Damage by Larvae of the Corn Earworm to Grain Sorghum12

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Abstract
The 1st and 2nd instars of the corn earworm, Heliothis zea (Boddie), preferred to feed on the flowering stage of sorghum; the remaining 4 instars preferred the milk stage. The 5th instar accounted for 17.4 and the 6th instar 65.6% of the grain consumed. Third-instar larvae placed on sorghum heads in the flowering stage and allowed to complete larval development accounted for 95% of grain consumed. When corn earworm larvae were caged on RS 610 sorghum heads, cach larva decreased the yield about 3.9 g per head at harvest. Yield reductions per larva were similar for heads of different sizes and for levels of infestations of 0, 4, 8, 12, and 16 larvae per head. About 20 corn earworm larvae per 10 heads would be considered an economically damaging population where the space between heads was an average of 8 inches and row spacing 40 inches.

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