Field and Laboratory Studies on Resistance of Corn to the Corn Earworm1

Abstract

The weights of larvae of corn earworm, Heliothis zea (Boddie), on silks and grain of several strains of corn were studied in field and laboratory experiments. Larvae feeding in ears of susceptible C68R gained more weight when forced to feed on grain than on silks, The laboratory-feeding trials indicated also that the larvae preferred grain to silk in this strain. Data from trials were variable and inconsistent with Seneca Chief and T11S×T15S, intermediate in resistance. Larvae that were fed on Zapalote Chico, P.I. 217413, gained little weight when forced to feed on the silk before reaching the grain, but gained more weight when allowed to feed on the grain immediately. The larvae also made poor gains in weight when fed on silks of this strain in the laboratory. The very long husk of P.I. 186225 from Australia lends good resistance under normal conditions. However, larvae thrived on both silks and grain. Larvae generally thrived better when transferred from silks to grain after 6 days in all strains. Transferring the larvae from gram to Silk after 6 days reduced the amount of weight gain ill all strains. Gains in weight practically ceased when larvae were transferred from grain to silk of Zapalote Chico, a strain very resistant under normal conditions owing to a tight, tough husk, which forces the larvae to eat through the silk channel before reaching the gram. I he small gain in weight of larvae on the silks may be due to the low moisture content of the silks, silks of low nutritional value, or some other form of silk resistance.