. WIGHTMANInternational Crop Research Institute for the Semi-Arid Tropics (ICRISAT)Patancheru, 502 324, Andhra Pradesh, India(Received November 6, 1995; accepted December 11, 1996)Abstract—Effects of malic acid and oxalic acid on oviposition of Helicoverpaarmigera were investigated in a laboratory cage choice experiment. Malicacid stimulated oviposition at a concentration of 0.6 ^imol/cm2 but inhibitedit at 3.4 fimol/cm2. Oxalic acid showed neither stimulation nor inhibition ofoviposition at 0.25-1.7 /^mol/cm2. Correlations between the amount of theseacids in trichome exudate on leaf and pod surface and H. armigera populationsand pod damage were investigated in a field experiment using 14 chickpeagenotypes. Malic acid on the leaves stimulated oviposition during the vege-tative and flowering stages, when its concentration was 0.1-0.7 ^mol/cm2.Later, during the podding stage there was no significant correlation betweeneither egg density or pod damage and malic acid levels. However, there wasa significant negative correlation between pod damage and oxalic acid levels.Oxalic acid, which had been reported to have an antibiotic effect on H. armi-gera larvae, has an important role in resistance to this pest in chickpea. Thelength of the podding period was also a factor influencing the extent of poddamage; a longer podding period resulted in prolonged exposure to H. armi-gera attack and more pod damage.Key Words—Helicoverpa armigera, Cicer arietinum, chickpea, host-plantresistance, trichome, exudate, oxalic acid, malic acid, oviposition, antibiosis.INTRODUCTIONChickpea (Cicer arietinum L.) is a grain legume adapted to dry and cool envi-ronments in southern and western Asia, northern and eastern Africa, Central*To whom correspondence should be addressed at National Institute of Agro-Environmental Sci-ences, Kannondai 3-1-1, Tsukuba, Ibaraki 305, Japan.11950098-0331/97/0400-1195$12.50/0
