Agrochemical research over the last two decades has resulted in the discovery of chemically novel insecticides that mimic the action of the two insect growth and developmental hormones, the steroidal 20-hydroxyecdysone (20E) and the sesquiterpenoid juvenile hormone (JH). Bisacylhydrazines are non-steroidal agonists of 20E and exhibit their insecticidal activity via interaction with the ecdysteroid receptor proteins. Interestingly, two of the bisacylhydrazine (tebufenozide and RH-2485) insecticides are very selectively toxic to lepidopteran pests. These insecticides are safe to beneficial insects and have a benign ecotoxicological profile. Aromatic non-terpenoidal insecticides (fenoxycarb and pyriproxyfen) mimic the action of JHs. However, like the JHs, their exact mode of action is not well understood. These insecticides are toxic to a broad spectrum of insects during their embryonic, last larval, or reproductive stages. The insecticidal, ecotoxicological properties and the mode of action of the two groups of insecticides are reviewed in this article.

New insecticides with ecdysteroidal and juvenile hormone activity.

Publisher Summary This chapter describes the premetamorphic actions and general consideration of cellular and molecular actions of juvenile hormone (JH). The chapter focuses on the biological role of JH and of the prevailing concepts of the modes of actions of hormones. It also concentrates on the premetamorphic actions of JH and the present understanding of the molecular basis of this action. Juvenile hormone (JH) has been known to be critical for the regulation of both metamorphosis and reproduction in insects. JH has been isolated and chemically identified as a sesquiterpenoid. The biological effects of various JHAs are remarkably similar to those of the natural JHs, allowance being made for differences in effective dose and stability. Extraction of JH from a natural source suggests the use of this hormone as a pesticide, as it can be absorbed through an insect's cuticle and prevent normal development, and would presumably be refractory to development of resistance.

Cellular and Molecular Actions of Juvenile Hormone I. General Considerations and Premetamorphic Actions

Publisher Summary Among animal hormones, juvenile hormone (JH) is distinctive because of its unique structure and the diversity of its effects on insect development and reproduction. This chapter reviews the actions of JH on the fat body, gonads, accessory glands, muscle, and nervous system of adult insects. Whereas the epidermis is a major target of premetamorphic JH action, it has been studied little in adult insects, which generally do not moult. However, since the development of yellow pigmentation that accompanies sexual maturation in adult male locusts is clearly dependent on JH-regulation processes, in which cellular and molecular mechanism are investigated. The rapid recent progress in understanding how ecdysteroids regulate the gene activities has resulted from the opportunities afforded by drosophila melanogaster: mapped and characterized mutants, polytene chromosomes with puffs marking active genes, efficient germ-line transformation. The recognition of two aspects of JH action in the tissues of adult insects is reviewed. A model for understanding some aspects of priming by JH may be found in the action of ecdysteroids, where early genes produce factors needed for the expression of late genes. In structure, thyroxine is very different from JH, but there is considerable resemblance between thyroxine and phenoxyphenoxy carbamate, fenoxycarb. Functionally, there are marked similarities. Thyroxine governs metamorphosis in amphibians, but is remarkably pleiotropic in governing many processes ranging from the maturation of the central nervous system to thermoregulation. The chapter emphasizes the importance of selecting insect systems on the basis of their optimal features for research, rather than historical precedent or economic importance. With selection of appropriate systems and application of the cell and molecular research techniques now available, the elusive problem of JH action should soon yield to enlightenment.

Cellular and Molecular Actions of Juvenile Hormone. II. Roles of Juvenile Hormone in Adult Insects

Oogenesis in insects is typically a nutrient-limited process, triggered only if sufficient nourishment is available. This nourishment can be acquired during the larval or adult stage, depending on the insect. Timing of food intake will have major effects on mechanisms of hormonal control. When nourishment for eggs is taken primarily by adults, insufficient nutrition inhibits egg development through mechanisms such as inhibition of corpora allata, as seen in Orthoptera and Blattaria. In adult Diptera, lack of protein inhibits release of brain factors that produce reproductive competency or ovarian stimulation. Lepidoptera have been characterized as lacking substantial regulation of oogenesis because egg development is underway at emergence. Many species for which ecological data are available do not mobilize reserves carried over from the larval stage until they feed as adults. The endocrine mechanisms underlying these systems are poorly understood. In many insects, mating and activity can affect nutritional state and therefore oogenesis. Mating can stimulate oogenesis through mobilization of reserves or through nutritional contributions by males to females. Activity, especially flight, and oogenesis can compete for energy. The flight apparatus, especially the muscle, can also compete with oogenesis for protein. Social insects exhibit extreme specializations in oogenesis; females range in fertility from completely sterile to hyperfecund. Food flow within colonies is a major factor regulating fecundity. Finally, maternal nourishment is not needed for oogenesis in parasitoids and pseudoplacental viviparous insects, which produce eggs with little or no yolk. Virtually nothing is known about the endocrine regulation of oogenesis on these insects.

The Role of Nourishment in Oogenesis

Vitellogenin is the generic name for a unique group of proteins that are synthesized extraovarially and become the major egg yolk protein, vitellin. Similar proteins are found in all animals with yolky eggs. Because of their high concentration in the egg, and the relative ease with which they can be purified, these proteins are excellent material for the study of the regulation of their synthesis from the molecular, developmental, and physiological points of view. This review covers the synthesis, uptake, and physical and chemical properties of vitellogenins and vitellins in insects. The term vitellogenin was derived from vitellogenesis (102), the period of rapid oocyte growth during which yolk is deposited. Once inside the oocyte these proteins are known as vitellins, because in some cases the molecules are changed during uptake. The definition of vitellogenins has traditionally included the following criteria: (a) They usually comprise 60-90% of the soluble egg yolk proteins (13, 69); (b) they are not made the oocyte, the fat body being the site of synthesis (22, 69, 102); (c) are present in large amounts only in females and thus have been called female-specific proteins (11, 102), although rigorous techniques have revealed small amounts in males (83, 119) and so this definition is not exclusive; and (d) they are selectively taken up by the oocyte during vitellogenesis (120). Because of the dynamics of the uptake mechanism (112,

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Vitellogenin and vitellin in insects

Publisher Summary Vitellogenins are defined as the predominant yolk protein precursors that are produced extraovarially and taken up by the growing oocytes against a concentration gradient. One of the most exciting aspects, and one that has attracted increasing attention during the last few years, is the mechanism of control of vitellogenin biosynthesis. This chapter focuses on the known control mechanisms that are amenable to experimental manipulation. The close analogy to the control mechanisms known for avian and amphibian vitellogenins makes research on insect vitellogenin even more rewarding. The chapter tabulates the identification of vitellogenin and vitellin according to the chronological documentation, the known species, grouped by orders, for which vitellogenins have been described. The very fact that only the female of the species contains a protein that is also the predominant yolk protein may allow speculating that ovaries transplanted into males may not incorporate yolk. However, as early as 1907 Meisenheimer found for the Lepidopteran Porthetria dispar that, larval ovaries transplanted into male larvae produced fully grown and chorionated eggs after metamorphosis. Contribution of non-specific proteins to protein yolk and uptake of haemolymph proteins by the oocytes have been discussed. The chapter discusses a model for endocrine controlled vitellogenin synthesis and vitellogenesis.

Insect Vitellogenin: Identification, Biosynthesis, and Role in Vitellogenesis

A specific protein is Present in serums of all of Leucophaea maderae that mature eggs but not in serums of males, nymphs of either sex, or females that are reproductively inactive. Ablations, microsurgery and remplantation showed that this protein is produced de novo under the influence of the corpus allatum hormone. This protein, essential for egg maturation, is synthesized in isolated abdimens of allatectomized females treated with 0.08 to 0.12 microgram of the t,t,t-isomer of the authentic juvenile hormone. The crops allatum hormone also stimulates toa similar degree the synthesis of other proteins which appear to be essential for egg maturation as well; these are not specific to females.

https://science.sciencemag.org/content/sci/165/3891/407.full.pdf

Franz Engelmann

Papers

Insect Vitellogenin: Identification, Biosynthesis, and Role in Vitellogenesis

Female specific protein: biosynthesis controlled by corpus allatum in Leucophaea maderae.

Juvenile hormone-controlled synthesis of female-specific protein in the cockroach Leucophaea maderae.

Food-stimulated synthesis of intestinal proteolytic enzymes in the cockroach Leucophaea maderae.

Studies on the endocrine control of metabolism in Leucophaea maderae (Blattaria): I. The hemolymph proteins during egg maturation