Juvenoid activity insects

The compound should demonstrate the ability to mimic JH at the three principle stages of insect development the eggs, the juvenile and the adult (female). Therefore, observation of ovicidal effects is suggestive of juvenoid activity but not definitive. 

Since juvenoids affect the insect specific endocrine system, they are expected to become insect-specific insecticides [2]. Some naturally occurring compounds have juvenoid activity, e.g., Schmialek [3] isolated farnesol (1) and farnesal (2) with juvenoid activity from the feces of mealworm, Tenehrio molitor, (Fig. 25.2.1). 

Although many compounds with juvenoid activity have been found in plants, they are not practical insecticides due to chemical instability and complexity of synthesis. Many compounds have been synthesized and their activities were checked against insects to find more active and stable compounds. The following describes representative juvenoids reported so far. 

Kokate CK, D Cruz JL, Kumar RA, Apte SS (1985) Anti-insect and juvenoidal activity of phytochemicals derived from Adhatoda vasica Nees. Ind J Nat Prod 1 7-9 Hassalani A, Lwande W (1989) Anti pest secondary metabolites from African plants. In Amason JT, Philogene BJR, Morand P (eds) Insecticides of plant origin. Am Chem Soc Symp series 387 78-94... 

One defensive strategy of plants against insect herbivory is the production of secondary metabolites which mimic JH activity [3]. Many of these compounds have been extracted from diverse plant species and are termed "juvenoids" based on their activity in vitro. However, a number of criteria should be met before these compounds are defined as JH mimics ... 

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. 

Although this compound did not show insecticidal activity against insects other than spider mites in the primary screening, it changed the body color of the tobacco cutworm, Spodoptera litura, to red. The compound was presumed to be a juvenoid with a completely different action mechanism from the conventional insecticides, and this was confirmed by a biological test, the Galleria wax test [15]. 

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