Relation of Gossypol Content of Cotton Plants to Insect Resistance12

Abstract

Striking differences in amount of feeding by insects between glanded varieties and glandless experimental strains of cotton were observed during greenhouse and small field-plot tests conducted to find plants resistant to different cotton-insect pests at Tueson, Arizona, and in similarly conducted replicated field-cage tests at Brownsville, Texas. At Tucson, the glandless experimental strain 30-8 was eaten in preference to either the glanded Acala or Pima varieties by beet armyworms, Spodoptera exigua (Hubner); bollworms, Heliathis zea (Boddie); a black fleahopper, Spanogonicus albofasciatus (Reuter); and grape colaspis, Maecolaspis flarida (Say). At Brownsville, cutworms (undet. spp), beet armyworms, pill bugs (Porcellio spp.), and rodents were observed to eat the glandless strains before attacking the glanded varieties. The toxic effect of gossypol was demonstrated in spray tests against cotton aphids, Aphis gossypii (Glover); lygus bugs, Lygus hesperus Knight; salt-marsh caterpillars, Estigmene acrea (Drury); and thurberia weevils, Anthonomus grandis thurberiae Pierce; and in tests with bollworms reared Oil medium containing gossypol. Chemical analyses showed roughly 3 and 4½ times more gossypol in glanded Acala 4-42-77 seedlings and leaves, respectively, than in comparable samples of glandless 4-42-77.