The absence of significant levels of the known juvenile hormones and related compounds in the milkweed bug, Oncopeltus fasciatus

Abstract

We measured levels of juvenile hormones (JH) in eggs and adults of the milkweed bug, Oncopeltus fasciatus. Using a method employing gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring, we detected little, if any, of the known JHs in three different strains of O. fasciatus. We modified the sample purification procedure in order to isolate and analyze for the acidic metabolites of JH (JH acids) as well. Very little of the known JH acids was detected. We developed three new methods to analyze for compounds chemically related to JH, namely, JH 10,11 diols, methyl farnesoate (MF) and farnesol. These methods also rely on quantification via GC/MS with selected ion monitoring. The limit of detection for farnesol and MF was about 1 ng/g. Only low levels (close to the limit of detection) of MF and farnesol were detected in eggs from animals reared on sunflower seeds. The known JH diols do not exist in significant quantities (<0.1 ng/g) in the Iowa strain or sunflower strain adults (males plus females). The levels of JH, JH acid, farnesol and MF which may exist are many orders of magnitude lower than those necessary to account for previously reported JH activity of extracts determined via bioassay procedures. We measured the biological activity of extracts from eggs and adult hemolymph from a California strain reared on milkweed seeds. Using the Galleria wax test, Manduca sexta black mutant larvae, and O. fasciatus nymphs for bioassay, we were unable to detect significant JH activity. Thus, contrary to prior reports, we found no evidence for the occurrence of high levels of JH in eggs or adults of the milkweed bug, Oncopeltus fasciatus. Finally, we were unable to observe JH biosynthesis by corpora allata removed from a California strain of adult female animals and cultured in vitro.