Ageratum juvenile hormone

We began to extract plants with apolar solvents and tested these extracts by contact and fumigation against the cotton stainer, Dysdercus cingulatus, and the milkweed bug, Oncopeltus fasciatus. Eventually we found that the extract of the bedding plant, Ageratum houstonianum, contained two potent anti-juvenile hormones. 

Figure 3. Anti-juvenile hormones from Ageratum houstoni-anum...

Chromenes (Phe a-pyran) include encecalin (a phototoxic antimicrobial from various Asteraceae) and the phloroglucinol derivative mallotochromene (cytotoxic and an HIV-1 reverse transcriptase inhibitor). Precocene 1 (7-methoxy-2,2-dimethylchromene) and pre-cocene 2 (6,7-dimethoxy-2,2-dimethylchromene) produced by Ageratum species (Asteraceae) inhibit the production of insect juvenile hormone (JH) as a result of suicidal conversion of these pro-toxins to cytotoxic derivatives by the JH-producing insect cells. 

Compounds with anti-juvenile-hormone activity have been found in Ageratum houstonianum, Asteraceae (see Chapter 18). In this case, the insects molt precociously and produce adults one or two stages too early. The females produced usually are sterile. 

Frequently dimethylallyl residues are attached to compounds with other chemical structures (see above). They may form additional rings as in ageratochro-mene, a compound isolated from the plant Ageratum haustoniatum with anti-juvenile hormone activity in insects (E 5.5.3). Isovaleric acid and 3,3-dimethyl-acrylic acid, which have been found in higher plants, are thought to be products of leucine metabolism (D 14). 

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