Effects of Fertilizers on Resistance of Antigua Corn to Fall Armyworm and Corn Earworm

Abstract

Larvae of the fall armyworm, Spodoptera frugiperda (J. E. Smith), and the corn earworm, Heliothis zea (Boddie), were exposed to excised foliage of an intermediately resistant Antigua corn that had been fertilized at the recommended level with a complete fertilizer (NPK) or with all possible combinations of the component nutrients. Both the fall armyworm and the corn earworm larvae preferred foliage from plants having N treatment over foliage from plants treated with P, K, or PK or the unfertilized check. Also, the weight gains of the corn earworm and fall armyworm and the days to pupation, pupal weight, and percentage larval mortality of fall armyworms indicated that treatment with N or with combinations of N increased susceptibility. The preference ratings of the fall armyworm and corn earworm on corn were significantly associated. Also, the fall armyworm preference ratings were significantly correlated with larval weights, pupal weights, days to pupation, and foliage production. Thus, the preferential responses were the predominant factors even though several characters measured were expressions of antibiosis. The corn earworm preference ratings were significantly correlated with larval weight and longevity. The percentage mortality before pupation, an expression of antibiosis, showed that the fertilizer treatments had a detrimental effect on fall armyworm larvae compared with no treatment (unfertilized check). It also appears that Antigua corn has an extremely high level of antibiosis since all corn earworm larvae died, even on the unfertilized check.