Two simple chromenes with anti-JH activity have been isolated and identified from the bedding plant Ageratum houstoianum. By contact and fumigation these compounds induce precocious metamorphosis and sterilization in several hemipteran species of insects. Certain holometabolous species are sterilized, forced into diapause, or both. Each of these biological actions is equivalent to removal of the corpora allata, which produce the JH's, and is reversible by treatment with exogenous JH. Thus, the action of these compounds is to stop the production or depress the titer of the JH's. To our knowledge, this is the first discovery of anti-JH, and we hope it will guide the way to the emergence of a fourth generation of safe and insect-specific pesticides.

A broadly interspecific aphid alarm pheromone was isolated from several economically important species of aphids and identified as trans-beta-farnesene.

A cDNA encoding a cytochrome P450 enzyme was isolated from a cDNA library of the corpora allata (CA) from reproductively active Diploptera punctata cockroaches. This P450 from the endocrine glands that produce the insect juvenile hormone (JH) is most closely related to P450 proteins of family 4 and was named CYP4C7. The CYP4C7 gene is expressed selectively in the CA; its message could not be detected in the fat body, corpora cardiaca, or brain, but trace levels of expression were found in the midgut and caeca. The levels of CYP4C7 mRNA in the CA, measured by ribonuclease protection assays, were linked to the activity cycle of the glands. In adult females, CYP4C7 expression increased immediately after the peak of JH synthesis, reaching a maximum on day 7, just before oviposition. mRNA levels then declined after oviposition and during pregnancy. The CYP4C7 protein was produced in Escherichia coli as a C-terminal His-tagged recombinant protein. In a reconstituted system with insect NADPH cytochrome P450 reductase, cytochrome b 5 , and NADPH, the purified CYP4C7 metabolized (2E,6E)-farnesol to a more polar product that was identified by GC-MS and by NMR as (10E)-12-hydroxyfarnesol. CYP4C7 converted JH III to 12-trans-hydroxy JH III and metabolized other JH-like sesquiterpenoids as well. This -hydroxylation of sesquiterpenoids appears to be a metabolic pathway in the corpora allata that may play a role in the suppression of JH biosynthesis at the end of the gonotrophic cycle.Juvenile hormone (JH) plays a central role in insect development, metamorphosis, and reproduction. This sesquiterpenoid epoxide is synthesized in endocrine glands, the corpora allata (CA)(1), and is degraded predominantly by esterases and epoxide hydrolases (2). The rate of JH synthesis by the CA is a major determinant of the titer of JH in the hemolymph (3), and the regulation of JH synthesis is seen as a potential target for insect control. The biosynthesis of JH has been extensively characterized during the reproductive cycle of the cockroach Diploptera punctata, an insect that serves as a convenient model system. In adult females of this insect, the cycle of JH synthesis is regulated by humoral factors and by innervation from neurosecretory cells in the brain (1). Production of JH by the CA increases 10-fold to reach a peak 5 days after adult emergence and mating, and this peak corresponds to the peak of vitellogenesis. Synthesis is then rapidly repressed and remains low from deposition of the eggs into the brood sac through pregnancy (4).The allatostatins, a family of brain-gut peptides (5-9) are known to inhibit JH synthesis in D. punctata at the end of a gonotrophic cycle, but these peptides are probably not alone responsible for repression of the intrinsic rate of JH synthesis in postvitellogenic insects. The mechanism of stable suppression of JH synthesis at the end of the cycle has received very little attention, in part because of the absence of molecular tools to dissect it. This repression occurs concomitant with changes in c...

The phytoecdysteroid, 20-hydroxyecdysone (20E), is a major molting hormone of invertebrates, possibly including nematodes. As 20E is inducible in spinach, the defensive role against plant-parasitic nematodes was investigated. The effects of direct application on nematodes was assessed by treating cereal cyst nematode, Heterodera avenae, juveniles with concentrations of 20E from 8.2 x 10(-8) to 5.2 x 10(-5) M before applying to Triticum aestivum growing in sand. H. avenae, Heterodera schachtii (sugarbeet cyst nematode), Meloidogyne javanica (root-knot nematode), and Pratylenchus neglectus (root lesion nematode) were treated with 5.2 x 10(-5) 20E and incubated in moist sand. To test the protective effects of 20E in plants, the latter three nematodes were applied to Spinacia oleracea in which elevated concentrations of 20E had been induced by methyl jasmonate. Abnormal molting, immobility, reduced invasion, impaired development, and death occurred in nematodes exposed to 20E either directly at concentration above 4.2 x 10(-7) M or in plants. Phytoecdysteroid was found to protect spinach from plant-parasitic nematodes and may confer a mechanism for nematode resistance.

A sesquiterpenoid ester with high juvenile hormone activity for Pyrrhocoris apterus (L.) was isolated from balsam fir, Abies balsamea (L.) Miller, and identified as the methyl ester of todomatuic acid.

When attacked by predators, aphids secrete alarm pheromones that cause nearby aphids to disperse. Ant-associated (myrmecophilous) aphid species disperse less readily than nonmyrmecophilous species. The ant Formica subsericea responds to aphid alarm pheromone in a way that is beneficial to the aphid. These findings support our hypothesis that myrmecophilous aphids depend more on ants for protection from predators than on their own dispersive powers.

No abstract

Plant produced insect molting hormones, termed phytoecdysteroids (PEs), are thought to function as plant defenses against insects by acting as either feeding deterrents or through developmental disruption. In spinach (Spinacia oleracea), 20-hydroxyecdysone (20E) concentrations in the roots rapidly increase following root damage, root herbivory, or methyl jasmonate (MJ) applications. In this inducible system, we investigated the plant defense hypothesis by examining interactions of roots, 20E concentrations, and larvae of the dark-winged fungus gnat (Bradysia impatiens). Root herbivory by B. impatiens larvae resulted in a 4.0- to 6.6-fold increase in root 20E concentrations. In paired-choice tests, increases in dietary 20E stimulated B. impatiens feeding deterrency. B. impatiens larvae preferred control diets, low in 20E, to those constructed from induced roots and those amended with 20E (25 to 50 micro g/g wet mass). When confined to 20E-treated diets, concentrations as low as 5 micro g/g (wet mass) resulted in significantly reduced B. impatiens survivorship compared to controls. The induction of root 20E levels with MJ resulted in a 2.1-fold increase in 20E levels and a 50% reduction in B. impatiens larval establishment. In a paired-choice arena, untreated control roots were damaged significantly more by B. impatiens larvae than MJ-induced roots that contained 3-fold greater 20E levels. Based on dietary preference tests, the 20E concentrations present in the MJ-induced roots (28 micro g/g wet mass) were sufficient to explain this reduction in herbivory. Interactions between spinach roots and B. impatiens larvae demonstrate that PEs can act as inducible defenses and provide protection against insect herbivory.