Oncopeltus fasciatus

Aposematic species from two different families produce pungent pyrazines, presumably as an additional warning to potential predators of their toxicity. These include Oncopeltus fasciatus (Lygaeidae, seed bug family) that secretes 2-isobutyl-3-methoxypyrazine [28], and the stink bug Murgantia histrionica (Pentatomidae), that oozes froth containing 2-isobutyl- and 2-sec-butyl-3-methoxypyrazine when molested [39]. 

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. 

The steroids known to play major regulatory roles in insect development and metamorphosis all fall into the class of polyhydroxylated ketosteroids called ecdysones (19-22). With the exception of Makisterone A (a C2 ecdysteroid identified from the milkweed bug Oncopeltus fasciatus) the known insect ecdysteroids constitute a group of eight or nine steroids that differ from one another... 

Preliminary results of antijuvenile hormone bioassays for precocious metamorphosis in immature stages of Oncopeltus fasciatus revealed that some of the non-linear derivatives (VI) showed higher activities and lower toxicities that those exhibited by natural precocenes or 7-ethoxy-6-methoxy-2,2-dimethylchromene, one of the most active synthetic analogs known. In addition, some of these compounds were unexpectedly inactive in the sterilization bioassay with adults of the same species (8). Further investigation of antijuvenile hormone activities of selected compounds of this series in other insects is now in progress. 

Oncopeltus fasciatus (Dallas) large milkweed bug adult nymph T GR 77 79... 

Larvae of the large milkweed bug, Oncopeltus fasciatus treated with precocene II undergo precocious metamorphosis and moult into diminutive forms with adult characters. Freshly hatched females treated with precocene II remain sterile and their corpora allata loose their ability to secrete juvenile hormone even when transplanted into an untreated body (Muller et al., 1979 Masner et al., 1979 Pener et al., 1978). 

Juvocimene I Sweet basil Ocimum basilicum L. Oncopeltus fasciatus 5th instar larvae Topical 50 pg 105... 

Roots, stem, fruits Iris Iris douglasiana Herb. Oncopeltus fasciatus 5th larval instars Topical -H- 114... 

The bioactivities of precocene I, 7-methoxy-2,2-dimethyl chromene, and precocene II, 6,7-dimethoxy-2,2-dimethyl chromene, are well established (Fig. (7)). These two compounds have been isolated from plants throughout the family Asteraceae [129-136, 154]. The chemical data for these compounds and references for their synthesis are compiled in Appendix IV, Tables 13 and 14. There is a wealth of information on the effects of these compounds on various insect species [42, 137]. For simplicity, we will focus on the effects of precocene II on the susceptible Hemipteran bug, Oncopeltus fasciatus. 

More epoxides (1) with juvenile hormone activity (Vol. 2, p. 7) have been made by epoxidizing the Wittig products of citronellal (2), and some of these substances also increase silk production.Reduction of the double bond sometimes increases the activity against Oncopeltus fasciatus. Insecticidal activity is also reported for certain terpenoid cyclopropanes [e.g. (3), made from limonene and ethyl diazoacetate] and for isobornyl thiocyanoethyl ether (made from cam-phene and ethylene chlorohydrin followed by treatment with potassium thiocyanate). The insect-repelling activity shown by thujic acid amides (4) is... 

Hemiptera. The large milkweed bug, Oncopeltus fasciatus, was the first phytophagous insect discovered to be incapable ofconverting the major phytosterols (C28 and C29) to cholesterol (17). 

Assassin bug, Acholla multispinosa, 251 Big-eyed bug, Geocoris punctipes, 251 Milkweed bug, Oncopeltus fasciatus, 284... 

Bowers [7] found that some compounds used as insecticide synergists (e.g., piper-onyl butoxide) possess juvenoid activity, and so he synthesized analogues of the synergists, e.g., some aromatic terpenoid ether compounds, and examined their morphogenetic activity against T. molitor and milkweed bug, Oncopeltus fasciatus. He found the first synthetic compound (4, Fig. 25.2.2) with high activity [8]. 

Other representatives of this group of compounds (such as compounds 13 and 14) from Ageratum houstonianum have antijuvenile hormone activity and cause precocious production of adult insects. Because of these properties, the compounds are called precocenes. Female insects that are exposed to these compounds never reach sexual maturity. External application of the compounds to second-instar larvae of the milkweed bug, Oncopeltus fasciatus, causes the nymphs to molt to normal third- and fourth-instar larvae and then to precocious, sterile adults (Proksch and Rodriguez, 1983, 1984 Rodriguez, 1983). 

Foe, V. E., Wikinson, L. A., and Laird, C. D., 1976, Comparative organization of active transcription units from oncopeltus fasciatus. Cell 9 131. 

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