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Title: NOVEL DITERPENOIDS AND HYDROCARBONS IN THE DUFOUR GLAND OF THE ECTOPARASITOID HABROBRACON HEBETER (SAY) (HYMENOPTERA: BRACONIDAE)

Author
item Howard, Ralph
item Baker, James
item MORGAN, E - KEELE UNIV, UK

Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2003
Publication Date: 10/1/2003
Citation: HOWARD, R.W., BAKER, J.E., MORGAN, E.D. NOVEL DITERPENOIDS AND HYDROCARBONS IN THE DUFOUR GLAND OF THE ECTOPARASITOID HABROBRACON HEBETER (SAY) (HYMENOPTERA: BRACONIDAE). ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY 54:95-109. 2003.

Interpretive Summary: A study was conducted on a major gland (known as the Dufour gland) found in a female parasitic wasp that is known to contain chemicals for helping them in their attacks on storage insect pests. Numerous studies of this gland have been done on ants, bees and wasps but few studies have been done on parasitic wasps. We studied a species of parasitic wasp that attacks stored product moths and described the gland and analyzed the chemical contents of this gland. Most of the chemicals were complex mixtures of compounds known as hydrocarbons that were similar to the hydrocarbons previously found on the body surfaces of these wasps. In addition, three compounds known as terpenes were present in these glands. These wasps are important biological control agents against stored product pests and our findings are important for gaining a better understanding of how these wasps use their Dufour gland chemicals for improving the efficiency of their attacks on the pests.

Technical Abstract: Chemical constituents contained in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) were characterized. Three terpenes, B-springene, homo-B-springene and homo- geranyllinalool constitute ca. 37% of the gland components, with the remaining 63% all being hydrocarbons. The hydrocarbons consist of a homologous series of n-alkanes (n-C21 to n-C31), a trace amount of 3-methyl C23, a homologous series of internally methyl branched alkanes (11-methyl C23 to 13-methyl C35), one dimethyl alkane (13,17-dimethyl C33), a homologous series of monoenes (C25:1 to C37:1) with the double bonds located at 9, 13 and 15 for alkenes of carbon number 25 to 31 and at 13 and 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 -springene and homo-geranyllinalool increased significantly with time after adult emergence from the cocoon. Although many hydrocarbons in the Dufour gland are the same as those on the cuticle of this species, 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 C23 to C29 and double bond locations at 5, 7 and 9, whereas the Dufour gland alkenes contains a greater range of carbon numbers and have no 5 or 7 alkenes. The Dufour gland contains only one of the long-chain dimethyl alkanes 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 freshly laid eggs indicated that no diterpenoids were present. Rather, the lipids present were n-alkanes, monomethyl alkanes, alkenes, and secondary alcohol wax esters. This composition did not reflect that of the Dufour gland, hence oviposited eggs are not being coated with Dufour gland components.