William S. Bowers

Natural and Synthetic Allatotoxins: Suicide Substrates for Juvenile Hormone Biosynthesis

Cytotoxic agents with antijuvenile hormone activity in insects have been discovered. Their mechanism of action may involve an oxidative bioactivation into a reactive quinone methide.

The stereoisomers of 3,7,11-trimethyldodeca-2,6,10-triene

Abstract Four geometrical steroisomers of 3,7,11-trimethyldodeca-2,6,10-triene have been synthesized. The PMR and 13 C NMR spectra of these compounds provide important information on the geometry of Me substituted double bonds, while the mass spectra distinguish (E and Z,E)-isomers from (E and Z,Z)-isomers.

The developmental effects of 6,7-dimethoxy-2,2-dimethyl chromene on the pre-imaginal stages of Aedes aegypti (Diptera: Culicidae).

The effects of 6, 7‐dimethoxy‐2, 2‐dimethyl chromene (precocene II) on pre‐imaginal development in Aedes aegypti were determined by exposure of eggs, larvae and pupae to this botanically derived compound. Precocene II prevented adult emergence when newly hatched larvae were exposed to dosages ranging from 2 to 4 ppm. Pupation was inhibited when early 4th‐instar larvae were exposed to dosages ranging between 1 and 10 ppm. Fourth‐instar larvae treated at concentrations above 0.1 ppm, also required more time to complete metamorphosis than controls. The pupal and egg stages were insensitive to treatments at concentrations up to 10 ppm.

Electroantennogram responses of the American cockroach to germacrene D sex pheromone mimic

Abstract Electroantennogram responses of adult American cockroaches were recorded from the sex pheromone mimic, germacrene D, and its related analogs. Germacrene D stimulated male antennae much greater than females, whereas other compounds produced significant responses of similar intensity with both male and female antennae. In the biological assay, only germacrene D induced the typical sexual behavior of males. The bioassay results imply that the conjugated system and isopropyl group of germacrene D are necessary chemical moieties for the sexual response in male cockroaches.

Synthesis of highly active juvenile hormone analogs, juvocimene I and II, from the oil of sweet basil, Ocimum basilicum L.

Juvocimene I and II are potent juvenile hormone mimics isolated from the essential oil of sweet basil,Ocimum basilicum L. The structures given by the formula I and II have been confirmed by synthesis withtrans-β-ocimene andp-methoxycinnamyl chloride. Biological activity of the natural and synthetic juvocimenes was found to be identical.

Antennal receptor response to sex pheromone mimics in the American cockroach

THE essential oils D-bornyl acetate, α- and β-santalol and several plant sesquiterpene hydrocarbons have been shown to induce sexual excitement in male American cockroaches1, and thus seem to mimic the cockroach sex pheromone. Tahara et al.2 have identified one of the active sesquiterpene hydrocarbon species obtained from Compositae plants as germacrene D. The contrast in structures of these various active compounds poses a serious problem as to the specificity of the sex pheromone receptor. To resolve this we have undertaken an electrophysiological study of the antennal receptors of both male and female cockroaches. The electroantennogram (EAG) responses of both sexes were examined during exposure to the compounds in question. Theoretically the sex specific receptors of the male antennae should respond singularly to natural sex-pheromone (and stereochemical mimics) whereas the female antennae should be unresponsive other than to general irritants and/or to food odours. In fact, the EAG response to the female sex attractant has been obtained in males but not in females3,4.

CHEMISTRY OF PLANT/INSECT INTERACTIONS

Publisher Summary Insect predation upon plants is highly specific. This specificity is largely dependent upon the defensive screen of chemicals produced by the plant. All plants have a variety of chemical methods of defense against attack by not only insects but also by plant pathogens, nematodes, etc. Because all plants are not equally preyed upon by all insects, successful attack of a particular plant species by an insect must depend upon the avoidance of the chemical screen or the development of resistance to the chemicals action upon the insect. Certain insects are able to attack only those portions of a plant that do not contain a defensive chemical, whereas other insects develop metabolic machinery able to rapidly inactivate or destroy the poison. These insects prey upon a plant that is otherwise able to overcome the attacks of less persistent and biochemically flexible insects. This chapter discusses the intricacies of the insect endocrine system, which is is the target of subtle plant chemical defenses that disrupt insect growth, development, reproduction, diapause, behavior, and communication.

Fatty acid composition of milkweed bugs Oncopeltus fasciatus and the influence of diet

Milkweed bugs, Oncopeltus fasciatus Dallas, show significant differences in the proportion of C16:1, C18:1 and C18:2 fatty acids in body lipids depending on the diets on which they were fed, sunflower seeds or milkweed seeds. Bugs reared entirely on sunflower seeds have no or only traces of C16:1 and C17:1 fatty acids, both of which are present in bugs reared on milkweed seeds and in the seeds themselves. About 90% of the fatty acids in whole body lipids are unsaturated on both diets and this proportion is high in each of the lipid classes examined. The diet clearly influences the fatty acid composition of body lipids of milkweed bugs.

Ovarian sequestration of [14C]-inulin by an insect: An index of vitellogenesis

Abstract [14C]-Inulin injected into the blood of female milkweed bugs (Oncopeltus fasciatus) undergoing vitellogenesis is sequestered in the eggs. Determination of ovarian radiocarbon uptake gives a reproducible index of the progression of vitellogenesis that permits quantitative measurements prior to oviposition or under conditions where vitellogenesis is incomplete. This assay allows intra- and interspecific comparisons of the rates of juvenile hormone biosynthesis by corpora allata (CA) when these endocrine glands are transplanted into milkweed bug females, whose CA have been chemically destroyed with precocene. The method has the potential of distinguishing between nervous and hormonal regulation of the CA.

ENDOCRINE STRATEGIES FOR INSECT CONTROL

Analogs of the insect juvenile hormone III have been successfully applied to the control of several species of insects which are pestiferous in the adult stages. These include insects of economic importance to man and to domestic animals such as mosquitos, manure breeding flies and fleas. However, the juvenile hormone analogs are ineffective for the control of the immature stages of insects which are most important in agriculture through their feeding damage to crops. Thus by the time the juvenile hormone analogs can be effective, the immature stages have already completed their feeding damage. It seemed to me that a method of interfering with the biosynthesis, secretion, or action of the juvenile hormone would be a very useful method of insect control against insects which do their damage as feeding immature stages. Whereas a number of insect hormone mimics have been discovered in plants it seemed possible that plants might be a useful resource to investigate for insect hormone antagonists. Since the juvenile hormones control immature development and adult reproduction, I believed that a juvenile hormone antagonist would be a more suitable endocrine strategy for the control of insects of importance in agriculture. We searched for and discovered two naturally-occurring anti-juvenile hormonal compounds in plants. These anti-hormones (precocenes) induce a lethal, precocious metamorphosis in the immature stages of many insects and also sterilize the adult females. n nThrough structure optimization, mode of action and metabolism studies, we have found that the precocenes undergo a lethal activation within the corpora allata into selective cytotoxic agents which destroy the endocrine gland. These studies have revealed that the precocenes are acting as suicide substrates for specific enzymes in the insect corpus allatum which is the gland responsible for juvenile hormone production. With the precocenes as a model, we have synthesized additional suicide substrates which are also activated by the same or similar enzymes in the corpus allatum into allatotoxic agents. These and similar approaches may provide new selective biorational methods of insect control.