Novel diterpenoids and hydrocarbons in the dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera : Braconidae)

摘要

Chemical constituents contained in the Dufour gland of the ectoporasitoid Habrobracon hebetor (Soy) (Hymenoptera: Braconidae) were characterized. Three terpenes, beta-springene, a homo-beta-springene, and a homo-geranyllinalool constitute approximately 37% of the gland components, with the remaining 63% all being hydrocarbons. The hydrocarbons consist of a homologous series of n-alkanes (n-C-21 to n-C-31), a trace amount of 3-methyl C-23, a homologous series of internally methyl-branched alkanes (11-methyl C-23 to 13-methyl C-35), one dimethylalkone (13,17-dimethyl C-33), a homologous series of monoenes (C-25:1 to C-37:1) with the double bonds located at Delta(9), Delta(13) and Delta(15) for alkenes of carbon number 25 to 31 and at Delta(13) and Delta(15) for carbon numbers 33 to 37 and three homologous dienes in very low amounts with carbon numbers of 31, 32, and 33. The terpenoid and hydrocarbon composition of the Dufour gland was similar in virgin and mated females. However, in contrast to the hydrocarbons, the amount of beta-springene and homo-geranyllinalool increased significantly with time after adult emergence from the cocoon. Although many hydrocarbons in the Dufour gland are the some as those on the cuticle of this species [Howard and Baker, Arch. Insect Biochem. Physiol. 53:1-18 (2003)], substantial differences also occur. Of particular note is the chain length of alkenes and location of the double bonds: cuticular alkenes have a chain length Of C-23 to C-29 and double bond locations at Delta(5), Delta(7), and Delta(9), whereas the Dufour gland alkenes contains a greater range of carbon numbers and have no Delta(5) or Delta(7) alkenes. The Dufour gland contains only one of the long-chain dimethylalkanes found on the cuticle. Also, no terpenoids are found on the cuticle, and the Dufour gland contains none of the secondary wax esters that are major components on the cuticle. GC-MS analysis of lipids carried in the hemolymph of H. hebetor indicated that all hydrocarbons found on both the cuticle and in the Dufour gland are present, as are some of the wax esters. However, none of the terpenoids were detected in the hemolymph. This suggests that the hydrocarbons are synthesized in other tissues or cells, probably by oenocytes, and differentially partitioned between the cuticle and the Dufour gland. The terpenoids are most likely synthesized within the Dufour gland. Analysis of surface lipids from eggs laid within 18 h indicated that no diterpenoids were present. Rather, the lipids present on the eggs were n-alkanes, monomethylalkanes, alkenes, and secondary alcohol wax esters. This composition did not reflect that of the Dufour gland, hence eggs are not being coated with Dufour gland components during oviposition. Arch. Insect Biochem. Physiol. 54:95-109, 2003. Published 2003 Wiley-Liss, Inc.