Insect neurobiology: Oviposition crowd control.

A new study examines how Helicoverpa armigera females detect chemicals released by conspecific eggs in order to avoid laying more eggs on the same substrate. This work opens new avenues for basic research inquiries and offers a potential strategy for controlling insect pests.

Pharmacological characterisation and functional roles for egg-laying of a ß-adrenergic-like octopamine receptor in the brown planthopper Nilaparvata lugens.

Octopamine, the invertebrate counterpart of adrenaline and noradrenaline, controls and modulates many physiological and behavioral processes in protostomes. It mediates its effects by binding to specific receptors belonging to the superfamily of G-protein coupled receptors. We report the cloning of a cDNA from the brown planthopper (Nloa2b2) sharing high similarity with members of the OA2B2 receptor class. Activation of NlOA2B2 by octopamine increased the production of cAMP in a dose-dependent manner (EC50 = 114 nM). Tyramine also activated the receptor but with much less potency than octopamine. Using a series of known agonists and antagonists of octopamine receptors and cAMP measurements, we observed a rather unique pharmacological profile of NlOA2B2. The potency ranking of the tested agonists was naphazoline > clonidine. The activated effect of octopamine is abolished by co-incubation with epinastine, mianserin, phentolamine, methiothepin, butaclamol or methysergide. Nloa2b2 was expressed in different developmental stages and in various tissues including female reproductive regions known to be involved in egg-laying behavior. Using in vivo pharmacology and RNAi methodology, we demonstrated that interference of NlOA2B2 signaling pathway had a strong impact on the egg-laying behavior of female brown planthopper. The data presented here mark the first comprehensive study-from gene to behavior-of a OA2B2 receptor in the rice brown planthopper.

Parasitization by Cotesia chilonis influences gene expression in fatbody and hemocytes of Chilo suppressalis.

BACKGROUND: During oviposition many parasitoid wasps inject various factors, such as polydnaviruses (PDVs), along with eggs that manipulate the physiology and development of their hosts. These manipulations are thought to benefit the parasites. However, the detailed mechanisms of insect host-parasitoid interactions are not fully understood at the molecular level. Based on recent findings that some parasitoids influence gene expression in their hosts, we posed the hypothesis that parasitization by a braconid wasp, Cotesia chilonis, influences the expression of genes responsible for development, metabolism and immune functions in the fatbody and hemocytes of its host, Chilo suppressalis. METHODOLOGY/PRINCIPAL FINDINGS: We obtained 39,344,452 reads, which were assembled into 146,770 scaffolds, and 76,016 unigenes. Parasitization impacted gene expression in fatbody and hemocytes. Of these, 8096 fatbody or 5743 hemocyte unigenes were down-regulated, and 2572 fatbody or 1452 hemocyte unigenes were up-regulated. Gene ontology data showed that the majority of the differentially expressed genes are involved in enzyme-regulated activity, binding, transcription regulator activity and catalytic activity. qPCR results show that most anti-microbial peptide transcription levels were up-regulated after parasitization. Expression of bracovirus genes was detected in parasitized larvae with 19 unique sequences identified from six PDV gene families including ankyrin, CrV1 protein, cystatin, early-expressed (EP) proteins, lectin, and protein tyrosine phosphatase. CONCLUSIONS: The current study supports our hypothesis that parasitization influences the expression of fatbody and hemocyte genes in the host, C. suppressalis. The general view is that manipulation of host metabolism and immunity benefits the development and emergence of the parasitoid offsprings. The accepted beneficial mechanisms include the direct impact of parasitoid-associated virulence factors such as venom and polydnavirus on host tissues (such as cell damage) and, more deeply, the ability of these factors to influence gene expression. We infer that insect parasitoids generally manipulate their environments, the internal milieu of their hosts.

Characterization of a ß-adrenergic-like octopamine receptor from the rice stem borer (Chilo suppressalis).

Octopamine, the invertebrate counterpart of adrenaline and noradrenaline, plays a key role in regulation of many physiological and behavioral processes in insects. It modulates these functions through binding to specific octopamine receptors, which are typical rhodopsin-like G-protein coupled receptors. A cDNA encoding a seven-transmembrane receptor was cloned from the nerve cord of the rice stem borer, Chilo suppressalis, viz. CsOA2B2, which shares high sequence similarity to CG6989, a Drosophila ß-adrenergic-like octopamine receptor (DmOctß2R). We generated an HEK-293 cell line that stably expresses CsOA2B2 in order to examine the functional and pharmacological properties of this receptor. Activation of CsOA2B2 by octopamine increased the production of cAMP in a dose-dependent manner (EC(50)=2.33 nmol l(-1)), with a maximum response at 100 nmol l(-1). Tyramine also activated the receptor but with much less potency than octopamine. Dopamine and serotonin had marginal effects on cAMP production. Using a series of known agonists and antagonists for octopamine receptors, we observed a rather unique pharmacological profile for CsOA2B2 through measurements of cAMP. The rank order of potency of the agonists was naphazoline > clonidine. The activated effect of octopamine is abolished by co-incubation with phentolamine, mianserin or chlorpromazine. Using in vivo pharmacology, CsOA2B2 antagonists mianserin and phentolamine impaired the motor ability of individual rice stem borers. The results of the present study are important for a better functional understanding of this receptor as well as for practical applications in the development of environmentally sustainable pesticides.

The characterization of a concentration-sensitive α-adrenergic-like octopamine receptor found on insect immune cells and its possible role in mediating stress hormone effects on immune function.

Octopamine (OA), the insect equivalent of norepinephrine, links the nervous system and immune system in insects. This study examines the underlying molecular mechanisms (i.e. second messenger systems) mediating OA effects on insect immune cells. At low concentrations (<1µM), OA stimulatedhemocyte spreading and phagocytosis in the larval Lepidopteran (caterpillar) Chilo suppressalis, whereas at high concentrations (>10 µM), OA inhibited hemocyte spreading and phagocytosis. Similarly, OA concentration had differential effects on two intracellular signaling pathways, Ca(2+) and cAMP. Low concentrations of OA increased intracellular Ca(2+), but only high concentrations of OA (>1 µM) led to an increase in both Ca(2+) and cAMP. We identified an α-adrenergic-like octopamine receptor in this species (CsOA1) and confirmed that it is expressed in hemocytes. After heterologous expression in HEK-293 cells, the CsOA1 receptor produced the same OA concentration-dependent responses on intracellular Ca(2+) and cAMP as had been observed in hemocytes. These findings support earlier work showing that OA has both stimulatory and suppressive effects on immune responses, depending on the OA concentration. Our evidence suggests that these biphasic effects are mediated by an octopamine receptor signaling through intracellular Ca(2+) and cAMP second messenger pathways. Stress hormones/neuromodulators have complex effects on immune function in animals across phyla. This complexity may be mediated, in part, by conserved connections between adrenergic-like G-coupled protein receptors and second messenger systems.