Control mechanisms of the behavior 'secondary defense' in the grasshopper Gomphocerus rufus L. (Gomphocerinae: Orthoptera).

In the female grasshopper Gomphocerus rufus mating elicits 'secondary defense' which makes remating impossible. The behavioral change is caused by the liquid white secretions, proteins of less than 90 kD, which are produced by the white tubuli of the male's accessory glands. Experimental injection of the white secretions directly into the spermathecal duct of receptive virgins provokes 'secondary defense' instantly whereas sperm transfer had no such effect. 'Secondary defense' is also released by eggs entering the oviducts and excerting pressure against the oviductal walls on their way to oviposition.

Neurons projecting from the brain to the corpora allata in orthopteroid insects: anatomy and physiology.

Retrograde and orthograde labeling of neurons projecting to the corpus allatum was performed in locust, grasshopper, cricket, and cockroach species in order to identify brain neurons that may be involved in the regulation of juvenile hormone production. In the acridid grasshopper Gomphocerus rufus L., and the locusts Locusta migratoria (R.&F.) and Schistocerca gregaria Forskal, the corpora allata are innervated by two morphologically distinguishable types of brain neurons. One group of 9-13 neurons (depending on species) with somata in the pars lateralis extend axons via the nervus corporis cardiaci 2 and nervus corporis allati 1 to the ipsilateral corpus allatum, whereas two cells in each pars lateralis have bilateral projections and innervate both glands. No direct connection between the pars intercerebralis and corpus allatum has been found. In contrast, neurons with paired axons innervating both glands are not present in Periplaneta americana (L.) and Gryllus bimaculatus de Geer. Instead, two cells in each pars lateralis project only to the gland contralateral to their somata. Electrophysiological experiments on acridid grasshoppers have confirmed the existence of a direct conduction pathway between the two glands via the paired axons of four cells that have been identified by neuroanatomy. These cells are not spontaneously active under experimental conditions. Ongoing discharges in the left and right nerves are unrelated, suggesting that the corpora allata receive independent neuronal inputs from the brain.

Nervous control of juvenile hormone biosynthesis in Locusta migratoria.

In Locusta migratoria migratorioides R. and F., two types of brain neurons innervate the juvenile hormone (JH)-producing corpora allata (CA). Thirteen cells in each pars lateralis (PL) innervate the ipsilateral CA, while four cells (two in each PL) innervate both glands. We investigated possible influences of these two neuronal types on JH production by a newly developed method. A radiochemical assay was used to measure hourly JH production by a CA with intact nerve connections to the brain. Then, changes in hormone production due to selective nerve stimulation or transection were assessed. In control preparations JH production per h remained approximately constant for at least 9 h. Simultaneous electrical stimulation of all neurons innervating one CA (i.e., 13 ipsilateral plus 4 bilaterally innervating cells) always inhibited JH production, while their transection led to a rapid progressive increase in JH biosynthesis in CA from females with oocytes longer than 4.5 mm. Thus, there is strong neurally mediated inhibition of the CA at certain phases of the vitellogenic cycle. The dramatic effects of nerve transection show that in vitro rates of JH production are an unreliable indicator of in vivo levels. Selective stimulation of the four neurons innervating both CA suggests that they do modulate JH biosynthesis but the effect varies qualitatively depending on the phase of the vitellogenic cycle.

De novo biosynthesis of arachidonic acid and 5,11,14-eicosatrienoic acid in the cricket Teleogryllus commodus.

The de novo biosynthesis of 5,11,14-eicosatrienoic acid (5,11,14-20:3), arachidonic acid (20:4(n - 6] and eicosadienoic acid (20:2(n - 6] and the elongation/desaturation of linoleic acid (18:2(n - 6] to 20:4(n - 6) and alpha-linolenic acid (18:3(n - 3] to eicosapentaenoic acid (20:5(n - 3] were demonstrated in adult males of the field cricket Teleogryllus commodus. Sodium [1-14C]acetate, [1-14C]18:2(n - 6) and [1-14C]18:3(n - 3) were injected into adult male crickets and after an incubation period, the testes and remaining tissues were extracted and the methyl esters obtained from the phospholipid and triacylglycerol fractions were analyzed. After 5 days of daily injections of [1-14C]acetate, the methyl esters of the triene and tetraene fatty acids from the testicular phospholipid fraction were purified by AgNO3-TLC and HPLC and analyzed by GLC, radio-HPLC, and radio-GLC of ozonolysis products. The results demonstrate the de novo biosynthesis of 20:2(n - 6), 20:4(n - 6) and an isomer of 20:3(n - 6) with double bonds in the 5,11,14 positions. the elongation/desaturation of 18:2(n - 6) to 20:4(n - 6) and 18:3(n - 3) to 20:5(n - 3) was demonstrated by analysis of the methyl esters derived from the testicular phospholipid fraction by radio-HPLC after injecting crickets with radiolabeled substrates.

Axonal projections within the brain-retrocerebral complex of the cricket, Teleogryllus commodus.

The cerebral origins and axonal trajectories of neurons projecting to the retrocerebral complex of the cricket, Teleogryllus commodus, were examined in silver-intensified nickel preparations. Spatially separate groups of somata in the pars intercerebralis (PI) and in the pars lateralis (PL), commonly accepted as neurosecretory loci, were found to give rise to axons which terminate in the nervus corporis allati 2, the corpus allatum, or the corpus cardiacum. Additional findings demonstrated a distinct group of somata from the PI whose axons run in the esophageal nerve (stomatogastric nervous system), nine somata in the subesophageal ganglion with axons projecting into the nervus corporis allati 2, and also a small cluster of tritocerebral perikarya with axons terminating in the corpus cardiacum. Somata residing in the PI and PL were found to be compartmentally organized based upon the retrocerebral destinations of their axons. Possible functional consequences of these results with respect to the insect neurosecretory system are discussed.

De novo biosynthesis of prostaglandins by the Australian field cricket, Teleogryllus commodus.

The accumulation and metabolism of certain polyunsaturated fatty acids by testes from the Australian field cricket, Teleogryllus commodus, are described. Testes accumulated a substantial proportion (about 16%) of label from radioactive C20:3n6 that was injected into the haemocoel. Fifty percent of the label accumulated by testes was associated with the phospholipid fraction, whereas in the remainder of the body 30% was incorporated into the phospholipid fraction. Prostaglandins (PG) E1, E2 and F2 alpha were quantified in extracts of the testes of adult insects by radioimmunoassay. Label from injected radioactive C18:2n6, C20:3n6 and C20:4n6 was recovered as prostaglandins PGE and PGF. The radioactivity from C18:2n6 that was recovered as PGE1 and PGF1 alpha indicated elongation/desaturation to C20:3n6 followed by conversion to PG. Since C18:2n6 is readily formed from acetate in T. commodus, these findings indicate the de novo biosynthesis of C20 polyunsaturated fatty acids and prostaglandins by this species.

Anatomy and electrophysiology of individual neurosecretory cells of an insect brain.

The structure and electrophysiological properties of individual neurosecretory cells of the pars intercerebralis, medial neurosecretory cells (MNSCs), in the brain of an insect, the cricket Teleogryllus commodus, were investigated by means of intracellular injections of the dye Lucifer Yellow and electrophysiological recordings. Action potentials recorded from these cells were of long duration, 8-50 msec. In the pars intercerebralis there are both neurosecretory cells with axons that join one of the tracts of the nervi corpori cardiaci I (NCC I) and cells without an axon or collateral that leaves the brain, local neurosecretory cells. MNSCs with axons that join NCC I and terminate in the anterior corpus cardiacum arborize extensively in the protocerebrum and to a lesser degree in the deutocerebrum. Other MNSCs have axons that pass through the corpus cardiacum and hypocerebral ganglion and join one of the oesophageal nerves. These MNSCs have sparse collateral arborizations in the protocerebrum but do have extensive terminal arborizations in the tritocerebrum. This type of cell is dye-coupled to other MNSCs. Among the local MNSCs, some have an unusual loop shape. These cells branch extensively in the protocerebrum and have massive terminal arborizations in a posterior ventromedial region of the brain. Both the long curved axons of the loop-shaped cells and their ventromedial branches are of large diameter, suitable for storage of neurosecretory material.

Prostaglandins: Their role in egg-laying of the cricket Teleogryllus commodus.

Mating of the Teleogryllus commodus female causes increased oviposition mediated by PGE(2), which is synthesized in the female's spermatheca from the precursor, arachidonic acid, in the presence of a PG-synthesizing complex. The latter, together with sperm, is transferred from the male to the female via a spermatophore. Only nanogram quantities of PGE(2) injected into oviduct are necessary to simulate mating-induced egg release.

Arrhythmically singing crickets: thermoperiodic reentrainment after bilobectomy.

The circadian control of the calling song of crickets is abolished by severance of the optic lobes. The arrhythmic singing activity of operated animals is unaffected by all possible light conditions, yet the singing can be reentained by a daily temperature cycle. The characteristics of this reentrainment indicate the that temperature is acting as an actual Zeitgeber. In light of these results the current hypothesis which ascribes a driving oscillator function to the optic lobes must be reevaluated.