ARS | Publication request: STEROL UTILIZATION AND METABOLISM BY HELIOTHIS ZEA

Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 21, 1997
Publication Date: N/A

Interpretive Summary: Caterpillar pests cause millions of dollars of damage to corn and other crops each year. Their damage is also often associated with corn ear molds that produce high toxic and cancer causing compounds. Caterpillars need specific fatty substances for proper growth. When a series of related fatty substances from corn were put in corn earworm diets, we found the corn earworms could only develop properly on a few of the fatty substances. Provided alterations do not harm plant development, selecting plants through breeding or altering plants through genetic engineering so that they produce fatty substances that the insects cannot use as nutrients should help reduce insect damage and associated ear molds and toxins.

Technical Abstract: Heliothis zea (corn earworm), an insect that fails to synthesize sterols de novo, was reared on an artificial diet treated with different sterol supplements. Delta**5-sterols substituted at C 24 in the side chain with a hydrogen atom, or with a methylene, E-and Z-ethylidene, and alpha- and beta-ethyl group (cholesterol, ostreasterol, sitosterol, isofucosterol, fucosterol, sitosterol and ellonasterol) supported normal larval growth to late-sixth instar (maturity; prepupal). The sterol requirement of H. zea could not be met satisfactorily by derivatives of 3beta cholestanol with a 9beta,19-cyclopropyl group, gem dimethyl group at C-4, a delta**5,7-bond or delta**8-bond, or by side chain modified sterols that possessed a delta**25(27)-24beta-ethyl group, delta**23(24)-24-methyl group or 24-ethyl group, or delta**24(25)-24-methyl or 24-ethyl group. Some sterols were found to support aberrant growth, then give rise to congenital deformities in the moth stage. The most effective sterols absorbed by the insect ranged from 27 to 66 micrograms per insect, whereas the least effective sterols absorbed by the insect ranged from 0.6 to 6 micrograms per insect. The results demonostrate for the first time that H. zea fails to synthesize three side chain reductase enzymes [delta**25(27)-, delta**23(24)- or delta**24(25)-reductase enzymes] synthesized in plants and that delta**24(28) alkene 24-methyl sterol isomers, (e.g., clerosterol) may not serve as appropriate substrates in the insect C-24 dealkylation pathway.