Insects, hormones juvenile, development

If insect pests can be prevented from maturing they fail to reproduce and can thus be brought under control. Juvenile insects control their development by means of a juvenile hormone , one of which is the monoepoxide of a triene. 

In addition to their well established role in catalyzing the metabolism of a wide variety of naturally occurring and synthetic xenobiotics, cytochrome P-450-mediated mixed-function oxidases are of critical Importance in the biosynthesis and regulation of the major hormones (ecdysteroids and juvenile hormone) that control insect growth and development. The characteristics of the mixed-function oxidases involved in the synthesis of insect hormones are described and the possibility that the enzymes might represent potential targets for insect control is discussed. 

The potential for using endocrine imbalance as a means of insect pest control was suggested by Williams (9,10) He proposed that exposing immature insects to juvenile hormone (JH) at the time of metamorphosis, when JH is normally absent, would cause abnormal development and individuals incapable of survival. Since insect metamorphosis is unique, JH disruption would affect only insects. This would result in an environmentally safe approach to insect control as compared to current chemical pesticides which are less insect specific and more biocidal. The JH approach to pest insect control is most effective when adults are the destructive stage, and commercial preparations of JH mimics are available for use in the control of adult flies, mosquitoes, and fleas and, recently, for cockroach reproduction. However, many pest insects are destructive as larvae. 

Plant secondary metabolites which mimic JH activity appear to be active on a narrow range of host species. What account(s) for this effect The majority of bioassays used last larval instars of P. apterus, O. fasciatus and pupae of T. molitor to test for activity of the juvenoids. Are these the most sensitive insects Six JHs have been identified to date different homologs have been isolated from specific insect orders. Juvenile hormone III appears to be ubiquitous [12, 13] and, in most species, is the only JH present. Juvenile hormone I and II are important in the regulation of metamorphosis and ovarian maturation in Lepidoptera [5] and the bis-epoxide appears to be the principle JH in higher Diptera [20]. Therefore, the nature of the JH in the test insect and the role that it plays in development must be considered in the selection of the bioassay a compound which mimics the action of JH in P. apterus (Hemiptera) is unlikely to be active in a Lepidopteran insect. 

Many secondary metabolites found in plants deter phytophagous invertebrates, sometimes even modifying insect growth and development if included in the diet [8]. Natural products can often act as insecticides via different pathways, as is the case with the analogues of insect juvenile hormones produced by plants. Thus, some derivatives of these analogues are used as commercial insecticides while others act as ecdysteroid antagonists [8]. 

Two hormones known to regulate insect metamorphosis and development are the juvenile hormones and 20-hydroxyecdysone. Juvenile hormone inhibits progress toward the adult form and 20-hydroxyecdysone is the driving force for molting. For 20 years juvenile hormone agonists have been the subject of intensive chemical research providing several new insecticides, including methoprene and kinoprene (2). 

Anti-juvenile hormone activity, and the resulting cessation of feeding, has long been considered by the agricultural chemical industry as a means for insect control. Juvenile hormone esterase (JHE) contributes to the decline in JH titer at certain times during larval development. 

The juvenile development of insects proceeds through a series of moltings (molting of larvae among the holometabola also molting of pupae) to result eventually in the adult insect. The most familiar example is the development caterpillar-pupa-butterfly. The process of molting involves three hormones, as shown in Fig. 56. 

Stable in acidic, neutral and basic aqueous solutions Pale yellowish solid, faint characteristic odor Flash point 119°C (Pensky-Martens closed tester) Pyriproxyfen is an insect growth regulator which acts both as an ovacide and as an inhibitor of development (juvenile hormone mimic) against white flies, scale, and psylla. The specificity of pyriproxyfen, and its low mammalian toxicity, allow for some variation in application timing. For example, the lack of toxicity to bees allows pyriproxyfen to be applied during bloom on apple trees, and its low mammalian toxicity allows for a very short pre-harvest interval on citrus The residue definition is for pyriproxyfen alone... 

Many people think the ultimate pesticide should be developed from research now being done on certain insect attractants and juvenile hormones. Isolation of naturally occurring sex attractants (pheromones) and juvenile hormones has been accomplished. The attractants could be used to congregate large numbers of insects in one place for extermination by the already existing insecticides. Alternatively, juvenile hormones have been found that prevent maturation or cause sterility in many pests. 

Gadot, M., Burns, E. and Schal, C. (1989). Juvenile hormone biosynthesis and oocyte development in adult female Blattella germanica effects of grouping and mating. Archives of Insect Biochemistry and Physiology 11 189-200. 

JUNVENILE HORMONES. One of several hormones, that retard the development of insects in the larval stage. So called because they prevent the insect from maturing by maintaining its juvenile characteristics. Obtained naturally from silk moths various syntheses indicate possible use as insecticides, especially for fire ants. Composition of one type is C18H30O3. 

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