Factors Involved in Differential Susceptibility of Corn Earworm Larvae to DDT1

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Abstract
Full-grown corm earworms, Heliothis zea (Boddie), require more than 1,000 times as much DDT on a weight basis as small larvae in order to obtain LD-50 values for topical applications in acetone, Injected DDT in acetone is only slightly less effective on large larvae than on small ones, Chemical and radiometrie analysis showed that lack of penetration by DDT through the integument of the large larvae was the chief factor causing the increase in LD-50 values. Addition of nonvolatile oils to the topically applied material increases the effectiveness of DDT to the larger larvae. Tests with different colored larvae indicate that light yellow larvae are approximately twice as susceptible as the dark red or black larvae.